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135-805:   See Spider taxonomy . Spiders ( order Araneae ) are air-breathing arthropods that have eight limbs, chelicerae with fangs generally able to inject venom , and spinnerets that extrude silk . They are the largest order of arachnids and rank seventh in total species diversity among all orders of organisms . Spiders are found worldwide on every continent except Antarctica , and have become established in nearly every land habitat . As of September 2024, 52,309 spider species in 134 families have been recorded by taxonomists . However, there has been debate among scientists about how families should be classified, with over 20 different classifications proposed since 1900. Anatomically , spiders (as with all arachnids) differ from other arthropods in that

270-487: A catalytic triad , stabilize charge build-up on the transition states using an oxyanion hole , complete hydrolysis using an oriented water substrate. Enzymes are not rigid, static structures; instead they have complex internal dynamic motions – that is, movements of parts of the enzyme's structure such as individual amino acid residues, groups of residues forming a protein loop or unit of secondary structure , or even an entire protein domain . These motions give rise to

405-489: A conformational ensemble of slightly different structures that interconvert with one another at equilibrium . Different states within this ensemble may be associated with different aspects of an enzyme's function. For example, different conformations of the enzyme dihydrofolate reductase are associated with the substrate binding, catalysis, cofactor release, and product release steps of the catalytic cycle, consistent with catalytic resonance theory . Substrate presentation

540-530: A cribellum , a modified spinneret with up to 40,000 spigots, each of which produces a single very fine fiber. The fibers are pulled out by the calamistrum , a comblike set of bristles on the jointed tip of the cribellum, and combined into a composite woolly thread that is very effective in snagging the bristles of insects. The earliest spiders had cribella, which produced the first silk capable of capturing insects, before spiders developed silk coated with sticky droplets. However, most modern groups of spiders have lost

675-466: A mutualistic relationship with a species of ant . Juveniles of some spiders in the families Anyphaenidae , Corinnidae , Clubionidae , Thomisidae and Salticidae feed on plant nectar . Laboratory studies show that they do so deliberately and over extended periods, and periodically clean themselves while feeding. These spiders also prefer sugar solutions to plain water, which indicates that they are seeking nutrients. Since many spiders are nocturnal,

810-406: A tracheal system, or both. Mygalomorph and Mesothelae spiders have two pairs of book lungs filled with haemolymph, where openings on the ventral surface of the abdomen allow air to enter and diffuse oxygen . This is also the case for some basal araneomorph spiders, like the family Hypochilidae , but the remaining members of this group have just the anterior pair of book lungs intact while

945-491: A better chance of survival if they have the opportunity to eat pollen. In captivity, several spider species are also known to feed on bananas , marmalade , milk , egg yolk and sausages . Airborne fungal spores caught on the webs of orb-weavers may be ingested along with the old web before construction of a new web. The enzyme chitinase present in their digestive fluid allows for the digestion of these spores. Spiders have been observed to consume plant material belonging to

1080-412: A combination of lightness, strength and elasticity superior to synthetic materials, and spider silk genes have been inserted into mammals and plants to see if these can be used as silk factories. As a result of their wide range of behaviors, spiders have become common symbols in art and mythology , symbolizing various combinations of patience, cruelty and creative powers. An irrational fear of spiders

1215-400: A dry material. Malphigian tubules ("little tubes") extract these wastes from the blood in the hemocoel and dump them into the cloacal chamber, from which they are expelled through the anus . Production of uric acid and its removal via Malphigian tubules are a water-conserving feature that has evolved independently in several arthropod lineages that can live far away from water, for example

1350-467: A few to 50,000 individuals. Social behavior ranges from precarious toleration, as in the widow spiders , to cooperative hunting and food-sharing. Although most spiders live for at most two years, tarantulas and other mygalomorph spiders can live up to 25 years in captivity. While the venom of a few species is dangerous to humans, scientists are now researching the use of spider venom in medicine and as non-polluting pesticides . Spider silk provides

1485-477: A first step and then checks that the product is correct in a second step. This two-step process results in average error rates of less than 1 error in 100 million reactions in high-fidelity mammalian polymerases. Similar proofreading mechanisms are also found in RNA polymerase , aminoacyl tRNA synthetases and ribosomes . Conversely, some enzymes display enzyme promiscuity , having broad specificity and acting on

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1620-423: A foot of sorts); the tarsus ends in a claw made up of either two or three points, depending on the family to which the spider belongs. Although all arthropods use muscles attached to the inside of the exoskeleton to flex their limbs, spiders and a few other groups still use hydraulic pressure to extend them, a system inherited from their pre-arthropod ancestors. The only extensor muscles in spider legs are located in

1755-704: A large variety of taxa and type. Conversely, cursorial spiders comprise the vast majority (over 80%) of reported incidents of plant-eating. The best-known method of prey capture is by means of sticky webs. Varying placement of webs allows different species of spider to trap different insects in the same area, for example flat horizontal webs trap insects that fly up from vegetation underneath while flat vertical webs trap insects in horizontal flight. Web-building spiders have poor vision, but are extremely sensitive to vibrations. The water spider Argyroneta aquatica build underwater "diving bell" webs that they fill with air and use for digesting prey and molting. Mating and raising

1890-464: A quantitative theory of enzyme kinetics, which is referred to as Michaelis–Menten kinetics . The major contribution of Michaelis and Menten was to think of enzyme reactions in two stages. In the first, the substrate binds reversibly to the enzyme, forming the enzyme-substrate complex. This is sometimes called the Michaelis–Menten complex in their honor. The enzyme then catalyzes the chemical step in

2025-439: A range of different physiologically relevant substrates. Many enzymes possess small side activities which arose fortuitously (i.e. neutrally ), which may be the starting point for the evolutionary selection of a new function. To explain the observed specificity of enzymes, in 1894 Emil Fischer proposed that both the enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another. This

2160-586: A reduced number of eyes, the most common having six eyes (example, Periegops suterii ) with a pair of eyes absent on the anterior median line . Other species have four eyes and members of the Caponiidae family can have as few as two. Cave dwelling species have no eyes (such as the Kauaʻi cave wolf spider ), or possess vestigial eyes incapable of sight (such as Holothele maddeni ). As with other arthropods, spiders' cuticles would block out information about

2295-531: A separate common origin (i.e. being synapomorphies ). One phylogenetic hypothesis based on molecular data shows the Haplogynae as a paraphyletic group leading to the Austrochilidae and Entelegynae. The Entelegynae have a more complex reproductive anatomy: females have two "copulatory pores" in addition to the single genital pore of other groups of spiders; males have complex palpal bulbs, matching

2430-437: A single one in the middle, and moved backwards close to the spinnerets . Spiders that have tracheae generally have higher metabolic rates and better water conservation. Spiders are ectotherms , so environmental temperatures affect their activity. Uniquely among chelicerates , the final sections of spiders' chelicerae are fangs, and the great majority of spiders can use them to inject venom into prey from venom glands in

2565-473: A small cylindrical section, the pedicel. The pattern of segment fusion that forms chelicerates' heads is unique among arthropods, and what would normally be the first head segment disappears at an early stage of development, so that chelicerates lack the antennae typical of most arthropods. In fact, chelicerates' only appendages ahead of the mouth are a pair of chelicerae , and they lack anything that would function directly as "jaws". The first appendages behind

2700-451: A species' normal level; as a result, enzymes from bacteria living in volcanic environments such as hot springs are prized by industrial users for their ability to function at high temperatures, allowing enzyme-catalysed reactions to be operated at a very high rate. Enzymes are usually much larger than their substrates. Sizes range from just 62 amino acid residues, for the monomer of 4-oxalocrotonate tautomerase , to over 2,500 residues in

2835-409: A spider consists of seven distinct parts. The part closest to and attaching the leg to the cephalothorax is the coxa ; the next segment is the short trochanter that works as a hinge for the following long segment, the femur ; next is the spider's knee, the patella , which acts as the hinge for the tibia ; the metatarsus is next, and it connects the tibia to the tarsus (which may be thought of as

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2970-449: A steady level inside the cell. For example, NADPH is regenerated through the pentose phosphate pathway and S -adenosylmethionine by methionine adenosyltransferase . This continuous regeneration means that small amounts of coenzymes can be used very intensively. For example, the human body turns over its own weight in ATP each day. As with all catalysts, enzymes do not alter the position of

3105-442: A thermodynamically unfavourable one so that the combined energy of the products is lower than the substrates. For example, the hydrolysis of ATP is often used to drive other chemical reactions. Enzyme kinetics is the investigation of how enzymes bind substrates and turn them into products. The rate data used in kinetic analyses are commonly obtained from enzyme assays . In 1913 Leonor Michaelis and Maud Leonora Menten proposed

3240-404: A trial-and-error approach. Spiders have primarily four pairs of eyes on the top-front area of the cephalothorax, arranged in patterns that vary from one family to another. The principal pair at the front are of the type called pigment-cup ocelli ("little eyes"), which in most arthropods are only capable of detecting the direction from which light is coming, using the shadow cast by the walls of

3375-586: A very small proportion of the total of around 49,000 known species. Mygalomorphae species comprise around 7% of the total, the remaining 93% being in the Araneomorphae. Mesothelae Mygalomorphae Austrochiloidea Entelegynae Haplogynae Hypochiloidea The Araneomorphae are divided into two main groups: the Haplogynae and the Entelegynae . The Haplogynae make up about 10% of

3510-457: Is k cat , also called the turnover number , which is the number of substrate molecules handled by one active site per second. The efficiency of an enzyme can be expressed in terms of k cat / K m . This is also called the specificity constant and incorporates the rate constants for all steps in the reaction up to and including the first irreversible step. Because the specificity constant reflects both affinity and catalytic ability, it

3645-838: Is orotidine 5'-phosphate decarboxylase , which allows a reaction that would otherwise take millions of years to occur in milliseconds. Chemically, enzymes are like any catalyst and are not consumed in chemical reactions, nor do they alter the equilibrium of a reaction. Enzymes differ from most other catalysts by being much more specific. Enzyme activity can be affected by other molecules: inhibitors are molecules that decrease enzyme activity, and activators are molecules that increase activity. Many therapeutic drugs and poisons are enzyme inhibitors. An enzyme's activity decreases markedly outside its optimal temperature and pH , and many enzymes are (permanently) denatured when exposed to excessive heat, losing their structure and catalytic properties. Some enzymes are used commercially, for example, in

3780-421: Is a process where the enzyme is sequestered away from its substrate. Enzymes can be sequestered to the plasma membrane away from a substrate in the nucleus or cytosol. Or within the membrane, an enzyme can be sequestered into lipid rafts away from its substrate in the disordered region. When the enzyme is released it mixes with its substrate. Alternatively, the enzyme can be sequestered near its substrate to activate

3915-569: Is called arachnophobia . The word spider derives from Proto-Germanic * spin-þron- , literally ' spinner ' (a reference to how spiders make their webs), from the Proto-Indo-European root * (s)pen- ' to draw, stretch, spin ' . Spiders are chelicerates and therefore, arthropods . As arthropods, they have: segmented bodies with jointed limbs, all covered in a cuticle made of chitin and proteins; heads that are composed of several segments that fuse during

4050-530: Is correct, the earliest members of the Entelegynae made webs defined by the substrate on which they were placed (e.g. the ground) rather than suspended orb webs. True orb webs evolved once, in the ancestors of the Orbiculariae, but were then modified or lost in some descendants. An alternative hypothesis, supported by some molecular phylogenetic studies, is that the Orbiculariae are paraphyletic , with

4185-437: Is described by "EC" followed by a sequence of four numbers which represent the hierarchy of enzymatic activity (from very general to very specific). That is, the first number broadly classifies the enzyme based on its mechanism while the other digits add more and more specificity. The top-level classification is: These sections are subdivided by other features such as the substrate, products, and chemical mechanism . An enzyme

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4320-749: Is fully specified by four numerical designations. For example, hexokinase (EC 2.7.1.1) is a transferase (EC 2) that adds a phosphate group (EC 2.7) to a hexose sugar, a molecule containing an alcohol group (EC 2.7.1). Sequence similarity . EC categories do not reflect sequence similarity. For instance, two ligases of the same EC number that catalyze exactly the same reaction can have completely different sequences. Independent of their function, enzymes, like any other proteins, have been classified by their sequence similarity into numerous families. These families have been documented in dozens of different protein and protein family databases such as Pfam . Non-homologous isofunctional enzymes . Unrelated enzymes that have

4455-483: Is hardly necessary to categorize one of them as a mygalomorph. Other, smaller, members of this suborder, however, look little different from the araneomorphs. (See the picture of Sphodros rufipes below.) Many araneomorphs are immediately identifiable as such since they are found on webs designed for the capture of prey or exhibit other habitat choices that eliminate the possibility that they could be mygalomorphs. Spiders in infraorder Mygalomorphae are characterized by

4590-466: Is mainly composed of a protein very similar to that used in insect silk. It is initially a liquid, and hardens not by exposure to air but as a result of being drawn out, which changes the internal structure of the protein. It is similar in tensile strength to nylon and biological materials such as chitin , collagen and cellulose , but is much more elastic . In other words, it can stretch much further before breaking or losing shape. Some spiders have

4725-476: Is often derived from its substrate or the chemical reaction it catalyzes, with the word ending in -ase . Examples are lactase , alcohol dehydrogenase and DNA polymerase . Different enzymes that catalyze the same chemical reaction are called isozymes . The International Union of Biochemistry and Molecular Biology have developed a nomenclature for enzymes, the EC numbers (for "Enzyme Commission") . Each enzyme

4860-418: Is often referred to as "the lock and key" model. This early model explains enzyme specificity, but fails to explain the stabilization of the transition state that enzymes achieve. In 1958, Daniel Koshland suggested a modification to the lock and key model: since enzymes are rather flexible structures, the active site is continuously reshaped by interactions with the substrate as the substrate interacts with

4995-462: Is only one of several important kinetic parameters. The amount of substrate needed to achieve a given rate of reaction is also important. This is given by the Michaelis–Menten constant ( K m ), which is the substrate concentration required for an enzyme to reach one-half its maximum reaction rate; generally, each enzyme has a characteristic K M for a given substrate. Another useful constant

5130-567: Is originally an end-product of protein metabolism, its excretion can be blocked in spiders, leading to an increase in its storage. Structural colors occur in some species, which are the result of the diffraction, scattering or interference of light, for example by modified setae or scales. The white prosoma of Argiope results from bristles reflecting the light, Lycosa and Josa both have areas of modified cuticle that act as light reflectors. The peacock spiders of Australia (genus Maratus ) are notable for their bright structural colours in

5265-404: Is seen. This is shown in the saturation curve on the right. Saturation happens because, as substrate concentration increases, more and more of the free enzyme is converted into the substrate-bound ES complex. At the maximum reaction rate ( V max ) of the enzyme, all the enzyme active sites are bound to substrate, and the amount of ES complex is the same as the total amount of enzyme. V max

5400-460: Is soft and egg-shaped. It shows no sign of segmentation, except that the primitive Mesothelae , whose living members are the Liphistiidae , have segmented plates on the upper surface. Like other arthropods, spiders are coelomates in which the coelom is reduced to small areas around the reproductive and excretory systems. Its place is largely taken by a hemocoel , a cavity that runs most of

5535-451: Is strong evidence that orb webs evolved only once, although only weak support for the monophyly of the Orbiculariae. One possible phylogeny is shown below; the type of web made is shown for each terminal node in order of the frequency of occurrence. Eresoidea, RTA clade – no web; substrate-defined web Deinopoidea – orb web Araneoidea – orb web ; aerial sheet web ; cobweb ; no web Nicodamidae – aerial sheet web If this

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5670-485: Is successful, the male injects his sperm from the palpal bulbs into the female via one or two openings on the underside of her abdomen. Female spiders' reproductive tracts are arranged in one of two ways. The ancestral arrangement ("haplogyne" or "non-entelegyne") consists of a single genital opening, leading to two seminal receptacles (spermathecae) in which females store sperm. In the more advanced arrangement ("entelegyne"), there are two further openings leading directly to

5805-403: Is the ribosome which is a complex of protein and catalytic RNA components. Enzymes must bind their substrates before they can catalyse any chemical reaction. Enzymes are usually very specific as to what substrates they bind and then the chemical reaction catalysed. Specificity is achieved by binding pockets with complementary shape, charge and hydrophilic / hydrophobic characteristics to

5940-413: Is up. Arthropods' proprioceptors , sensors that report the force exerted by muscles and the degree of bending in the body and joints, are well-understood. On the other hand, little is known about what other internal sensors spiders or other arthropods may have. Some spiders use their webs for hearing, where the giant webs function as extended and reconfigurable auditory sensors. Each of the eight legs of

6075-790: Is useful for comparing different enzymes against each other, or the same enzyme with different substrates. The theoretical maximum for the specificity constant is called the diffusion limit and is about 10 to 10 (M s ). At this point every collision of the enzyme with its substrate will result in catalysis, and the rate of product formation is not limited by the reaction rate but by the diffusion rate. Enzymes with this property are called catalytically perfect or kinetically perfect . Example of such enzymes are triose-phosphate isomerase , carbonic anhydrase , acetylcholinesterase , catalase , fumarase , β-lactamase , and superoxide dismutase . The turnover of such enzymes can reach several million reactions per second. But most enzymes are far from perfect:

6210-549: The Araneoidea are ecribellate – the adhesive properties of their webs are created by fine droplets of "glue". In spite of these differences, the webs of the two groups are similar in their overall geometry. The evolutionary history of the Entelegynae is thus intimately connected with the evolutionary history of orb webs. One hypothesis is that there is a single clade, Orbiculariae, uniting the orb web makers, in whose ancestors orb webs evolved. A review in 2014 concluded that there

6345-614: The DNA polymerases ; here the holoenzyme is the complete complex containing all the subunits needed for activity. Coenzymes are small organic molecules that can be loosely or tightly bound to an enzyme. Coenzymes transport chemical groups from one enzyme to another. Examples include NADH , NADPH and adenosine triphosphate (ATP). Some coenzymes, such as flavin mononucleotide (FMN), flavin adenine dinucleotide (FAD), thiamine pyrophosphate (TPP), and tetrahydrofolate (THF), are derived from vitamins . These coenzymes cannot be synthesized by

6480-712: The Devonian period , about 386  million years ago , but these animals apparently lacked spinnerets. True spiders have been found in Carboniferous rocks from 318 to 299 million years ago and are very similar to the most primitive surviving suborder , the Mesothelae. The main groups of modern spiders, Mygalomorphae and Araneomorphae , first appeared in the Triassic period, more than 200  million years ago . The species Bagheera kiplingi

6615-672: The World Spider Catalog , currently ignore classification above the family level. At the higher level, the phylogeny of spiders is now often discussed using informal clade names, such as the " RTA clade ", the "Oval Calmistrum" clade or the "Divided Cribellum" clade. Older names previously used formally are used as clade names, e.g. Entelegynae and Orbiculariae . Enzyme Enzymes ( / ˈ ɛ n z aɪ m z / ) are proteins that act as biological catalysts by accelerating chemical reactions . The molecules upon which enzymes may act are called substrates , and

6750-628: The exocuticle of the legs and prosoma is modified by a tanning process, resulting in a brown coloration. Bilins are found, for example, in Micrommata virescens , resulting in its green color. Guanine is responsible for the white markings of the European garden spider Araneus diadematus . It is in many species accumulated in specialized cells called guanocytes . In genera such as Tetragnatha , Leucauge , Argyrodes or Theridiosoma , guanine creates their silvery appearance. While guanine

6885-499: The genus Tidarren amputate one of their palps before maturation and enter adult life with one palp only. The palps are 20% of the male's body mass in this species, and detaching one of the two improves mobility. In the Yemeni species Tidarren argo , the remaining palp is then torn off by the female. The separated palp remains attached to the female's epigynum for about four hours and apparently continues to function independently. In

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7020-512: The jumping spiders that patrol the outside walls of buildings, and so on. They are characterized by having fangs whose tips approach each other as they bite, and (usually) having one pair of book lungs . Spiders were long classified into families that were then grouped into superfamilies, some of which were in turn placed into a number of higher taxa below the level of infraorder. When more rigorous approaches, such as cladistics , were applied to spider classification, it became clear that most of

7155-511: The law of mass action , which is derived from the assumptions of free diffusion and thermodynamically driven random collision. Many biochemical or cellular processes deviate significantly from these conditions, because of macromolecular crowding and constrained molecular movement. More recent, complex extensions of the model attempt to correct for these effects. Enzyme reaction rates can be decreased by various types of enzyme inhibitors. A competitive inhibitor and substrate cannot bind to

7290-480: The thorax . Similarly, arguments can be formed against the use of the term "abdomen", as the opisthosoma of all spiders contains a heart and respiratory organs, organs atypical of an abdomen. Unlike insects , spiders do not have antennae . In all except the most primitive group, the Mesothelae , spiders have the most centralized nervous systems of all arthropods, as all their ganglia are fused into one mass in

7425-415: The Entelegynae. Although some studies based on both morphology and DNA suggest that the Haplogynae form a monophyletic group (i.e. they comprise all the descendants of a common ancestor), this hypothesis has been described as "weakly supported", with most of the distinguishing features of the group being inherited from ancestors shared with other groups of spiders, rather than being clearly indicative of

7560-695: The Haplogynae. Earlier analyses regarded the Hypochiloidea as the sole representatives of a group called the Paleocribellatae, with all other araneomorphs placed in the Neocribellatae. The Haplogynae are a group of araneomorph spiders with simpler male and female reproductive anatomy than the Entelegynae. Like the mesotheles and mygalomorphs, females have only a single genital opening ( gonopore ), used both for copulation and egg-laying; males have less complex palpal bulbs than those of

7695-461: The abdomen becomes green. Environmentally induced color changes may be morphological (occurring over several days) or physiological (occurring near instantly). Morphological changes require pigment synthesis and degradation. In contrast to this, physiological changes occur by changing the position of pigment-containing cells. An example of morphological color changes is background matching. Misumena vatia for instance can change its body color to match

7830-400: The ability to carry out biological catalysis, which is often reflected in their amino acid sequences and unusual 'pseudocatalytic' properties. Enzymes are known to catalyze more than 5,000 biochemical reaction types. Other biocatalysts are catalytic RNA molecules , also called ribozymes . They are sometimes described as a type of enzyme rather than being like an enzyme, but even in

7965-432: The active hunters have acute vision and hunters of the genus Portia show signs of intelligence in their choice of tactics and ability to develop new ones. Spiders' guts are too narrow to take solids, so they liquefy their food by flooding it with digestive enzymes . They also grind food with the bases of their pedipalps , as arachnids do not have the mandibles that crustaceans and insects have. To avoid being eaten by

8100-437: The active site and are involved in catalysis. For example, flavin and heme cofactors are often involved in redox reactions. Enzymes that require a cofactor but do not have one bound are called apoenzymes or apoproteins . An enzyme together with the cofactor(s) required for activity is called a holoenzyme (or haloenzyme). The term holoenzyme can also be applied to enzymes that contain multiple protein subunits, such as

8235-502: The active site. Organic cofactors can be either coenzymes , which are released from the enzyme's active site during the reaction, or prosthetic groups , which are tightly bound to an enzyme. Organic prosthetic groups can be covalently bound (e.g., biotin in enzymes such as pyruvate carboxylase ). An example of an enzyme that contains a cofactor is carbonic anhydrase , which uses a zinc cofactor bound as part of its active site. These tightly bound ions or molecules are usually found in

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8370-407: The animal fatty acid synthase . Only a small portion of their structure (around 2–4 amino acids) is directly involved in catalysis: the catalytic site. This catalytic site is located next to one or more binding sites where residues orient the substrates. The catalytic site and binding site together compose the enzyme's active site . The remaining majority of the enzyme structure serves to maintain

8505-578: The average values of k c a t / K m {\displaystyle k_{\rm {cat}}/K_{\rm {m}}} and k c a t {\displaystyle k_{\rm {cat}}} are about 10 5 s − 1 M − 1 {\displaystyle 10^{5}{\rm {s}}^{-1}{\rm {M}}^{-1}} and 10 s − 1 {\displaystyle 10{\rm {s}}^{-1}} , respectively. Michaelis–Menten kinetics relies on

8640-502: The body de novo and closely related compounds (vitamins) must be acquired from the diet. The chemical groups carried include: Since coenzymes are chemically changed as a consequence of enzyme action, it is useful to consider coenzymes to be a special class of substrates, or second substrates, which are common to many different enzymes. For example, about 1000 enzymes are known to use the coenzyme NADH. Coenzymes are usually continuously regenerated and their concentrations maintained at

8775-403: The cephalothorax acts as a pump that sends the food deeper into the digestive system. The midgut bears many digestive ceca , compartments with no other exit, that extract nutrients from the food; most are in the abdomen, which is dominated by the digestive system, but a few are found in the cephalothorax. Most spiders convert nitrogenous waste products into uric acid , which can be excreted as

8910-579: The cephalothorax. Unlike most arthropods, spiders have no extensor muscles in their limbs and instead extend them by hydraulic pressure. Their abdomens bear appendages, modified into spinnerets that extrude silk from up to six types of glands. Spider webs vary widely in size, shape and the amount of sticky thread used. It now appears that the spiral orb web may be one of the earliest forms, and spiders that produce tangled cobwebs are more abundant and diverse than orb-weaver spiders . Spider-like arachnids with silk-producing spigots ( Uraraneida ) appeared in

9045-471: The chemical equilibrium of the reaction. In the presence of an enzyme, the reaction runs in the same direction as it would without the enzyme, just more quickly. For example, carbonic anhydrase catalyzes its reaction in either direction depending on the concentration of its reactants: The rate of a reaction is dependent on the activation energy needed to form the transition state which then decays into products. Enzymes increase reaction rates by lowering

9180-425: The conversion of starch to sugars by plant extracts and saliva were known but the mechanisms by which these occurred had not been identified. French chemist Anselme Payen was the first to discover an enzyme, diastase , in 1833. A few decades later, when studying the fermentation of sugar to alcohol by yeast , Louis Pasteur concluded that this fermentation was caused by a vital force contained within

9315-616: The cribellum. Even species that do not build webs to catch prey use silk in several ways: as wrappers for sperm and for fertilized eggs; as a " safety rope "; for nest-building; and as " parachutes " by the young of some species. Spiders reproduce sexually and fertilization is internal but indirect, in other words the sperm is not inserted into the female's body by the male's genitals but by an intermediate stage. Unlike many land-living arthropods , male spiders do not produce ready-made spermatophores (packages of sperm), but spin small sperm webs onto which they ejaculate and then transfer

9450-446: The cup. However, in spiders these eyes are capable of forming images. The other pairs, called secondary eyes, are thought to be derived from the compound eyes of the ancestral chelicerates , but no longer have the separate facets typical of compound eyes. Unlike the principal eyes, in many spiders these secondary eyes detect light reflected from a reflective tapetum lucidum , and wolf spiders can be spotted by torchlight reflected from

9585-444: The decades since ribozymes' discovery in 1980–1982, the word enzyme alone often means the protein type specifically (as is used in this article). An enzyme's specificity comes from its unique three-dimensional structure . Like all catalysts, enzymes increase the reaction rate by lowering its activation energy . Some enzymes can make their conversion of substrate to product occur many millions of times faster. An extreme example

9720-428: The development of the embryo . Being chelicerates, their bodies consist of two tagmata , sets of segments that serve similar functions: the foremost one, called the cephalothorax or prosoma , is a complete fusion of the segments that in an insect would form two separate tagmata, the head and thorax ; the rear tagma is called the abdomen or opisthosoma . In spiders, the cephalothorax and abdomen are connected by

9855-433: The energy of the transition state. First, binding forms a low energy enzyme-substrate complex (ES). Second, the enzyme stabilises the transition state such that it requires less energy to achieve compared to the uncatalyzed reaction (ES ). Finally the enzyme-product complex (EP) dissociates to release the products. Enzymes can couple two or more reactions, so that a thermodynamically favorable reaction can be used to "drive"

9990-496: The ensuing 250 years, thousands more species have been described by researchers around the world, yet only a dozen taxonomists are responsible for more than one-third of all species described. The most prolific authors include Eugène Simon of France, Norman Platnick and Herbert Walter Levi of the United States, Embrik Strand of Norway, and Tamerlan Thorell of Sweden, each having described well over 1,000 species. At

10125-592: The enzyme urease was a pure protein and crystallized it; he did likewise for the enzyme catalase in 1937. The conclusion that pure proteins can be enzymes was definitively demonstrated by John Howard Northrop and Wendell Meredith Stanley , who worked on the digestive enzymes pepsin (1930), trypsin and chymotrypsin . These three scientists were awarded the 1946 Nobel Prize in Chemistry. The discovery that enzymes could be crystallized eventually allowed their structures to be solved by x-ray crystallography . This

10260-483: The enzyme at the same time. Often competitive inhibitors strongly resemble the real substrate of the enzyme. For example, the drug methotrexate is a competitive inhibitor of the enzyme dihydrofolate reductase , which catalyzes the reduction of dihydrofolate to tetrahydrofolate. The similarity between the structures of dihydrofolate and this drug are shown in the accompanying figure. This type of inhibition can be overcome with high substrate concentration. In some cases,

10395-422: The enzyme converts the substrates into different molecules known as products . Almost all metabolic processes in the cell need enzyme catalysis in order to occur at rates fast enough to sustain life. Metabolic pathways depend upon enzymes to catalyze individual steps. The study of enzymes is called enzymology and the field of pseudoenzyme analysis recognizes that during evolution, some enzymes have lost

10530-403: The enzyme. As a result, the substrate does not simply bind to a rigid active site; the amino acid side-chains that make up the active site are molded into the precise positions that enable the enzyme to perform its catalytic function. In some cases, such as glycosidases , the substrate molecule also changes shape slightly as it enters the active site. The active site continues to change until

10665-427: The enzyme. For example, the enzyme can be soluble and upon activation bind to a lipid in the plasma membrane and then act upon molecules in the plasma membrane. Allosteric sites are pockets on the enzyme, distinct from the active site, that bind to molecules in the cellular environment. These molecules then cause a change in the conformation or dynamics of the enzyme that is transduced to the active site and thus affects

10800-505: The evolutionary chronicle and the underlying diversity patterns that have resulted in one of the most extraordinary radiations of animals". Mesothelae resemble the Solifugae ("wind scorpions" or "sun scorpions") in having segmented plates on their abdomens that create the appearance of the segmented abdomens of these other arachnids. They are both few in number and also limited in geographical range. Suborder Opisthothelae contains

10935-565: The extent of nectar consumption by spiders may have been underestimated. Nectar contains amino acids , lipids , vitamins and minerals in addition to sugars, and studies have shown that other spider species live longer when nectar is available. Feeding on nectar avoids the risks of struggles with prey, and the costs of producing venom and digestive enzymes. Various species are known to feed on dead arthropods (scavenging), web silk, and their own shed exoskeletons. Pollen caught in webs may also be eaten, and studies have shown that young spiders have

11070-505: The female genital structures ( epigynes ). The monophyly of the group is well supported in both morphological and molecular studies. The internal phylogeny of the Entelegynae has been the subject of much research. Two groups within this clade contain the only spiders that make vertical orb webs: the Deinopoidea are cribellate – the adhesive properties of their webs are created by packets of thousands of extremely fine loops of dry silk;

11205-501: The females, which are typically much larger, male spiders identify themselves as potential mates by a variety of complex courtship rituals. Males of most species survive a few matings, limited mainly by their short life spans. Females weave silk egg cases, each of which may contain hundreds of eggs. Females of many species care for their young, for example by carrying them around or by sharing food with them. A minority of species are social, building communal webs that may house anywhere from

11340-407: The ganglia of all segments behind the esophagus are fused, so that the cephalothorax is largely filled with nervous tissue and there are no ganglia in the abdomen; in the Mesothelae, the ganglia of the abdomen and the rear part of the cephalothorax remain unfused. Despite the relatively small central nervous system, some spiders (like Portia ) exhibit complex behaviour, including the ability to use

11475-424: The gut, with paired ganglia as local control centers in all segments; a brain formed by fusion of the ganglia for the head segments ahead of and behind the mouth, so that the esophagus is encircled by this conglomeration of ganglia. Except for the primitive Mesothelae , of which the Liphistiidae are the sole surviving family, spiders have the much more centralized nervous system that is typical of arachnids: all

11610-478: The large females from eating the small males before fertilization, except where the male is so much smaller that he is not worth eating. In web-weaving species, precise patterns of vibrations in the web are a major part of the rituals, while patterns of touches on the female's body are important in many spiders that hunt actively, and may "hypnotize" the female. Gestures and dances by the male are important for jumping spiders , which have excellent eyesight. If courtship

11745-405: The length of the body and through which blood flows. The heart is a tube in the upper part of the body, with a few ostia that act as non-return valves allowing blood to enter the heart from the hemocoel but prevent it from leaving before it reaches the front end. However, in spiders, it occupies only the upper part of the abdomen, and blood is discharged into the hemocoel by one artery that opens at

11880-414: The likely number of offspring by ensuring that the females are well-fed. However, males of most species survive a few matings, limited mainly by their short life spans. Some even live for a while in their mates' webs. Females lay up to 3,000 eggs in one or more silk egg sacs, which maintain a fairly constant humidity level. In some species, the females die afterwards, but females of other species protect

12015-445: The major groupings used in the 20th century were not supported. Many were based on shared characteristics inherited from the ancestors of multiple clades ( plesiomorphies ), rather than being distinct characteristics originating in the ancestors of that clade only ( apomorphies ). According to Jonathan A. Coddington in 2005, "books and overviews published prior to the last two decades have been superseded". Listings of spiders, such as

12150-432: The males. While in many spiders color is fixed throughout their lifespan, in some groups, color may be variable in response to environmental and internal conditions. Choice of prey may be able to alter the color of spiders. For example, the abdomen of Theridion grallator will become orange if the spider ingests certain species of Diptera and adult Lepidoptera , but if it consumes Homoptera or larval Lepidoptera, then

12285-854: The males. Most spiders live for only one to two years, although some tarantulas can live in captivity for over 20 years, and an Australian female trapdoor spider was documented to have lived in the wild for 43 years, dying of a parasitic wasp attack. Spiders occur in a large range of sizes. The smallest, Patu digua from Colombia, are less than 0.37 mm (0.015 in) in body length. The largest and heaviest spiders occur among tarantulas , which can have body lengths up to 90 mm (3.5 in) and leg spans up to 250 mm (9.8 in). Only three classes of pigment ( ommochromes , bilins and guanine ) have been identified in spiders, although other pigments have been detected but not yet characterized. Melanins , carotenoids and pterins , very common in other animals, are apparently absent. In some species,

12420-461: The meantime, the female feeds on the palpless male. In over 60% of cases, the female of the Australian redback spider kills and eats the male after it inserts its second palp into the female's genital opening; in fact, the males co-operate by trying to impale themselves on the females' fangs. Observation shows that most male redbacks never get an opportunity to mate, and the "lucky" ones increase

12555-401: The midgut into the prey and then suck the liquified tissues of the prey into the gut, eventually leaving behind the empty husk of the prey. Others grind the prey to pulp using the chelicerae and the bases of the pedipalps , while flooding it with enzymes; in these species, the chelicerae and the bases of the pedipalps form a preoral cavity that holds the food they are processing. The stomach in

12690-474: The mixture. He named the enzyme that brought about the fermentation of sucrose " zymase ". In 1907, he received the Nobel Prize in Chemistry for "his discovery of cell-free fermentation". Following Buchner's example, enzymes are usually named according to the reaction they carry out: the suffix -ase is combined with the name of the substrate (e.g., lactase is the enzyme that cleaves lactose ) or to

12825-555: The mother's back, and females of some species respond to the "begging" behaviour of their young by giving them their prey, provided it is no longer struggling, or even regurgitate food. In one exceptional case, females of the jumping spider Toxeus magnus produce a nutritious milk-like substance for their offspring, and fed until they are sexually mature. Like other arthropods , spiders have to molt to grow as their cuticle ("skin") cannot stretch. In some species males mate with newly molted females, which are too weak to be dangerous to

12960-693: The mouth are called pedipalps , and serve different functions within different groups of chelicerates. Spiders and scorpions are members of one chelicerate group, the arachnids . Scorpions' chelicerae have three sections and are used in feeding. Spiders' chelicerae have two sections and terminate in fangs that are generally venomous , and fold away behind the upper sections while not in use. The upper sections generally have thick "beards" that filter solid lumps out of their food, as spiders can take only liquid food. Scorpions' pedipalps generally form large claws for capturing prey, while those of spiders are fairly small appendages whose bases also act as an extension of

13095-413: The mouth; in addition, those of male spiders have enlarged last sections used for sperm transfer. In spiders, the cephalothorax and abdomen are joined by a small, cylindrical pedicel, which enables the abdomen to move independently when producing silk . The upper surface of the cephalothorax is covered by a single, convex carapace , while the underside is covered by two rather flat plates. The abdomen

13230-541: The number of species in the families is bound to change and only reflects the present state of knowledge. Nevertheless, the species numbers given here are useful as a guideline – see the table of families at the end of the article. Spider taxonomy can be traced to the work of Swedish naturalist Carl Alexander Clerck , who in 1757 published the first binomial scientific names of some 67 spiders species in his Svenska Spindlar ("Swedish Spiders"), one year before Linnaeus named over 30 spiders in his Systema Naturae . In

13365-549: The offspring happens in the female's bell. They live almost entirely within the bells, darting out to catch prey animals that touch the bell or the threads that anchor it. A few spiders use the surfaces of lakes and ponds as "webs", detecting trapped insects by the vibrations that these cause while struggling. Spider taxonomy Arachnologists currently divide spiders into two suborders with about 129 families . Due to constant research, with new species being discovered every month and others being recognized as synonyms ,

13500-521: The outside world, except that they are penetrated by many sensors or connections from sensors to the nervous system. In fact, spiders and other arthropods have modified their cuticles into elaborate arrays of sensors. Various touch sensors, mostly bristles called setae , respond to different levels of force, from strong contact to very weak air currents. Chemical sensors provide equivalents of taste and smell , often by means of setae. An adult Araneus may have up to 1,000 such chemosensitive setae, most on

13635-438: The ovarian cavity where fertilization occurs. The only known example of direct fertilization between male and female is an Israeli spider, Harpactea sadistica , which has evolved traumatic insemination . In this species the male will penetrate its pedipalps through the female's body wall and inject his sperm directly into her ovaries, where the embryos inside the fertilized eggs will start to develop before being laid. Males of

13770-609: The phylogeny of the Entelegynae being as shown below. Araneoidea – orb web ; aerial sheet web ; cobweb ; no web Deinopoidea , Oecobiidae – orb web ; substrate-defined web RTA clade – no web; substrate-defined web On this view, orb webs evolved earlier, being present in the early members of the Entelegynae, and were then lost in more groups, making web evolution more convoluted, with different kinds of web having evolved separately more than once. Future advances in technology, including comparative genomics studies, and whole-genome sampling should lead to "a clearer image of

13905-440: The posterior pair of breathing organs are partly or fully modified into tracheae, through which oxygen is diffused into the haemolymph or directly to the tissue and organs. The tracheal system has most likely evolved in small ancestors to help resist desiccation . The trachea were originally connected to the surroundings through a pair of openings called spiracles , but in the majority of spiders this pair of spiracles has fused into

14040-528: The precise orientation and dynamics of the active site. In some enzymes, no amino acids are directly involved in catalysis; instead, the enzyme contains sites to bind and orient catalytic cofactors . Enzyme structures may also contain allosteric sites where the binding of a small molecule causes a conformational change that increases or decreases activity. A small number of RNA -based biological catalysts called ribozymes exist, which again can act alone or in complex with proteins. The most common of these

14175-549: The propulsive force for their jumps. Most spiders that hunt actively, rather than relying on webs, have dense tufts of fine bristles between the paired claws at the tips of their legs. These tufts, known as scopulae , consist of bristles whose ends are split into as many as 1,000 branches, and enable spiders with scopulae to walk up vertical glass and upside down on ceilings. It appears that scopulae get their grip from contact with extremely thin layers of water on surfaces. Spiders, like most other arachnids , keep at least four legs on

14310-406: The reaction and releases the product. This work was further developed by G. E. Briggs and J. B. S. Haldane , who derived kinetic equations that are still widely used today. Enzyme rates depend on solution conditions and substrate concentration . To find the maximum speed of an enzymatic reaction, the substrate concentration is increased until a constant rate of product formation

14445-733: The reaction rate of the enzyme. In this way, allosteric interactions can either inhibit or activate enzymes. Allosteric interactions with metabolites upstream or downstream in an enzyme's metabolic pathway cause feedback regulation, altering the activity of the enzyme according to the flux through the rest of the pathway. Some enzymes do not need additional components to show full activity. Others require non-protein molecules called cofactors to be bound for activity. Cofactors can be either inorganic (e.g., metal ions and iron–sulfur clusters ) or organic compounds (e.g., flavin and heme ). These cofactors serve many purposes; for instance, metal ions can help in stabilizing nucleophilic species within

14580-411: The rear end of the abdomen and by branching arteries that pass through the pedicle and open into several parts of the cephalothorax. Hence spiders have open circulatory systems . The blood of many spiders that have book lungs contains the respiratory pigment hemocyanin to make oxygen transport more efficient. Spiders have developed several different respiratory anatomies, based on book lungs ,

14715-425: The roots of the chelicerae. The families Uloboridae and Holarchaeidae , and some Liphistiidae spiders, have lost their venom glands, and kill their prey with silk instead. Like most arachnids , including scorpions , spiders have a narrow gut that can only cope with liquid food and two sets of filters to keep solids out. They use one of two different systems of external digestion. Some pump digestive enzymes from

14850-416: The sacs by attaching them to their webs, hiding them in nests, carrying them in the chelicerae or attaching them to the spinnerets and dragging them along. Baby spiders pass all their larval stages inside the egg sac and emerge as spiderlings, very small and sexually immature but similar in shape to adults. Some spiders care for their young, for example a wolf spider 's brood clings to rough bristles on

14985-410: The same enzymatic activity have been called non-homologous isofunctional enzymes . Horizontal gene transfer may spread these genes to unrelated species, especially bacteria where they can replace endogenous genes of the same function, leading to hon-homologous gene displacement. Enzymes are generally globular proteins , acting alone or in larger complexes . The sequence of the amino acids specifies

15120-461: The secondary eyes are immobile. The visual acuity of some jumping spiders exceeds by a factor of ten that of dragonflies , which have by far the best vision among insects . This acuity is achieved by a telephotographic series of lenses, a four-layer retina, and the ability to swivel the eyes and integrate images from different stages in the scan. The downside is that the scanning and integrating processes are relatively slow. There are spiders with

15255-454: The sexes apart, it is assumed the blood scent is mixed with pheromones. Spiders also have in the joints of their limbs slit sensillae that detect force and vibrations. In web-building spiders, all these mechanical and chemical sensors are more important than the eyes, while the eyes are most important to spiders that hunt actively. Like most arthropods, spiders lack balance and acceleration sensors and rely on their eyes to tell them which way

15390-456: The sperm to special syringe -styled structures, palpal bulbs or palpal organs, borne on the tips of the pedipalps of mature males. When a male detects signs of a female nearby he checks whether she is of the same species and whether she is ready to mate; for example in species that produce webs or "safety ropes", the male can identify the species and sex of these objects by "smell". Spiders generally use elaborate courtship rituals to prevent

15525-427: The spermathecae, creating a "flow through" system rather than a "first-in first-out" one. Eggs are as a general rule only fertilized during oviposition when the stored sperm is released from its chamber, rather than in the ovarian cavity. A few exceptions exist, such as Parasteatoda tepidariorum . In these species the female appears to be able to activate the dormant sperm before oviposition, allowing them to migrate to

15660-504: The spiders that have no plates on their abdomens. Opisthothelae is divided into two infraorders, Mygalomorphae and Araneomorphae, which can be distinguished by the orientation of their fangs. It can be somewhat difficult on casual inspection to determine whether the fang orientation would classify a spider as a mygalomorph or araneomorph. The spiders that are called " tarantulas " in English are so large and hairy that inspection of their fangs

15795-412: The structure which in turn determines the catalytic activity of the enzyme. Although structure determines function, a novel enzymatic activity cannot yet be predicted from structure alone. Enzyme structures unfold ( denature ) when heated or exposed to chemical denaturants and this disruption to the structure typically causes a loss of activity. Enzyme denaturation is normally linked to temperatures above

15930-519: The substrate is completely bound, at which point the final shape and charge distribution is determined. Induced fit may enhance the fidelity of molecular recognition in the presence of competition and noise via the conformational proofreading mechanism. Enzymes can accelerate reactions in several ways, all of which lower the activation energy (ΔG , Gibbs free energy ) Enzymes may use several of these mechanisms simultaneously. For example, proteases such as trypsin perform covalent catalysis using

16065-490: The substrate it lives on which makes it more difficult to be detected by prey. An example of physiological color change is observed in Cyrtophora cicatrosa , which can change its body color from white to brown near instantly. Although spiders are generally regarded as predatory, the jumping spider Bagheera kiplingi gets over 90% of its food from Beltian bodies , a solid plant material produced by acacias as part of

16200-405: The substrates. Enzymes can therefore distinguish between very similar substrate molecules to be chemoselective , regioselective and stereospecific . Some of the enzymes showing the highest specificity and accuracy are involved in the copying and expression of the genome . Some of these enzymes have " proof-reading " mechanisms. Here, an enzyme such as DNA polymerase catalyzes a reaction in

16335-437: The surface while walking or running. The abdomen has no appendages except those that have been modified to form one to four (usually three) pairs of short, movable spinnerets , which emit silk . Each spinneret has many spigots , each of which is connected to one silk gland . There are at least six types of silk gland, each producing a different type of silk. Spitting spiders also produce silk in modified venom glands. Silk

16470-399: The synthesis of antibiotics . Some household products use enzymes to speed up chemical reactions: enzymes in biological washing powders break down protein, starch or fat stains on clothes, and enzymes in meat tenderizer break down proteins into smaller molecules, making the meat easier to chew. By the late 17th and early 18th centuries, the digestion of meat by stomach secretions and

16605-413: The tapeta. On the other hand, the secondary eyes of jumping spiders have no tapeta. Other differences between the principal and secondary eyes are that the latter have rhabdomeres that point away from incoming light, just like in vertebrates, while the arrangement is the opposite in the former. The principal eyes are also the only ones with eye muscles, allowing them to move the retina. Having no muscles,

16740-435: The tarsi of the first pair of legs. Males have more chemosensitive bristles on their pedipalps than females. They have been shown to be responsive to sex pheromones produced by females, both contact and air-borne. The jumping spider Evarcha culicivora uses the scent of blood from mammals and other vertebrates, which is obtained by capturing blood-filled mosquitoes , to attract the opposite sex. Because they are able to tell

16875-555: The three hip joints (bordering the coxa and the trochanter). As a result, a spider with a punctured cephalothorax cannot extend its legs, and the legs of dead spiders curl up. Spiders can generate pressures up to eight times their resting level to extend their legs, and jumping spiders can jump up to 50 times their own length by suddenly increasing the blood pressure in the third or fourth pair of legs. Although larger spiders use hydraulics to straighten their legs, unlike smaller jumping spiders they depend on their flexor muscles to generate

17010-490: The total number of spider species, the Entelegynae about 83%. The phylogenetic relationships of the Haplogynae, Entelegynae and the two smaller groups Hypochiloidea and Austrochiloidea remain uncertain as of 2015 . Some analyses place both Hypochiloidea and Austrochiloidea outside Haplogynae; others place the Austrochiloidea between the Haplogynae and the Entelegynae; the Hypochiloidea have also been grouped with

17145-436: The tubules of insects and arachnids develop from completely different parts of the embryo . However, a few primitive spiders, the suborder Mesothelae and infraorder Mygalomorphae , retain the ancestral arthropod nephridia ("little kidneys "), which use large amounts of water to excrete nitrogenous waste products as ammonia . The basic arthropod central nervous system consists of a pair of nerve cords running below

17280-438: The type of reaction (e.g., DNA polymerase forms DNA polymers). The biochemical identity of enzymes was still unknown in the early 1900s. Many scientists observed that enzymatic activity was associated with proteins, but others (such as Nobel laureate Richard Willstätter ) argued that proteins were merely carriers for the true enzymes and that proteins per se were incapable of catalysis. In 1926, James B. Sumner showed that

17415-418: The usual body segments are fused into two tagmata , the cephalothorax or prosoma, and the opisthosoma , or abdomen, and joined by a small, cylindrical pedicel . However, as there is currently neither paleontological nor embryological evidence that spiders ever had a separate thorax-like division, there exists an argument against the validity of the term cephalothorax, which means fused cephalon (head) and

17550-486: The vertical orientation of their fangs and the possession of four book lungs. Most, if not all, of the spiders one is likely to encounter in everyday life belong to infraorder Araneomorphae . It includes a wide range of spider families, including the orb-weaver spiders that weave their distinctive webs in gardens, the cobweb spiders that frequent window frames and the corners of rooms, the crab spiders that lurk on flowers waiting for nectar- and pollen-gathering insects,

17685-477: The very top level, there is broad agreement on the phylogeny and hence classification of spiders, which is summarized in the cladogram below. The three main clades into which spiders are divided are shown in bold; as of 2015 , they are usually treated as one suborder, Mesothelae , and two infraorders, Mygalomorphae and Araneomorphae , grouped into the suborder Opisthothelae . The Mesothelae, with about 140 species in 8 genera as of October 2020 , make up

17820-486: The yeast cells called "ferments", which were thought to function only within living organisms. He wrote that "alcoholic fermentation is an act correlated with the life and organization of the yeast cells, not with the death or putrefaction of the cells." In 1877, German physiologist Wilhelm Kühne (1837–1900) first used the term enzyme , which comes from Ancient Greek ἔνζυμον (énzymon)  ' leavened , in yeast', to describe this process. The word enzyme

17955-495: Was described as herbivorous in 2008, but all other known species are predators , mostly preying on insects and other spiders, although a few large species also take birds and lizards. An estimated 25 million tons of spiders kill 400–800 million tons of prey every year. Spiders use numerous strategies to capture prey: trapping it in sticky webs, lassoing it with sticky bolas , mimicking the prey to avoid detection, or running it down. Most detect prey mainly by sensing vibrations, but

18090-581: Was first done for lysozyme , an enzyme found in tears, saliva and egg whites that digests the coating of some bacteria; the structure was solved by a group led by David Chilton Phillips and published in 1965. This high-resolution structure of lysozyme marked the beginning of the field of structural biology and the effort to understand how enzymes work at an atomic level of detail. Enzymes can be classified by two main criteria: either amino acid sequence similarity (and thus evolutionary relationship) or enzymatic activity. Enzyme activity . An enzyme's name

18225-457: Was used later to refer to nonliving substances such as pepsin , and the word ferment was used to refer to chemical activity produced by living organisms. Eduard Buchner submitted his first paper on the study of yeast extracts in 1897. In a series of experiments at the University of Berlin , he found that sugar was fermented by yeast extracts even when there were no living yeast cells in

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