AS Biology - Enzymes - Chapter 3 - Book Molecules & Cells
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| Enzyme | are substances that act as catalysts->they increase the rate of chemical reactions.-> once prod. is formed they leave active site of enzyme which is left free again->E. are NOT used up in reactions->can be used over and over again. | Enzymes greatly increase the rate of formation of a product ( A + B -> C) by a factor of at least 1 m. ->Enzymes are large globular protein molecules->E. are specific!
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| Catalysts | increase the rate of chemical reactions | (blank)
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| Carbonic anhydrase | is one of the fastest enzymes-> catalyses following reaction: CO2 + H2O <=> H2CO3 // | (blank)
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| What does "Enzymes are specific" mean? | That each enzyme only catalyses ONE reaction | (blank)
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| Substrate | The substance with which the enzyme combines. | (blank)
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| Active Site | The particulat place where the enzyme combines with the substrate on the enzymes surface. (usually relatively small part of the enzyme->the rest of the enzyme is involved in maintaining the active site) | The precise shape of AS is important as it is complementary to the shape of substrate molecule->"lock-and-key-mechanism"
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| Induced Fit | is the process that the shape of some active sites changes when the substrate molecule attaches to it. | (blank)
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| exotherm | chemical reaction which produces heat (ie. combustion) | Most reactions that occur spontaneously
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| endothermic | chemical reaction which "takes" heat->absorb heat. | (blank)
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| Free energy | some energy that is produced dissipate (ie. heat, light) and is therefore not available for other processes. Other forms of energy can be used by organsim to drive other processes=>they are called "Free Energy" | change in free energy is given the symbol "A"G, reaction only occurs spontaneously if "A"G is negative.
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| Exergonic | reaction only occurs spontaneously if "A"G is negative. | (blank)
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| Endergonic | reaction only occurs spontaneously if "A"G is positive->input of free energy is needed to drive reaction. | (blank)
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| Activation Energy | In living cells, most chemical reactions require input of energy before the molecules react together. | (blank)
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| The overall reactions between an enzyme and its substrate can be represented by following equation: | Enzyme + Substrate -> Enzyme-Substrate complex -> Enzyme + Product | (blank)
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| Turnover Number | the number of substrate molecules which an enzyme can act upon in a given time. | (blank)
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| equilibrium | reactions proceed from left to richt (or vice versa)->in time reactions reach a point where reactants and products are in equilibrium with one another. =>Enzymes catalyse the forward and reverse reactions equally. | ->and do noth therefore alter the equilibrium itself, but only the speed at which it is reached.
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| Enzyme concentration | enzymes work efficiently at very low concentrations as they may be used again and again. To work efficiently temperature & other conditions must be suitable. | Provided there are excess substrate mol. the rate of a reactions is directly proportional to the enzyme concentration. ->if amnt is restricted it limits the rate of reaction->further enzymes cannot increase rate!
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| Enzyme Specificity | enzymes usually work on very specific substrates-> like a key->some are highly specific, others may not be so much: ie. will break particular chemical linkage wherever it occurs wheras others will only act on particular isomers. | (blank)
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| Substrate concentration | For a given amnt of enzyme the rate of an enzyme controlled reaction increases with increasing substrate concentration- up to a point. | ->low concentration of substrates->not all active sites of Emolec r used, ie. occupied. , very high substrate concentration->all sites are being used->rate of reaction cannot increase more->graph tails off.
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| Enzymes - Temperature | has 2 main effects: 1. increase kenetice energy ->faster movement->more often substrate & enz. collide->greater rate of reaction., 2. atoms (which make up enzymes) vibrate->breaking up hydrogen bonds etc. ->shape of enz. is altered->active site no longer | fits substrate->enzyme is said to be denatured->loses its catalytic property//optimum temperatures of enz. varies between appr. 10-80 C-> most commonly areoung 40 C->denaturing usually occurs at appr. 60C.
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| Denaturing | i.e increase of temperature->. atoms (which make up enzymes) vibrate->breaking up hydrogen bonds etc. ->shape of enz. is altered->active site no longer fits substrate->enzyme is said to be denatured->loses its catalytic property | or change in pH->3-dimensional mol. shape is vital to functioning of enzymes->they are partly results of hydrogen bonding which may be broken by conc. of (H+)ions present and may lead to denaturing.
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| Definition pH | is a measure of hydrogen ion concentration (H+)->is usually measured on a scale of 1-14 with pH7 being neutral. pH less than 7 is acid, pH greater than 7 is alkaline | Each enzyme works best at a particular pH and deviations from this optimum may result in denaturation->Optimum pH various from enzyme to enzyme.
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| Hydrogen ions | (H+) | (blank)
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| Kinetic Energy | Energy due to the motion of an object ->be translation (motion along a path from one place to another), rotation about an axis, vibration, or any combination of motions. | The kinetic energy of an object depends on its mass and velocity
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| Inhibitors | rate of enzyme reactions may be decreased by their presence->there are 2 main types: 1. reversible inhibtors, 2. non-reversible inhibitors | (blank)
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| Reversible inhibitors | effect is temporary and cause no permanent damage to enzymes, bcs their association with enzymes is loos->can easily be removed. | 2 types: competetive (active site-directed) and 2. non-competetive (non-active-site-directed)
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| Competetive inhibitors | Reversible inhibitors->active site-directed->compete with the substrate for active site of enzyme mol. ->their struct. combines with AS->therefore prevents substrates to occupy site->reduces rate of reaction | ->the same quantity of product is formes (->as substrate continues to use any enzyme molecules that are unafected)->but it takes longer!, ie. MALONIC ACID which dompetes with succinate
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| Non-competetive inhibitors | Reversible Inhibitors->attach themselves not to the active site of the enzyme but elsewhere. ->they alter shape of E. that that the AS can no longer properly accomodate the substrate | ->as substrate & inhibitors attach to different parts they do not compete for same site->increase in substrate cons. therefore doen's reduce effect of inhibitors.
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| Non-reversible inhibitors | leave enzyme permanently damaged->E. are therefore unable to carry out their catalytic function.->ie. heavy metal ions such as mercury (Hg2+) and silver (Ag+) casue sisulphide bonds to break (those bonds help to maintain the shape of E. mol.)->permanent | loss of catalytic properties.
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| Cofactor | is a non-protein substance which is essential for some enzymes to function efficiently | There are 3 types: 1. activators , 2. coenzymes, 3. prosthetic groups
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| Activators | are substances which are necessary for the functioning of certain enzymes. | it is possible that activators asist in froming the enzyme-substrate complex by moulding either the enzyme or substrate molecules into a more suitable shape.
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| Coenzymes | are non-protein organic substances which are essential to the efficient functioning of some enzymes, but are NOT themselves bound to enzymes. They are often derived from vitamines. | Need to know example?
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| Prosthetic groups | are organic molecules (like coenzymes), but they ARE bound to enzymes themselves. | example is haem.
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| Classification of enzymes | are classified into 6 groups according to the type of reaction they catalise: 1. Oxidoreductase, 2. Transferases, 3. Hydrolases, 4. Lyases, 5. Isomerases, 6. Ligases | (blank)
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| negative feedback | This occurs where the products of a process can act at an earlier stage in the process to inhibit their own formation. | Where the end product (E) of a pathway inhibits (the enzyme) at the start (A) ->ie. high concentration of E reduces its own production rate (A). they are usually reversible
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