2.4 Enzymes

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  • Created by: elbungay1
  • Created on: 01-06-19 17:45
What is a catalyst?
Chemical that speeds up the rate of reaction and remains unchanged and reusable at the end of the reaction
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What is a substrate?
Molecules that is altered by an enyzme-catalysed reaction
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What is a product?
Molecule produced from substrate molecules, by an enzyme-catalysed reaction
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What is the active site?
Indented area on the surface of an enzyme moleucle, with a shape that is complementary yo the shape of substrate molecule. Can be altered by changes in temperature and pH. Highly specific in its function
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What are intracellular enzymes?
Enzymes that work inside the cell. Make parts of metabolic pathways, reactants products and intermediates are metabolites. Catabolic reactiosn where metabolites are broken down. Anabolic reactions where energy used to synthesise larger molecules.
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What is catalase?
Intracellular enzyme consiting of four polypeptide chains and contains a haem group with iron. Breaks down hydrogen peroxide to water and oxygen. In eukaryotes, found in vesicles called peroxisomes. Phagocytes release catalase to destroy microbes
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What are extracellular enzymes?
Secreted from cells where they are made and act on their substrates extracellularly. Digestive enzymes secreted from lining tissues and digest carbohydrates, proteins lipids which are then absorbed into bloodstream.
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What is Amylase?
Produces in salivary glands and acts in mouth to digest the polysaccharide starch to disaccharide maltose. Also made in pancreas to act in lumen of small intestine
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What is trypsin?
Made in pancreas and acts in lumen of small intestine to digest proteins into smaller peptides by hydrolysing peptide bonds.
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What is a cofactor?
A substance that has to be present to ensure that an enzyme-catalysed reaction takes place at the appropriate rate. Some cofactors (prosthetic groups) are part of enzyme structure and others (mineral ion cofactors and organic coenzymes) temporary
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What is a Prosthetic group?
Cofactor that is permanently bound by covalent bonds to an enzyme molecule.
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Describe an example of a prosthetic group
Enzyme carbonic anhydrase contains a zinc ion permanently bound as a prosthetic group to its active site. Found in erthrocytes and catlayses interconversion of CO2 and H2O to carbonic acid, which then dissociates into protons and hydrogencarbonate io
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What are co-substrates?
Cofactors that bind alongside the substrate in the active site to form the correct shape in active site
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What are Coenzymes?
Small organic non-protein molecules that bind temporarily to the active iste of enzyme molecules, either just before or at the same time as the substrate.
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What is an enzyme-substrate complex
Enzyme molecule with substrate molecule in it active site. The two are joined temporarily by non-covalent forces
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What is an enzyme-product complex?
Enzyme molecule with product moleucle(s) in its active site. The two are joined temporarily by non-covalent forces
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What is the lock-and-key hypothesis?
Tertiary structure of enzyme's active site gives it a shape that is complementary to that of the substrate molecule.
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What is the induced fit hypothesis?
When substrate molecule fits into the enzyme's active site. The active site changes shape slightly to mould itself around the substrate molecule. Still complementary but R-chains in active site conforms for a more concise fit. ESC forms then EPC
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Describe the process in which a product is formed from its substrate
Substrate enters active site of enzyme and temporary non-covalent forces (hydorgen, london, ionic) forms Enzyme-substrate complex. Enzyme-product complex formed, product molecules have a slightly different shape so detach from active site.
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How do enzymes lower the activation energy of reactions?
In living cells, temperatures cannot be raised too much otherwise proteins would denature. Active site only complementary to substrate, bringing substrate molecules close enough together to react, without need for excessive heat. Lower Ea
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What happens when a reaction mixture containing and substrate and enzymes is heated?
Both types of molecules will gain kinetic energy and move faster. Increase rate (no, per second) of successful collisions. Rate of formation of ESC increases, rate increases, formation of EPC per seconds, up to a point. Rate at max at optimum temp
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How do enzymes become denatured?
Increasing heat causes molecules to vibrate, break weak bonds (hydrogen and ionic) Active site shape begins to change and substrate dont fit as well and rate decreases. As more heat applied site irreversibly changes, reaction cant proceed
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What is the Temperature Coefficient Q10?
Refers to increase in the rate of a process when temperature increased by 10°C. Is approximately 2, rate doubles with every 10°C. Q10 = (rate of reaction at T+10°)/(rate of reaction at T).
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How does changes in pH affect bonds within molecules?
Protons are attratced to negatively charged ions, molecules or parts of molecules. Excess will interfere with hydrogen bonds and ionic bonds and so active site changes shape, rate of reaction will be lowered. Positive charge will prevent binding too
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Describe changes in pH either side of Optimum
Small changes of pH, either side of optimum slow rate of reaction, as active site is disrupted. If normal pH is restored the shape is restored. At extremes of pH, enzyme's active site may be permanently changed, reaction cannot continue.
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Why do not all enzymes have the same optimum pH
Extracellular enzymes in stomach have a very low optimum pH as hydrochloric acid kills bacteria and other pathogens e.g. protease. Amylase enzymes in mouth and pancreas have optimum pH of 6.8
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Describe the effect of increasing substrate concentration on rate?
Rate of reaction increases as more enzyme-sibstrate complexes (ESCs) can form. As a result, more product molecules are formed. Susbtrate conc is limiting reaction as when it increases, rate increases. Substrate conc is limiting factor
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Why does the reaction reach a maximum rate with increasing substrate concentration?
Adding more substrate molecules will not increase the rate of reaction. This is because all enzyme's active sites are occupied with substrate molecules. If more substrate molecules are added, then they cannot successfully collide with and fit into AS
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What is the effect of increasing enzyme concentration in an enzyme-controlled reaction
More active sites on the enzyme become available, more successful collisions between enzyme and substrate occurs, more ESC can form per unit time so rate of reaction increases. Enzyme concentration is limiting factor, as it increases, rate does
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Why is the initial rate of reaction greater?
Initially, enzyme and substrate molecules are first mixed and then are moving randomly, there is a great chance of successful collisions, as reaction proceeds, substrate concentration decreases, frequency of successful collisions decreases
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What is an inhibitor?
A substance that reduces the activity of an enzyme
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What are Competitive Inhibitors
Molecules that have a similar shape to substrate molecules. Competitive inhibitor fits into active site and so a substrate cannot enter. Degree of inhibition relates to relative concentration and inhibitor. Still reaches max rate but slower
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What are Non-competitive Inhibitors
Bind to allosteric site of enzyme disrupting tertiary structure, distortion changes active site so is no longer complementary to shape of substrate, ESC cannot form. Maximum rate reduced, irreversible change
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What is End-product Inhibition?
Way of regulating enzyme-catalysed reactions. E.g. product may stay tightly bound to enzyme preventing any more ESCs being formed.
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Describe a control of metabolic sequences
Product of one enzyme-controlled reaction becomes the substrate to the next. Cells dont want to accumulate too much end product, so end product may act as non-competitive inhibitor to first enzyme. When concentration of product falls, they detach
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Describe how Cyanide acts a inhibitor
Forms CN- which binds irreversibly to enzymes in mitochondria preventing final stage of aerobic respiration, earlier stages cannot occur so aerobic respiration stops
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Describe how Snake Venom acts as an inhibitor
Inhibits enzyme acetylcholinesterase, meaning ACH stays attached to receptors on msulce membranne and keeps muscle contracted. Causes paralysis and is breathing muscles are paralysed, victims die from suffocation
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What are ACE inhibitors?
ACE increases blood pressure, so inhibitors are used a drug to lower blood pressure in pateints with hypertension, who cannot take beta-blockers. Treats heart failure and minimises risk of second heart attack or stroke.
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What is a product?

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Card 4

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What is the active site?

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Card 5

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