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Biology 2.1.3

AS OCR biology - enzymes

What is the structure of enzymes? Globular proteins with specific tertiary structure, water soluble as hydrophilic R groups face outwards. Specifically shaped active site depends on R groups.
What is the function of enzymes? Biological catalysts, speed up the rate of a metabolic reaction, unchanged at the end of the reaction. Enzyme action may be intracellular or extracellular
How are enzymes better than inorganic catalysts? They don't produce a range of unwanted by-products
Enzymes are highly __?__ for their substrate - this means: Specific - they only bind to one type of substrate
What are the two types of enzyme action? Intracellular (e.g. respiration in mitochondria) or extracellular (e.g. digestion)
What are cofactors + types? Substances that cause enzyme-controlled reactions to take place at the appropriate rate e.g. coenzymes, inorganic ion cofactors, prosthetic groups
What are coenzymes + function? Organic non-protein molecules that bind to the active site at the same time as the substrate for a short time - carry chemical groups between enzymes to allow an enzyme cascade reaction
What are prosthetic groups? Coenzymes that are permanent parts of the quaternary structure of the protein
What is the function inorganic ion cofactors? Increase the rate of reaction - bind to enzyme or substrate, affect charge distribution so enzyme-substrate complex forms more easily
What is activation energy and how do enzymes reduce it and why? Activation energy is the amount of energy required for a reaction to proceed. Enzymes reduce the amount of activation energy required because the active site fits the substrate perfectly, lowering the amount of energy needed to start a reaction
Describe how an enzyme catalyses a reaction 1 The substrate binds to the active site due to bonds between oppositely-charged groups, forming an enzyme substrate complex. 2 Bonds are made or broken producing an enzyme product complex. 3 Product leaves active site and enzyme is available for reuse
What is the lock-and-key hypothesis? The enzyme’s active site and the substrate molecule have complementary shapes
What is the induced-fit hypothesis? Substrate collides with active site, enzyme molecule changes shape slightly so active site fits more closely around substrate.Shape change puts strain on/destabilises substrate so faster rate of reaction. Product doesnt fit in active site so leaves
What are oxidoreductases? Enzymes that catalyse the transfer of electrons between different substrates
How do you keep temperature constant in an experiment of enzyme activity? By carrying out a reaction in a water bath with a thermostat. Equilibration - enzyme and substrate must be placed separately in a water bath so they reach the required temperature before the investigation begins
How do you keep enzyme concentration constant in an experiment of enzyme activity? By accurately measuring surface area and mass of enzyme, and volume of enzyme in solution
How do you keep pH constant in an experiment of enzyme activity? pH buffers keep pH at a set level by maintaining a constant H+ concentration
How + why does enzyme activity change with temperature? Low temp - very slow reaction, low KE, few successful collisions. Optimum temp - highest ror, high KE, many collisions between enzyme and substrate, many enzyme-substrate complexes form. High temp - denaturing, high KE, vibration, weak bonds break
What is pH a measure of? pH is a measure of the H+ ion concentration, high concentration means acidic
How + why does enzyme activity change with pH? Curve= symmetrical bell-shaped curve, effective in narrow pH ranges. Optimum pH - conc of H+ ions in solution holds tertiary structure of active site in best shape complementary to substrate.
Continued Too high/low - H+ ions interfere with hydrogen and ionic bonds, affecting tertiary structure of active site so it isn’t complementary to substrate and reduces the formation of enzyme-substrate complexes. Enzymes denature at extreme pHs so activity stops
How + why does substrate concentration affect enzyme activity? Higher chance of collision of substrate & active site so more enzyme-substrate complexes form, more product. V-max is max rate of reaction where all active sites are occupied at a time, so enzyme conc is limiting factor, higher substrate conc has no effec
How + why does enzyme concentration affect enzyme activity? Higher number of active sites + chance of collision of substrate and active site, so more enzyme-substrate complexes form. Max rate of reaction-where all substrate is being catalysed, so enzyme conc is limiting factor + higher substrate conc has no effect
What is a limiting factor? A factor that in higher concentration would increase the rate of reaction, if all other conditions are kept constant
What are inhibitors, types + uses? Inhibitors reduce the reaction rate in an enzyme-controlled reaction by affecting the enzyme molecule. Competitive inhibitors = active-site directed. Non-competitive inhibitors = non-active site directed. Poisons + medicinal drugs.
How do competitive inhibitors work? the inhibitor is a similar shape to the true substrate and occupies and blocks the active site for a short while, reversible
How do non-competitive inhibitors work? the inhibitor attaches to the enzyme (not active site) and disrupts tertiary structure of active site so it isn’t complementary to the substrate so no enzyme-substrate complexes can form, many are irreversible, e.g. poison
What is a potassium cyanide and how does it work? Poison- non-competitive inhibitor for a respiratory enzyme called cytochrome oxidase found in mitochondria which prevents ATP formation - organism can’t respire aerobically and anaerobic respiration causes lactic acid to build up in the blood
How is infection by virus treated? Infection by viruses (e.g. HIV) can be treated using competitive inhibitors that inhibit protease activity, which is an enzyme needed by viruses to build virus coats, preventing viruses from replicating
Created by: 11043