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49 Cards in this Set
- Front
- Back
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What are Enzymes and what do they do?
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Enzymes are biological catalysts. Enzymes are globular proteins. They speed up the rate of reaction by lowering the activation energy. They are not used up in the reaction. |
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How is the active site of an enzyme formed?
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The active site is formed from the precise folding of to enzyme into its secondary, tertiary and sometimes quaternary structure. |
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How many amino acids make up the active site?
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6-10
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"The active site makes the enzyme specific", what does this mean?
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It can only bond to certain substrates
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Describe the lock and key model
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An enzyme and substrate are exactly complementary to each other and fit exactly to form an enzyme substrate complex.
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Describe and explain the induced fit model
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1. Enzyme and substrate randomly collide 2. Active site shape changes slightly to mould itself to the substrate and the substrate binds more effectively. 3. ESC forms and puts strain on the bonds in the substrate 4. Product formed and EPC formed 5. Product leaves the active site because it is no longer complementary and leaves the enzyme free. |
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What do intracellular enzymes do?
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Catalyse reactions inside cells
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Where are intracellular enzymes found?
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In the cytoplasm or attached to the cell membrane
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Give an example of an intracellular enzyme and its function
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Chloroplasts catalyse photosynthesis
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What do extracellular enzymes do?
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Catalyse reactions outside the cell
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Give an example of an extracellular enzyme
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Digestive enzymes (amylase or trypsin) Saprophytic fungi secrete enzymes to digest food |
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Define a cofactor and state the 3 types of cofactor |
Any substance that must be present to ensure that an enzyme controlled reaction takes place at an appropriate rate. Prosthetic groups, Coenzymes and inorganic ion cofactors. |
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Are prosthetic groups a permanent or impermanent cofactor and how do they bond to the enzyme?
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They are permanent and bound with covalent bonds.
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How are prosthetic groups added to the enzyme?
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Added in the Golgi apparatus where protein modification takes place
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Give an example of a prosthetic group
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Zinc ion in carbonic anhydrase
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What are coenzymes
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A small organic non-protein molecule which can participate in the reaction and be changed but are recycled back to be reused. Often function as a carrier which transfers chemical groups from the active site of one enzyme to the active site of another. |
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Where and how to coenzymes bind?
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Bind temporarily to the active site (via ionic or hydrogen bonds)
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Give an example of a coenzyme
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NAD made of vitamin B3 assists pyruvate dehydrogenase in respiration
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What is an inorganic ion cofactor and how does it benefit the enzyme?
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Any charged ion that is not bound, it acts as a co-substrate to effect the shape of the substrate . can also change the charge distribution in the enzyme. Overall, helps the ESC to form. |
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Give an example of an inorganic ion cofactor
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Iron in catalase bonds with hydrogen peroxide
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How do you calculate rate of reaction?
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Rate of reaction = Volume (or mass) of product produced / set time period
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What is the effect on an enzyme and the overall rate of reaction if the temperature is initially increased?
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Increased kinetic energy of molecules, more movement, more successful collisions, increased likelihood of ESC forming, more product produced, increased rate of reaction.
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What is the effect on an enzyme and the overall rate of the reaction if the temperature continues to be increased?
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Energy increases and molecules vibrate, puts strain on bonds in the enzymes, the shape of the active site changes, no longer complementary to the substrate, no ESC forms, enzyme is denatured, rate of reaction decreases.
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Define denaturation
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Change in the tertiary structure of the enzyme such that it cannot function and the function cannot be restored
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Define optimum temperature
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The temperature at which there is a balance between increasing kinetic energy of the molecules and increasing vibration of atoms within the molecules. Where the enzyme works best in order to achieve a maximum rate of reaction.
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What is the temperature coefficient
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Refers to the rate of a process when the temperature is increased by 10 degrees
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How do you calculate the temperature coefficient?
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o Q10 = rate of reaction at T + 10/ rate of reaction at T
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What is pH?
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A measure of H+ ion concentration
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How might pH affect an enzyme?
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It may interfere with hydrogen and ionic bonds, the active site of the enzyme may change shape. The charge distribution around the active site may be changed. Interferes with the binding site of the substrate molecule
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What is optimum pH?
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The pH at which the enzyme can operate at its maximum rate of reaction. Where the active site is held in a way that best fits the substrate |
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What is a buffer?
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A solution that resists changes in pH by donating or accepting protons.
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What happens if the substrate concentration in an enzyme controlled reaction is increased?
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Rate of reaction initially increases. More successful collisions, more ESCs form, more product is formed, initially the substrate concentration is the limiting factor. Reaction rate then plateaus at maximum as enzyme concentration becomes the limiting factor. All enzyme active sites are occupied with substrate, more substrate added cannot collide with active site. Enzymes are working are max rate. |
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What do cells do to excess enzymes?
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They are degraded
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Why do cells degrade enzymes?
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They eliminate abnormally shaped proteins that might otherwise accumulate and harm the cell. They control the number of enzymes in order to regulate metabolism. |
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What happens to an enzyme controlled reaction id the enzyme concentration is increased?
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When the enzyme concentration is the limiting factor, More active sites become available, More successful collisions can occur, so more ESCs form and rate of reaction increases. If the substrate concentration is limited, All substrate will be converted to product, The rate reaches a maximum,The graph plateaus. Substrate concentration becomes the limiting factor. |
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What happens in an enzyme controlled reaction if the substrate concentration is unlimited and the enzyme concentration continues to be increased?
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The reaction will continue indefinitely. The rate of reaction will continue to increase in proportion to the concentration of the enzyme.
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What do enzyme inhibitors do?
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Slow down the rate of an enzyme controlled reaction by affecting the enzyme in some way.
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How do competitive inhibitors work?
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1. Competitive inhibitor has a similar shape to the substrate 2. Competitive inhibitor is complementary to the active site 3. Therefore, an enzyme inhibitor complex forms and blocks active site 4. So, an ESC cannot form 5. And therefore, no product is produced |
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What happens if you continue to increase the substrate concentration in a reaction which is inhibited by a competitive inhibitor?
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The substrate will outcompete the inhibitor and the maximum rate of reaction will eventually be obtained.
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Why are competitive inhibitors usually reversible?
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Because they bind temporarily with weak ionic or hydrogen bonds
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What is penicillin an inhibitor of?
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Bacterial enzymes
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Why is competitive inhibition useful is Ethylene glycol (antifreeze) is consumed?
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Both ethylene glycol and alcohol can be broken down by alcohol dehydrogenase. Alcohol --> non toxic waste products Antifreeze --> toxic waste products Alcohol acts as an inhibitor to the break down of antifreeze as substrates compete for the active site of the enzyme. |
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How does non-competitive inhibition work?
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1. Inhibitor binds to the allosteric site (another binding site on the enzyme) 2. Causes the tertiary structure of the enzyme to change 3. Therefore, the shape of the active site changes 4. The substrate is no longer complementary to the active site 5. The ESC cannot form so no product is produced |
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Why does a reaction inhibited by a non-competitive inhibitor not reach the same maximum rate of reaction as the non-inhibited reaction?
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The enzyme is effectively denatured so its active site is no longer complementary to the substrate. The extent of the rate reduction depends on the concentration of the inhibitor.
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Are non-competitive inhibitors reversible or irreversible?
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Irreversible (They bind permanently with strong covalent bonds) |
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How does Cyanide effect an organism?
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Inactivated cytochrome oxidase which is involved in respiration. Prevents organisms respiring aerobically. The lactic acid build up poisons the body.
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How do nerve gases effect an organism?
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Bind with chlorinesterase. Prevent the controlled transmission of nerve impulses across synapses. The nervous system becomes overstimulated and muscles contract uncontrollably.
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How are metabolic processes controlled by enzyme inhibitors?
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Metabolic processes are a series of steps where each is controlled by a different and specific enzyme. The first step is often catalysed by an enzyme which is often inhibited by the end product. The end product stops the production of unrequired product. |
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How are enzyme inhibitors useful in asprin? |
Binds to enzymes that catalyse the formation of cell signalling molecules produced by damaged cells, they make nerve cells more sensitive and increase swelling
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