enzymes

Question 1

what are enzymes?

Answer 1

biological catalysts in living cells which speed up chemical reactions whilst remaining unchanged- essential for survival

Question 2

what do enzymes do to the equilibrium?

Answer 2

• DO NOT alter the equilibrium
• just accelerate the time taken to reach the equilibrium

Question 3

what is enzyme alkaline phosphatase involved in?

Answer 3

mineralisation of tissue and bone

Question 4

what is enzyme amylase involved in?

Answer 4

found in saliva, converts starch into sugars

Question 5

what is enzyme maltase involved in?

Answer 5

found in saliva, breaks sugar maltose into glucose

Question 6

what is enzyme lysozyme involved in?

Answer 6

antimicrobial, breaks down the peptidoglycan layer in the cell wall of bacteria

Question 7

what is enzyme pepsin involved in?

Answer 7

digestion in stomach, breaks down proteins into smaller peptides

Question 8

what is enzyme trypsin involved in?

Answer 8

found in small intestine, breaks down proteins into amino acids

Question 9

what is enzyme acetylcholinesterase involved in?

Answer 9

breaks down the neurotransmitter acetylcholine in nerves and muscles

Question 10

what is enzyme DNA polymerase involved in?

Answer 10

synthesises DNA from doexyribonucleotides

Question 11

what are the two ways in which an enzyme can work?

Answer 11

• lock and key
• induced fit

Question 12

what is lock and key?

Answer 12

Enzyme active site complementary in shape to that of substrate
Active site precisely shaped to hold specific substrates

Question 13

what is induced fit?

Answer 13

Active site and substrate do not fit together exactly
Enzyme changes shape when substrate binds
Active site has a shape complementary to the substrate only after the substrate has bound

Question 14

what is induced fit?

Answer 14

Active site and substrate do not fit together exactly
Enzyme changes shape when substrate binds
Active site has a shape complementary to the substrate only after the substrate has bound

Question 15

what kind of molecule are most enzymes?

Answer 15

proteins (exceptions are catalytic RNA molecules)

Question 16

what affects the nature of an enzyme?

Answer 16

pH
temperature

Question 17

what is the optimum?

Answer 17

the conditions at which the enzyme works best at

Question 18

what happens to the enzyme at extreme conditions?

Answer 18

it may lose its 3D structure- denature, and become totally inactive

Question 19

what is the standard free energy change of a reaction? (G)

Answer 19

Difference between energies of reactants (initial state) and products (final state) is the

Question 20

what is the activation energy of a reaction? (Ea)

Answer 20

the energy input required to initiate a reaction

Question 21

what effect do enzymes have on activation energy?

Answer 21

enzymes lower activation energy (enzymes cannot alter free energy)

Question 22

what are factors which can affect the rate of an enzyme reaction?

Answer 22

Temperature
pH
Enzyme concentration
Substrate concentration
Inhibitors and activators
Covalent modification

Question 23

what will an increase in enzyme concentration do to a reaction?

Answer 23

increase the reaction rate

Question 24

what effect does increasing substate concentration have on the rate of an enzyme reaction?

Answer 24

originally, increasing S will increase reaction rate, until all active sites are occupied whereafter it will remain constant

Question 25

what is Vmax?

Answer 25

the maximum rate of reaction, where the enzyme is saturated with substrate

Question 26

what does the relationship between reaction rate and substrate concentration depend on?

Answer 26

affinity (Km) of an enzyme for its substrate (Km is the concentration of substrate at which the rate of reaction is half its max value)

Question 27

what is the difference between a low Km and high Km?

Answer 27

Low Km: enzyme is normally saturated with substrate, acts at a fairly constant rate regardless of variations in substrate concentration High Km: enzyme is not normally saturated with substrate, its activity will vary as substrate concentration varies – rate of product formation depends on substrate availability

Question 28

what happens to substrate concentration overtime?

Answer 28

decreases

Question 29

what are the two types of enzyme inhibitors?

Answer 29

- irreversible - reversible

Question 30

describe irreversible inhibitors

Answer 30

- damage enzymes beyond repair - generally cause covalent modification of the enzyme

Question 31

describe reversible inhibitors

Answer 31

- full enzyme activity is regained when the inhibitor is removed - most natural enzyme inhibitors fall into this category

Question 32

what is feedback inhibition?

Answer 32

- When the product of a metabolic pathway builds up in the cell, inhibition of the pathway often occurs - This is often done by the product of the pathway acting as an inhibitor of an earlier step in the pathway - This is known as feedback inhibition - An example of this is the pathway that forms isoleucine from threonine

Question 33

what types of inhibitors are there?

Answer 33

- competitive - non-competitive

Question 34

what is a competitive inhibitor?

Answer 34

Substrate and inhibitor compete for same active binding site – structural analogues, prevent substrate from binding Inhibition can be overcome (reversible) with large quantities of substrate – substrate will ultimately occupy all binding sites, enzyme fully operative

Question 35

what is non-competitive inhibition?

Answer 35

Bind to an allosteric site on the enzyme i.e. one other than active site Structurally unrelated to substrate Inhibition cannot be reversed by adding large quantities of substrate

Question 36

what is an allosteric enzyme?

Answer 36

- Allosteric enzymes possess multiple subunits - In addition to active sites they also possess regulatory (allosteric) sites to which non-substrate modulators bind, creating conformational change in subunits - Subunits interact such that the binding of a substrate, inhibitor, or activator to one subunit alters the conformation of all the subunits: - positive modulators (increase affinity for substrate at active site) - negative modulators (decrease affinity for substrate at active site) - Many important regulatory enzymes are allosteric

Question 37

what is a common enzyme modification?

Answer 37

addition of a phosphate group to serine, threonine, tyrosine or hydroxyl group