Enzymes

Question 1

What an an active site?

Answer 1

cleft, contains AA side chains that participate in substrate binding and catalysis, lock + key, non-covalent bonds

Question 2

What are the properties of enzymes?

Answer 2

1. Increase rate of reaction
2. Lower activation energy
3. Highly specific
4. Located in specific organelles, serves to isolates substrate or product from competing reactions
5. Do not affect reaction equilibrium
6. Unchanged after reaction

Question 3

What are enzyme inhibitors?

Answer 3

1. irreversible (covalent bonds)

2. reversible (non-covalent): competitive, binds at active site OR non-competitive, binds at another site on enzyme

Question 4

What is activation energy?

Answer 4

min energy reactant must have to allow reaction

Question 5

Describe transition state

Answer 5

high energy intermediate that lies between reactant and product

Question 6

Describe rate of reaction

Answer 6

must contain sufficient energy to overcome energy barrier. Rate determined by number of energised molecules

Question 7

List the factors that affect reaction velocity

Answer 7

Substrate conc (more likely to interact), temp (increase energy), pH

Question 8

How can enzymes be used in clinical diagnosis?

Answer 8

Tissue damage = can result in increased release of enzymes into plasma. levels = extent of tissue damage

Question 9

What is Km?

Answer 9

SUBSTRATE CONC that gives half maximal velocity

Km values = measure of affinity for enzyme

low = high affinity / high = low affinity

Question 10

explain why enzymes do not affect the reaction equilibrium?

Answer 10

it catalyses the forwards and backwards reactions equally

Question 11

what is the lock and key hypothesis?

Answer 11

active sites are complementary in shape to the substrate

Question 12

what is the induced fit hypothesis?

Answer 12

binding of substrates cause conformational changes in the enzyme

Question 13

what bonds are formed between the active site and the substrate?

Answer 13

weak hydrogen bonds, hold it in correct orientation, but allow it to be released

Question 14

what is Vmax?

Answer 14

maximal rate when all enzyme active sites are saturated with substrate. NEVER TOUCHES THE TOP OF THE CURVE

Question 15

what is the lineweaver-burk plot?

Answer 15

reciprocal graph that gives -1/KM at the X intercept and 1/Vmax at the Y intercept

Km = X axis, lower the -ve value the higher the affinity

Vmax = Y axis, 1/V, higher the value higher the maximal rate of reaction

Question 16

why do competitive inhibitors not affect Vmax?

Answer 16

adding enough substrate will overcome the affect of the inhibitor so the max rate can still be reached

Question 17

why do competitive inhibitors affect Km?

Answer 17

the inhibitor competes with the substrate for the active site so the Km increases (affinity decreases)

Question 18

why do non-competitive inhibitors lower Vmax?

Answer 18

bind enzyme, not active site, change enzyme shape = decrease the turnover rate of enzyme

Question 19

what is the unit of enzyme activity?

Answer 19

micromoles per minute per litre

Question 20

what affect does doubling the enzyme conc have on the rate?

Answer 20

doubles the rate of reaction

Question 21

what are the 2 long-term regulation methods for enzymes?

Answer 21

1. change in protein synthesis

2. change in protein degradation

Question 22

what are the 2 short-term regulation methods for enzymes?

Answer 22

1. change in sub/prod conc

2. change in enzyme conformation

Question 23

what graph shape do allosteric enzymes show?

Answer 23

sigmoidal

Question 24

what do allosteric activators do?

Answer 24

increases the proportion of enzymes in the R state

Question 25

what direction do allosteric activators shift the binding curve?

Answer 25

left

Question 26

what do allosteric inhibitors do?

Answer 26

increases the proportion of enzymes in the T state

Question 27

What are the 3 methods of regulation of enzymes by change in enzyme conc?

Answer 27

allosteric regulation, covalent modification, proteolytic cleavage

Question 28

What is allosteric regulation?

Answer 28

Substrate binding to one subunit (NOT ACTIVE SITE) makes subsequent binding to other subunits progressively easier, T state (low affinity), R state (high affinity).Allosteric activators = Increase the proportion of enzyme in the R state. Allosteric inhibitors = Increase the proportion of enzyme in the T state

Question 29

Give an example of allosteric regulation

Answer 29

PFK Phosphofructokinase: key regulatory enzyme in glycolysis, phosphorylates fructose 6-phosphate, ACTIVATORS = AMP, fructose-2,6 bisphosphate. INHIBITORS = ATP, citrate, H+

Question 30

What is the T state?

Answer 30

Low affinity

Question 31

What is the R state?

Answer 31

High affinity

Question 32

What is an isoenzyme?

Answer 32

different forms of the same enzyme that have different kinetic properties

Question 33

what is product inhibition?

Answer 33

accumulation of product inhibits the forward reaction

Question 34

what is V0?

Answer 34

initial rate of reaction, tangent from T=0 drawn against curve