Topic 3 - Enzymes

Question 1

How do enzymes affect the rate of a chemical reaction

Answer 1

Catalysts - increase reaction rate, do not alter equilibrium, just alter the rate at which reach equilibrium
They do this by decreasing the activation energy of the reaction - more molecules have the energy for the reaction to occur

Question 2

What is activation energy

Answer 2

Difference between substrate and transition state

Question 3

How do enzyme-substrate complexes form

Answer 3

Binding of enzyme to substrate
Specific religion of enzyme - active site
Binding is stabilised by interaction of amino acid residues surrounding

Question 4

What are the key features of the active site?

Answer 4

Occupies a small part of the enzyme
Formed by amino acids from different parts of the primary sequence
Clefts or crevices - the folds hide active site to prevent water entry to affect reactions
Complementary shape to substrate - lock key or induced
Substrates are bound to enzymes by multiple weak bonds so products can be released

Question 5

How do you find V0 (initial rate)

Answer 5

Tangent to the curve

Question 6

What does the rate of reaction depend on

Answer 6

Substrate concentration

Question 7

What is the michealis-menten equation

Answer 7

V0 = Vmax [S] / Km + [S]

For curve

Question 8

What is vmax and how do you find it

Answer 8

The theoretical maximum rate when all enzyme molecules are saturated with substrate

Extrapolate tangent until level out = vmax

Measured in ..M/min

Question 9

What is the Km and how do you find it

Answer 9

The substrate concentration that gives half the maximal rate of reaction
Low - higher enzyme affinity

Find vmax
1/2 that on V0
Across to curve down to substrate concentration

Measure in mM

Question 10

1 unit

Answer 10

The amount of enzyme that produces 1 micromol of product per min under standard conditions

Rate of enzyme catalysed reaction proportional to concentration of enzyme

Question 11

What is the lineweaver-burn plot

Answer 11

V0 = vmax [S] / Km + [S]

Y = Mc delta T

Eg: y intercept = -1/km
Slope = km/vmax
Intercept = 1/vmax

Straight line

Question 12

What is competitive inhibition?

Answer 12

Binds at active site
Reduce proptiln of enzyme molecules able to bind

Adding enough substrate will overcome effect of inhibitor so no effect on vmax whereas Km increases

Question 13

What is non competitive inhibitor

Answer 13

Bind sat site other than active site
Causes conformational change
Decreases concentration of functional enzyme

Even if add more substarte will not over crime the effect so Km unaffected and vmax decreases

Question 14

Km is independent of…

Answer 14

The concentration of enzyme

Question 15

If twice as much enzyme used, and halves

Answer 15

Vmax double, Km unchanged

Vmax halves, Km unchanged

Question 16

Less units of enzyme

Answer 16

Takes longer for enzyme to break down

Question 17

For individuals on a milk diet, this reaction is rate-limiting for the utilization and metabolism of lactose. Lactose intolerance occurs when the individual is unable to metabolise lactose sufficiently rapidly. Would a suitable response to this condition be to evolve a new enzyme with a lower Km or, alternatively, a higher Vmax or simply to make more of the standard enzyme? Explain your answer.

Answer 17

Higher Vmax would do but cannot do that so must change amino acid sequence of the active site to a higher affinity - change gene expression to make more enzymes or mutate

Due to the higher lactose diet - thus not a big impact with Km

Question 18

(a) What is the activity of the enzyme in Units per litre of serum? (1 unit is the amount of enzyme
that produces 1mol of product per minute)

Answer 18

0.1ml = 1.t x10-7 ml/min
0.1 ml = 0.15 micromol/min
X10000
1l = 1500 units/litre

Question 19

If states what would activity of enzyme in units per litre of serum be even if ml change

Answer 19

Per litre = same as standardised unit

Question 20

Why is ethanol beneficial for methanol poisoning

Answer 20

Has lower arm do higher affinity for enzyme so outcompetes meta molecules so ethanol given so not toxic product formed