2.1.4 Enzymes

Question 1

Enzymes

Answer 1

Biological catalysts made of globular proteins
Active site is specific and unique due to specific folding + bonding in tertiary structure.
Can only attach to substrates that are complementary in shape.
Catalyse intracellular and extracellular reactions.
E.g. Catalase - intracellular enzyme inside liver cells that breaks down hydrogen peroxide into oxygen and water.
Trypsin is an extracellular enzyme, in small intestine - hydrolyses proteins

Question 2

Activation energy

Answer 2

Certain amount of energy required required for a reaction to occur.
Ea lowers when enzyme attaches to substrate so reaction speeds up.

Question 3

Lock and Key Hypothesis

Answer 3

Enzyme like a lock
Substrate like a key that fits into it due to specific tertiary structure.
Enzyme active site is fixed shape - random collision causes substrate to collide + attach - forming enzyme-substrate complex.
The charged groups within the active site distort the substrate + lower Ea

Question 4

Induced Fit Hypothesis

Answer 4

Enzyme like a glove
Substrate like a hand
Enzyme active site is induced/slightly changes shape, to mould around the substrate.
Enzyme-substrate complex occurs - puts strain on the bonds + lowers Ea

Question 5

Factors affecting enzymes

Answer 5

1. Temp
2. pH
3. Enzyme conc
4. Substrate conc

Question 6

How temp affects enzymes

Answer 6

Temp too low:
Insufficient kinetic energy for successful collisions.
Temp increases:
Frequency of successful collisions increases.
Temp too high:
Enzymes denature - active site changes shape + enzyme -complexes cannot form.
Bonds break + 3’ structure alters - change in shape of active site.

Question 7

Temperature coefficient - Q10

Answer 7

Measure of rate of change of an enzyme-controlled reaction as a result of increasing temp by 10C
R1 = rate of reaction at temp XC
R2 = rate of reaction at temp (X + 10)*C

Question 8

Affect of pH on enzymes

Answer 8

Too high or too low pH interferes with charges in amino acids in active site.
Causes (ionic/hydrogen) bonds to break.
Alters 3’ structure + changes shape of active site + enzyme denatures.
Enzymes have different optimal pH they work at.

Question 9

Substrate and Enzyme Conc

Answer 9

Low conc substrate: reaction will be lower - fewer collisions between enzyme + substrate.
Inc substrate conc - inc rate of reaction
High conc substrate: rate of reaction plateu - all enzyme active sites are in use (saturated).
Low conc enzyme: lower rate of reaction.
Inc conc enzyme: increase rate of reaction - enzyme-substrate complexes more likely to form.
Unless unlimited substrate is added, rate of reaction plateaus - insufficient substrate to bind with number of enzymes.

Question 10

Competitive inhibitors

Answer 10

Same shape as substrate + complementary to active site - bind to enzyme.
Prevents substrate from binding + enzyme-inhibitor complexes form instead - RoR lower.
If a high enough conc of substrate is added - substrate can knock out the inhibitor + RoR will increase.

Question 11

Non-competitive inhibitors

Answer 11

Bind to the enzyme at the allosteric site.
Causes active site to change shape
So substrate cannot bind regardless of how much substrate is added
Enzyme-substrate complexes are less frequent - ror low

Question 12

End-product inhibition

Answer 12

Products of some reactions are reversible inhibitors for the enzymes involved in controlling the reaction.
Enables reactions to be controlled.
If there’s a lot of product - inhibit the enzymes + cause reaction to stop

Question 13

Coenzymes + Cofactors

Answer 13

Carry atoms from one reaction to the next
Non-protein molecule binds to the active site to make it complementary to the substrate.
Coenzymes - organic
Cofactors - inorganic

Question 14

Prosthetic groups

Answer 14

Type of cofactor but are permanently attached to enzyme.
Precursor activation - cofactor attaches to enzyme, changing the tertiary structure so they are active + active site is complementary to the substrate