Topic 2 - enzymes

Question 1

What are enzymes and how do they change at the end of the reaction

Answer 1

Enzymes are biological catalysts that speeds up the rate of reaction and remains unchanged and reusable at the end of the reaction.

Question 2

What do enzymes do to the activation energy of a reaction

Answer 2

Enzymes lower the activation energy of a reaction

Question 3

What is the lock and key model

Answer 3

​The lock and key model proposed that each substrate is a key that only fits a specific lock or enzyme.

Question 4

Describe the alternative induced fit model

Answer 4

Although it is very similar to the lock and key hypothesis, in this model the enzyme and substrate interact with each other:
The enzyme and its active site (and sometimes the substrate) can change shape slightly as the substrate molecule enters the enzyme
These changes in shape are known as conformational changes
The conformational changes ensure an ideal binding arrangement between the enzyme and substrate is achieved
This maximises the ability of the enzyme to catalyse the reaction

Question 5

What structure gives enzymes it’s specificity

Answer 5

The specificity of enzymes is due to the tertiary structure of its active site, allowing complementary binding to substrates.

Question 6

Enzymes catalyse both intracellular and extracellular reactions which determine (1…)

Answer 6

1 - structures and functions from cellular to whole organism level.

Question 7

Is catalase intra or extra cellular and what does it do (and does it require a cofactor)

Answer 7

Catalase intracellularly breaks down hydrogen peroxide into water and oxygen

No cofactor

Question 8

Is amylase intra or extra cellular and what does it do (and does is require a cofactor)

Answer 8

Amylase is secreted from the salivary glands and pancreas to extracellularly break down starch.

Requires Cl- cofactor

Question 9

Is trypsin intra or extra cellular and what does it do (and does is require a cofactor)

Answer 9

Trypsin is secreted from the pancreas to extracellularly break down proteins

No cofactor

Question 10

Some enzymes are synthesised in an (1)

Answer 10

1 - inactive precursor form

Question 11

What needs to happen if an enzyme is synthesised in an inactive precursor form

Answer 11

Some enzymes are synthesised in an inactive precursor form and need to be activated e.g. another enzyme removes part of the molecule in trypsin, forming the correct active site shape

Question 12

Some enzymes require a cofactor, what is a cofactor?

Answer 12

A substance which must be present to enable an enzyme to catalyse a reaction at the appropriate rate.

Question 13

what is a prosthetic group and give an example

Answer 13

A prosthetic group is the non-amino acid component that is part of the structure of the heteroproteins or conjugated proteins, being tightly linked to the apoprotein.

A prosthetic group is permanently bound e.g. Zn^2+ bound to carbonic anhydrase CO2 ⟷ H2CO3 ⟷ H^+ + HCO3

Question 14

What do coenzymes form and what are they derived from

Answer 14

A coenzyme forms temporary associations and are derived from vitamins.

Question 15

What are coenzymes

Answer 15

A coenzyme is defined as an organic molecule that binds to the active sites of certain enzymes to assist in the catalysis of a reaction.

Question 16

State 4 factors that affect enzyme activity and how it affects it

Answer 16

pH
As pH increases, so does enzyme activity until the optimal pH is reached. Past this point, the enzyme denatures and therefore enzyme activity decreases till 0

Temperature
As temperature increases, so does enzyme activity until the optimal temperature is reached. Past this point, the enzyme denatures and therefore enzyme activity decreases till near 0

Enzyme concentration
As enzyme concentration increases, so does rate of reaction

Substrate concentration
As substrate concentration increases, so does rate of reaction until the point of saturation is reached at which point the graph plateaus and increasing concentration no longer affects reaction rate.

Question 17

Draw a graph showing the rate of reaction / substrate concentration with 3 lines:
(1) enzyme controlled reaction without an inhibitor
(2) same reaction with a competitive inhibitor
(3) same reaction with a non competitive inhibitor

Answer 17

1 - curve that plateaus at top
2 - slightly lower than first and plateaus further along to the right but lower generally
3 - way lower and never reaches the same plateau as the other two curves (less than half the amplitude)

Question 18

Describe what a competitive inhibitor is

Answer 18

A competitive inhibitor is any compound which closely resembles the chemical structure and molecular geometry of the substrate. The inhibitor competes for the same active site as the substrate molecule. The inhibitor may interact with the enzyme at the active site, but no reaction takes place.

Question 19

Describe what a non competitive inhibitor is

Answer 19

The noncompetitive inhibitor reacts either remotely from or very close to the active site. The net effect of a noncompetitive inhibitor is to change the shape of the enzyme and thus the active site so that the substrate can no longer interact with the enzyme to give a reaction.

Question 20

What is the temperature coefficient

Answer 20

The temperature coefficient (Q10) for a specific reaction is the effect of a 10°C rise in temperature on the rate of the reaction

Question 21

Give the equation of the temperature coefficient

Answer 21

Q10 = [rate of reaction at (T+10)C] / rate of reaction at T C