Enzymes

Question 1

Explain the mode of action of enzymes in terms of an active site.

Answer 1

The amino acids at the active site are grouped into contact residues and catalytic residues.
* Contact residues contribute to enzyme specificity and form the shape of the active site that is complementary to the substrate
* Catalytic residues contribute to the ability of enzyme to catalyse biochemical reactions and increase reactivity of the substrate by altering charges

The other amino acids help maintain the globular shape of enzyme

Question 2

Explain the mode of action of enzymes in terms of their specificity.

Answer 2

Lock-and-key hypothesis:
* Substrate is completely complementary in shape to active site of enzyme, fits perfectly, no change in shape of active site –> enzymes are specific to their substrates

Induced-fit hypothesis:
* Active site is not completely complementary to shape of substrate, slight conformation change in enzyme that allows substrate to fit more snugly into active site –> enzymes lower activation energy of reaction and perform catalytic function more effectively

Question 3

Explain the mode of action of enzymes in terms of lowering activation energy.

Answer 3

Via formation of enzyme-substrate complex.
* When ES complex is formed, R groups of catalytic residues at active site are very close to parts of the substrate
* R groups change the charge on substrate, altering distrubution of electrons within the bonds, increasing reactivity of substrate
* Substrate molecules are forced together in the correct orientation for reaction to occur, facilitating bond formation between substrate molecules

Question 5

Enzymatic reaction at low enzyme concentration.

Question 6

Enzymatic reaction at high enzyme concentration.

Question 7

Enzymatic reaction at low substrate concentration.

Question 8

Enzymatic reaction at high substrate concentration.

Question 9

Enzymatic reaction as temperature increases towards optimum temperature.

Question 10

Enzymatic reaction when optimum temperature is reached.

Question 11

Enzymatic reaction at above optimum temperature.

Question 12

Enzymatic reaction at optimum pH levels.

Question 13

Enzymatic reaction at pH higher/lower than optimum pH.

Question 14

What is the Vmax of an enzymatic reaction?

Answer 14

Maximum rate of enzymatic reaction at a given enzyme concentration, temperature and pH, in the presence of excess substrate.

Question 15

What is Km of an enzymatic reaction?

Question 16

What is 1/Km in an enzymatic reaction?

Question 17

Explain the process of competitive inhibition.

Question 18

Explain the process of non-competitive inhibition.

Question 19

Explain the process of allosteric inhibition.

Answer 19

Allosteric enzymes have more than one subunit that have their own active sites.

Cooperativity occurs when substrate binding to active site of one subunit changes conformation of whole enzyme to active form, facilitating substrate binding to other active sites in other subunits

Considered a form of non competitive inhibition.

Result in an S-shaped graph of substrate concentration against rate of reaction. this is due to cooperativity as more enzymes are active, thus are more likely to form ES complex, increase ROR