Enzymes

Question 1

What are enzymes?

Answer 1

• proteins that act as biological catalysts for intra and extra cellular reactions therefore effecting the organisms metabolism
• specific tertiary structure determines shape of active site complementary to a specific substrate
• formation of enzyme-substrate complexes lowers the activation energy of metabolic reactions

Question 2

Give an example of an enzyme that catalyses intracellular reactions?

Answer 2

• catalase
• catalyses decomposition of hydrogen peroxide into water and oxygen

Question 3

Give 2 examples of enzymes that catalyse extracellular reactions?

Answer 3

Amylase
- catalyses the digestion of starch to maltose (found in saliva and small intestine)

Trypsin
- catalyses hydrolysis of peptide bonds in small intestine lumen

Question 4

Explain the induced fit model of enzyme action?

Answer 4

• shape of active site is not directly complementary to substrate and is flexible
• conformational changes enable enzyme substrate complexes to form when substrate is adsorbed
• puts strain on substrate bonds lowering activation energy, bonds in enzyme-product complex are weak so product desorbs

Question 5

Explain the lock and key model of enzyme action?

Answer 5

• the active site has a rigid shape determined by tertiary structure so it’s only complementary to 1 substrate
• formation of enzyme substrate complex lowers activation energy
• bonds in enzyme-product complex are weak so product desorbs

Question 6

Name 5 factors that affects the rate of enzyme-controlled reactions?

Answer 6

• enzyme concentration
• substrate concentration
• concentration of inhibitors
• PH
• temperature

Question 7

How does substrate concentration affect rate of reaction?

Answer 7

• rate increases proportionally to substrate concentration
• rate levels of when maximum number of enzyme-substrate complexes form

Question 8

How does enzyme concentration affect rate of reaction?

Answer 8

• rate increases proportionally to enzyme concentration
• rate levels off when maximum number of enzyme-substrate complexes form

Question 9

How does temperature affect the rate of enzyme-controlled reactions?

Answer 9

• rate increases as temperature increases (due to increased Ke)
• rate peaks at optimum temperature
• above optimum temp ionic and hydrogen bonds break causing the active site to no longer be complementary to substrate (denaturing)
• this causes a rapid decrease in rate of reaction

Question 10

What is the temperature coefficient?

Answer 10

• Q10 measures the change in rate of reaction per 10c temperature increase
• Q10 = rate 2 / rate 1

Question 11

How does PH affect rate of reaction?

Answer 11

• enzymes have a narrow PH range
• outside the range hydrogen and ionic bonds break causing the enzyme to denature

Question 12

How do competitive inhibitors work?

Answer 12

• they bind to the active site as they have a similar shape to substrate
• temporarily prevent enzyme substrate complexes being formed until released

Question 13

How can competitive inhibitors be counteracted?

Answer 13

by increasing substrate concentration

Question 14

How do non-competitive inhibitors work?

Answer 14

• bind at allosteric binding site
• trigger conformational change of active site

Question 15

What is end product inhibition?

Answer 15

• a product from a reaction acts as a competitive or non-competitive inhibitor for an enzyme involved in the pathway
• prevents further product formation

Question 16

What are irreversible inhibitors?

Answer 16

• permanently prevent the formation of enzymes substrate complexes
• bind to the enzyme by strong covalent bonds

Question 17

What are reversible inhibitors?

Answer 17

• temporarily bind to enzyme
• can be competitive or non-competitive
• enzyme substrate complexes can form once inhibitor is released

Question 18

Define metabolic poison?

Answer 18

substance that damages cells by interfering with metabolic reactions (usually inhibitor)

Question 19

Give three examples of metabolic poison?

Answer 19

• cyanide
• malonate
• arsenic

Question 20

Give an example of a medical drugs acting as an inhibitor?

Answer 20

Penicillin
- non-competitve inhibitor
- prevents formation of peptidoglycan cross-links in bacteria cell walls

Question 21

What are inactive precursors in metabolic pathways?

Answer 21

• prevent damage to cells
• some enzymes in metabolic pathways are synthesised as inactive precursors
• one part of the precursor acts as an inhibitor
• enzyme substrate complexes form when it is removed

Question 22

What are cofactors?

Answer 22

Non-protein compounds required for enzyme activity
- coenzymes
- inorganic cofactors
- prosthetic group

Question 23

What are coenzymes?

Answer 23

• organic cofactors that don’t permanently bind
• often transport molecules or electrons between molecules
• frequently derived from water-soluble vitamins

Question 24

What are inorganic cofactors and give an example?

Answer 24

• facilitate temporary binding between enzyme and substrate
• CL- is the cofactor for amylase

Question 25

What are prosthetic groups and give an example?

Answer 25

• tightly-bound cofactors act a permanent part of enzyme’s binding site
• ZN2+ for carbonic anhydrase

Question 26

Suggest how a student could produce a desired concentration of solution from a stock solution?

Answer 26

volume of stock solution = required conc x final volume needed/ stock solution conc

volume of distilled water = final volume needed - volume of stock solution