Enzymes

Question 1

What are enzymes?

Answer 1

Proteins that act as biological catalysts

Question 2

Give an example of an enzyme that catalyses intracellular reactions

Answer 2

Catalase - Catalyses decomposition of hydrogen peroxide (which causes oxidative stress) into water and oxygen

Question 3

Give 2 examples of enzymes that catalyse extracellular reactions

Answer 3

Amylase - Carbohydrase catalyses digestion of starch to maltose in saliva/small intestine lumen
Trypsin - Pancreatic endopeptidase catalyses hydrolysis of peptide bonds in small intestine lumen, to help with digestion

Question 4

Explain the induced fit model

Answer 4

• Shape of active site is not directly complementary to substrate and is flexible
• Initial interaction is weak, but these weak interactions rapidly induce changes in the enzymes tertiary structure to strengthen binding
• Also puts strain on substrate, weakening bonds and lowering activation energy

Question 5

Name 5 factors that affect the rate of enzyme controlled reactions

Answer 5

• Enzyme concentration
• Temperature
• Substrate concentration
• Concentration of inhibitors
• pH

Question 6

What happens after the optimum temperature is reached in an enzyme controlled reaction?

Answer 6

• After roughly 45 degrees
• Ionic and hydrogen bonds break in enzyme
• Active site no longer complementary as it has denatured

Question 7

What is the temperature coefficient

Answer 7

• Q10 measures the change in rate of reaction per 10 degree temperature increase
• Q10 = R2/R1 (where R represents rate)

Question 8

How does pH affect rate of reaction?

Answer 8

• Enzymes have a narrow optimum pH range
• Outside range, hydrogen and hydroxide ions interact with hydrogen and ionic bonds
• This changes concentration and interaction of R groups with each other, so causes denaturation

Question 9

How do non competitive inhibitors work?

Answer 9

• Bind to enzyme at allosteric binding site
• Trigger tertiary structure of enzyme to change, so the active site changes shape
• Increasing substrate concentration has no impact on their effect

Question 10

What is end product inhibition?

Answer 10

• One of the products of a reaction act as a competitive or non competitive inhibitor for an enzyme involved in the pathway
• Prevents further formation of products

Question 11

What are irreversible inhibitors?

Answer 11

• Permanently prevent formation of enzyme substrate complexes
• Non competitive
• Heavy metal ions like mercury and silver cause disulphide bonds in tertiary structure to break
• Bind to enzymes by strong, covalent bonds like cyanide binds to cytochrome c

Question 12

What are cofactors?

Answer 12

Non-protein compounds required for enzyme activity
- Co-enzymes
- Inorganic cofactors
- Prosthetic groups

Question 13

What are coenzymes?

Answer 13

• Organic compounds
• Do not bind permanently
• Often transport electrons or molecules between enzymes
• Frequently derived from water soluble vitamins

Question 14

What are inorganic cofactors? Give an example

Answer 14

• Facilitate temporary binding between substrate and enzyme.
• Often metal ions
• eg Cl- is the cofactor for amylase

Question 15

What are prosthetic groups? Give an example

Answer 15

• Tightly bound cofactors act as a permanent part of enzyme’s binding site
• eg Zn2+ for carbonic anhydrase

Question 16

Describe the practical investigating the effect of substrate concentration on an enzyme controlled reaction

Answer 16

• Collect 5 beakers of 20 vol, 16 vol, 8 vol, 4 vol and 2 vol hydrogen peroxide
• 100ml of hydrogen peroxide into 20 vol, and 160ml into 16 vol, with 40ml water
• Pour 100ml of that into the 8 vol beaker, with 100ml water. Repeat
• Turn a measuring cylinder with water upside down into a water trough, and have it connecting to the delivery tube
• Place a potato chip into the conical flask, then the 20 vol hydrogen peroxide, add the bung and start a stopwatch
• Record oxygen given off by water loss in measuring cylinder