Unit 2 - Ch 7 - Enzymes

Question 1

Describe the biological importance of enzymes.

2

Answer 1

Allow warm chemistry (vs. hot) by lowering activation energies of organic molecules

Precise regulation is possible - each step in metabolism is catalyzed by a different enzyme

Question 2

Substrate

Answer 2

pairs with the enzyme

- reactant

Question 3

Active Site

Answer 3

E+S»>E-S Complex»>E+Product

Question 4

“Ase”

Answer 4

enzyme names end with “ase”

- isomerase, dehydrogenase, lipase, amylase, proteinase

Question 5

Induced Fit Hypothesis

Answer 5

replaced lock and key model

• current model
• E-S complex changes enzyme shape

Question 6

Characteristics of enzymes (7)

Answer 6

1. Catalysts
2. Proteins - subject to denaturation (heat and changes in pH)
3. Temperature Sensitive
4. pH Sensitive
5. Substrate Specific (most)
6. Reversible - depending upon chemical equilibria
7. Subject to Saturation - often used to identify reactions catalyzed by enzymes

Question 7

Catalysts

Answer 7

lower activation energy, speed up reactions

- not chemically changed nor consumed in the reaction

Question 8

Temperature sensitivity of enzymes

Answer 8

each enzyme has an optimal temperature

• cryophiles
• thermophiles = heterotherms (“cold blooded”), insects and snakes

Question 9

pH sensitivity of enzymes

Answer 9

each enzyme has an optimum pH - important for buffering to occur in cells

Question 10

What makes enzymes substrate specific?

Answer 10

due to tertiary structure

= cellulase is needed to hydrolyze cellulose

Question 11

Example of reversible enzyme reaction

Answer 11

triglyceride+3H2O«<»>3FA+glycerol

• lipase is the enzyme catalyst in the reaction, condensation on the left, hydrolysis on the right

Question 12

Types of Enzymes

Answer 12

1. Simple - consist of only amino acids

2. Conjugated - have a prosthetic group

Question 13

Conjugated enzymes

Answer 13

have a prosthetic group

1. Apoenzyme - protein portion (inactive)
   +
2. # Cofactor - non-protein portion (often form the active site)
3. Holoenzyme - active conjugated enzyme

Question 14

Cofactors

Answer 14

non-protein portion (often form the active site)

a. Mineral Ion - K+ and Mg2+

b. Coenzymes
- complex organic molecules
- NAD requires niacin
- FAD requires riboflavin

Question 15

Competitive Inhibition

Answer 15

inhibitor that blocks the active site - excess substrate counteracts (helps with identification)
= sulfa drugs (example in book)

Question 16

Noncompetitive Inhibition

Answer 16

inhibitor binds elsewhere and alter the active site

- excess substrate won’t counteract (ID)

Question 17

Irreversible Inhibition

Answer 17

tertiary structure cannot be restored

= nerve gas irreversibly inhibits acetylcholinesterase

Question 18

Regulatory Enzymes

Answer 18

key enzymes in metabolic sequences (often first enzyme)

Question 19

Feedback Inhibition

Answer 19

end product of a reaction sequence inhibits the regulatory enzyme

Question 20

Allosteric Regulation and types

Answer 20

regulators bind to the allosteric site (not the active site)

1. Positive - regulator stimulates the reaction
2. Negative - regulator inhibits the reaction - similar to noncompetetive inhibition