Chapter 6: Basic Concepts of Enzyme action

Question 1

Enzymes are …….

Answer 1

• proteins with catalytic properties
• Accelerate the rate of a reaction
• decrease activation energy
• not degraded or destroyed
• highly specific for substrates

Question 2

Carbonic anhydrase

Answer 2

catalyzes the reaction of adding H2O to CO2

+ fastest known enzymes

Question 3

Proteolytic enzymes

Answer 3

• catalyze the hydrolysis of peptide bonds
• perform proteolysis -> hydrolysis of peptide bond
• also termed proteases

Question 4

Proteolytic enzymes’ activity can be specific - T or F

Answer 4

True

Question 5

Trypsin

Answer 5

• cleavage of a peptide bond on the carboxylic acid of a Lys or Arg.
• specific

+ digestive enzyme

Question 6

Thrombin

Answer 6

• Cleaves only Arg - Gly bond

+ enzyme found in blood clotting process
+ more specific than trypsin

Question 7

Papain

Answer 7

• Non-specific cleavage at any peptide bond

+ found in papaya
+ indiscriminate

Question 8

Oxidoreductase

Answer 8

catalyze oxidation-reduction rxns
(transfer of electrons b/w molecules)

Question 9

Transferase

Answer 9

• move functional groups Between molecules

Question 10

Hydrolase

Answer 10

• cleave bonds with the addition of water
  -e.g. trypsin

Question 11

Lyase

Answer 11

• remove atoms to from double bonds or ass atoms to double bonds

+e.g. fumerase -> aerobic fuel metabolism

Question 12

Isomerase

Answer 12

• move functional groups within a molecule

Question 13

Ligase

Answer 13

• join 2 molecules at the expense of ATP
  -e.g. DNA ligase

Question 14

4 ways enzymes are named

Answer 14

1. naming based on substrate
2. naming based on reactions
3. having common names (trypsin)
4. systematic naming by enzyme commission

Question 15

Coenzymes

Answer 15

• cofactor
• organic compounds derived from vitamins
• tightly bound are called prosthetic groups
• can also be loosely bound
• e.g. ascorbate (VIT C)

Question 16

Metals that act as cofactors ….

Answer 16

• Mg (hexokinase)
• Zn (carbonic anhydrase

Question 17

Apoenzyme

Answer 17

enzyme with no cofactor present

Question 18

Holoenzyme

Answer 18

(complete) catalytically active enzyme

Question 19

Describe conditions for different ∆G values

Answer 19

Negative:
- rxn is spontaneous (favored)
- releases E
- Exergonic

Positive:
- non-spontaneous rxn (not favored)
- E input required
- Endergonic

@ Equilibrium:
- no net change in concentration of products and reactants

Question 20

Reaction Pathway matters for ∆G. T or F

Answer 20

False
- it does not matter
- multistep or single step pathways are possible

Question 21

∆G° vs ∆G°’

Answer 21

∆G° = standard free energy change
- Standard conditions:
- products/reactants all at 1M
- 298 K (25 C°)
- Pressure at 1 atmosphere

∆G°’ = standard free energy change at pH 7
- For biochemistry

Question 22

∆G°’ of the hydrolysis of ATP

Answer 22

∆G° = -30.5 kJ/mol
= -7.3 Kcal/mole
- Exergonic reaction

Question 23

Enzymes alter reaction equilibrium. T or F

Answer 23

• enzymes do not alter equilibrium
• They alter (speed up) the reaction rate
• equilibrium determined ONLY by the free energy difference

Question 24

Transition State

Answer 24

• molecule is no longer a substrate but not yet the product
• formed during an ezyme/substrate complex

Question 25

∆G++ or activation energy

Answer 25

• energy required to get to transition state

Question 26

Enzyme Active Site description

Answer 26

• 3-dimensional cleft or crevice (created by a.a. from different parts of the primary structure
• Catalytic site to facilitate enzymatic rxn
• Constitutes a small portion of total enzyme volume.
• enzyme specificity depends on the molecular architecture at the active site

Question 27

What influences specificity of an enzymes active site

Answer 27

• size, structure, charges, polarity, hydrophobicity
• Substrates and products
• several weak bonds needed (short range and directional)

Question 28

Lock and Key active sites

Answer 28

• enzyme bonds to substrate that can fit into active site

Question 29

Induced Fit

Answer 29

• Enzyme changes shape during binding to accommodate for substrate shape