Enzymes and Metabolism

Question 1

Enzymes have specific functions based on their structure. What happens if the structure of an enzyme is changed/mutated? What are two ways in which enzyme structure can be altered?

Answer 1

Change in structure = change in function

extreme temperature and pH

Question 2

How do enzymes lower the activation energy of a reaction?

Answer 2

Lower the energy of the transition state intermediate

Question 3

Do enzymes have an effect on kinetics and/or thermodynamics?

Answer 3

Enzymes only affect the kinetics of a reaction. The rate constant (k) changes, but NOT Keq

Question 4

Why doesn’t enzymes change Keq

Answer 4

Lowers activation energy for both forward and reverse reactions

Question 5

Describe the two models that determine enzyme specificity. How does each differ in their interpretation of the nature of the active?

Answer 5

1. Lock and key - rigid active site

2. Induced fit - flexible active site

Question 6

Can enzymes can be what two molecules?

Answer 6

RNA or protein

Question 7

What are the four levels of enzyme structure?

Answer 7

1. Primary - AA or mRNA sequence
2. Secondary - hydrogen bonding between AA backbone
3. Tertiary - side chain (R group) interaction
4. Quaternary - multiple subunit interaction

Question 8

What are three modes of controlling enzyme activity and their mechanisms? Where does the inhibitor bind on the enzyme?

Answer 8

1. Feedback inhibition - downstream product of pathway inhibits pathway
2. Competitive inhibition - inhibitor competes substrate for active site; same Vmax, different Km; over come by adding more substrate
3. Noncompetitive inhibition - inhibitor binds to allosteric site; different Vmax, same Km; cannot be overcome

Question 9

Compare and contrast the steps to aerobic and anaerobic metabolism?

Answer 9

1. Both undergo glycolysis
2. Aerobic: oxidative decarboxylation–>Krebs Cycle–>Electron transport
3. Anaerobic: alcohol or lactic acid fermentation

Question 10

Glucose + O2 –> 6CO2 + 6H2O

Trace the atoms

Answer 10

Carbon and oxygen atoms in carbon dioxide come from glucose

Oxygen atom in water comes from oxygen we breathe in

Question 11

What is the difference in NET ATP from aerobic metabolism and anaerobic metabolism of glucose?

Answer 11

aerobic - 36 ATP

anaerobic - 2 ATP

Question 12

What is the purpose of anaerobic fermentation?

Answer 12

Regeneration of NAD+ which is required for the first step in the pay-off phase

Question 13

How many NADH are produced in one glucose molecule during glycolysis?

Answer 13

2 NADH

Question 14

What enzyme is primarily responsible for regulating glycolysis?

Answer 14

Phosphofructokinase-1 (PFK-1)

Question 15

What two hormones regulate PFK-1? What are their effects on PFK-1?

Answer 15

Insulin - activates PFK-1

Glucagon - inhibits PFK-1

Question 16

What are three modes of regulating glycolysis? What enzyme gets regulated?

Answer 16

Regulation occurs on PFK-1

1. Hormones - insulin/glucagon
2. ATP/AMP - AMP activates/ATP inhibits
3. Fructose-6-P/Fructose-1,6-BP - F6P activates; F1,6,BP inhibits

Question 17

What are the primary and secondary locations of gluconeogenesis?

Answer 17

1. Primary - liver

2. Secondary - kidneys

Question 18

How is glycogen metabolism regulated?

Answer 18

1. Insulin - activates glycogenesis

2. Glucagon/Epinephrine - activates glycogenolysis

Question 19

What tissues store glycogen?

Answer 19

1. Liver

2. Muscles

Question 20

What is the name of the cycle that restores lactic acid to glucose? Where does this occur?

Answer 20

Cori Cycle - liver

Question 21

What is the energy yield per glucose in terms of ATP, GTP, NADH, and FADH2?

Answer 21

1. 2ATP (glycolysis)
2. 10 NADH - 2 NADH (glycolysis) + 2 NADH (pyruvate decarboxylation) + 6 NADH (Krebs)
3. 2 FADH2

Question 22

What two molecules inhibit Krebs Cycle?

Answer 22

ATP and NADH

Question 23

What are the two locations of fat metabolism?

Answer 23

Ester hydrolysis - cytoplasm

Beta-oxidation - matrix

Question 24

What are the products of beta-oxidation?

Answer 24

Acetyl-CoA + NADH + FADH2

Question 25

Conversion of triacylglycerides to free fatty acids and glycerol is performed by what enzyme? How is this enzyme regulated?

Answer 25

Hormone-sensitive lipase converts TAG–>FFA + Glycerol. Glucagon and epinephrine activate hormone sensitive lipase in response to stress, fasting, exercise

Question 26

What are the fates of the FFAs and glycerol? Where are they transported to?

Answer 26

FFAs - transported to other tissues (primarily heart and muscles) for beta-oxidation
Glycerol - transported to liver for glycolysis or gluconeogenesis

Question 27

What is the mechanism that FFAs undergo to be transported into the mitochondrial matrix to undergo beta-oxidation? What is the enzyme and ATP involved?

Answer 27

ATP–>AMP + PPi (-2ATP)

Acyl-CoA synthetase “activates” FFA and covalently bonds it to CoA-SH

Question 28

Acylcarnitine is the intermediate that gets transported across the inner mitochondrial membrane into the matrix to undergo beta oxidation? What enzyme is responsible for the synthesis of this molecule and reconversion?

Answer 28

Carnitine acyl transferase I converts activated FFA into acylcarnitine. Acylcarnitine is reconverted back to its activated form (with CoA-S) by same enzyme

Question 29

How many rounds of beta-oxidation are there for a 18-C fatty acid?

Answer 29

9 acetyl-CoA produced

8 rounds of beta-oxidation –>8 NADH + 8 FADH2