Biochem 4

Question 1

What is metabolism?

Answer 1

All linked chemical reactions in the cell

Reactions are arranged in metabolic pathways.

Question 2

What are the types of metabolic pathways?

Answer 2

• Catabolic
• Anabolic
• Amphibolic

Catabolic pathways oxidize carbon to release energy, while anabolic pathways use energy to build molecules.

Question 3

A reaction is favorable when ΔG is what?

Answer 3

ΔG < 0

ΔG changes with concentrations: ΔG = ΔG°′ + 1.37 log(products/reactants).

Question 4

What is the main energy currency of the cell?

Answer 4

ATP

ATP contains two high-energy phosphoanhydride bonds (β and γ).

Question 5

What are examples of high-energy molecules with higher ΔG of hydrolysis than ATP?

Answer 5

• PEP
• 1,3-BPG
• Creatine-P

Creatine-P acts as a short-term energy buffer in muscle.

Question 6

Define oxidation and reduction.

Answer 6

• Oxidation: loss of H / gain of O
• Reduction: gain of H / loss of O

Redox reactions always occur as pairs.

Question 7

What are activated carriers in metabolism?

Answer 7

• ATP – phosphoryl groups
• NAD⁺ / FAD – electron carriers
• CoA-SH – acyl groups via thioester bond

Most carriers come from B-vitamins.

Question 8

Name the six classes of enzymes.

Answer 8

• Oxidoreductases
• Transferases
• Hydrolases
• Lyases
• Isomerases
• Ligases

Each class has a specific type of reaction it catalyzes.

Question 9

What are the key regulated steps in glycolysis?

Answer 9

• Hexokinase (Step 1)
• Phosphofructokinase (PFK) (Step 3)
• Pyruvate kinase (Step 10)

These steps are irreversible and crucial for regulation.

Question 10

What is the net ATP yield from glycolysis per glucose molecule?

Answer 10

Net ATP: 2

Total ATP made: 4, ATP used: 2.

Question 11

What is the role of phosphofructokinase (PFK) in glycolysis?

Answer 11

Main regulatory step of glycolysis

Inhibited by high ATP, activated by AMP.

Question 12

What happens to pyruvate in aerobic conditions?

Answer 12

Converted to Acetyl-CoA

Enters TCA cycle for oxidative phosphorylation.

Question 13

What is the purpose of the TCA cycle?

Answer 13

• Oxidize Acetyl-CoA to CO₂
• Capture high-energy electrons as NADH & FADH₂
• Generate building blocks for biosynthesis

Takes place in the mitochondrial matrix.

Question 14

What are the main regulated enzymes in the TCA cycle?

Answer 14

• Pyruvate Dehydrogenase Complex (PDC)
• α-Ketoglutarate Dehydrogenase

Regulation involves reversible phosphorylation and allosteric regulation.

Question 15

What is oxidative phosphorylation?

Answer 15

Coupling of electron transport and ATP synthesis

Occurs in the mitochondria using electrons from NADH & FADH₂.

Question 16

What is the function of ATP synthase?

Answer 16

Converts proton flow to ATP

Has stationary and rotating parts that facilitate ATP production.

Question 17

What are uncouplers in oxidative phosphorylation?

Answer 17

Allow H⁺ to reenter the matrix without ATP synthesis

Produce heat instead of ATP.

Question 18

Regulation of metabolism

Answer 18

1. Amount of enzyme (synthesis/degradation)
2. Allosteric regulation (activators/inhibitors)
3. Covalent modification (phosphorylation)
4. Proteolytic activation
5. Substrate availability (compartmentalization)