Lecture 3A

Question 1

What is the overall purpose of central metabolic pathways?

Answer 1

To generate energy-rich molecules (e.g., ATP) and precursor metabolites for anabolic biosynthesis

Question 2

What are the two major types of metabolism?

Answer 2

Anabolic (build up) and Catabolic (break down).

Question 3

How is energy from catabolism captured by the cell?

Answer 3

In the form of energy-rich bonds like anhydride bonds in ATP.

Question 4

What are the three major catabolic respiratory pathways?

Answer 4

Aerobic respiration, Anaerobic respiration, Fermentation

Question 5

What is the primary carbon source in respiration?

Answer 5

Glucose.

Question 6

What are the three key pathways involved in central metabolism?

Answer 6

Glycolysis, Pentose Phosphate Pathway, Tricarboxylic Acid (TCA) Cycle

Question 7

What is glycolysis also known as?

Answer 7

Embden-Meyerhof-Parnas pathway.

Question 8

What is the net yield of glycolysis per glucose molecule?

Answer 8

2 pyruvate, 2 ATP, 2 NADH, 2 H+

Question 9

What is substrate-level phosphorylation?

Answer 9

Direct transfer of phosphate from a substrate to ADP to form ATP.

Question 10

What occurs in glycolysis’ investment phase?

Answer 10

Energy is used to convert glucose to G3P using ATP.

Question 11

What occurs in glycolysis’ pay-off phase?

Answer 11

ATP and NADH are produced; pyruvate is formed.

Question 12

What molecule is the intermediate between glycolysis and the TCA cycle?

Answer 12

Pyruvate.

Question 13

What is the main role of fermentation?

Answer 13

To regenerate NAD+ from NADH under anaerobic conditions.

Question 14

What are the three stages of fermentation?

Answer 14

ATP investing, ATP yielding, Redox stage (NADH)

Question 15

What is homolactic fermentation?

Answer 15

Fermentation pathway that only produces lactic acid.

Question 16

What is heterolactic fermentation?

Answer 16

Fermentation that produces lactic acid and other byproducts.

Question 17

How can fermentation generate additional ATP?

Answer 17

Through substrate-level phosphorylation involving CoA derivatives.

Question 18

What CoA derivative helps generate ATP in fermentation?

Answer 18

Butyryl-CoA (e.g., in Clostridium butyricum fermentation)

Question 19

What determines whether a cell respires or ferments?

Answer 19

Availability of oxygen.

Question 20

Why does Saccharomyces cerevisiae prefer respiration when oxygen is present?

Answer 20

Because respiration yields more ATP than fermentation.

Question 21

How is anaerobic respiration different from fermentation?

Answer 21

It uses a terminal electron acceptor other than oxygen.

Question 22

What is the transition step between glycolysis and the TCA cycle?

Answer 22

Conversion of pyruvate to Acetyl-CoA.

Question 23

What are the products of the transition step?

Answer 23

NADH, CO2, and Acetyl-CoA

Question 24

Where does the TCA cycle occur in prokaryotes?

Answer 24

In the cytoplasm.

Question 25

What are the key products of the TCA cycle?

Answer 25

6 NADH, 2 FADH2, 2 ATP, and 4 CO2 per glucose

Question 26

What happens to NADH and FADH2 after the TCA cycle?

Answer 26

They donate electrons to the ETC for oxidative phosphorylation.

Question 27

What is the total ATP yield from aerobic respiration per glucose?

Answer 27

38 ATP (including glycolysis and TCA).

Question 28

What connects the TCA cycle to glycolysis?

Answer 28

Reversible reactions involving PEP and pyruvate.

Question 29

What is the purpose of TCA cycle in biosynthesis?

Answer 29

To provide precursors for amino acids, cytochromes, chlorophyll, and fatty acids

Question 30

What cycle helps replenish TCA intermediates when using acetate?

Answer 30

The glyoxylate cycle.

Question 31

What is the key intermediate in the glyoxylate cycle?

Answer 31

Glyoxylate.

Question 32

Why can't the TCA cycle alone oxidize acetate?

Answer 32

Because it cannot regenerate oxaloacetate when intermediates are drawn off.

Question 33

What regenerates NAD+ in the absence of oxygen?

Answer 33

Fermentation.

Question 34

Which pathways require NAD+?

Answer 34

Glycolysis, TCA cycle, Pyruvate to Acetyl-CoA conversion

Question 35

What is oxidative phosphorylation?

Answer 35

ATP synthesis powered by proton motive force across the membrane via ATPase.

Question 36

How many protons are needed to generate 1 ATP via ATPase?

Answer 36

3 protons.

Question 37

What is substrate-level phosphorylation?

Answer 37

ATP formation by direct phosphate transfer from an intermediate substrate to ADP.

Question 39

What is the function of NAD+ in metabolism?

Answer 39

It acts as an electron acceptor in glycolysis, TCA cycle, and pyruvate to Acetyl-CoA conversion

Question 40

Why is regeneration of NAD+ crucial during fermentation?

Answer 40

It ensures glycolysis can continue producing ATP in the absence of oxygen.

Question 41

What is the role of the electron transport chain (ETC) in respiration?

Answer 41

It transfers electrons from NADH and FADH2 to a terminal electron acceptor, generating proton motive force

Question 42

Which complex does NADH feed into in the ETC?

Answer 42

Complex I.

Question 43

Which complex does FADH2 feed into in the ETC?

Answer 43

Complex II.

Question 44

Why does FADH2 generate less ATP than NADH?

Answer 44

It bypasses Complex I and enters at a lower energy level.

Question 45

What is the total ATP yield from NADH in the ETC?

Answer 45

Approximately 3 ATP per NADH (varies slightly).

Question 46

What is the total ATP yield from FADH2 in the ETC?

Answer 46

Approximately 2 ATP per FADH2 (varies slightly).

Question 47

Why is glucose a preferred substrate in metabolism?

Answer 47

It yields high ATP and provides multiple biosynthetic precursors.

Question 48

What is the role of α-ketoglutarate in anabolism?

Answer 48

It serves as a precursor for amino acid synthesis.

Question 49

What is the role of oxaloacetate in metabolism?

Answer 49

It functions in the TCA cycle, amino acid synthesis, and gluconeogenesis

Question 50

What is succinyl-CoA used for in biosynthesis?

Answer 50

It’s a precursor for cytochromes and chlorophyll synthesis.

Question 51

What is phosphoenolpyruvate (PEP) a precursor for?

Answer 51

It contributes to glucose synthesis and connects glycolysis and the TCA cycle.

Question 52

Why is the TCA cycle considered amphibolic?

Answer 52

It functions in both catabolism (energy production) and anabolism (biosynthesis).

Question 53

How does the glyoxylate cycle support growth on acetate?

Answer 53

It bypasses CO2-producing steps and regenerates oxaloacetate for biosynthesis.

Question 54

Which two enzymes are unique to the glyoxylate cycle?

Answer 54

Isocitrate lyase and malate synthase.

Question 55

What molecule condenses with oxaloacetate to begin the TCA cycle?

Answer 55

Acetyl-CoA.

Question 56

What is citrate converted into during the TCA cycle?

Answer 56

It is oxidized and transformed into 2 CO2 and oxaloacetate.

Question 57

Why must oxaloacetate be regenerated in the TCA cycle?

Answer 57

To allow continuous functioning of the cycle.

Question 58

What happens if oxaloacetate is siphoned off for biosynthesis?

Answer 58

The cycle will halt unless oxaloacetate is replenished.

Question 59

What metabolic process adds CO2 to pyruvate to form oxaloacetate?

Answer 59

Carboxylation.

Question 60

What organism uses glyoxylate cycle for growth on acetate?

Answer 60

Bacteria and some fungi like *Saccharomyces cerevisiae*.

Question 61

What is the importance of the electrochemical gradient across the membrane?

Answer 61

It drives ATP synthesis via ATP synthase.

Question 62

How is energy stored in the proton motive force (PMF) used?

Answer 62

To power ATP synthase for ATP production.

Question 63

How does ATP synthase work?

Answer 63

It uses the flow of H+ ions across the membrane to drive phosphorylation of ADP to ATP.

Question 64

What is the primary energy-conserving step in fermentation?

Answer 64

Substrate-level phosphorylation.

Question 65

What makes CoA derivatives like Acetyl-CoA energy-rich?

Answer 65

They contain thioester bonds that release energy upon hydrolysis.

Question 66

What is the final electron acceptor in aerobic respiration?

Answer 66

Oxygen (O2).

Question 67

What can serve as terminal electron acceptors in anaerobic respiration?

Answer 67

Nitrate, sulfate, CO2, or metals

Question 68

How do cells prioritize fermentation or respiration?

Answer 68

They choose the pathway yielding the most ATP, depending on oxygen availability

Question 69

What is a key energetic advantage of respiration over fermentation?

Answer 69

Respiration yields significantly more ATP per glucose molecule.