Carbohydrate Metabolism I (CH9)

Question 1

A cytoplasmic pathway that converts glucose into two pyruvate molecules, releasing a modest amount of energy in two substrate-level phosphorylations and one oxidation reaction (ATP and NADH).

Answer 1

Glycolysis

Question 2

True/False: All cells carry out glycolysis (including red blood cells).

Answer 2

True

Question 3

Is widely distributed in tissues and inhibited by its product, G6P.

Answer 3

Hexokinase

Question 4

Only found in liver cells and is induced by insulin.

Answer 4

Glucokinase

Question 5

This enzyme is inhibited by high ATP, glucagon and citrate. Essentially, without this enzyme, F6P would not turn into F-1,6 BP. This makes sense because the cell should turn off glycolysis when it has sufficient energy (rate limiting step).

Answer 5

PFK-1 (Phosphofructokinase-1)

Question 6

What stimulates PFK-1?

Answer 6

Low energy (high AMP), insulin and F-2,6 BP

Question 7

PFK-2 is what converts F6P and increases levels of F-2,6 BP. So what stimulates PFK-2?

Answer 7

Insulin stimulates PFK-2

Question 8

What inhibits PFK-2 (thus inhibiting the stimulation of PFK-1)?

Answer 8

Glucagon

Question 9

When and where is insulin released?

Answer 9

Insulin is released from ß-pancreatic cells when blood glucose levels rise.

Question 10

What is produced in glycolysis in aerobic vs anaerobic conditions?

Answer 10

• Aerobic: 2 ATP and 2 NADH

- Anaerobic: 2 ATP (only)

Question 11

Pyruvate kinase (PK) is the enzyme that converts PEP to pyruvate in glycolysis. What activates/stimulates PK?

Answer 11

PFK-1 (Feed-Foward Activation)

Question 12

What reaction happens in the absence of oxygen (in glycolysis) and what does it do?

Answer 12

Fermentation; which replenishes NAD+ for glycolysis via oxidation into lactate.

Question 13

What is the rate limiting step for fermentation?

Answer 13

Lactate Dehydrogenase (LDH)

Question 14

What two intermediates generate ATP in glycolysis?

Answer 14

1,3 - BPG (Biphosphoglycerate) and PEP (Phosphoenolpyruvate)

Question 15

What are the irreversible enzymes of glycolysis?

Answer 15

How Glycolysis Pushes Forward the Process: Kinases

• Hexokinase
• Glucokinase
• PFK-1
• Pyruvate Kinase (PK)

Question 16

What is the rate limiting step for the citric acid cycle and what activates it?

Answer 16

Isocitrate Dehydrogenase and ADP

Question 17

What inhibits and stimulates PDH?

Answer 17

Insulin stimulates and its product inhibits PDH (acetyl-CoA).

Question 18

A branched polymer of glucose, represents a storage form of glucose.

Answer 18

Gylcogen

Question 19

The synthesis of glycogen granules.

Answer 19

Glycogensis

Question 20

What is the rate limiting step of glycogenesis? What stimulates and inhibits it?

Answer 20

• Glycogen Synthase
• Stimulated by G6P, high ATP and insulin.
• Inhibited by epi and glucagon.

Question 21

This is the opposite of glycogenesis; which is the breaking down of glycogen.

Answer 21

Glycogenolysis

Question 22

What is the rate limiting step of glycogenolysis? What stimulates and inhibits it?

Answer 22

• Gylcogen Phosphorylase
• Stimulated by epi, high AMP and glucagon.
• Inhibited by high ATP and insulin.

Question 23

The production of lactate from fermentation is useful for what metabolic process?

Answer 23

Gluconeogensis

Question 24

During the fasting state, the liver maintains glucose levels in blood through what two processes (essentially, the opposite of glycolysis)?

Answer 24

Glycogenolysis or Gluconeogensis

Question 25

What are the two ketogenic amino acids?

Answer 25

Lysine and Leucine

Question 26

What amino acids are glycogenic and ketogenic?

Answer 26

F, W, Y + TI | TI Fucks With You

Question 27

True/False: Outside of amino acids F, W, Y, T, I and LK, they are all glycogenic amino acids.

Answer 27

True

Question 28

Glucogenic amino acids can feed into gluconeogensis as intermediates. However, which AA is most commonly used?

Answer 28

Alanine

Question 29

What is the rate limiting step of gluconeogensis?

Answer 29

F-1,6 BiphosphaTASE

Question 30

How does ß-oxidation interplay with gluconeogensis?

Answer 30

The energy used by ß-oxidation will inhibit PDH, which stimulates pyruvate carboxylase. Without this enzyme, gluconeogensis would not start.

Question 31

True/False: The acetyl-CoA from fatty acids cannot be used in gluconeogensis (it has no OAA). This is only possible AFTER ketogenesis.

Answer 31

True

Question 32

What is the main function of the pentose phosphate pathway?

Answer 32

It produces NADPH (which is different from NADH in that it is a donater of electrons) and it supplies glutathione to protect against reactive oxygen.

Question 33

What is the rate limiting step of PPP?

Answer 33

G6PD (Glucose 6 Phosphate Dehydrogenase)

Question 34

True/False: Glycolysis and gluconeogensis work inversely of one another.

Answer 34

True

Question 35

What does pyruvate dehydrogenase do?

Answer 35

It converts pyruvate to acetyl-CoA and also creates two NADH's for one glucose molecule.