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MCAT Biochemistry > Carbohydrate Metabolism I (CH9) > Flashcards

Carbohydrate Metabolism I (CH9) Flashcards

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MCAT flashcards
1
Q

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).

A

Glycolysis

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2
Q

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

A

True

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3
Q

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

A

Hexokinase

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4
Q

Only found in liver cells and is induced by insulin.

A

Glucokinase

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5
Q

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).

A

PFK-1 (Phosphofructokinase-1)

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6
Q

What stimulates PFK-1?

A

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

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7
Q

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

A

Insulin stimulates PFK-2

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8
Q

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

A

Glucagon

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9
Q

When and where is insulin released?

A

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

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10
Q

What is produced in glycolysis in aerobic vs anaerobic conditions?

A
  • Aerobic: 2 ATP and 2 NADH

- Anaerobic: 2 ATP (only)

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11
Q

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

A

PFK-1 (Feed-Foward Activation)

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12
Q

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

A

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

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13
Q

What is the rate limiting step for fermentation?

A

Lactate Dehydrogenase (LDH)

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14
Q

What two intermediates generate ATP in glycolysis?

A

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

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15
Q

What are the irreversible enzymes of glycolysis?

A

How Glycolysis Pushes Forward the Process: Kinases

  • Hexokinase
  • Glucokinase
  • PFK-1
  • Pyruvate Kinase (PK)
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16
Q

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

A

Isocitrate Dehydrogenase and ADP

17
Q

What inhibits and stimulates PDH?

A

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

18
Q

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

A

Gylcogen

19
Q

The synthesis of glycogen granules.

A

Glycogensis

20
Q

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

A
  • Glycogen Synthase
  • Stimulated by G6P, high ATP and insulin.
  • Inhibited by epi and glucagon.
21
Q

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

A

Glycogenolysis

22
Q

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

A
  • Gylcogen Phosphorylase
  • Stimulated by epi, high AMP and glucagon.
  • Inhibited by high ATP and insulin.
23
Q

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

A

Gluconeogensis

24
Q

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

A

Glycogenolysis or Gluconeogensis

25
Q

What are the two ketogenic amino acids?

A

Lysine and Leucine

26
Q

What amino acids are glycogenic and ketogenic?

A

F, W, Y + TI

TI Fucks With You

27
Q

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

A

True

28
Q

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

A

Alanine

29
Q

What is the rate limiting step of gluconeogensis?

A

F-1,6 BiphosphaTASE

30
Q

How does ß-oxidation interplay with gluconeogensis?

A

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

31
Q

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

A

True

32
Q

What is the main function of the pentose phosphate pathway?

A

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.

33
Q

What is the rate limiting step of PPP?

A

G6PD (Glucose 6 Phosphate Dehydrogenase)

34
Q

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

A

True

35
Q

What does pyruvate dehydrogenase do?

A

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

MCAT Biochemistry (7 decks)

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