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NUTR 3210 > Lecture 6 > Flashcards

Lecture 6 Flashcards

1
Q

What are the six processes that involve carbohydrate metabolism?

A
  1. glycogenesis
  2. glycogenolysis
  3. glycolysis
  4. hexose monophosphate shunt
  5. Krebs cycle
  6. gluconeogenesis
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2
Q

What are the three fates of glucose in the cell?

A

First turned into G6P and then:
1. glycogenesis - energy storage
2. glycolysis - energy production
3. hexose monophosphate shunt (pentose phosphate pathway) - generates precursors for biogenesis

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3
Q

Where does glycogenesis occur in the body?

A

Liver or muscles

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4
Q

When does glycogenesis come into effect?

A

when we are eating

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5
Q

What is the purpose of glycogenesis?

A

Store excess glucose for use by the body at a later time

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6
Q

What is glycogenin?

A

An enzyme that serves as a scaffold on which to attach glucose molecules to build glycogen. A primer, it initially attaches glucose molecules to itself before glycogen synthase takes over and adds glucose to the growing glycogen store, this process requires energy

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7
Q

What are the brief steps to glycogenesis?

A
  1. Glucose (blood) enters the liver/muscles through insulin stimulation
  2. Glucose (blood) uses ATP and hexokinase/glucokinase to form G6P
  3. G6P is converted into G1P by hexo/glucokinase and then converted into glycogen through glycogen synthase (which is activated by insulin)
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8
Q

What are the brief steps to glycogenolysis?

A
  1. Glycogen is broken down into G1P by glycogen phosphorylase (breaks alpha 1-4 glycosidic bonds) which is initiated by glucagon
  2. G1P is converted to G6P which has two possible fates: can be turned into fructose 6 phosphate which can be used for glycolysis OR can be converted into glucose by glucose 6 phosphatase for the blood-stream
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9
Q

What is the function of glycogenolysis

A

breaking down glycogen when starving

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10
Q

Which organ is the only organ that can release glucose back into the blood?

A

the liver

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11
Q

What is insulin resistance?

A

When the body produces insulin, but the cell doesn’t know it exists

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12
Q

What is the function of insulin?

A

Insulin reduces blood sugar, it helps package glucose in the liver, it is an anabolic hormone

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13
Q

What is the process of blood sugar levels and the pancreas and liver?

A

High blood sugar:
- promotes insulin release in the pancreas which goes to the liver to stimulate glucose -> glycogen which lowers blood sugar

Low blood sugar:
- promotes glucagon release in the pancreas which goes to the liver to stimulate glycogen -> glucose which raises blood sugar

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14
Q

Where does glycolysis take place?

A

cytoplasm

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15
Q

What are the brief steps to glycolysis?

A

Investment phase:
Glucose -> G6P -> Fructose-1,6-bisphosphate using glucokinase and hexokinase (step 1) and phosphofructokinase (step 3)
Generation phase:
Fructose-1,6-bisphosphate -> 2x Glyceraldehyde-3 phosphate -> 2x pyruvate

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16
Q

What is phosphofructokinase inhibited by?

A

ATP and glucagon (in the liver) therefore, if enough ATP is being produced by glycolysis, it inhibits phosphofructokinase so that it doesn’t continue glycolysis and keeps glucose for storage

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17
Q

What is the ATP and NADH usage and gained in glycolysis?

A

Investment: 2 ATP
Generation: 4 ATP and 2 NADH
Net energy yield from 1 glucose:
2 NADH + 2ATP
(1 NADH = 3 ATP)
2 NADH (3) + 2 ATP
8 ATP

18
Q

What are the two fates of pyruvate?

A

Aerobic: Krebs cycle
Anaerobic: Lactate

19
Q

What are the steps to anaerobic metabolism of glucose?

A

Pyruvic acid -> (pyruvate decarboxylase) acetaldehyde -> (alcohol dehydrogenase, NADH) ethanol
Pyruvic acid -> (lactate dehydrogenase, NADH) Lactic acid

20
Q

When does lactic acid production occur?

A

In anaerobic conditions after glycolysis
- occurs in muscle during prolonged exercise and in RBC
- pyruvate converted to lactate in cytosol
- regenerates NAD+ which allows glycolysis to cont
- net of 2 ATP produced when glucose -> lactate

21
Q

When does ethanol production occur?

A

In anaerobic conditions:
- doesn’t happen in the body
- basis of fermentation
- yeast breaks down pyruvate into CO2 and ethanol
- regenerates NAD+ to allow glycolysis to cont

22
Q

What is the cori cycle steps?

A

In the liver:
2 lactate -> 2 pyruvate (reversible) -> glucose (gluconeogenesis) using 6 ATP

In the muscle:
Glucose -> 2 pyruvate using 2 ATP (glycolysis) -> 2 lactate (reversible)

glucose can be transported from liver-> muscles through blood and reverse

23
Q

Where does the hexose monophosphate shunt occur?

A

cytoplasm

24
Q

What is the hexose monophosphate shunt important for?

A

Important for NADPH production and ribose synthesis

25
Q

What are the steps to the hexose monophosphate shunt?

A
  • Glucose → G6P, enters pathway
  • 2 phases can be entered depending on requirements of cell
    • Oxidative phase is unidirectional
    • Nonoxidative phase (regenerative phase) is bidirectional
26
Q

Which cells use non-oxidative phase vs oxidative phase?

A

All cells use the nonoxidative phase (for R5P), but only cells that perform biosynthesis (making fatty acids, antioxidant activity) will use the oxidative phase

27
Q

What is the oxidative phase of the hexose monophosphate shunt?

A

G6P-> glucose-6-phosphate dehydrogenase 6PG-> 6PG lactone-> Ribulose-5-phosphate-> ribose-5-phosphate which synthesizes nucleotides
produces 2 NADPH
can be converted back to G6P

28
Q

What is the non-oxidative phase of the hexose monophosphate shunt?

A

G6P-> F6P-> intermediates -> ribose-5-phosphate which synthesizes nucleotides

29
Q

What are the NADH produced in the oxidative phase of the hexose monophosphate shunt used for?

A

biosynthesis of fatty acids, role in anti-oxidant production

30
Q

What inhibits glucose-6-phosphate dehydrogenase?

A

NADH produced in the oxidative phase of the hexose monophosphate shunt

31
Q

What are the vitamins that are cofactors the pyruvate dehydrogenase complex?

A

thiamine
niacin
riboflavin
pantothenic acid

32
Q

What is the net energy yield of pyruvate dehydrogenase?

A

about 6 ATP

33
Q

What are the steps of the Krebs cycle?

A

acetyl coA-> citrate-> isocitrate-> alpha ketoglutarate-> succinyl coA-> succinate-> fumarate-> malate-> oxaloacetate

34
Q

Which products of the krebs cycle can amino acids form?

A

succinyl-CoA: amino acids can be converted into succinyl CoA
Oxaloacetate: amino acids can be converted into pyruvate and oxaloacetate

35
Q

What does acetyl-CoA activate?

A

Activates pyruvate carboxylase which catalyzes the conversion of pyruvate to oxaloacetate to initiate the krebs cycle

36
Q

What is the total energy yield for the krebs cycle?

A

energy yield from 1 acetyl CoA
3NADH, 1FADH2, 1GTP
equivalent to 12 ATP

37
Q

How much energy do you get from one molecule of glucose?

A

Glycolysis, pyruvate dehydrogenation, krebs cycle

38 ATP

38
Q

What is the conversion of other energy molecules to atp?

A

1 NADH = 3 ATP
1 FADH2 = 2 ATP
1 GTP = 1 ATP

39
Q

What is gluconeogenesis used for?

A

pathway that is active when glucose is needed by the body

40
Q

Where does gluconeogenesis occur?

A

very active in the liver but can also happen in the kidney during starvation

41
Q

What parts of the body lack enzymes for gluconeogenesis?

A

Muscle and adipose tissue

42
Q

What are the enzymes involved in gluconeogenesis?

A
  • Pyruvate carboxylase and PEP carboxylase
  • Fructose-1,6-bisphosphatase
  • Glucose-6-phosphatase
    enzymes to bypass irreversible steps and allow gluconeogenesis

NUTR 3210 (17 decks)

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