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FLC > Carbohydrate Metabolism > Flashcards

Carbohydrate Metabolism Flashcards

1
Q

How often does the body require food intake?

A

Our bodies have evolved to cope with intermittent food intake

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2
Q

How is excess food stored in our bodies?

A

Excess food is stored as glycogen

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3
Q

Compared to our needs, how much food do we intake?

A

Intake > needs

we take in excess food

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4
Q

Where is the long term glycogen store?

A

Fat in adipose tissues

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5
Q

Where is the short term supply of glycogen stored?

A

Liver / Muscle

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6
Q

What is gluconeogenesis?

A

Formation of glucose from precursors that aren’t carbohydrates
e.g. amino acids + glycerol -> gucose

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7
Q

What happens when food source is low or there’s an increase in demand ?

A

Stored energy is mobilised to glucose or fatty acids

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8
Q

Which hormone stimuates gluconeogenesis?

A

Glucagon

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9
Q

Which processes make up the metabolic pathway of carbohydrates?

A
  • Glycolysis (glucose -> pyruvate)
  • Pyruvate dehydrogenated (pyruvate -> acetyl coa)
  • Citric acid cycle
  • oxidative phosphorylation
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10
Q

What is hyperglycaemia?

A

Critically high blood glucose levels

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11
Q

What does the body do when glucose levels get too high?

A

Synthesise glycogen and fatty acids via the Pentose 5 pathway

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12
Q

What is hypoglycaemia?

A

Critically low blood glucose levels

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13
Q

What occurs when glucose levels get very low?

A

Glycogen degradation (gluconeogenesis)

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14
Q

What is the normal critical blood glucose level?

A

2.5mM

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15
Q

Outline the stages of the Pentose 5 Pathway

A
  1. Glucose is phosphorylated to G6P (glucose-6-
    phosphate)
  2. G6P converted to Glucose-1-phosphate by the enzyme
    phosphoglucomutase
  3. UDP added to glucose molecule forming UDP-Glucose
    by UDP-glucosephosphorylase
  4. Glycogenin enzyme reacts with UDP-Glucose to
    catalyse the addition of the first glucose molecule
  5. Glycogen synthase adds glucose residues in a 1-4
    configuration until am 11 residue length is formed
  6. stimulates branching enzyme to add a 1-6 branch
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16
Q

What is the role of the glycogenin enzyme?

A

Acts as a primer to polymerise the first few glucose residues
- without glycogenin glycogen wouldn’t form

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17
Q

Explain why glycogen is a better storage molecule than glucose

A

Glucose is very osmotically active so large concentrations cannot be stored
Glycogen is more compact so can be stored
(400mM of glucose stored as 0.01um glycogen)

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18
Q

What are the products of glycogen degradation?

A

Glucose-1-phosphate and glucose

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19
Q

Explain why glycogen is a better energy store than fat

A

Glycogen is hevaliy branched so potential residues can be released very quickly
Fat can’t be mobilised easily
Fat can only be used as an energy store in the presence of O2
Fat can’t be converted back to glucose

20
Q

What is the benefit of adding UDP to glucose during the Pentose 5 Pathway?

A

Makes the glucose more readily reactive

21
Q

Which enzyme synthesises glycogen?

A

Glycogen synthase

22
Q

Describe the structural arrangement of Glycogen

A
  • Branched molecule
  • LInear glucose residues
  • ɒ 1-4 links and ɒ 1-6 branched molecules
  • glycogenin enzyme present
23
Q

Outline the process of degradation of glycogen

A
  1. ɒ 1-4 links degraded by phosphorylase
    => forms Glucose-1-Phosphate
  2. Glucose-1-phosphate converted to G6P by
    phosphoglucomutase
  3. Debranching transferase takes all, but last residue on
    branch and adds it to the 1-4 chain
  4. Debranching glucosidase removes 1-6 branching link
  5. Directly generates glucose
24
Q

What happens to the glucose produced from glycogen degradation?

A

In muscle, glucose phosphorylated and reused or phosphorylated to Glucose-1-phosphate

25
Q

What are the 4 enzymes required to break down glycogen?

A
  • Phosphorylase
  • Translocase
  • Debranching enzyme
  • Phosphoglucomutase
26
Q

Where is the G6P produced in degradation used?

A

In muscles used in either the glycolytic pathway or citric acid cycle
- provides fuel for working muscles

27
Q

Describe the structure of glycogen phosphorylase enzyme

A

Large and multisubunit enzyme

- many phosphorylases bind to each glycogen molecule

28
Q

Where is glucose-6-phosphatase enzyme found in the body?

A

Liver and KIdney (not in muscle)

29
Q

In the liver, what happens to glucose-6-phosphate?

A

G6P is phosphorylated by G6phosphatase and secreted into the blood, maintaining the 5mmolL-1 blood sugar

30
Q

What is the role of glycogen phosphorylase?

A

Key enzyme in glycogenolysis in converting glycogen to glucose

31
Q

Which enzyme is required for glucose formation from glycogen?

A

Glucose-6-phosphatase

32
Q

How is phosphorylase enzyme an example of an allosteric enzyme?

A

Allosteric site away from active site - induce shape changes

33
Q

What is the role of phosphorylase b kinase?

A

Converts inactive Glycogen phosphorylase b to the active a form

34
Q

In muscles how else can glycogen phosphorylase b kinase be activated?

A

Activated by 5’ AMP without being phosphorylated

35
Q

How is glycogenolysis so rapid?

A

Many phosphorylases bind to glycogen molecules for max activity

36
Q

What regulates the activation of glycogen phosphorylase b kinase activation in muscles?

A

ATP and G6P are both competitive inhibitors

37
Q

How does phosphorylase b kinase work?

A

Transfers a phosphate from an ATP to one serine residue on each phosphorylase subunit

38
Q

When is the Pentose 5 Pathway activated?

A

Under high levels of G6P

39
Q

What activates the phosphorylase b kinase enzyme?

A

calcium ions

40
Q

How is maximum activity achieved in muscle cells?

A

With both calcium ions release and phosphorylation

41
Q

Summarise how glycogen synthase is regulated

A

Activated by ATP and G6P
Activated by dephosphorylation by protein phosphatase-1
Inactivated by phosphorylation (protein kinase a)

42
Q

How is phosphorylase b kinase activity regulated in the liver?

A

Inhibited by glucose as glycogen breakdown is inhibited by glucose presence even after the enzyme has been converted to its active form

43
Q

What are the two receptor types regulating phosphorylase kinase?

A
  • cAMP elevation and PKA activation

- Calcium mediated by ɒ adrenergic/IP3 pathway

44
Q

When is 5’ AMP formed?

A

When ATP is depleted

45
Q

In the liver what activates the release of calcium ions?

A

ɒ adrenergic receptors activation stimulates the release of calcium ions

46
Q

How is glycogen phosphorylase/ degradtion regulated?

A

Inactivated by ATP and G6P
Inactivated by dephosphorylation by protein phosphatase-1
Activated by phosphorylation of phosporylase b kinase

FLC (34 decks)

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