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GI 2018 > Metabolic pathways: Glycogen > Flashcards

Metabolic pathways: Glycogen Flashcards

1
Q

Define glycogenesis?

A

Synthesis of glycogen from glucose

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2
Q

Define glycogenolysis?

A

Breakdown of glycogen to form glucose

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3
Q

What is glycogen?

A

Main storage form of glucose

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4
Q

Where is glycogen present?

A

Liver and muscle

  • same molecule
  • different function
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5
Q

Why does liver store glycogen?

A

broken down between meals and released to maintain blood glucose levels for RBCs and brain

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6
Q

What is the use of glycogen in muscle?

A

Not available for maintenance of blood glucose

Provides energy via glycolysis and the TCA during bursts of physical activity

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7
Q

When does glycogenolysis occur?

A

Fluctuates dependant on meal times

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8
Q

What is the primary source of glucose overnight?

A

Gluconeogenesis when hepatic glycogen is depleted

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9
Q

Describe the structure of glycogen?

A

Polymer consisting of glucose molecules

a 1-4 and a 1-6 glycosidic links

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10
Q

Where are a 1-4 glycosidic links found?

A

Between the number 1 carbon of one glucose and the number 4 carbon of another glucose

Form long chains

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11
Q

Where are a 1-6 glycosidic links found?

A

Between the number 1 carbon of one glucose and the number 6 carbon of another glucose

Introduce branches

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12
Q

How does synthesis of glycogen occur?

A

Sticking glucose molecules to the ends of glycogen

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13
Q

How does breakdown of glycogen occur?

A

Cleaving glucose molecules from the ends of glycogen

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14
Q

What is found at the centre of glycogen?

A

Glycogenin protein

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15
Q

What is the function of glycogenin?

A

Can add glucose molecules to itself

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16
Q

Why is glycogenin important?

A

Acts ad a primer for glycogen synthase which can only add glucose to existing glycogen

17
Q

What happens to glucose in order for it to be used?

A

phosphorylated to glucose-6-phosphate by hexokinase and ATP

18
Q

What can glucose-6-phosphate be used for?

A

Glycolysis

or synthesis of glycogen

19
Q

How can glucose-6-phosphate be used for glycogen?

A

Converted to glucose-1-phosphate by phosphoglucomutase

THEN

converted to UDP glucose by UDP- glucose pyrophosphorylase and UTP

20
Q

What is the substrate for glycogen synthase?

A

Glucose part of UDP glucose

21
Q

What happens do left-over UDP?

A

Phosphorylated to UTP by ATP

22
Q

What is UDP glucose?

A

Uridine-diphosphate bound to glucose

23
Q

What makes UDP glucose active?

A

bond between second phosphate and glucose.

Ester linkage releases energy on hydrolysis

24
Q

What does glycogen synthase do?

A

Adds one glucose molecule to glycogen at a time

Rate limiting

25
Q

Where do glycogen branches come from?

A

Transglycosylase produces a1-6 glycosidic branches into glycogen

26
Q

what catalyses glycogenolysis?

A

Glycogen phosphorylase

27
Q

What does glycogen phosphorylase do?

A

Cleave one glucose at a time

Rate-limiting

28
Q

What happens to glucose-6-phosphate in the liver during glycogenolysis?

A

De-phosphorylated and the resulting glucose is released into blood stream?

29
Q

What happens to glucose-6-phosphate in the skeletal muscle during glycogenolysis?

A

Cannot be de-phosphorylates by instead used to provide energy via glycolysis and the TCA cycle

30
Q

What does debranching require?

A

Additional enzymes

31
Q

How does free glucose enter the blood?

A

Via GLUT2 transporter

32
Q

What is the hormone of the fed state? what does it do?

A

Insulin
Stimulates glycogen synthatse
Inhibits glycogen phosphorylase

33
Q

What is the hormone of the fasting state? What does it do?

A

Glucagon
Stimulate glycogen phosphorylase

Inhibits glycogen synthase

34
Q

What is the role of adrenaline and cortisol?

A

Signal a need for energy

Stimulate glycogen phosphorylase

GI 2018 (10 decks)

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