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MEH > MEH 4. Glycogen And Fat > Flashcards

MEH 4. Glycogen And Fat Flashcards

1
Q

Which tissues have an absolute requirement for glucose as an energy source?

A

Red blood cells
Neutrophils
Innermost cells of kidney medulla
Lens of the eye

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2
Q

What are the 2 locations of glycogen storage?

A
  1. Muscle

2. Liver - hepatocytes

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3
Q

Glycogen is stored as ___________.

A

Granules

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4
Q

Glycogen is a polymer consisting of chains of which monomer?

A

Glucose

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5
Q

Which two glycosidic bonds are present in glycogen?

A

Alpha 1-4 glycosidic bonds between glucose residues.

Alpha 1-6 glycosidic bonds forming branches every 8-10 residues.

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6
Q

Which protein dimer is present at the core of glycogen?

A

Glycogenin

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7
Q

Outline the first step of glycogen synthesis from glucose, naming the enzyme required.

A

Glucose + ATP -> Glucose-6-phosphate + ADP.

Hexokinase or glucokinase (in liver)

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8
Q

The second step of glycogenesis converts glucose-6-phosphate to glucose 1-phosphate. Which enzyme is responsible for this?

A

Phosphoglucomutase ( this step is reversible)

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9
Q

In the 3rd reaction of glycogenesis, what is glucose-1-phosphate converted to?

A

UDP-glucose

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10
Q

What form of glucose is able to be incorporated to glycogen?

A

UDP-glucose

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11
Q

Which 2 enzymes are responsible for the addition of UDP-glucose to glycogen?

A 
Glycogen synthase (alpha 1,4 glycosidic bonds)
Branching enzyme (alpha-1,6-glycosidic bonds)
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12
Q

Which enzymes are responsible for degradation of glycogen to produce glucose 1-phosophate?

A

Glycogen phosphorylase

De-branching enzyme

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13
Q

Why is glycogenolysis not simply the reversal of glycogenesis?

A

Different enzymes are involved in order to allow inhibition of one pathway and stimulation of another.

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14
Q

Why can only liver glycogen (and not muscle glycogen) act as a buffer for blood glucose levels?

A

In the liver, Glucose 6-phosphate is converted to glucose by glucose-6-phosphatase and exported to blood.

Muscle lacks the enzyme glucose-6-phosphatase, so glucose 6-phosphate enters glycolysis for energy production.

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15
Q

What is the rate limiting enzyme in glycogen synthesis?

A

Glycogen synthase

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16
Q

What is the rate limiting enzyme in glycogen degradation?

A

Glycogen phosphorylase

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17
Q

Which 3 hormones regulate glycogen metabolism?

A

Glucagon, adrenaline and insulin

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18
Q

What effect do glucagon and adrenaline have on glycogen synthase?

A

Decrease it’s activity

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19
Q

What effect do glucagon and adrenaline have on glycogen phosphorylase?

A

Increase its activity

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20
Q

What effect does insulin have on glycogen synthase?

A

Increase its activity

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21
Q

What effect does insulin have on glycogen phosphorylase?

A

Decreases activity

22
Q

How does regulation of muscle stores differ to liver stores?

A

Glucagon has no effect on muscle glycogen stored (no receptors).
AMP is an allosteric activator of muscle glycogen phosphorylase, but NOT the liver form of the enzyme.

23
Q

How do the mechanisms of glucagon and adrenaline differ to insulin?

A

Glucagon + adrenaline - phosphorylate

Insulin - de-phosphorylates

24
Q

Give 2 examples of glycogen storage diseases.

A
  1. Von Gierke’s disease

2. McArdle disease

25
Q

Which enzyme is deficient in von Gierke’s disease?

A

Glucose 6-phosphatase

26
Q

Which enzyme is deficient in McArdle disease?

A

Muscle glycogen phosphorylase

27
Q

Where does gluconeogenesis occur?

A

Liver and to a lesser extent in kidney cortex.

28
Q

What are the 3 major precursors of gluconeogenesis?

A
  1. Lactate (from anaerobic glycolysis)
  2. Glycerol ( from adipose tissue breakdown of triglycerides)
  3. Amino acids (alanine)
29
Q

Why is Acetyl CoA unable to be converted to glucose?

A

Acetyl-CoA cannot be converted to pyruvate. Pyruvate deyhydrogenase enzyme regulated reaction is irreversible.

30
Q

After how many hours of fasting is gluconeogenesis required?

A

8 hours

Liver glycogen stores start to deplete at this point and alternative source is required.

31
Q

What are the 3 key regulatory enzymes in gluconeogenesis?

A
  1. PEPCK
  2. Fructose 1,6-bisphosphatase
  3. Glucose-6-phosphatase
32
Q

Which hormones will function to stimulate gluconeogenesis? Through which enzymes does it exert this effect?

A

Glucagon
Cortisol

PEPCK
Fructose 1,6 bisphosphatase

33
Q

Which hormone will function to decrease gluconeogenesis?

A

Insulin

Through PEPCK
Fructose 1,6 bisphosphatase

34
Q

What molecule are excess lipids stored as?

A

Triglycerol

35
Q

Under what conditions might a TAG store become utilised? How is this controlled?

A

Prolonged exercise
Stress
Starvation
Pregnancy

Hormonal control

36
Q

Outline the structure of an adipocyte.

A

Large lipid droplet (mainly TAG and cholesterol ester)

Cytoplasm and organelles pushed to the side of the cell

37
Q

How might adipocytes in an overweight individual differ to those in a healthy individual?

A

Upon weight gain, adipocytes increase in size before dividing to increase the total number of fat cells.

38
Q

Which is the role of hormone sensitive lipase?

A

Mobilises TAG stores in adipose tissue, converting them to FA and glycerol.
FA is then transported by albumin to the tissues to be oxidised to produce energy.

39
Q

Where does lipogenesis occur?

A

Liver

40
Q

What is the major source of carbon used for lipogenesis?

A

Dietary glucose

41
Q

What is the function of the malate shuttle in lipogenesis?

A

Production of NADPH, which is required by fatty acid synthase

42
Q

What is the key regulatory enzyme in lipogenesis?

A

Acetyl-CoA carboxylase

43
Q

What effect does insulin have on acetyl-CoA carboxylase?

A

Increases activity to increase lipogenesis following a meal.

44
Q

In addition to insulin, what else will increase the activity of Acetyl-CoA carboxylase?

A

Citrate

45
Q

What hormones and molecules will decrease the activity of Acetyl-CoA carboxylase?

A

Glucagon
Adrenaline
AMP

46
Q

What is the substrate and product of the reaction catalysed by Acetyl-CoA carboxylase?

A

Acetyl Co A converted to Malonyl CoA

47
Q

In fatty acid synthesis, what molecule are C2 atoms added as?

A

Malonyl CoA

48
Q

Where does fatty acid synthesis occur?

A

Cytoplasm

49
Q

How do glucagon and insulin mobilise TAG stored in adipose tissue?

A

Phosphorylate and activate hormone sensitive lipase, which converts TAG to glycerol and fatty acids which can travel by albumin to tissues to undergo beta oxidation.

50
Q

How does insulin inhibit mobilisation of TAG stores in adipose tissue?

A

Insulin leads to de-phosphorylation and inhibition of hormone sensitive lipase.

51
Q

What is the fate of glycerol produced when TAG is mobilised from adipose stores?

A

Travels to the liver and utilised as carbon source for gluconeogenesis.

52
Q

What is the main difference in fuel stores in an obese man compared to a healthy man?

A

Significantly raised triacylglycerol levels

MEH (19 decks)

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