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MEH > 4 MEH > Flashcards

4 MEH Flashcards

1
Q

Which tissues have an absolute requirement for glucose as an energy source? (4)

A
  1. Red blood cells (no mitochondria)
  2. Neutrophils
  3. Innermost cells of kidney medulla
  4. Lens of the eye
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2
Q

Arounf which value is plasma glucose maintained?

A

5 mmol/L

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3
Q

At which concentration does confusion due to hypoglycaemia appear ?

A

2.8 mmol/L

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4
Q

At which concentration of plasma glucose does brain damage and potentially death occur?

A

0.6 mmol/L

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5
Q

to enable blood glucose to be kept at required levels, a store of glucose is required, this is called?

A

glycogen

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6
Q

Which form (appearance) does glycogen have under electron microscopy?

A

granules

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7
Q

Which 2 organs can stock glycogen?

A
  1. Liver 100g

2. Muscle 300g

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8
Q

What is glycogen, ie what is it amde of?

A

glycogen is a stocked form of glucose, it is a polymer consisting of chains of glucose residues.

  • chains are organized like branches on a tree originating form a dimer of the protein glycogenin.
  • glucose residues linked by a-1-4 glycosidic bonds with a1-6 glycosidic bonds forming branch point every 8-10 residues
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9
Q

Which element of cellulse structure explains why we can’t break it down?

A

Cellulose has b-1-4 glycosidic bonds and we dont have the enzymes necessary for that breakdown (our glycogen is a-1-4 glycosidic bonded).

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10
Q

What is glycogen synthesis called?

A

glycogenesis

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11
Q

The first reaction of glycogenesis is the same as the first reaction of…?

A

glycolysis:
glucose + ATP => glucose 6-phosphate
BY HEXOKINASE (glucokinase in the liver)

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12
Q

Does the synthesis of glycogen require energy?

A

yes! reactions 1 and 3

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13
Q

Which enzyme is responsible for the formation of branch point bonds (a-1-6 glycosidic)?

A

Branching enzyme forms a1-6 glycosidic bonds in glycogen synthesis

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14
Q

Which enzyme is responsible for the glycosidic bonds linking glucose residues in glycogenesis?

A

glycogen synthase

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15
Q

If we need glucose released from glycogen we need enzymes to break the gylcosidic bonds.
Which enzyme breaks a-1-6 glycosidic bonds?

A

de-branching enzyme

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16
Q

Which enzyme breaks a-1-4 glycosidic bonds?

A

glycogen phosphorylase

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17
Q

Is glycogenolysis the reverse of glycogenesis?

A

No! Because not all the reactions of glycogenesis are reversible.
Different enzymes allow for simultaneous inhibition of one pathway and stimulation of another

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18
Q

What function do glycogen stores serves in the muscle?

A

Muscle glycogen is exclusively reserved for the muscle’s own energy production.

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19
Q

What function do glycogen stored in the liver serve?

A

liver glycogen will be converted into glucose and exported to the blood compartment where is will buffer blood glucose levels.

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20
Q

Why can the glycogen stores of the muscle not join the blood to be used by the body?

A

Because muscle cells dont have glucose-6-phosphatase need to convert glucose-6P into glucose.

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21
Q

Which are the 2 enzymes responsible for glycogen degradation?

A
  1. Glycogen phosphorylase

2. De-branching enzyme

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22
Q

Which is the rate limiting enzyme of glycogen synthesis?

A

glycogen synthase

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23
Q

Which is the rate limiting enzyme of glycogen degradation?

A

Glycogen phosphorylase

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24
Q

LIVER: What effect does glucagon have on glycogen synthase?

A

Inhibits by phosphorylation

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25
Q

LIVER: What effect does glucagon have on glycogen phosphorylase?

A

activates by phosphorylation

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26
Q

What effect does insulin have on glycogen synthase?

A

Insulin stimulates glycogen synthase by dephosphorylation.

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27
Q

What effect does insulin exert on glycogen phosphorylase?

A

Insulin decreases glycogen phosphorylase activity by dephosphorylation.

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28
Q

Is glycogen synthase activated when dephosphorylated or phosphorylated?

A

Dephosphorylated

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29
Q

Is glycogen phosphorylase active when phosphorylated or dephosphorylated?

A

phosphorylated

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30
Q

In the MUSCLE, what effect does glucagon have on glycogen phosphorylase?

A

none! the msucle does not have receptors to glucagon, it would be useless as it can’t release glucose into the blood stream anyway.

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31
Q

What is the allosteric activator of MUSCLE glycogen phosphorylase? (but not the lover glycogen phosphorylase)

A

AMP

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32
Q

Glycogen storage diseases that diminish glycogen stores can lead to … (2)

A
  1. Hypoglycaemia

2. Poor exercise tolerance

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33
Q

What enzyme is deficient in von Gierke’s disease?

A

glucose 6-phosphatase (ie, liver only)

34
Q

Which enzyme of glycogen metabolism is deficient in McArdle disease?

A

muscle glycogen phosphorylase

35
Q

What is gluconeogenesis?

A

the production of new glucose beyond 8 hours of fasting when glycogen stores are depleted.

36
Q

Where does gluconeogenesis occur?

A
  1. Liver ++

2. Kidney cortex

37
Q

Which precursors can be used for gluconeogenesis? (3)

A
  1. Lactate form anaerobic glycolysis in exercising muscle and red blood cells.
  2. Glycerol released from adipose tissue breakdown of triglycrides
  3. Amino acids, mainly alanine (and other glucogenic aas)
38
Q

What is the Cori cycle?

A

It is the pathway for recycling lactate from anaerobic muscle activity to make glucose.

39
Q

Is gluconeogenesis the reversal of glycolysis?

A

No, because some reactions of glycolysis are not reversible, the enzyme only works one way.

40
Q

Which reactions of glycolysis are not reversable and must be bypassed in gluconeogenesis?

A

1, 3 and 10 of glycolysis

41
Q

Which enzymes are rate limiting for gluconeogenesis?

A

They are the ones that bypass irreversible reactions of glycolysis:

  • PEPCK
  • Fructose 1,6-biphodphatase
  • Glucose 6-phosphatase
42
Q

Which 2 key enzymes of gluconeogenesis are regulated by hormones?

A
  • PEPCK

- fructose 1,6-biphosphatase

43
Q

What action do glucagon and cortisol exert on gluconeogenesis?

A

Increase amount of rate limiting enzymes = stimulate gluconeogenesis

44
Q

On which enzyme do glucagon and cortisol act to stimulate gluconeogenesis?

A

Glucagon and cortisol act on PEPCK and fructose 1,6-phosphatase.
they increase amount of these enzymes.

45
Q

What action does insulin exert on gluconeogenesis?

A

Insulin inhibits gluconeogenesis by decreasing amount of rate limiting enzymes PECK and fructose 1,6-biphosphatase

46
Q

What sort of receptor does glucagon have?

A

GPCR

47
Q

What sort of receptor does cortisol have?

A

Nuclear receptor

48
Q

What sort of receptor does insulin have?

A

Tyrosine kinase rceptor

49
Q

Which source of glucose is used for 2 hours post-meal?

A

glucose form food

50
Q

from 1 to 10 hours after a meal, what is the source of glucose for the body?

A

glycogenolysis

51
Q

8-10 hours after meal, what is the source of glucose for the body?

A

gluconeogenesis form lactate, amino acids and glycerol

52
Q

How is excess energy stored in the body?

A

in the form of Triacylglycerols TAG

53
Q

Which specialised tissue stocks TAGS’s?

A

adipose

54
Q

TAGs are hydrophobic and so stored without water, this is called

A

anhydrous

55
Q

Recently, adipocytes have been discovered a function in the endocrinal system, what is it?

A

they secrete leptin

56
Q

Can dietary fat be absorbed as it is into small intestine wall?

A

No, fat can only be absorbed under the form of fatty acids + glycerol

57
Q

Which digestive enzyme is essential for fat absorbtion by the small intestine?

A

pancreatic lipase

58
Q

What happens to TAGs in the intestinal epithelial cells?

A

they are packaged into chylomicrons

59
Q

Do dietary lipids get absorbed straight into the blood stream like other nutrients?

A

no, they joins the lymph once packaged into chylomicrons

60
Q

at which point will dietary lipids end up in the blood stream?

A

When the thoracic duct drains into the left subclavian veins.

61
Q

The TAGs in the blood have 2 destinies, these are

A
  1. Tissues for fatty acids oxidation to provide energy (NOT in cells lacking mitochondria or in the brain because FAs cant pass the blood-brain barrier)
  2. Adipose for storage
62
Q

TAGs of adipose tissue can be mobilised as a source of energy. What is released from the cells into the blood?

A

Fatty acids.

These will bind to albumin so as to be soluble in blood.

63
Q

Which enzyme is able to mobilise the TAGs of adipose as an energy source?

A

Hormone sensitive lipase

64
Q

What is hormone sensitive lipase?

A

Hormone sensitive liaose is the enzyme responsible for mobilising the TAG store in adipose. It breaks TAGs down and releases FAs into the blood stream.

65
Q

What are the effects of glucagon and adrenaline on hormone sensitive lipase?

A

activates lipase

66
Q

What action does insulin exert on hormone sensitive lipase?

A

inhibition

67
Q

What is the main site for fatty acid synthesis?

A

liver

68
Q

Which 2 substrates does lipogenesis require?

A

ATP

NADPH

69
Q

For which processes is NADPH important?

A
  1. Anabolic, lipogenesis

2. Protection against oxidative stress, by contributing to glutathione production

70
Q

Which enzyme is the key regulator of lipogenesis?

A

Acetyl-CoA carboxylase

converts acetyl-CoA into Malonyl-CoA

71
Q

How does insulin act on acetyl-coA carboxylase (lipogenesis)

A

increases activity by dephosphorylation

72
Q

How does citrate act on acetyl-CoA carboxylase (lipogenesis)?

A

allosterically stimulates

73
Q

How do glucagon and adrenaline act on acetyl-CoA carboxylase?

A

decrease activity by phosphorylation

74
Q

How does AMP regulate acetyl-CoA carboxylase?

A

allosterically inhibits

75
Q

Where does fatty acid oxidation (b-oxydation) occur?

A

in the mitochondria

76
Q

Where does fatty acid synthesis occur?

A

in the cytoplasm

77
Q

Hormone sensitive lipase will degrade TAGs in adipose into fatty acids and glycerol. Where do these go now?

A
  1. Glycerol travels to the liver in the blood and utilised as carbon source for gluconeogenesis
  2. Free fatty acids travel in the blood complexed to albumin to muscle and other tissues for b-oxidation
78
Q

Does the liver or the muscle have a bigger mass of glycogen?

A

The muscle does.
- muscle 300g
- liver 100g
… in 70kg male

79
Q

Do a healthy 70kg man and an obese person 135kg have the same mass of glycogen?

A

yes

80
Q

What type of store is increased in a 135kg obese man?

A

triacylglycerols!

MEH (4 decks)

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