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2nd yr- IBMS- glucose homeostasis > Glycogen Breakdown > Flashcards

Glycogen Breakdown Flashcards

1
Q

Go through the steps our body goes through to increase out glucose levels in fasting state

A
  1. Glucose is converted into pyruvate
  2. Pyruvate converted into acetyl CoA
  3. Acetyl CoA enters the citric acid cycle
  4. Citric acid cycle produces high energy electrons that go to the electron transport chain
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2
Q

How is glucose stored?

A

Stored as glycogen in our muscles and liver

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3
Q

When is liver glucose released?

A
  1. Can be released into the blood during fasting

2. During fight or flight liver can metabolise glycogen stored and releases glucose for use by muscle

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4
Q

Does the liver use the stored glycogen for fuel?

A

no it can use glycogen derived glucose for the pentose phosphate pathway

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5
Q

What happen when prolonged fasting occurs?

A

Glycogen reserves will be used up and metabolism needs to start synthesising glucose from non-carbohydrates to maintain blood glucose levels (gluconeogenesis)

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6
Q

What is gluconeogenesis

A

The synthesis of glucose from non carbohydrate sources

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7
Q

Why is glucose important ?

A
  1. AS it is the only energy source used by the brain and is required by cells with no mitochondria
  2. It is the energy source for exercising muscles and is the substrate for anaerobic glycolysis
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8
Q

Why has the body developed mechanisms for storage and supply of glucose?

A

As dietary intake of glucose is sporadic and not always reliable

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9
Q

Between meal and during exercise where do we get glucose from?

A

From glycogen when it’s metabolised

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10
Q

Name the main stores of glycogen

A

Muscles

Liver

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11
Q

What is the molecular mass of one glycogen molecule

A

Can be up to 10^8 (100,000,000)

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12
Q

How does glycogen exist?

A

Exists as discrete cytoplasmic granules which contain most of the enzymes necessary for glycogen synthesis and degradation

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13
Q

Describe the structure of glycogen

A
  1. it is a homopolysaccharide made form only alpha D glucose
  2. Made up of multiple chains
  3. Is highly branches
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14
Q

Name the bond that links each unit of glycogen

A

Glycosidic bond

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15
Q

What type of glycosidic bond is present in glycogen?

A

Alpha 1,4 link between each unit

Alpha 1,6 link at branch points

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16
Q

When does Glycogen branching occur?

A

Occurs every 8-10 glucosyl residues

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17
Q

What does the alpha stand for in the alpha 1,6 AND 1,4 LINKS

A

Means theres the same stereochemistry between both glycogen been combines

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18
Q

What is the significance of branching?

A

Branching creates countless non reducing ends which means glycogen can be synthesised or broken down rapidly

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19
Q

What is the difference between glycogen and starch

A

Starch is not as branched

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20
Q

How is glycogen synthesised and broken down?

A

By adding or removing glucose units from non reducing ends

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21
Q

What is the main function of liver glycogen

A

To maintain blood glued between meals and during early stages of fasting

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22
Q

What is the main function of muscle glucose

A

It isa fuel reserve for muscle contraction

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23
Q

Is the glucose released from LIVER glycogen exportable?

A

Yes as it is released from the lover into the blood stream to be used by other tissues

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24
Q

Is the glucose released from muscle glycogen exportable?

A

No as this glucose cannot leave the muscle

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25
Q

How big is the glycogen store in the liver

A

10% wet weight of liver

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26
Q

How long does the glycogen stored in the liver last?

A

Around 24 hours during fasting

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27
Q

How big is the glycogen store in the muscles

A

1-2% of wet weight of muscles

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28
Q

Name the hormones that promote the breakdown of liver glycogen

A

Glucagon and adrenaline

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29
Q

Name the hormones that promote the breakdown of liver glycogen

A

Adrenaline

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30
Q

Name the hormone that promotes synthesis os glycogen

A

insulin

31
Q

When is liver glycogen broken down from non reducing terminals?

A
  1. When blood glucose levels begin to fall

2. When musclesneed glucose for ATP production

32
Q

Is more glycogen stored in the liver or in muscles?

A

Muscles a we have more muscles than liver

33
Q

When is muscle glycogen broken down from non reducing terminals?

A

When musclesneed glucose for ATP production

34
Q

State the chemical formula for the break down of glycogen

A

Glycogen + Pi -> Glucose 1 phosphate +Glycogen (in 1 less residue)

35
Q

Name the enzyme that aids glycogen breakdown

A

Glycogen phosphorylase

36
Q

What does glycogen break down release?

A

Glucose 1-phophate not free glucose

37
Q

Describe phosphorylated glucose

A

Phosphorylated glucose is a more “energy rich” molecule than glucose.

38
Q

When does glycogen phosphorylate stop cleaving

A

When it gets to within 4 resides of a branch point

39
Q

What happens when glycogen phosphorylase hits a branch point?

A

It stops cleaving

40
Q

Name the 2 additional enzymes required to break down glycogen at a branch point

A
  1. Transferase

2. Hydrolase

41
Q

Talk through the break down of glycogen at a branch point

A
  1. Glycogen phosphorylase Stops cleaving 4 residues from a branch point
  2. Transferase enzyme transfers 3 glucose unit to end of glycogen molecule
  3. Hydrolase Enzyme hydrolyses the single glucose unit left behind
42
Q

State the ratio between glucose 1-phosphate production and glucose production during glycogen breakdown

A

8:1

43
Q

How do we use glucose 1-phosphate in the liver?

A
  1. First we convert it into glucose 6-phosphate via enzyme Phosphoglucomutase
  2. Then glucose 6-phosphate is converted into glucose via enzyme Glucose 6-phosphatase
  3. Glucose is then released into the blood to maintain blood glucose levels
44
Q

What does Phosphoglucomutase do?

A

Converts glucose 1-phosphate into glucose 6-phospahte

45
Q

What does Glucose 6-phosphatase do

A

Converts Glucose 6-phosphate into glucose

46
Q

Name the enzyme that might be defected in patients suffering from type 1 diabetes

A

Glucose 6-phosphatase

47
Q

How do we use glucose 1-phosphate in our muscles ?

A
  1. First we convert it into glucose 6-phosphate via enzyme Phosphoglucomutase
  2. glucose 6-phosphate is then trapped in the muscles cell for use in glycolysis
48
Q

Why isn’t glucose 6-phosphate converted into glucose in muscle cells

A

As muscles don’t have the glucose 6-phosphatase enzyme

49
Q

How is glucose used in the muscles?

A

It is converted into glucose 6-phosphate via hexokinase then used for glycolysis

50
Q

What does hexokinase do?

A

Converts glucose into glucose 6-phosphate

51
Q

When do we need to synthesis glycogen?

A

When we have a surplus of glucose (usually after a meal)

52
Q

How is glycogen metabolism regulated?

A
  1. By hormones

2. Allosteric Control regulates glycogen metabolism

53
Q

What does adrenaline do in muscles?

A

It stimulates muscle glycogen breakdown

54
Q

What does adrenaline do in the liver?

A

stimulate glycogen breakdown in the liver.

55
Q

What does glucagon do in the liver?

A

stimulate glycogen breakdown in the liver.

56
Q

Talk through the stages of hormonal control of glycogen breakdown

A
  1. Adrenaline and glucagon receptors activate adenylate
    cyclase
  2. This adenylate
    cyclase catalyses the formation of cAMP
  3. cAMP activated Protein kinase A
    Protein kinase does 2 thing:
    A. The catalytic side of Protein kinase A activates Phosphorylase kinase. This activates Phosphorylase kinase which in turn breaks down glycogen
    B. The regulator side of Phosphorylase kinase inhibits glycogen synthase so Glycogen synthesis
    switched off
57
Q

What does cAMP do to stimulate glycogen breakdown?

A

cAMP activated Protein kinase A

58
Q

What does protein kinase A do?

A
  1. The catalytic side of Protein kinase A activates Phosphorylase kinase. This activates Phosphorylase kinase which in turn breaks down glycogen
  2. The regulator side of Phosphorylase kinase inhibits glycogen synthase so Glycogen synthesis
    switched off
59
Q

What does insulin do to regulate glycogen metabolism?

A

Insulin is released when blood glucose levels are elevated and stimulates glycogen synthesis whilst inhibiting breakdown.

60
Q

What is the hormone control of glycogen break down known as

A

The Amplification cascade

61
Q

Talk through the stages of hormonal control of glycogen synthesis

A
  1. Insulin receptor (Tyrosine kinase) activates protein kinase
  2. Protein kinase activates Phosphoprotein
    phosphatase 1
  3. Phosphoprotein
    phosphatase 1 does 2 things:
    A, It inhibits Glycogen
    phosphorylase b so glycogen break down is switched off
    B. It activates Glycogen
    synthase a so glycogen synthesis occurs
62
Q

Name the 5 main glycogen stage disease

A
  1. Von Gierke’s disease
  2. Pompe’s disease
  3. Forbes’ disease
  4. Andersen disease
  5. McArdle disease
63
Q

What does the Von Gierke’s disease affect?

A

Affects the Liver, intestines and kidneys

Glucose 6-phosphatase is defected

64
Q

What does the Pompe’s disease affect?

A

Affects the liver, muscles and heart

Lysosomal Alpha glucosidase is inhibited

65
Q

What does the Forbes’ disease affect?

A

Affects the liver and muscles
Leads to an abnormal glycogen structure
The Amylo-1-6- glucosidase is defected

66
Q

What does the Andersen disease affect?

A

Affects the liver and muscles
Leads to an abnormal glycogen structure
The 1- 4- glucan branching enzyme is defected

67
Q

What does the McArdle disease affect?

A

Affects muscles only

The phosphorylase enzyme is defected

68
Q

What is the outcome of the Von Gierke’s disease

A

If the patent survives the initial hypoglycaemia then prognosis is good
Hyperuricaemia is a late complication

69
Q

What is the outcome of the Pompe’s disease

A

Death in the first 6 months

70
Q

What is the outcome of the Forbes’ disease

A

Good prognosis

71
Q

What is the outcome of the Andersen disease

A

Death in first 3 years

72
Q

What is the outcome of the McArdle disease

A

Normal lifespan but exercise must be avoided

73
Q

Whta is non alcoholic steato hepatitis?

A

It can be defined as the liver manifestation
of a metabolic disorder, and is the most severe
form of non-alcoholic fatty liver disease

2nd yr- IBMS- glucose homeostasis (3 decks)

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