Lecture 3- Energy storage (glycogen) Flashcards

1
Q

which tissues have an absolute requirment for glucose as an energy source

A
  • RBC
  • Neutrophils- resp burst
  • Innermost cells of kidney medulla- blood supply low because so deep
  • Lens of the eye- not very rich blood supply (oxidative phos limited)
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2
Q

brain’s energy source

A
  • Stable BG essential for normal brain function
  • Brain has a requirement for glucose
  • Can use ketones but takes a while to adapt
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3
Q

normal BG

A

5mmol

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4
Q

To enable bg to be kept at stable levels glucose is stored as

A

glycogen

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5
Q

consequence of hypoglycaemia (2.8 mmol/L)

A

confusion

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6
Q

consequence of hypoglycaemia (1.7 mmol/l)

A

weakness and nausea

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7
Q

consequence of hypoglycaemia (1.1 mmol/l)

A

muscle cramps

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8
Q

consequence of hypoglycaemia (0.6 mmol/l)

A

brain damage and death

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9
Q

glycogen is stored as ……….. in the ….. and ……

A
  • Glycogen is stored as granules
  • Muscle
  • Liver
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10
Q

glycogen in muscle

A

Distinction between intra and intermyofibrillar glycogen

Glycogen in muscle= for muscle contraction

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11
Q

how is glycogen stored in the liver

A

Glycogen stored as granules in hepatocytes

Glycogen store in liver= buffers plasma glucose levels

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12
Q

examples of conditions which cause hypoglycaemia

A
  • e.g. diabetic patient which has taken insulin injections and forgotten to eat meal
  • e.g. Someone with acute alcoholic poisoning
  • e.g. Athlete which has pushed themselves over the limit
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13
Q

see the effects of hypoglycaemia if the bg drops to

A

2.8 mmol/l

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14
Q

structure of glucogen

A
  • Glycogen is a polymer consisting of chains of glucose residues
  • Chains are organised like the branches of a tree originating from a dimer of the protein glycogenin (acts as a primer at core of glycogen structure)
  • Glucose residues linked by alpha1-4 glyosidic bonds with alpha 1-6 glyosidic bonds forming branch points every 8-10 residues
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15
Q

protein glycogenin

A

(acts as a primer at core of glycogen structure)

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16
Q

why does glycogen have this structure

A
  • Will release glucose quickly
  • Reduces the osmotic effect on the cell
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17
Q

glycogenesis is the pathway by which

A

glycogen is synthesised

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18
Q

glycogenolysis is the pathway by which

A

glycogen is degraded to produce glucose or be used in glycolysis

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19
Q

synthesis of glycogen requires

A

Energy (ATP)

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20
Q

outline glycogenesis

A
  1. glucose is convert to glucose 6-phosphate by hexokinase
  2. glucose 6-phosphate is converted to glucose 1-phosphate by phosphoglucomutase
  3. glucose 1 phohate is converted to UDP glucose by G1P uridylyltransferase
  4. glycogen (n residues) + UDP-glucose –> glucogen (n +1 + UDP
    • glycogen synthase–> alpha 1-4 glycosidic bonds
    • branching enzyme –> alpha 1-6 glycosidic bonds
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21
Q

glycogen synthase

A

enzyme which catalyses the formation of 1-4 glycosidic bonds

22
Q

branching enzyme

A

enzyme which catalyses the formation of 1-6 glycosidic bonds

23
Q

outline glycogenolysis

A
  1. glycogen (n residues) + Pi –> Glycose 1-phosphate _ glycogen (n-1 residues)
    • glycogen phosphorylates or de-branching enzyme
    • glucose 1-phosphate –> glucose 6-phopshate
  2. in the muscle glucise 6-phosphate is used by muscle for energy production
  3. in the liver glucose-6 phophate is converted to glucose and rleeased into the blood
24
Q

in the muscle glucose 6-phosphate

A
  • is used by muscle for energy production
    *
25
Q

in the liver glucose-6 phophate is converted to

A

glucose and released into the blood

26
Q

glycogenolysis is not

A

a simple reversal of glycogenesis

27
Q

function of glycogen storesin the liver

A
  • G6P converted to glucose and exported to the blood
  • Acts as a buffer of blood glucose levels
28
Q

Function of glycogen stores in the muscle

A
  • Muscle lacks the enzyme glucose-6-phosphatase
  • G6P enters glycolysis for energy production
29
Q

summary of glycogenolysis and glycogenesis

A
30
Q

rate limiting enzyme of glycogen synthesis

A

glycogen synthase

31
Q

rate limiting enzyme of glycogen degradation

A

glycogen phosphorylase

32
Q

as rate limiting enzymes, glycogen synthase and glycogen phosphorylase are under

A

hormonal control- mainly to maintain plasma glucose

33
Q

which hromones increase BG and by which mechangism

A

glucagon and adrenaline

Glycogen synthase —> phosphorylation - decrease enzyme activity- increase BG

Glycogen phosphorylase —> phosphorylation - increase enzyme activity - increase BG

34
Q

which hormoens decrease blood glucose

A

insulin

Glycogen synthase—> de-phos – increase

Glycogen phosphorylase—> de-phos - decrease

35
Q

glucagon has no effect on which cells

A

muscle - no glucagon receptros

AMP is an allosteric activator of muscle glycogen phosphorylase but not of the liver form of

the enzyme

36
Q

glycogen storage disease

A

Inborn error of metabolism (inherited)

Deficiency or dysfunction in enzymes involved in glycogen metabolism

12 types

37
Q

in glycogen storage disease liver and /or muscle can be affected

A
  • Excess glycogen storage can lead to tissue damage
  • Diminished glycogen stores can lead to hypoglycaemia and poor exercise tolerance
38
Q

examples of glycogen storage disease (2)

A

von Gierkes disease - G6P deficiency

McArdle disease – muscle glycogen phosphorylase deficiency

39
Q

Beyond 8 hours of fasting, liver glycogen stores start to deplete and alternative some of glucose is required……

A
  • gluconeogenesis
40
Q

where does glucoseneogenesis occur

A

Occurs in liver and to lesser extent in kidney cortex

41
Q

three major precursors of glucoseneogenssi

A

lactate

glycerol

amino acids

42
Q

lactate from

A

anaerobic glycolysis in exercising muscle and red blood cells (cori cycle)

43
Q

glycerol

A

released from adipose tissue breakdown of triglycerides

44
Q

amino acid

A

mainly alanine

45
Q

why is there no net syn thess from acetyl-coA

A

acetyl coA cannot be converted into pryuvate (pyruvate dehydreogenase reaction is irreversible)

46
Q

Although similar, the gluconeogenesis pathway is not

A

simply the opposite of glycolysis

Has PEPCK instead of pyruvate kinase

47
Q

Key enzymes of glucoseneogenesis

A

1) Phosphoenolpyruvate carboxykinase (PEPCK)
2) Fructose 1,6-bisphosphatase
3) Glucose-6- phosphatase

48
Q

Regulation of gluconeogenesis

A

2 enzymes regulated by hormones in response to:

  • Starvation/fasting
  • Prolonged exercise and stress

Glucagon and cortisol

49
Q

in response to starvation which hormones are released and what is effect on glucoseneogenesis enzymes

A

glucagon and cortisol are released

  • PEPCK - increased amount
  • fructose 1,6 bisphosphatase - icnreased amount snad activitity

effect- stimulates glyconeogensis

50
Q

in response to higher BG which hormones are released and what is effect on glucoseneogenesis enzymes

A

insulin

  • PEPCK - decreased amounts
  • Fructose 1,6 bisphosphatase - decreased amkoutn and activity

Effect- inhibits glucoseneogenesis