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Fundamentals Of The Living Cell > Carbohydrate metabolsim > Flashcards

Carbohydrate metabolsim Flashcards

1
Q

What is the critical blood glucose level?

A

2.5mM

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2
Q

What are the symptoms of hypoglycaemia?

A 
• Muscle weakness
• Loss of coordination
• Mental confusion
• Sweating
Hypoglycaemic coma and death
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3
Q

What can hyperglycaemia lead to?

A 
It can lead to non enzymatic modification of proteins:
  Cataracts
  Modification to lipoproteins 
  which is important in 
  atherosclerosis
  Hyperosmolar coma
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4
Q

What synthesis does excess blood glucose lead to ?

A

• Glycogen synthesis
• Pentose phosphate synthesis
Fatty acid synthesis

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5
Q

What does a lack of blood glucose lead to?

A
  • Glycogen breakdown

* Gluconeogenesis

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6
Q

What does the liver mainly store?

A

Main storage of excess glucose

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7
Q

What is glucose phosphorylated by?

A

Glucose phosphorylated by glucokinase and traps glucose in the cell

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8
Q

What is excess glucose synthesised into?

A

Excess glucose is synthesised into glycogen which is branched and compact.

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9
Q

Why isn’t glucose just stored as glucose in cells?

A

Glucose itself is too osmotically active causing an osmotic effect that draw in water and damages the cell.

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10
Q

What are the steps for glycogen synthesis?

A

• G6P converted to Glucose 1 phosphate by phosphoglucomutase
• G1P activated by UTP forming UDP-glucose
• UDP glucose binds to glycogenin to start glycogen synthesis
Alpha 1-6 bonds formed at the 11th residue

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11
Q

Why is glucose stored as glycogen?

A

• Cannot store glucose as its osmotically driven
• 400mM glucose is stored as 0.01 mM glycogen
• Fats can’t be mobilised as readily
• Fat cannot be used as an energy source in the absence of oxygen
Fats cannot be converted in to glucose

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12
Q

What are the 2 products formed from the breakdown of glycogen and which is the major product?

A

Glucose 1 phosphate and glucose

Glucose 1 phosphate is the major product

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13
Q

What is glycogen phosphorylase?

A

Key enzyme in glycogenolysis and its activity forms glucose-1-phosphate

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14
Q

What does glycogen phosphorylase break?

A

Breaks the 1-4 link

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15
Q

What is the structure of glycogen phosphorylase and how is this advantageous?

A

§ Many phosphorylase molecules are bound to each glycogen particle:
Therefore glycogenolysis can be switched on rapidly

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16
Q

What is ultimately formed and what does this provide?

A

G6P ultimately formed provides fuel for working muscles

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17
Q

What happens to G6P in the liver and what is the level maintained?

A

In liver, G6P is de-phosphorylated and secreted into the blood, maintaining 5 mmol/l blood sugar

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18
Q

What type of enzyme is glycogen phosphorylase and how is it regulated?

A

An allosteric enzyme which is activated by phosphorylation but modulated by other factors

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19
Q

What type of enzyme is translocase?

A

De-branching enzyme

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20
Q

What are the two activities associated with glycogen phosphorylase?

A

□ Transferase activity moves the last glucose residues to the non-reducing end of the existing chain

Glucosidase that removes the 1-6 link releasing glucose

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21
Q

How can glycogen phosphorylase b activated in muscles?

A

In muscle, glycogen phosphorylase b can be activated by 5’-AMP without being phosphorylated

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22
Q

How does 5’AMP form?

A

5’-AMP forms when ATP is depleted

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23
Q

What does ATP do at the binding site of glycogen phosphorylase?

A

ATP binds to the same site and blocks activation

24
Q

What else blocks 5’AMP activation?

A

G6P also blocks 5’-AMP activation

25
Q

What inhibits activated phosphorylase a in the liver?

A

In the liver the activated phosphorylase a is inhibited by glucose

26
Q

What activates phosphorylase b kinase ?

A

Ca2+ activate phosphorylase b kinase

27
Q

What does Ca2+ in muscles mediate?

A

In muscle, mediating glycogenolysis during muscle contraction

28
Q

When is their maximum activity in muscles?

A

Max activity with Ca2+ and phosphorylation

29
Q

How is Ca2+ release stimulated in the liver?

A

In liver, α-adrenergic activation stimulates Ca2+ release

30
Q

When is glycogen synthase activated?

A

Activated in times of plenty of glucose

31
Q

What activates glycogen synthase?

A

Activated by ATP and G6P

32
Q

How is glycogen synthase inactivated?

A

Inactivation by phosphorylation by protein Kinase A

33
Q

How is glycogen synthase activated?

A

Activated by dephosphorylation by protein phosphatase-1

34
Q

When is glycogen phosphorylase activated?

A

Activated when glucose in short supply

35
Q

What is glycogen phosphorylase inactivated by?

A

Inactivated by ATP and G6P

36
Q

How is glycogen phosphorylase activated?

A

Activated by phosphorylation by phosphorylase kinase A

37
Q

How is glycogen phosphorylase inactivated?

A

Inactivated by dephosphorylation by protein phosphatase-1

38
Q

When is the pentose phosphate pathway activated?

A

Activated when plenty of glucose is present

39
Q

Why is the pentose phosphate pathway important and why?

A

• Important for generating ribose 5 phosphate

Important precursor for component of DNA and RNA and also important for coenzymes the body needs

40
Q

What does the pentose phosphate pathway generate when excess glucose is present?

A

Pathway generates NADPH which is required for fatty acid synthesis

41
Q

What can ribose 5 phosphate be converted back into in pentose phosphate pathway?

A

Ribose 5 phosphate can be converted back to G6P

42
Q

What is gluconeogenesis?

A

When glucose is produced from non-carb sources at low glucose levels

43
Q

Why is blood glucose maintained?

A

• Blood glucose maintained as it is the preferred fuel for the brain and only fuel for red blood cells

44
Q

What are the daily requirements of the body in terms of glucose?

A

Daily requirement 160g

45
Q

How much glucose does the brain require?

A

120g

46
Q

What are the total body reserves?

A

210g

47
Q

What does the glucogenic pathway convert?

A

Gluconeogenic pathway converts pyruvate to glucose

48
Q

Where does gluconeogensis mostly take place?

A

Mostly takes place in the liver and a little in the kidney, however during starvation, kidney production rises to 40%

49
Q

What are the 3 most important substrates for gluconeogenesis?

A

○ Alanine
○ Lactate
Glycerol

50
Q

What are the steps involved in gluconeogenesis?

A
  1. Pyruvate caboxylase which converts pyruvate to oxaloacetic acid which is then converted into phosphoenol pyruvate by phosphoenol pyruvate carboxykinase.
  2. 3 C converted to G6P by fructose biphosphatase which is then converted to glucose by glucose 6 phosphotase
51
Q

Another way for glucose to be synthesised

A

Glycerol can be used to synthesise glucose from the backbone of fatty acids

52
Q

Where is oxaloacetic acid generated?

A

Oxaloacetic acid from pyruvate is generated in the mitochondria

53
Q

Where is pyruvate synthesised?

A

Pyruvate is synthesised in the cytosol

54
Q

How is phosphoneol pyruvate synthesised?

A

○ Pyruvate transported to mitochondria from cytosol
○ Then converted to oxaloacetate by pyruvate carboxylase which cannot exit the mitochondria

Therefore converted to malate which is then transported out back to the cytosol where its converted to oxaloacetate and then phosphoneol pyruvate.

55
Q

Why is pyruvate first transported to the mitochondria in the synthesis of phosphoneol pyruvate?

A

Because the enzymes required for the production of oxaloacetate are present inside the mitochondria

Fundamentals Of The Living Cell (31 decks)

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