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Lizzie's Metabolism > Energy Storage > Flashcards

Energy Storage Flashcards

0
Q

What happens once glycogen stores have been depleted? (After 8-12 hours)

A

Gluconeogenesis

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1
Q

What are the main energy stores in a 70kg man?

A

Triacylglycerols - 15kg
Glycogen - 0.4kg
Muscle proteins - 6kg

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2
Q

Which two types of glycosidic bonds are present in glycogen?

A

Alpha 1-4 and a1-6

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3
Q

Which bonds are the branch points in glycogen?

A

Alpha 1-6

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4
Q

What does the highly branched structure of glycogen allow?

A

Many sites to which glucose residues can be added/removed, allowing rapid synthesis/degradation of glycogen

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5
Q

Where is glycogen stored?

A

Granules in liver and skeletal muscle

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6
Q

Why is there a limit to how much glycogen can be stored?

A

A highly polar molecule so attracts lots of water

No specialised storage tissue so has to be stored in tissues with other important functions

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7
Q

What is glycogenesis?

A

Synthesis of glycogen

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8
Q

Name the six enzymes needed for glycogenesis

A

Hexokinase / glucokinase in liver
Phosphoglucomutase
Glycogen synthase
Branching enzyme

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9
Q

When is glycogen degraded?

A

In skeletal muscle - exercise

In liver - during fasting, stress response

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10
Q

Glycogen degradation is not a reversal of the synthetic pathway. What does this allow for?

A

Greater metabolic flexibility

Independent control

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11
Q

What does glycogen phosphorylase do?

A

Involved in glycogen degradation
Attacks alpha 1-4 bonds by phosphorolysis
This releases glucose residues as glucose 1P

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12
Q

What does debranching enzyme do in glycogen degradation?

A

Breaks down alpha 1-6 bonds and releases free glucose.

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13
Q

What does glucose 6-phosphatase do?

A

Converts glucose 6-P releases from glycogen degradation into glucose in the liver.

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14
Q

Which two enzymes are regulated in glycogen synthesis/degradation?

A

Glycogen synthase

Glycogen phosphorylase

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15
Q

How are the enzymes activated/inhibited in glycogen regulation?

A

Synthase - inhibited by phosphorylation and activated by dephosphorylation

Phosphorylase - inhibited by dephosphorylation and activated by phosphorylation

Regulated by glucagon and insulin

16
Q

How does insulin and glucagon regulate the enzymes of glucagon synthesis/degradation?

A

Insulin promotes dephosphorylation

Glucagon promotes phosphorylation

17
Q

What are consequences of glycogen storage diseases?

A

Too much/little glycogen can cause

  • tissue damage if excessive
  • fasting hypoglycaemia
  • poor exercise tolerance
20
Q

What can be used in gluconeogenesis?

A

Lactate, pyruvate, amino acids and glycerol

21
Q

Which reactions is gluconeogenesis from pyruvate similar to?

A

Glycolysis

22
Q

Which enzymes are involved in gluconeogenesis from pyruvate?

A

Glucose 6-phosphatase
Fructose 1,6-bisphosphatase
Pyruvate carboxylase
PEPCK

23
Q

Which two enzymes are controlled in gluconeogenesis and how?

A

PEPCK and fructose 1,6-bisphosphatase

Activity is increased by glucagon and cortisol and decreased by insulin

33
Q

When does gluconeogenesis occur?

A

When all of the glycogen has been used up after 8-10hrs of fasting

34
Q

What is the overall equation of gluconeogenesis?

A

2 pyruvate + 4ATP + 2GTP + 2NADH

——-> glucose + 2NAD+ + 4ADP + 2GDP + 6Pi + 2H+

35
Q

List the enzymes which reduce storage of triacylglycerols.

A

Glucagon
Cortisol
Thyroxine
Growth hormone

36
Q

What is lipogenesis?

A

Fatty acid synthesis

37
Q

What are fatty acids synthesised from and where does it occur?

A

Acetyl CoA

Cytoplasm

38
Q

What does fatty acid synthesis require and where do they come from?

A

NADPH - from the pentose phosphate pathway

Acetyl CoA - comes from the mitochondria as citrate
Citrate -> oxaloacetate + acetyl CoA

ATP

39
Q

Where does FA synthesis occur?

A

Cytoplasm

40
Q

Describe the process of FA synthesis

A

Carried out by FA synthase complex

C2 added as malonyl CoA (a C3 molecule) in each turn of the cycle to the growing FA chain with a subsequent loss of carbon dioxide

41
Q

How is malonyl CoA produced?

A

From acetyl CoA

Done by the enzyme acetyl CoA carboxylase.

42
Q

How is acetyl CoA carboxylase regulated?

A

Allosteric regulation - citrate activates and AMP inhibits

Covalent modification - insulin activates by promoting its dephosphorylation and glucagon inhibits by phosphorylation

43
Q

Why are TAGs an efficient way of storing energy

A

Can be stored in bulk in an anhydrous form

Lizzie's Metabolism (14 decks)

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