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Metabolism > Lipid Metabolism > Flashcards

Lipid Metabolism Flashcards

1
Q

Principle form of energy storage in mammals?

A

TAGs

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2
Q

When does Fatty acid synthesis primarily occur?

A

When there is excess energy.

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3
Q

What is not a major site of fatty acid synthesis?

A

Adipose.

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4
Q

What enzyme catalyses Fatty acid synthesis?

A

Acetyl CoA Carboxylase

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5
Q

What cofactor does the enzyme for fatty acid synthesis require?

A

Biotin

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6
Q

What is the first committed step of fatty acid synthesis?

A

Acetyl CoA + Bicarbonate = Malonyl CoA

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7
Q

What hormones inhibit fatty acid synthesis?

A

Epinephrine and Glucagon.

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8
Q

What is used up every time 2 Acetyl CoA join together?

A

1 ATP and 2 NADPH

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9
Q

Where does synthesis of TAG occur?

A

Liver and Adipose.

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10
Q

When does synthesis of TAG in adipose occur?

A

When glycolysis is activated in the fed state.

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11
Q

What do we use for TAG synthesis in Adipose?

A

Dihydroxyacetone phosphate.

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12
Q

Are cholesterol hydrophobic or hydrophilic?

A

Hydrophobic.

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13
Q

Solubility of cholesterol?

A

Low in water.

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14
Q

What is cholesterol a precursor for?

A

Bile acids, steroid hormones, and vitamin D.

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15
Q

How much cholesterol is absorbed?

A

70% approx.

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16
Q

Where is cholesterol synthesised?

A

Mainly liver, but also adrenal cortex and gonads.

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17
Q

What is the key regulatory enzyme wrt cholesterol?

A

HMG-CoA reductase.

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18
Q

Can cholesterol be digested in the GIT?

A

No.

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19
Q

How is cholesterol removed?

A

transfer into GIT and excretion via faeces. Eliminated after conversion to bile acids.

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20
Q

Structure of Lipoproteins?

A
  • Hydrophobic core = insoluble lipid, TAG, and cholesterol esters.
  • Polar external coat = single phospholipids, free cholesterol and apoproteins.
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21
Q

What triggers mobilisation of TAG from Adipose Tissue?

A

Adrenaline and Glucagon.

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22
Q

What do the hormones do?

A

Adrenaline and Glucagon stimulate hormone sensitive triacylglycerol lipase to cleave TAG into fatty acids and glycerol.

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23
Q

Where do the fatty acids from TAG breakdown go?

A

BETA OXIDATION

  • Bind to the albumin in blood.
  • Dissociate from albumin and enter cytosol of cells
  • in cytosol, FA are bound to binding proteins or enzymes.
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24
Q

Structure of TAG?

A

3 Fatty Acid chains attached to glycerol.

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25
Q

Structure of Phospholipids?

A

2 Fatty acid chains.

26
Q

What are apolipoproteins?

A

Small protein particles sitting in the external coat of lipoproteins.

27
Q

What is the function of apolipoproteins?

A
  • Differentiate each type of lipoprotein

- Structurally stabilise lipoproteins

28
Q

Function of apolipoprotein (2)?

A
  • Act as cofactors that inhibit or activate enzymes acting on lipids.
  • Act as ligands for receptors that may take up lipoproteins.
29
Q

Can apolipoproteins be transferred between lipoproteins?

A

Yes.

30
Q

What is the function of lipoproteins?

A

Transport Lipids and release different lipids under different circumstances.

31
Q

What happens to lipoproteins after a meal?

A

Lipoproteins are released into blood from GIT cells.

32
Q

What are chylomicrons?

A

Type of lipoprotein.

33
Q

Where are chylomicrons synthesised?

A

In cells lining GIT after meals.

34
Q

What do chylomicrons do?

A

Transport DIETARY lipids around.

35
Q

What happens to chlyomicrons?

A

They travel and interact with other cells to release lipids and give off fatty acids.

36
Q

What is left of the chylomicrons?

A

When FA and lipids are released, Chylomicron remnants are left behind.

37
Q

What is the final fate of chylomicrons?

A

They interact with receptors on the surface of the liver cells, and are taken up by the liver.

38
Q

What lipoproteins are made during fasting mode?

A

VLDL.

39
Q

What happens to VLDL remnants?

A
  • They can be taken up by the liver and components recycled.

- They can stay in the blood stream and give off more FA’s.

40
Q

What happens to VLDL’s if they stay in the bloodstream?

A

They are known as LDL’s.

41
Q

What happens to LDL’s after they stay around in the blood stream giving off FA’s?

A

Cholesterol is left over.

42
Q

Why is LDL bad?

A

The cholesterol from the LDL remnants is packaged in LDL, and so is able to stay in the blood stream for longer, be oxidised, and form plaques in the blood vessels.

43
Q

What do HDL’s do?

A

They reverse cholesterol transport.

44
Q

Structure of HDL’s?

A

Empty sac, relatively.

45
Q

How do HDL’s function?

A

They collect cholesterol from blood and cells and take cholesterol back to liver.

46
Q

Why are HDL’s good?

A

They remove high cholesterol from blood stream.

47
Q

What is approx TAG content of chylomicrons?

A

88%

48
Q

What is TAG content of VLDL’s?

A

56%

49
Q

What is the cholesterol content of LDL’s?

A

58%

50
Q

What are the 3 types of lipids?

A

TAG’s, Sterols, Phospholipids.

51
Q

How many Carbon Molecule is Malonoyl CoA?

A

3.

52
Q

What is the source of Glycerol in Adipose Tissue?

A

Glycerol is sourced from Glycolysis. Adipose lacks Glycerol Kinase.

53
Q

What is the source of Glycerol in Liver?

A

Glycerol from blood is converted into G-3-P by Glycerol Kinase.

54
Q

What happens to G-3-P?

A

It combines with 2 Fatty acids to form Diacylglycerol.

55
Q

How is a phospholipid formed from Diacylglycerol?

A

The Diacylglycerol is converted phosphatidate, a precursor to phospholipids.

56
Q

How is a TAG formed from Diacylglycerol?

A

The phosphate group is replaced with another Fatty Acid.

57
Q

What happens to the FA’s from TAG breakdown?

A

BETA OXIDATION.

  • An enzyme Thiolase cleaves a 16 Carbon FA, 2 Carbon atoms at a time releasing Acetyl CoA’s.
  • Each cleave releases 1 NADH and 1 FADH2 (7 cleaves)
  • Acetyl CoA is then metabolised.
58
Q

Energy Yield from Fatty Acids?

A

131 ATP total.

-35 from beta oxidation, 96 from the 8 Acetyl CoA’s

59
Q

What happens to Glycerol from TAG’s?

A

Glycerol –> G-3-P (glycerol kinase)
G-3-P –> Dihydroxyacetone (G-3-P Dehydrogenase)
DHAP enters gluconeogenesis or glycolysis.

60
Q

Where does Sterol synthesis occur?

A

Liver.

61
Q

What does sterol synthesis use?

A

Acetyl CoA.

62
Q

Are Lipoproteins soluble?

A

Yes.

Metabolism (11 decks)

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