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Biochem Take 2. > Fatty Acid Synthesis. > Flashcards

Fatty Acid Synthesis. Flashcards

1
Q

What is prosthetic group?

A

A cofactor or coenzyme that is often covalently bonded to the enzyme.

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2
Q

What is enzyme induction?

A

The up-regulation or synthesis of more of a particular enzyme.

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3
Q

De-novo fatty acid synthesis in humans take place?

A

In the liver and in the lactating mammary gland.

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4
Q

What will the liver use to make fatty acids?

A

Glucose.

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5
Q

Why will the liver make fatty acids?

A

To reduce blood glucose levels.

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6
Q

What condition will the synthesis of fatty acids prevent?

A

Hyperglycaemia.

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7
Q

Will the liver ever store fat?

A

No.

Fat is always stored in the fat cells.

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8
Q

What organelle will fatty acid synthesis take place in in liver cells?

A

In the cytoplasm and the mitochondria.

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9
Q

What are the 3 main enzymes or enzyme complexes that are involved in fatty acid synthesis?

A

Citrate lyase.

Carboxylase.

The fatty acid synthase complex.

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10
Q

What happens in step 1 of fatty acid synthesis?

A

ACoA is synthesised in the cytoplasm by converting citrate to ACoA and oxaloacetate.

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11
Q

Where is ACoA normally made?

A

In the mitochondria.

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12
Q

Why does ACoA need to be made in the cytoplasm for fatty acid synthesis?

A

Because ACoA cannot leave the mitochondria.

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13
Q

How is mitochondrial ACoA formed?

A

Citrate will leave the mitochondria and enter the cytoplasm where citrate lyase can break it down to ACoA and oxaloacetate.

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14
Q

When will citrate leave the mitochondria to enter the cytoplasm?

A

When levels of mitochondrial citrate are high.

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15
Q

How is mitochondrial citrate formed?

A

By combining ACoA and oxaloacetate with citrate lyase.

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16
Q

What happens in step 2 of fatty acid synthesis when ACoA is found in the cytoplasm

A

It can be used to form fatty acids.

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17
Q

How is ACoA used to form fatty acids in step 2 of fatty acid synthesis?

A

ACoA is carboxylated to malonyl-CoA by ACoA carboxylase.

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18
Q

What cofactor will ACoA carboxylase use?

A

Biotin.

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19
Q

What is the rate limiting step in fatty acid synthesis?

A

When ACoA is carboxylated to malonyl-CoA.

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20
Q

What happens to malonyl CoA once it has been synthesised in step 2 of fatty acid synthesis?

A

It can enter fatty acid synthase complex and be converted to palmitate.

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21
Q

What is the substrate for the fatty acid synthase complex?

A

Malonyl CoA.

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22
Q

What energy is used by the fatty acid synthase complex to convert malonyl CoA to palmitate?

A

2 NADPH molecules.

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23
Q

How many carbons will palmitate have?

A

16.

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24
Q

What is the only step of fatty acid synthesis that will take place in the mitochondria?

A

The formation of citrate.

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25
Q

What energy does ACoA carboxylase require to convert ACoA to malonyl CoA?

A

1 ATP.

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26
Q

How many carbons are added to ACoA when it is converted to malonyl CoA?

A

It increases by 1 carbon.

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27
Q

How many carbons does ACoA have?

A

2.

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28
Q

How many carbons does malonyl CoA have?

A

3.

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29
Q

What substrates are used by ACoA carboxylase?

A

ACoA + CO2.

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30
Q

The fatty acid synthase complex is composed of how many subunits?

A

2.

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31
Q

How many fatty acids are synthesised by the fatty acid synthase complex at the same time?

A

2.

32
Q

How many enzymatic activities does each subunit of the fatty acid synthase complex have?

A

7.

33
Q

What 2 components does each subunit of the fatty acid synthase complex have?

A

an acyl carrier protein domain (ACP).

A temporary holding domain with a cysteine residue.

34
Q

Will the fatty acid synthase complex synthesise fatty acids with any double bonds in them?

A

No.

35
Q

What kind of fatty acid synthesis is carried out at the fatty acid synthase complex?

A

FAS-1.

36
Q

What is the 1st thing that happens at the fatty acid synthase complex?

A

The CO2 that was added by acyl CoA carboxylase is released to give an ACoA molecule.

37
Q

What provides the energy needed for fatty acid synthesis in the fatty acid synthase complex?

A

The cleavage of the CO2 from malonyl CoA in step 1.

38
Q

De novo fatty acid synthesis is based around what molecule?

A

An ACoA molecule.

39
Q

What happens in step 2 of fatty acid synthesis in the fatty acid synthase complex?

A

The acetyl group of ACoA binds the ACP and is transferred to the SH of the cysteine residue in the holding domain.

40
Q

Why is the ACoA moved to the holding domain in step 2?

A

To free up the ACP so it can grab another malonyl CoA.

41
Q

What happens in step 3 of fatty acid synthesis in the fatty acid synthase complex?

A

ACoA’s are added to the ACoA in the holding domain until palmitate is formed.

42
Q

What molecule provides the energy needed for FA synthase to function?

A

Malonyl CoA.

43
Q

What molecule is formed when the 2 ACoA molecules are combined in step 3 of fatty acid synthesis in the fatty acid synthase complex?

A

A 3-keto acyl group.

44
Q

How many carbons does the 3-keto acyl group formed in the fatty acid synthase complex have?

A

4.

45
Q

What happens once palmitate is formed in the FA synthase complex?

A

It is activated in the ER to form palmitoyl CoA.

46
Q

What enzyme activates palmitate in the ER?

A

Acyl CoA synthetase.

47
Q

What can happen to palmitoyl CoA?

A

It can be elongated further, desaturated or esterified in the ER.

48
Q

The FA synthase complex in the liver will always produce what kind of fatty acids?

A

Palmitate.

49
Q

The FA synthase complex in the lactating mammary gland will always produce what kind of fatty acids?

A

Palmitate and medium chain fatty acids.

50
Q

What are the benefits of using the FA synthase complex to synthesise fatty acids?

A

It allows for fast processing and prevents the release of short chain fatty acids.

51
Q

What is the substrate for the FA synthase complex?

A

Malonyl CoA.

52
Q

How does insulin affect the fatty acid synthase complex?

A

It induces enzyme complex formation and substrate availability.

53
Q

What co-enzymes are used by the fatty acid synthase complex?

A

2 NADPH molecules per elongation of the chain.

54
Q

Do bacteria use FAS-1 fatty acid synthesis?

A

No, they use FAS-2 synthesis and can add double bonds when the fatty acyl group is 10 carbons long.

55
Q

What molecule will activate ACoA carboxylase?

A

Citrate.

56
Q

What molecule will inhibit ACoA carboxylase?

A

Palmitoyl CoA.

57
Q

What is the only cytoplasmic enzyme that can break down citrate to form ACoA and OAA.

A

Citrate lyase.

58
Q

Why does citrate activate ACoA carboxylase?

A

Cytoplasmic citrate must be broken down quickly or it will inhibit the enzyme PFK-1

59
Q

Why is it important that fatty acid synthesis does not inhibit glycolysis?

A

Because blood glucose levels are high.

60
Q

What will lead to an up-regulation of ACoA carboxylase?

A

The presence of citrate in the cytoplasm.

61
Q

What is palmitoyl CoA also known as?

A

Palmitate.

62
Q

Why will palmitoyl CoA inhibit ACoA carboxylase?

A

To stop production of palmitate as it has detergent characteristics.

63
Q

How are the detergent characteristics of palmitate usually bypassed?

A

It is immediately converted to palmitoyl CoA.

64
Q

Why might palmitate build up in the cytoplasm?

A

Because the free CoA pool is limited and there may not be any available to form palmitoyl CoA.

65
Q

What is the mode of inhibition by which an accumulation of palmitate in the cytoplasm will inhibit ACoA carboxylase known as?

A

Feedback inhibition.

66
Q

When is ACoA carboxylase active?

A

When it is de-phosphorylated.

67
Q

When is ACoA carboxylase inactive?

A

When it is phosphorylated.

68
Q

What will lead to the de-phosphorylation of ACoA carboxylase?

A

Insulin will lead to the de-phosphorylation and activation of ACCase.

69
Q

What hormone leads to the induction of ACoA carboxylase?

A

Insulin.

70
Q

What will lead to the phosphorylation of ACoA carboxylase?

A

Glucagon and epinephrine via the CAMP system.

71
Q

How do glucagon and epinephrine phosphorylate ACoA carboxylase?

A

They will use the CAMP system and phosphorylate AMP kinase kinase.

AMP kinase kinase will phosphorylate and activate AMP kinase.

AMP kinase will then phosphorylate and inhibit ACoA carboxylase.

72
Q

What will allosterically activate AMP kinase?

A

AMP.

73
Q

What will covalently activate AMP kinase?

A

Phosphorylation.

74
Q

How will AMP activate AMP kinase?

A

High levels of AMP leads to the phosphorylation of ACCase by activating an AMP-dependent kinase.

The AMP-dependent kinase phosphorylate ACCase and inhibit it.

75
Q

The presence of AMP will indicate that the body is in what state?

A

The fasting state.

76
Q

What mode of FA synthesis regulation overrules all other forms of regulation?

A

The phosphorylation and inhibition of ACCase by AMP kinase.

Biochem Take 2. (24 decks)

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