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BB10004 > Fatty acid biosynthesis > Flashcards

Fatty acid biosynthesis Flashcards

1
Q

Give an example of specialised signalling molecules

A

phosphatidyl inositol

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2
Q

What is the biosynthesis of fatty acids

A
  1. Synthesis requires energy and reducing equivalents- opposite of breakdown (beta-oxidation)
  2. Breakdown (oxidation) of fatty acids- releases energy and reducing equivalents
  3. The body is a dynamic system in which fatty acids are constantly being broken down and synthesised
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3
Q

How much fatty acids are generally turned over per day

A
  1. 200g of fatty acids are turned over per 24 hrs

2. This turnover accounts for 8% of the body’s basal 02 consumption

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4
Q

What is the major biosynthetic product of fatty acid synthesis

A
  1. Palmitic acid: C16:0

2. CH3(CH2)14COOH

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5
Q

What do most naturally occurring fatty acids have

A
  1. Most naturally occurring fatty acids have an even number of carbon atoms
  2. Synthesised in way that adds 2 carbon units at a time to the growing fatty acid chain
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6
Q

Where does breakdown occur and where does synthesis occur

A
  1. Breakdown- mitochondria

2. Synthesis- cytoplasmic

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7
Q

What else does breakdown need

A
  1. NAD+/NADH

2. No CO2

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8
Q

What does synthesis need

A
  1. NADP+/NADPH

2. CO2 required as HCO3-

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9
Q

Describe the first two steps in the experiment which showed that synthesis occurs in the cytosol

A
  1. Homogenise tissue- make into a mixture that looks all the same- by blending tissue
  2. release internal contents
  3. Centrifuge at 100000 x g
  4. Centrifuge separates contents-Lumpy and heavy things sink quickly
  5. Forms a soluble fraction and a pellet
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10
Q

Describe what is found in the soluble fraction and pellet

A
  1. Soluble fraction-
    a) No membrane fractions
    b) Only soluble proteins
  2. Pellet-
    a) Nuclear material
    b) Mitochondrial fragments
    c) All membranous debris
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11
Q

What happens once the soluble fraction and pellet have formed

A
  1. Can then assay pellet and soluble fraction to see where activity is- which will synthesis fatty acid
  2. Soluble fraction- synthesis fatty acids
  3. Treat with a salt (proteins have a hydration cell with lots of water molecules in the outside and hold each other in solution)
  4. Take away water with salt and so doesn’t have a hydration cell around it and so comes out of solution
  5. Makes solution more concentrated effectively
  6. See which protein precipitate first and eventually have all the proteins without the salt or water
  7. Fractionate the original and test each fraction to see if it has the reaction were looking for
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12
Q

What was the result of the experiment

A
  1. none of fractions give fatty acid biosynthesis on its own
  2. Only need to combine 2 fractions (unusual because lots of enzymes involved in breakdown)
  3. One of these fractions contain biotin
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13
Q

What are the two steps of fatty acid biosynthesis

A
  1. The ATP-dependent carboxylation of acetyl-CoA by acetyl-CoA carboxylase forming malonyl-CoA
  2. Exergonic decarboxylation of malonyl group in the condensation reaction catalysed by fatty acid synthase
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14
Q

Describe the basics of the first step of fatty acid biosynthesis

A
  1. Activation step Acetyl-CoA is carboxylated to form malonyl-CoA
  2. This step does not occur without biotin
  3. Catalysed by acetyl CoA carboxylase
  4. This stage is irreversible
  5. Is a two-step process very similar to that of pyruvate carboxylase
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15
Q

Describe the mechanism of the first step of fatty acid biosynthesis

A
  1. First carbon part from bicarbonate ion attaches to biotin which is covalently linked to biotin to form biotin-CO2 complex
  2. This is transcarboxylated to move CO2 on to acetyl part of CoA
  3. Acetyl-CoA carboxylase is not a single protein- made up of 3 protein parts each carry out different thing
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16
Q

Give the equations for the first step of fatty acid biosynthesis

A
  1. Overall: Acetyl-CoA + bicarbonate + ATP –> malonyl-CoA + water + ADP + Pi
  2. First part catalysed by biotin carboxylase:
    Biotin + HCO3- + ATP –> Biotin-CO2- + ADP + Pi
  3. Second part catalysed by transcarboxylase:
    Biotin-CO2- + acetyl-CoA –> biotin + malonyl-CoA
17
Q

Describe the basics of the second step of fatty acid biosynthesis

A
  1. Chain elongation
  2. Long chain fatty acids are formed from acetyl-CoA and malonyl-CoA by the successive additions to a growing chain
  3. Catalysed by fatty acid synthase/synthetase
18
Q

Describe the mechanism of the second step of fatty acid biosynthesis

A
  1. Enzyme takes single acetyl-CoA and multiple malonyl-CoA (7) and 14 NADPH (2 for each malonate) and releases CO2 and CoA
  2. 1 acetyl CoA - primes the reaction and becomes the methyl terminus of the fatty acid chain
  3. 7 malonyl CoA - each provides a 2 carbon unit to extend the chain by 7x2 = 14 carbons
  4. Total length is 14 + 2 = 16
19
Q

What is the overall reaction for the second step in the biosynthesis of palmitate

A
  1. acetyl-CoA + 7 malonyl-CoA + 14 NADPH + 14 H+ –> palmitate + 7CO2 + 14NADP+ + 8CoA + 6H2O
20
Q

What is the overall equation for the biosynthesis of pamlitate

A
  1. 8 acetyl-CoA + 7ATP + 14NADPH + 14H+ –> palmitate + 8CoA + 6H2O + 7ADP + 7Pi + 14NADP+
21
Q

Describe fatty acid synthase

A
  1. Catalyses seven separate reactions each of which has to have an active site
  2. is found in the cytosolic fraction of cells
  3. requires malonyl-CoA & acetyl-CoA
  4. requires NADPH
  5. relatively insoluble proteins
  6. no free, unbound intermediates accumulate-
  7. 4 phosphopantetheine required
22
Q

What is the first reaction of fatty acid synthase reactions to form palmitate

A
  1. Acetyl CoA is first attached to the protein ACP (ACYL CARRIER PROTEIN)- by acetyl transacylase.
  2. The Acetyl is then transferred to the beta-ketoacyl ACP synthase protein/domain
23
Q

What is the second reaction of fatty acid synthase reactions to form palmitate

A
  1. Malonyl transacylase then transfers a malonyl group to ACP from malonyl CoA
24
Q

What is the third reaction of fatty acid synthase reactions to form palmitate

A
  1. Condensation and decarboxylation reaction catalysed by beta-ketoacyl-ACP synthase
  2. acetyl-synthase + malonyl-ACP form beta-ketoacyl-ACP and CO2 is released
  3. Energy comes from cleavage of CO2
25
Q

What is the fourth reaction of fatty acid synthase reactions
to form palmitate

A
  1. Reduction catalysed by beta-ketoacyl ACP reductase
  2. beta-ketoacyl-ACP reduced to beta-hydroxyacyl-ACP
  3. NADPH + H+ –> NADP+
26
Q

What is the fifth reaction of fatty acid synthase reactions to form palmitate

A
  1. DEHYDRATION catalysed by beta-hydroxyacyl-ACP dehydrase
  2. removes water –> double bond
  3. beta-hydroxyacyl-ACP forms trans enoyl-ACP
27
Q

What is the sixth reaction of fatty acid synthase reactions to form palmitate

A
  1. REDUCTION catalysed by Enoyl-ACP reductase
  2. This acyl group is then transferred to the β-ketoacyl synthase domain of the protein- this was where the original acetyl group was attached
  3. Freeing the ACP to bind another malonyl group
  4. trans enoyl-ACP forms acyl-ACP
28
Q

What is the seventh reaction of fatty acid synthase reactions to form palmitate

A
  1. palmitoyl-ACP –> palmitate + ACP-SH

2. Catalysed by palmitoyl thioesterase

29
Q

At what point are the steps repeated to build up the fatty acid chain

A
  1. After step 6
  2. With a C4 acyl group attached to the β-ketoacyl synthase domain and Malonyl attached to ACP the steps can begin again to produce a C6 acyl.
  3. This is repeated until there is a C16 acyl group attached to ACP- palmitoyl-ACP
30
Q

Where is palmitate mainly produced

A
  1. Major product in mammalian liver

2. Other tissues and species produce different products – in those a secondary thioesterase is likely active

BB10004 (14 decks)

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