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Biochemistry > lipid and fatty acid metabolism > Flashcards

lipid and fatty acid metabolism Flashcards

1
Q

describe digestion and absorption

A
  1. Dietary fats consumed through diet
  2. Emulsified by bile salts into fat droplets
  3. Triacylglycerols degraded by lipases producing FREE fatty acids
  4. Free Fatty Acids are absorbed in epithelial cells  triacylglycerols then synthesised
  5. Triacyclglycerols are insoluble in blood and lymph therefore transported via chylomicrons (LIPOPROTEIN)
  6. Transported to MUSCLE for ENERGY (or ADIPOSE TISSUE for STORAGE)
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2
Q

what happens in troglycerol breakdown

A

triclyglycerol is converted to glycerol

tricylglycerol = diacylglycerol (=lipase is removed)
diacylglycerol= monoacylglycerol (=lipase removed)
monoaacylglycerol = glycerol (=lipase removed)

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3
Q

what happens in glycerol breakdown in the liver

A

glycerol is converted to dihydroxyacetone phosphate

glycerol = glycerol-3-phosphate = dihydroxyacetone phosphate

1st = glycerol kinase (ATP = ADP)
2nd = glycerol-3-phosphate dehydrogenase (NADH+ = NADH+ H+)

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4
Q

What is dihydroxyacetone phosphate

A

an intermediate in glycolysis used for energy production

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5
Q

what happens if blood glucose is low in triacylglycerol breakdown

A

energy is still needed and therefore breakdown of triacylglycerol

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6
Q

what happens if blood glucose is high in triacylglycerol breakdown

A

insulin responds to high glucose levels and inactivates lipase and stops lipolysis

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7
Q

what is fatty acid breakdown

A

called beta oxidation and occurs in the mitochondria (somoetimes the peroxisomes) and is a reoccurring cycle that has 4 steps and it produces FADH2 AND NADH

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8
Q

What happens in the activation step

A

FA is activated by a coenzyme A resulting in an acyl-CoA. This allows FA and acyl CoA to diffuse into the mitochondria.

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9
Q

what is the first step

A

Oxidation
Removes a pair of hydrogen atoms from the FA
Reduction of FAD to FADH2 (2ATP)
Outcome = forms a C=C bond on the fatty acyl chain

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10
Q

what is the second step

A

hydration
Hydration of the double bond
Beta-carbon is hydroxylated

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11
Q

what is the third step

A

Oxidation reaction
Hydroxyl group of the beta-carbon is now hydrogenated
NAD+ is reduced to NADH –

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12
Q

what is the fourth step

A

Final reaction
Catalysed by thiolase
Cleavage and release of Acetyl CoA
The thiol is inserted between C-2 (alpha) and C-3 (beta)
An acetyl CoA molecule, and an acyl CoA molecule that is two carbons shorter

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13
Q

what are peroxisomes

A

small organelles with single membrane and found in cytoplasm.
Longer chain FAs are initially broken down into shorter units in peroxisomes
Partly degraded FAs move to mitochondria where process is complete

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14
Q

what happens in the first step of fatty acid breakdown in peroxisomes

A

Step 1 – enzyme converts electrons to H20 producing Hydrogen peroxide
Catalase converts hydrogen peroxide back to water and oxygen species
Associated with variety of toxic compounds such as phenols and alcohol

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15
Q

what are the main points for tricylglycerol breakdown

A

broken down by lipases (releasing FAs to be further degraded)
Glycerol further degradation
Fatty acid breakdown (beta-oxidation):
Occurs in mitochondria or peroxisomes
Activation step Fatty acids converted to Acyl CoA derivatives
Carnitine used for longer and/or unsaturated FA
4 key steps
Outcome  to yield ENERGY

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16
Q
A

Glycolysis and Beta-oxidation occur at the same rate
Steady supply of pyruvate  oxaloacetate
An adequate supply of oxaloacetate is needed for acetyl CoA (from beta-oxidation) to efficiently enter TCA/Kerb cycle
Low supply of carbohydrates  energy comes from FA degradation
Ketone bodies are produced from Acetyl CoA

17
Q

what are three examples of ketone bodies

A

Acetone
Acetoacetic acid
Beta-hydroxybutyric acid

18
Q

what are ketones functions

A

Ketone bodies can be used by the heart and brain for energy

19
Q

how are fatty acids synthesised from acetyl-CoA and malonyl CoA

A

through fatty acid synthase FAS enzymes

20
Q

where does fatty acid synthase occurs

A

Occurs in the cytosol, when carbohydrate and energy supplies are plentiful

21
Q

what is fatty acid synthase not

A

a simple reverse of beta oxidation

22
Q

what cannot be synthesised and has to be obtained from the diet

A

Essential PUFA (alpha-linolenic and linoleic acid)

23
Q

what is the first stage of fatty acid biosynthesis

A

Elongation/Condensation of acetyl-ACP to malonyl-CoA to form acetoacetyl-ACP, a ketoacid, releasing CO2

24
Q

what is the second stage of fatty acid biosynthesis

A

Reduction of acetoacetyl-ACP to form β-hydroxy acid derivative, using NADPH

25
Q

what is the third stage of fatty acid biosynthesis

A

Dehydration to make a trans-double bond

26
Q

what is the fourth stage of fatty acid biosynthesis

A

Reduction by NADPH to form the saturated fatty acid butyryl-ACP (4 C)

27
Q

what number can humans synthesise

A

Humans can only synthesise up to 16-carbons long fatty acids
C18 fatty acids (i.e., ESSENTIAL) only obtained in DIET!

28
Q

what 2 acids are obtained from dietary sources and are deemed essential

A

Linoleic acid (LA) (C18 n-6)

Alpha-linolenic acid (ALA) (C18 n-3)

29
Q

what acids obtained from the diet are not termed essential

A

Arachidonic acid (AA) (C20 n-6)
Eicosapentaenoic acid (EPA) (C20 n-3)
Docosahexaenoic acid (DHA) (C22 n-3)

30
Q

what are the key differences between beta oxidation and fatty acid biosynthesis

A

beta= occurs in mitochondria, has 4 non associated enzymes, 2Cs removed as acetyl CoA, starts at the carboxyl end, occurs in muscle and liver, nutritional status is starvation and has a low insulin/glucagon ratio.

bio= occurs in cytosol, a multi enzyme complex, 2Cs added using malonyl CoA, starts at methyl end, occurs in liver, nutritional status is well-fed and has a high insulin/glucagon ratio

31
Q

what occurs in Triacylglycerol synthesis/storage

A

Adipose tissue  STORAGE
Muscle cells  ENERGY

32
Q

liver

A

Major role in regulation of blood glucose concentrations
role in lipid metabolism as Excess fuel
liver converts FA to ketones

33
Q

brain

A

Normal conditions – brain uses glucose as source of energy

Starvation depletes glycogen stores
ketone bodies (acetoacetate and beta-hydroxybutyrate) are used as alternative energy source

34
Q

muscle tissue

A

Energy demands of resting muscle is usually via beta-oxidation

Working muscle – energy obtained from degradation of own supply of glycogen

Heart muscle prefers ketone bodies over glucose

35
Q

adipose tissue

A

Adipose tissue is a major storage depot of fatty acids

Triglycerides released from liver are carried by VLDL and absorbed by adipose tissue

Biochemistry (20 decks)

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