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MCD: metabolism > Lipids > Flashcards

Flashcards in Lipids Deck (35)
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1

3 sources of fats

Diet
De novo biosynthesis in the liver - (starting from new in the liver)
Adipocyte stores - they can be hydrolysed to give free fatty acids and glycerol

2

Describe the process of lipid digestion

- there is a mix of free fatty acids, mono and diacylglycerols that are solubilised

- These then get taken up by the enterocytes within the intestine

- The lipid digestion by lipases form monoacylglycerols (MAG), diacylglycerols (DAG) and free fatty acids (FAs) which join Bile Salts, Cholesterol, Lysophosphatidic Acid and fat soluble vitamins to form mixed micelles.

- the mixed micelles are absorbed by enterocytes

- Triacylglycerols (TAGs) are resynthesised

- TAGs are packaged into chylomicrons which then enter the lymphatic system and join the circulatory system

3

Describe beta oxidation

- Fatty acid -> acyl coA using 2 ATPs in outer mitochondrial membrane
enzyme = acyl CoA synthethase


- the Acyl CoA enters the mitochondria from the outer mitochondrial membrane by carnitine shuttle

- Fatty acyl coA oxidised and FAD is reduced to FADH2

- the molecule produced is then hydrolysed

- the product is then oxidised so NAD+ --> NADH

- remove a molecule of acetyl coA by bringing in a molecule of CoA using beta- ketothiolase

- The remaining part of fatty acyl CoA which has been shortened by two carbons then repeats the cycle


overall the original fatty acyl CoA has been shortened by 2 carbons

- during each cycle 1 NADH and 1FADH2 are formed

4

Overall equation for breakdown of palmitate

Palmitoyl coA + 7FAD + 7 NAD+ + 7H20 + 7CoA ——> 8 acetyl coA + 7 FADH2 + 7 NADH

5

When can acetyl coA from beta oxidation enter TCA?

When beta oxidation and carbohydrate metabolism are balanced as oxaloacetate is needed

6

Which 2 enzymes are involved in biosynthesis of lipids?

Acetyl coA carboxylase
Fatty acid synthase

7

What happens if acetyl coA can’t enter TCA?

Produces:
Acetoacetate
D 3 hydroxybutyrate
Acetone

8

Describe lipogenesis

Acetyl coA + HCO3 = malonyl coA using acetyl coA carboxylase
Transfer malonyl to ACP = malonyl ACP using malonyl-coA-ACP transferase
Transfer acetyl from acetyl coA to ACP = acetyl ACP using acetyl-coA-ACP transferase
Condensation of acetyl ACP and malonyl ACP = acetoacyl ACP
Reduction using ketoreductase
Dehydration using dehydratase
Reduction using Ebola reductase

9

Differences between fat metabolism and synthesis

Synthesis = ACP and uses NADP as reducing agent, happens in ER and mitochondria
Metabolism = coA and uses NAD+ and FAD as reducing agents , happens in mitochondria

10

Lipogenesis equation

Acetyl coA + 7 malonyl coA + 14 NADP + 14H+ = palmitate + CO2 +6H2O + 8 coA + 14 NADP+

11

Diseases to do with lipid metabolism

Medium chain acyl coA dehydrogenase deficiency (MCADD)
- autosomal recessive
- part of heel prick test
- no fasting
- have a high carb diet
Primary carnitine deficiency
- autosomal recessive
- carnitine supplements given

12

what are saturated fatty acids like?

- they are completely saturated with hydrogen (there are no double bonds) they are straight

- solids

13

what are unsaturated fatty acids like?

- they have double bonds which inhibit rotation, therefore, there are kinks in the chain
- these are liquids

14

what are adipocytes?

in mammals specialised cells called adipocytes take on the role of fatty acid storage

15

how does bile emulsify fats?

- bile salts are generated by the liver and stored in the gall bladder
- during digestion they are secreted into the intestine
- They emulsify fats and aid their absorption
- biles convert fats into a soluble form so that the lipases can start breaking them down

16

what does a lack of bile salts cause?

- Lack of bile salts causes fats to pass through the digestive tract undigested and unabsorbed resulting in steatorrhea (fatty stool)

17

what is the structure of bile and how does that relate to how bile works?

- bile salts have a hydrophobic face and hydrophilic face which allows the bile salts to interact with solute and triacylglyerols

- Bile salts present the hydrophobic face to the triacylglycerols and the hydrophilic face to the solvent.

18

what is a mixed micelle?

A Mixed Micelle forms which is a mixture of triacyl-, diacyl-, monoacylglycerols and free fatty acids.

19

why is having anhydrous food supplies needed?

- good way of keeping compact food stores for subsequent mobilisation when needed

- if stored as glycogen people would be much heavier as glycogen needs water to be soluble

- every gram of glycogen needs 2 grams of water

20

what is orlistat?

reduces fat absorption by 30% which is almost completely excreted by the faecal route - treats obesity.

21

compare caloric yield of fatty acids and carbohydrates?

- The caloric yield of fatty acids is about double that of carbohydrates

- More than half the body's energy needs (including the liver but NOT the brain) comes from the oxidation of fatty acids.

22

how can acetyl CoA enter the TCA cycle?

- can only enter is beta oxidation and carbohydrate metabolism are balanced

- this is because oxaloacetate is needed for entry of acetyl CoA into the TCA cycle

23

what happens is fat breakdown predominates carbohydrate metabolism?

If fat breakdown predominates (e.g. when fasting/starving), acetyl CoA forms:
• Acetoacetate
• D-3-hydroxybutyrate
• Acetone

24

how many of what kind of bond generate the Acyl CoA from the fatty acid?

2 phosphoanhydride bonds

this is the same as ATP

these are needed to start off the reaction

25

how does the Carnitine Shuttle
work?

- the species is firstly coupled to a molecule of carnitine (catalyst = Carnitine Acyltransferase I) to form Acyl Carnitine

- Acyl Carnitine is then transported across the membrane by a translocase

- Carnitine Acyltransferase II then removes the acyl group from acyl carnitine and passes it on to CoA to form Acyl CoA and reform carnitine.

- The carnitine is moved back across the membrane to the cytoplasmic side by a translocase to pick up more Acyl CoA

26

net ATP production of palmitate B oxidation?

You get far more ATP from fatty acids compared to from glucose metabolism

27

what enzymes does fatty aid biosynthesis involve?

- Acetyl CoA Carboxylase
- Fatty Acid Synthase (FAS)

28

how are fatty acids formed?

decarboxylative condensation reactions involving the molecules Acetyl-CoA and Malonyl-CoA.

29

what does the fatty acid undergo after elongation?

- the fatty acid undergoes reduction and dehydration
Ketoreducatase (KR)
Dehydratase (DH)
Enol Reductase (ER

30

what is the lipogenesis process?

- first acetyl CoA is converted to malonyl CoA using the enzyme Acetyl CoA carboxylase

- malonyl is transferred from malonyl CoA to the Acyl carrier protein to make malonyl - ACP.

- Transfer of acetyl from a CoA species to acyl carrier protien (ACP) to form Acetyl-ACP (catalysed by Acetyl-CoA-ACP Transferase)