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Metabolism and Homeostasis > Lipid synthesis > Flashcards

Lipid synthesis Flashcards

1
Q

What is the first step of fatty acid synthesis?

A

Transport of acetyl CoA to cytosol by the citrate shuttle

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2
Q

What is the function of the citrate shuttle?

A

Transports acetyl CoA and NADPH into the cytosol from the mitochondria

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3
Q

When is citrate high?

a) fasted state
b) fed state

A

b

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4
Q

Why can citrate move into the cytosol?

A

It has a carrier

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5
Q

What happens to citrate when it enters the cytosol?

A

Splits into acetyl CoA and oxaloacetate

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6
Q

What is the fate of acetyl CoA from citrate?

A

Substrate for fatty acid synthesis

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7
Q

What is the fate of oxaloacetate from citrate?

A

Converted to pyruvate and NADPH is made.

Pyruvate enters the mitochondria

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8
Q

What is the 2nd step fo fatty acid synthesis?

A

Activation of acetyl CoA - carboxylation to from malonyl CoA.
Acetyl CoA + CO2 –> Malonyl CoA
(ATP –> ADP)
Acetyl CoA Carboxylase

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9
Q

What enzyme catalyses the activation of acetyl CoA?

A

Acetyl CoA carboxylase

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10
Q

What enzyme catalyses the sequential addition of 2 carbon units?

A

Fatty acid synthase

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11
Q

What is the structure of fatty acid synthase?

A

It is a dimer that contains 2 acyl carrier proteins

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12
Q

How does acetyl CoA interact with fatty acid synthase?

A

Each acyl carrier protein on the fatty acid synthase accepts malonyl CoA and acetyl CoA.
The CoAs are released

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13
Q

What happens once the CoAs are released from he fatty acid synthase acyl carrier protein complex?

A

Acetyl ACP is cleaved off and transferred to malonyl ACP in a condensation reaction. CO2 is released.
This forms acetoacetyl ACP

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14
Q

What 3 steps elongate acetoacetyl ACP?

A

Reduction, dehydration, reduction

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15
Q

How does the chain get elongated further?

A

The elongated chain takes the place of acetyl CoA in the cycle

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16
Q

What activates acetyl CoA carboxylase?

A

Citrate and ATP allosterically, insulin by de-phosphorylation

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17
Q

When does fatty acid synthesis stop?

A

When 16 carbon chain is formed.

Cleaves off ACP and forms palmitate

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18
Q

What inhibits acetyl CoA carboxylase?

A

Palmitate by product feedback.

Glucagon and adrenaline by phosphorylation

19
Q

Where does phosphorylation occur beyond C16?

A

Endoplasmic reticulum

20
Q

How are double bonds introduced?

A

Oxidases

21
Q

What is cholesterol a precursor of?

A

Bile and all steroid hormones

22
Q

How is cholesterol formed and where?

A

In cytosol.

From HMG using HMG-CoA reductase

23
Q

How are fatty acids transported in the blood stream?

A

Bound to albumin

24
Q

How are triglycerides and cholesterol transported in the blood stream?

A

Bound to lipoproteins

25
Q

What are the 5 classes of lipoproteins?

A 
Chylomicrons
VLDL
IDL
LDL
HDL
26
Q

Describe the general structure of lipoproteins?

A

Phospholipid circle with hydrophobic core and store triglycerides and esterified cholesterol in the centre

27
Q

What is the function of chylomicrons?

A

Transport triglycerides

28
Q

What do chylomicrons contain?

A

Triglycerides, cholesterol and apo protein B48

29
Q

What occurs to chylomicrons hone they enter the blood?

A

HDL donates apo CII and E

This activates lipoprotein lipase not he endothelial surface of vascular system

30
Q

What happens to chylomicrons when triglyceride levels are low?

A

Return CII and E back to HDL and then go to the liver to be degraded

31
Q

What is the function of VLDL and IDL?

A

Transport lipids from the liver to the rest of the body

32
Q

Where is VLDL made?

A

Hepatocytes

33
Q

What do VLDL contain?

A

TAG, cholesterol and apo100

34
Q

What occurs to VLDL when it enters blood?

A

HDL donates apo CII and E

Lipoprotein lipase activated, TAG hydrolysed into glycerol and fatty acids

35
Q

How does VLDL become IDL?

A

TAG is hydrolysed, as they off load TAG become IDL.

CII returned to cholesterol

36
Q

What happens to IDL remaining in circulation?

A

Receives cholesterol from HDL. Donates phospholipid and ATG in return to become LDL

37
Q

What is the function of LDL?

A

Transport cholesterol to tissues

38
Q

What happens to LDL in circulation?

A

Enters cells by endocytosis and fuses with lysosomes to release cholesterol

39
Q

What does HDL contain?

A

Phospholipids and apo proteins

40
Q

What is the function of HDL?

A

Accepts free cholesterol from peripheral cells and esterifies it and passes to VLDL, IDL, LDL

41
Q

What causes genetic dyslipidaemias?

A

Elevated TAG or cholesterol due to abnormal lipid metabolism

42
Q

What causes abnormal lipid metabolism?

A

Abnormal api-protein, receptors or lipoprotein lipase

43
Q

What do genetic dyslipidaemias cause?

A

Fatty deposits in artery

Metabolism and Homeostasis (13 decks)

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