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Fundamentals of the living cell > Lipid synthesis and degradation > Flashcards

Lipid synthesis and degradation Flashcards

1
Q

How are fats obtained

A

Mainly from de novo from carbohydrates but also from diet

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2
Q

What do lipids do

A

They play an essential role in

  1. Membranes
  2. Uptake of lipid soluble vitamins
  3. Precursor of steroid hormones
  4. Energy store
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3
Q

What are different types of fats

A
  1. Fatty acids
  2. Triglycerides or neutral fats
  3. Cholesterol
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4
Q

Which tissues prefer fats as their energy source

A

Tissues such as cardiac muscle

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5
Q

What stores and what synthesises lipids

A

Stored in adipose tissue

Synthesised in the liver

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6
Q

What is the major product of fatty acid synthesis

A

Palmitic acid (16 carbon molecule)

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7
Q

How is compartmentalisation taking place

A

Synthesis occurs in the cytosol but breakdown occurs in the mitochondria, absolute separation

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8
Q

What does lipid synthesis require

A

Acetyl-CoA, NADPH and ATP

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9
Q

What is the first step of lipid synthesis

A

Acetyl-CoA (2C) + ATP + HCO3- is made into malonyl-CoA (3C) + ADP + Pi

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10
Q

What does the first step of lipid synthesis require

A

Vitamin biotin and acetyl-CoA carboxylase

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11
Q

What is the first step of lipid synthesis regulated by

A

Activated by citrate and inhibited by palmitic acid

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12
Q

What is the second step of lipid synthesis

A
  1. Reaction with ACP (acyl carrier protein) to produce malonyl-ACP (C3)
  2. Condensation reaction with Acetyl-ACP (C2) plus decarboxylation to form acetoactyl-ACP (C4)
  3. Reduction, dehydration and reduction to form butyryl-ACP (C4)
  4. Combines with malonyl-ACP (3C) and undergoes decarboxylation to create C6 molecule
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13
Q

Fatty acid synthase

A

Exists as a dimer so that the synthesis is as efficient as it can be
Products enters the complex and binds to the enzyme, and its passed along the active sites, the last one adds the 2 carbons, and it then moves to the other side of the dimer

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14
Q

What is cholesterol

A

A rigid hydrophobic molecule virtually insoluble in water

Its a precursor of sterols, steroids and bile salts

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15
Q

How is it transported

A

Transported in circulation as cholesteryl esters

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16
Q

What is it used for and why

A

Its important in membrane components

It cannot be oxidised to O2 and H20 therefore it cannot provide any energy

17
Q

Where is cholesterol synthesised

A

In the ER

18
Q

What is the major regulatory step in cholesterol synthesis and why

A

Conversion of 3-hydroxyl-3-methlglutaryl CoA (HMGCoA) to mevalonate
Cholesterol inhibits HMGCoA reductase

19
Q

What are the steps in the degradation of fatty acid and where do they occur

A
  1. Mobilisation of fat stores, mainly triglycerides occurs in adipocytes
  2. Activation of triglyceride and transport to mitochondria occurs in liver cytosol
  3. Degradation occurs in liver mitochondrion
20
Q

What happens in the mobilisation of fat stores

A
  1. cAMP will activate protein kinase
  2. Protein kinase activates and phosphorylates triacyglycerol lipase
  3. This makes triacyglycerol into diacylglycerol
  4. This is made into free fatty acids and glycerol by other lipases
  5. The free fatty acids will leave the cell
  6. Glucagon and adrenaline are involved in this mobilisation
21
Q

What is the fate of glycerol

A

Its absorbed by the liver as its the only part of the triglyceride that can be used to make glucose

22
Q

How is glycerol processed

A
  1. First its phosphorylated to glycerol-3-phosphate
  2. This is then oxidised to dihydroxyacetone phosphate
  3. This is isomerised to glyceraldehyde-3-phosphate
  4. This is either used in glycolysis or gluconeogenesis which is used to maintain blood glucose
23
Q

How are the free fatty acids activated and transported to the mitochondria

A
  1. Fatty acids are transported to the liver by acyl-CoA synthase in the cytoplasm
  2. The acyl-CoA reacts and oxidises carnitine, producing acyl carnitine
  3. Acyl carnitine can pass through translocase into the matrix of mitochondria
  4. CoA is oxidised forming Acyl-CoA and carnitine again
24
Q

How is this transport regulated and why

A

Malonyl-CoA inhibits transport since the cell the cell is storing energy when there is excess glucose present

25
Q

What is carnitine deficiency

A

Causes muscle weakness or even death

26
Q

What happens in lipid degradation

A

Acyl-CoA is degraded by sequential removal of 2 carbon units

FADH2, NADH and acetyl-CoA is made

27
Q

What is ketogenesis

A

Acetyl-CoA is converted into acetoactyl-CoA
This is converted to HMG-CoA
This is made into acetoacetate
This is reduced to 3-beta-hydroxybuterate or non-enzymically to acetone

28
Q

What happens to ketone bodies

A

Its a major source for cardiac muscle and the renal cortex

During starvation up to 75% of the brains energy is derived from acetoacetate

Fundamentals of the living cell (15 decks)

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