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Metabolism > Lipid Metabolism > Flashcards

Lipid Metabolism Flashcards

0
Q

What are the two types of fatty acids and which can be essential?

A
  • Saturated and unsaturated

- Certain unsaturated FAs are essential dietary components eg arachidonic acid for eicosanoid synthesis

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1
Q

What are the three groups of lipid?

A
  • FA derivatives (TAGs, FAs, Phospholipids, Eicosanoids -local mediators)
  • Hydroxy-methyl-glutaric acid derviatives (Ketone bodies, cholesterol, cholesterol esters and bile acids/salts
  • Vitamins A, D, E and K
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2
Q

Are lipids soluble or insoluble in water?

A

-Insoluble as they are hydrophobic

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3
Q

What are lipids synthesised from?

A

-1 glycerol and three FAs by esterification

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4
Q

What is the main use of lipids

A

-Fuel store

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5
Q

Are lipids or carbs more reduced?

A

Lipids

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6
Q

Lipid synthesis is under what type of control; give examples

A
  • Hormonal control
  • Insulin increases synthesis
  • Glucagon, adrenaline and cortisol decrease synthesis
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7
Q

What is the first stage in lipid metabolism?

A
  • Hydrolysing dietary lipids extracellularly by pancreatic lipase in the small intestine (lipolysis)
  • Complex - involves bile salts and cofactor colipase
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8
Q

What are the products of lipolysis?

A
  • 1 glycerol

- 3 FAs

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9
Q

What happens to glycerol after lipolysis?

A

-Enters bloodstream
-Transported to liver for metabolism
-Metabolised into DHAP and enters glycolysis
OR
-Metabolised into glycerol phosphate and enters TAG synthesis

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10
Q

What is stage 2 in lipid metabolism and where does it occur?

A
  • FA catabolism
  • FA carried to the tissues in the bloodstream bound to albumin
  • Occurs in liver, heart and skeletal muscle as they have high mitochondria
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11
Q

Why does FA catabolism not occur in the CNS or RBCs?

A
  • RBCs have no mitochondria

- FAs cannot readily cross BBB

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12
Q

Describe the first step in FA catabolism

A
  • FA activation
  • Activated by linking a CoA molecule with S-H to a FA
  • CoAS-H has a high energy bond of hydrolysis which acitvates the FA
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13
Q

What is the activated FA product of FA catabolism?

A

-Fatty acyl-CoA

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14
Q

What two things does FA activation require for the reaction to happen?

A
  • ATP

- Fatty acyl CoA synthase

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15
Q

What is the second step in FA catabolism

A

-Carnitine shuttle into mitochondrial matrix

16
Q

Why does fatty acyl coA require a carnitine shuttle into the mitochondrial matrix?

A

-Does not readily cross the inner mitochondrial membrane

17
Q

Describe the process of FA transport into the mitochondrial matrix

A
  • Fatty acyl coA + Carnitine -> Acyl carnitine
  • Catalysed by carnitine acyl transferase 1
  • Acyl carnitine + coA -> Fatty acyl Co A + carnitine
  • Catalysed by CAT 2
  • Requires CoA to be in matrix
18
Q

How does the carnitine shuttle regulate FA oxidation?

A
  • Regulates the rate at which FA enter the matrix
  • Transport is inhibited by malonly-CoA, an intermediate of FA synthesis
  • Ensures that newly synthesised FAs are not being immediately oxidised
19
Q

What is the third step in FA catabolism once FA are in the mitochondrial matrix?

A

-B-oxidation

20
Q

What are the important end products of B-oxidation?

A

-Acetyl coA, NADH and FADH2

21
Q

What does B-Oxidation require to work?

A

-NAD+, FAD+ and O2

22
Q

What is B-Oxidation?

A
  • A sequence of oxidation reactions in which FAs are oxidised and C2 is removed in a stepwise fasion until only C2 remains
  • All intermediate products are linked to CoA
  • All C2 get converted to acetyl coA
  • Releases high amount of free energy captured by NAD+ and FAD+
23
Q

Name the three ketone bodies produced from Acetyl CoA?

A
  • Acetoacetate
  • Acetone
  • B-Hydroxybuterate
24
Q

Where are the three ketone bodies produced?

A
  • Acetoacetate and B-hydroxybuterate in the liver from acetlycoA
  • Acetone from spontaneous decarboxylation of acetoacetate
25
Q

How are the three ketone bodies excreted?

A
  • Water-soluble and thus can be excreted in the urine

- Acetone is volatile and is excreted via the lungs

26
Q

What are ketone body levels normally like and when would they rise?

A
  • Normallu at low conc in blood

- Rise during starvation and in untreated T1 diabetes mellitus

27
Q

What is the result of high ketones in the blood?

A

-Ketoacidosis

28
Q

Describe ketone body/cholesterol synthesis

A

-Acetyl Co A-> HMG-CoA (by a synthase enzyme)
-HMG-CoA to Actoacetate/B-hydroxybuterate (By lyase enzyme)
OR
-HMG-CoA to mevalonate (By HMG reductase) to cholesterol

29
Q

What exogenous drug stops cholesterol production and how?

A

-Statins by blocking HMG reductase

30
Q

How does insulin/glucagon control ketone body production

A
  • High insulin:glucagon ratio causes acetyl coA to be converted to cholesterol not ketones by inhibiting lyase/activating HMG reductase
  • Low insulin:High glucoagon ratio causes acetyl CoA to be converted to ketone bodies by activating lyase and inhibiting HMG reductase
31
Q

How does citrate control ketone body production?

A

-Activates lyase when high citrate allosterically inhibits the TCA cycle

32
Q

How can ketone bodies be useful in the brain?

A
  • Acetyl coA can not be transported across the BBB
  • Converted to ketones bodies as a shuttle as can cross BBB
  • Converted back to acetyl coA once in the brain
33
Q

Why is Acetyl Co A described as a central convergence in metabolism?

A

Catabolic

  • Proteins to a’a to aceryl coA
  • Carbs to monocaccharides to pyruvate to acetyl co A
  • TAGs to glycerol to pyruvate to acetyl co A
  • TAGs to FA to acetyl co A
  • Alcohol to Acetyl coA

Anabolic

  • Acetyl co A to FAs (TAGs and phospholipids)
  • Acetly CoA to ketones
  • Acetyl coA to cholesterol

Metabolism (14 decks)

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