11. Post Absorption Processing of Lipids

Question 1

What are lipids transported in in circulation?

Answer 1

Lipoprotein particles: chylomicrons

Question 2

What is fat principally absorbed as?

Answer 2

2-monoacylglycerol

FAs

Question 3

What are FAs converted to?

Answer 3

Acyl-CoA

Question 4

Where are FAs converted to Acyl-CoA?

Answer 4

ER of intestinal mucosal cells

Question 5

What converts FAs to acyl-CoA?

Answer 5

Acyl-CoA Synthetase

Question 6

What happens once proteins and lipids are secreted from the smooth ER and golgi?

Answer 6

Released into extracellular space as fat droplets
Collected by local lymph
Transported via the thoracic duct to the left brachycephalic vein

Question 7

What is the structure of monoacylglycerol?

Answer 7

Glycerol linked to a FA via an ester bond

Question 8

What is the structure of triacylglycerol?

Answer 8

Ester derived from glycerol and 3 FAs

Question 9

What is the structure of cholesterol ester?

Answer 9

Ester bond formed between the carboxylate group of a fatty acid and the hydroxyl group of cholesterol

Question 10

What does utilisation of TAGs require?

Answer 10

Lipoprotein Lipase

Question 11

Where is lipoprotein lipase not found?

Answer 11

Liver

Brain

Question 12

What is LPL attached to?

Answer 12

Heparan sulphate glycoproteins on the surface of the capillary endothelium on adipose

Question 13

What increases the activity of LPL?

Answer 13

Insulin

Question 14

What happens to TAGs when going from a fed state to a fasting one?

Answer 14

TAGs are re-routed from adipose to muscle

Question 15

Where do most of the FAs used in TAG synthesis in adipose tissue come from?

Answer 15

Chylomicrons

Question 16

Where do most of the FAs used in TAG synthesis after a high carb meal come from?

Answer 16

Acetyl CoA

Question 17

What form do FAs participate in TAG synthesis as?

Answer 17

CoA-thioesters

Question 18

What form does glycerol participate in TAG synthesis as?

Answer 18

Glycerol-3-phosphate

Question 19

How does insulin regulate fat synthesis?

Answer 19

Increases rate of glycolysis
Increases LPL activity
Induces glycerolphosphate-acyl transferase which catalyses the first step in TAG synthesis

Question 20

What enzyme carries out the first cleavage of a FA from TAGs?

Answer 20

Hormone-sensitive adipose tissue lipase

Question 21

What activates adipose tissue lipase?

Answer 21

Phosphorylation by cAMP-dependent Protein Kinase A

Question 22

What are the most important human lipolytic agents?

Answer 22

Noradrenaline and adrenaline

Question 23

How does noradrenaline work to promote TAG breakdown?

Answer 23

Acts via beta-adrenergic receptors, cAMP, Protein Kinase A

Question 24

What are other lipolytic hormones?

Answer 24

Glucocorticoids
GH
Thyroid hormone

Question 25

What conditions increase TAG hydrolisation?

Answer 25

Cold exposure Stress Physical exercise

Question 26

What do free FAs bind to in circulation?

Answer 26

Albumin

Question 27

Where does beta oxidation occur?

Answer 27

In the mitochondrion

Question 28

What types of cells can't oxidise FAs?

Answer 28

Neurons | Erythrocytes

Question 29

How do short FAs enter the mitochondrion?

Answer 29

Passive diffusion

Question 30

How do longer FAs enter the mitochondrion?

Answer 30

Converted to CoA-thioesters by Fatty Acyl CoA Synthetase Carnitine transports acyl group across the membrane Known as the carnitine shuttle

Question 31

What is the carnitine shuttle composed of?

Answer 31

Carnitine Palmitoyltransferase 1 and 2 | Carnitine-acylcarnitine translocase

Question 32

What inhibits CPT-1?

Answer 32

Malonyl-CoA

Question 33

What is the net result of beta oxidation?

Answer 33

Each cycle removes 2 carbons from the FA as acetyl-CoA | Production of NADH, H+ and FADH2

Question 34

How does beta oxidation produce energy?

Answer 34

FADH2 and NADH feed into oxidative phosphorylation | Acetyl-CoA enteres TCA cycle

Question 35

How is beta oxidation regulated?

Answer 35

Supply of free FAs Activity of hormone-sensitive adipose tissue lipase Inhibted by malonyl-CoA

Question 36

Name 3 ketone bodies

Answer 36

Acetoacetate B-hydroxybutyrate Acetone

Question 37

How are acetoacetate and B-hydroxybutyrate formed?

Answer 37

From Acetyl-CoA in the liver mitochondria by ketogenesis

Question 38

How is acetone formed?

Answer 38

Spontaneous decarboxylation of acetoacetate

Question 39

Where are ketone bodies especially important for energy?

Answer 39

Heart Adrenal glands Renal cortex

Question 40

When are circulating ketone body levels high?

Answer 40

Fasting Diabetes mellitus Whenever fat breakdown exceeds carbohydrate breakdown

Question 41

What is brown adipose tissue characterised by?

Answer 41

Good blood supply High mitochondria and cytochromes Low activity of ATP synthetase

Question 42

What are the main clinical signs of Medium Chain Acyl-CoA Dehydrogenase Deficiency?

Answer 42

``` Intolerance to prolonged fasting Hypoglycaemia Impaired ketogenesis Hypoglycaemic coma Medium-chain dicarboxylic aciduria ```