Lipid metabolism

Question 1

What are the three classes of lipids

Answer 1

• fatty acid derivative
• hydroxy-methyl-glutaric acid
• vitamins

Question 2

what types of lipids are fatty acid derivatives

Answer 2

• fatty acids
• triacylglycerols
• phospholipids
• eicosanoids

Question 3

what types of lipids are hydroxy-methyl-glutaric acids

Answer 3

• ketone bodies
• cholesterol
• cholesterol esters
• bile acids and salts

Question 4

what type of vitamins are lipid soluble

Answer 4

A
D
E
K

Question 5

what and where is the first stage of lipid metabolism

Answer 5

extracellular digestion in GI tract

Question 6

how are triacylglycerols first metabolised in the GI tract

Answer 6

• hydrolysed by pancreatic lipase in small intestine
  broken into glycerol and fatty acids
  (requires bile salts and protein factor colipase)

Question 7

after triacylglycerols are broken into glycerol and fatty acids where does the glycerol go

Answer 7

enters blood to liver to be metabolised

Question 8

how does the liver metabolise glycerol

Answer 8

• phosphorylated by glycerol kinase to glycerol phosphate which can either be used for triacylglycerol synthesis or enter glycolysis by converting DHAP

Question 9

How are triacylglycerols stored

Answer 9

• converted to triacylglycerol in GI
• packed into lipoprotein particle called chylomicrons
• travel through lymphatics to adipose tissue where stored

Question 10

What is lipolysis

Answer 10

the release of lipids from storage when needed
- hormone controlled
- stimulated by high adrenaline and glucagon
- inhibited by insulin

Question 11

How are lipids released from lipolysis carries to tissues

Answer 11

by blood covalently bound to albumin= albumin-fatty acid complex

Question 12

What are the three stages of fatty acid metabolism

Answer 12

1) activation
2) transport to mitochondria
3) b- oxidation

Question 13

How are fatty acids activated for metabolism

Answer 13

by linking to CoA via S atom forming high energy hydrolysis bond
via enzyme: fatty acyl CoA synthase

Question 14

How are fatty acids transported to the mitochondria

Answer 14

via carnitine shuttle

Question 15

Why do fatty acids require a carnitine shuttle for transport to mitochondria

Answer 15

activated fatty acids do not readily cross inner membrane of mitochondria

Question 16

Describe the action of the carnitine shuttle

Answer 16

• acyl group transferred to carnitine by CAT1 (carnitine acyltransferases 1) which then moves across the mem
• acyl group from acyl carnitine transferred to CoA on inside using CAT2

Question 17

how is the transport of fatty acids to mitochondria regulated

Answer 17

• AMP and insulin
  -inhibited by malonyl CoA (intermediate of FA synthesis) as means new FA made do not go directly to mitochondria

Question 18

Describe the process of beta oxidation

Answer 18

• a spiral that removes a C2 unit (acetate) each time until only 2C remain which are all bound to CoA to make acetyl CoA

Question 19

What molecules does beta oxidation require

Answer 19

• FAD
• NAD
• O2

Question 20

What are the features of triacylglycerols

Answer 20

• hydrophobic
• stored in anhydrous form (no water weight)
• stored in adipose tissue
• used in exercise, starvation and pregnancy

Question 21

What are the three ketone bodies produced in the body

Answer 21

-acetoacetate
- acetone
- B- hydroxybutyrate

Question 22

what are features of ketone bodies

Answer 22

• soluble in water
• produced when acetyl CoA is high
• used by muscle
• alternative fuel to glucose in brain as can cross blood brain barrier

Question 23

Where are ketone bodies synthesised

Answer 23

liver

Question 24

What does the first enzyme do in ketone body synthesis do

Answer 24

Enzyme : synthase
function: converts acetyl CoA to Hydroxymethyl glutaryl-CoA (HMG-CoA)

Question 25

What can HMG-CoA be converted

Answer 25

• to ketone bodies by enzyme lyase
  HMG-CoA –> acetoacetate which can either degrade into acetone or be converted to beta-hydroxybutyrate
• to cholesterol via enzyme HMG - CoA reductase

Question 26

What enzyme do statin drugs target

Answer 26

HMG - CoA reductase

Question 27

how is synthesis of ketone bodies controlled

Answer 27

controlled by inhibition of TCA cycle so acetyl CoA diverted to ketone synthesis

• low NAD or high NADH enzymes of TCA cycle inhibited so acetyl CoA diverted

Question 28

How are ketone bodies synthesised

Answer 28

acetoacetate enters blood and is converted to acetoacetyl in muscle as is a intermediate of TCA

Question 29

how is ketone synthesis regulated in the fed state

Answer 29

• fed means high insulin so inhibits lyase and reductase activated so cholesterol synthesis

Question 30

how is ketone synthesis regulated in the early starvation state

Answer 30

• starvation means low insulin and high glucagon
• lyase activated and reducatase inhibited so ketone synthesis

Question 31

how do ketone bodies spare glucose

Answer 31

reserve glucose for brain and other tissues use ketone bodies

Question 32

how do ketone bodies spare glucose in late starvation

Answer 32

• very low insulin
• ketones produced for all other tissues but glucose for brain from breakdown of muscle and glycogen

Question 33

what happens in diabetes with ketone production and glucose

Answer 33

• high glucose as not being utlilised
• ketone bodies still being produced as glucose not used so uncontrolled ketogenesis

Question 34

what are the plasma levels of ketones in the normal state

Answer 34

less than 1nm

Question 35

what are the plasma levels of ketones in the starvation state

Answer 35

2-5nm (physiological ketosis)

Question 36

what are the plasma levels of ketones in diabetes

Answer 36

greater than 10m (pathological ketosis)