Lipid metabolism

Question 1

Lipid definition

Answer 1

Chemically diverse group of compounds which aren’t soluble in water

Question 2

What is a fatty acid?

Answer 2

A long hydrocarbon chain with a terminal carboxyl group

Question 3

Triacylglycerol (TAG)

Answer 3

Esters of 3 fatty acids with glycerol

Question 4

What are phospholipids?

Answer 4

Esters of 2 fatty acids with glycerol attached to phosphate group and another alcohol

Question 5

How are polyunsaturated fats made?

Answer 5

Further desaturation of monounsaturated fats

Question 6

Animal vs Plant bonds

Answer 6

Animal: double bond between bond and carboxyl group
Plant: double bond between bond and methyl group

Question 7

Prokaryote vs Eukaryote synthesis of fatty acids

Answer 7

Prokaryote: separate enzymes
Eukaryote: multifunctional enzyme complex

Question 8

Acyl carrier protein (ACP)

Answer 8

• In bacteria, it is a 77 amino acid protein joined to a phosphopanthenine (PP)
• In animals, it is part of the fatty acid complex

Question 9

When do chains become terminated?

Answer 9

At 16 carbons (palmitic acid)

Question 10

What can phospholipids be synthesised into?

Answer 10

• Diacylglycerol
• Phosphatidylcholine
• Phosphatidylethanolamine
• Phosphatidylserine
• CDP-Diacylglycerol
• Phosphatidylinositol
• TAG

Question 11

Intestine lipid transport

Answer 11

Transported as lipoproteins

Question 12

Liver lipid transport

Answer 12

Transported as lipoproteins

Question 13

Adipose tissue lipid transport

Answer 13

Releases fatty acids into bloodstream

Question 14

What are apolipoproteins (apo)?

Answer 14

Diverse group of lipoproteins with a wide range of sizes

Question 15

Functions of apolipoproteins (apo)

Answer 15

• Holds particle together
• Activation or inhibition of lipoprotein lipase (LPL)
• Recognition by receptors

Question 16

Exogenous pathway

Answer 16

• Lipids are absorbed into small intestine
• Phospholipid, cholesterol, cholesterol ester, TAG are incorporated with apoB48 to form chylomicrons
• Chylomicrons are secreted into bloodstream and anchored to LPL
• LPL hydrolyses TAG and releases fatty acids
• When TAG has been broken down particle is released back into the circulation as a remnant
• The remnant is removed from the circulation after binding to receptors in the liver

Question 17

Endogenous pathway

Answer 17

• In the liver phospholipid, cholesterol, cholesterol ester and TAG combine with apoB100 to form very low-density lipoprotein (VLDL)
• VLDL are secreted into the blood stream and interact with the LPL
• When TAG has been hydrolysed the particle is released as intermediate density lipoprotein (IDL) which is further converted into low density lipoprotein (LDL)
• This is removed from the circulation after interaction with specific cell surface receptors

Question 18

What is discoidal HDL?

Answer 18

Products of liver and intestine rich in protein, phospholipid and free cholesterol

Question 19

LDL vs HDL

Answer 19

LDL: deposits cholesterol in the arteries causing heart attacks
HDL: removes cholesterol from arteries

Question 20

Where can fatty acid be metabolised?

Answer 20

Adipose tissue, liver, muscle

Question 21

Name the 3 ways fatty acids are used for energy

Answer 21

• Released by LPL from chylomicrons
• Released by LDL from VLDL
• Released as NEFA from adipose tissue