6 - Lipid Metabolism

Question 1

What is the structure of a fatty acid?

Answer 1

a molecule containing a hydrocarbon chain with a carboxylic acid group (hydrophilic) at the end

Question 2

Give an example of a saturated FA

Answer 2

stearic acid

Question 3

Give an example of an unsaturated FA

Answer 3

oleic acid

Question 4

How are fatty acids usually stored within a cel?

Answer 4

as triacylglycerols (TAGs)

Question 5

Triacylglycerols come together to form _____

Answer 5

lipid droplets

Question 6

In mammals, what cells store fatty acids?

Answer 6

adipocytes

Question 7

Where are bile slats produced and stored?

Where are they secreted into?

Answer 7

produced in the liver
stored in the gall bladder
secreted into small intestine

Question 8

What is the role of bile salts?

Answer 8

to emulsify fats

Question 9

What does a lack of bile salts result in?

Answer 9

steatorrhoea

because fat passes through the digestive tract undigested and unabsorbed

Question 10

What easily allows bile salts to interact with TAGs and solute/solvent?

Answer 10

hydrophilic and hydrophobic faces

Question 11

Describe emulsification by bile

Answer 11

• bile salts present the hydrophobic face to TAGs and the hydrophilic face to the solvent
• this breaks the lipid droplets into small droplets in ‘a soluble form’, increasing the SA
• pancreatic lipases break the TAGs down
• results in (TAGs), DAGs, MAGs and FFAs

Question 12

How are mixed micelles formed from soluble, digested lipid droplets?
What happens to them after they have formed?

Answer 12

• the DAGs, MAGs and FFAs join bile salts, cholesterol, lysophosphatidic acid and fat soluble vitamins to form mixed micelles
• they are then absorbed by enterocytes in the small intestine
• TAGs are resynthesised and packaged into chylomicrons
  (chylomicrons = TAGs + other proteins + apoproteins)
• chylomicrons enter the circulation via lymph

Question 13

What is orlistat?

Answer 13

a potent inhibitor of gastric and pancreatic lipases
designed to treat obesity
reduced fat absorption by 30% (excited by faecal route)

Question 14

Which body part does not use energy from the β-oxidation/fats?
Where does it get its energy from instead?

Answer 14

the brain - uses energy from ketone bodies when glucose supply is low

Question 15

Where does β-oxidation occur in a cell?

What does it produce?

Answer 15

in the mitochondria

results in the formation of acetyl CoA

Question 16

What is the first step in β-oxidation?

Answer 16

fatty acids —–> acyl CoA
enzyme = acyl CoA synthetase
NOTE: ATP —> AMP (2 high energy bonds are used)

Question 17

Where dies the first step in β-oxidation take place?

Answer 17

on the outer mitochondrial membrane

Question 18

How do the products of the first step in β-oxidation get into the mitochondria?
What are the enzymes used in this process? What do they do?

Answer 18

carnitine shuttle

translocase - to carry carnitine and acylcarnitine across the inner mitochondrial membrane
carnitine acyltransferase I/II - to transfer the acyl group

Question 19

Describe the β-oxidation cycle

What is the overall result of this?

Answer 19

OHOT
1- fatty acyl CoA is oxidised (FAD—>FADH2)
2- hydrolysis
3- oxidation (NAD+—>NADH)
4- thiolysis (a molecule of acetyl CoA cleaved off by bringing in CoA and using β-ketothiolase)

the original fatty acyl CoA has been shorted by 2 carbons and a module of acyl CoA has been produced

Question 20

During each cycle of β-oxidation, how many NADH and FADH2 are produced?

Answer 20

1 NADH

1 FADH2

Question 21

KEY POINT: Acetyl CoA formed from β-oxidation can only enter the TCA cycle if β-oxidation and carbohydrate metabolism are balanced.
Why is this?

Answer 21

because OXALOACETATE is needed for entry of Acetyl CoA into the TCA cycle.

Question 22

If fat breakdown predominates (e.g. when fasting/starving), what does acetyl CoA form instead?

Answer 22

KETONE BODIES

• Acetoacetate
• D-3-hydroxybutyrate
• Acetone

Question 23

How many ATP are produced from palmitate β-oxidation?

Answer 23

129

Question 24

Where does lipogenesis take place?

Answer 24

in the liver, in the cytoplasm of cells

Question 25

What is the order of reactions of elongation (in lipogenesis)?

Answer 25

condensation
reduction
dehydration
reduction

Question 26

In lipogenesis, the growing acyl group is linked to an ________

Answer 26

Acyl carrier protein

swinging arm mechanism to move fatty acid chain

Question 27

β-oxidation vs lipogenesis:

1) where do each take place?
2) what are the carriers?
3) What are the coenzmes?

Answer 27

1) mitochondria vs cytoplasm
2) CoA vs ACP
3) FAD and NAD vs NADPH