Fat metabolism (lecture 30)

Question 1

how are fats stored?

Answer 1

triglycerides

Question 2

what are triglycerides made of?

Answer 2

glycerol and 3 fatty acids

an ester

Question 3

how are triglycerides stored?

Answer 3

in white adipose tissue
provides thermal and electrical insulation
helps maintain body temp and cell structure

Question 4

why is cholesterol bad for your health?

Answer 4

body cannot metabolise cholesterol

has to be recycled in the liver

Question 5

why are fats a more efficient energy source compared to carbohydrates?

Answer 5

in glucose, carbons are partially oxidised

in palmitic acid, carbons are fully saturated
• releases more electrons
• can generate more ATP
• main storage of fatty acids

Question 6

how do triglycerides vary?

Answer 6

in length and saturation

a double bond makes a ∆ fatty acid
• looses 2 hydrogens
• cis/trans isomerism

Question 7

why are saturated fats bad?

Answer 7

straight molecules form very dense layers which are difficult to metabolise

double bonds form kinks which make it less dense when stored - makes it more accessible for enzymes

Question 8

what is catabolism?

Answer 8

the breakdown of triglycerides (fatty acids)

Question 9

what are the 3 stages of catabolism?

Answer 9

lipolysis
activation of fatty acids
oxidation of fatty acids - beta oxidation

Question 10

what happens in lipolysis?

Answer 10

triglyceride broken up into glycerol and fatty acids

lipase breaks ester bond to release fatty acids
glycerol is recycled back to the liver
• glycerol converted to glycerol-3-phosphate by glycerol kinase
• this is oxidised to dihydroxyacetone phosphate by glycerol phosphate dehydrogenase

Question 11

what happens in fatty acid activation?

Answer 11

fatty acids enter cytoplasm
activated by addition of CoA by acyl CoA synthetase

ATP to AMP in one step to release more energy
high affinity of pyrophosphorylase to the free phosphates keeps reaction going in 1 direction

Question 12

mitochondria is impermeable to acyl CoA, how is this overcome?

Answer 12

acyl group is transported into the mitochondria as acyl-carnitine

translocate allows acyl carnitine to enter the mitochondria

carnitine is recycled back outside the mitochondria

Question 13

what happens in beta oxidation?

Answer 13

activated fatty acid is oxidised by FAD
removes hydrogens to form FADH2 and introduces a double bond
water is added to the double bond
dehydrogenate to oxidise the beta carbon
cleavage - CoA can break the bond in beta oxidation spiral

Question 14

what are the 4 stages if beta oxidation?

Answer 14

oxidation
hydration
oxidation
cleavage

Question 15

what do you get from cleavage of a 16C molecule?

Answer 15

8 acetyl CoA
7 FADH2
7 NADH + H+

Question 16

how many ATPs do you get out of 1 palmitic acid?

Answer 16

108

only 32 from glucose

Question 17

what is the activation factor in beta oxidation?

Answer 17

CoA

Question 18

what happens during starvation?

Answer 18

body swaps to fatty acid metabolism
glucagon is activated and gluconeogenesis starts
fatty acids cannot enter the CAC so fats are converted to ketone bodies
ketone bodies rise pH of the blood which is dangerous for diabetes

Question 19

ketone properties

Answer 19

produced mainly in the liver
ketosis common in type 1 diabetes
distinctive fruity smell

Question 20

ketone body formation

Answer 20

2 acetyl CoA joined together by thiolase to from acetoacetyl CoA

this can then form 3-hydroxy-3-methyl-glutaryl CoA

this can produce 3 ketone bodies

Question 21

what are the 3 ketone bodies?

Answer 21

acetoacetate
acetone
D-3-hydroxy-butyrate

Question 22

what is lipogenesis?

Answer 22

fatty acid synthesis

Question 23

what are the 4 stages of lipogenesis?

Answer 23

condensation
reduction
dehydration
reduction

Question 24

what is the committed step in lipogenesis?

Answer 24

formation of malonyl CoA

produced by adding CO2 to acetyl CoA by acetyl CoA carboxylase

Question 25

what does lipogenesis lead to?

Answer 25

non alcoholic fatty liver disease (NAFLD)

• increases fat build up in the liver
• insulin resistance
• overweight and obesity
• type 2 diabetes

Question 26

what is the activation factor in lipogenesis?

Answer 26

acyl carrier protein (ACP)

Question 27

what is the key enzyme in controlling fatty acid synthesis?

Answer 27

acetyl CoA carboxylase

Question 28

when are ketone bodies generated?

Answer 28

from fatty acid metabolism under prolonged starvation in type 1 diabetes