Lipid Anabolism

Question 1

lipogenesis

Answer 1

de novo synthesis of fatty acids

reductive process - requires electrons

Question 2

where does lipogenesis take place

Answer 2

mainly in;
cytoplasm of liver
kidney
mammary glands
adipose tissue
brain

Question 3

when does lipogenesis take place

Answer 3

during excess energy intake

Question 4

how does lipogenesis occur

Answer 4

when excess carbohydrate is taken in;

1. conversion to fatty acids and triglycerides in the liver
2. free fatty acids are transported in plasma bound to albumin
3. triglycerides formed in the liver are transported to adipose tissue for very low density lipoprotein for storage

Question 5

how is acetyl-CoA transported from matrix of mitochondria to cytoplasm of liver

Answer 5

citrate

at high concentrations (abundance of acetyl-CoA and ATP), citrate will then transport into the cytoplasm

Question 6

how is citrate formed

Answer 6

allosterically by condensation of acetyl-CoA with oxaloacetate (first step in the TCA cycle)

Question 7

first step of lipid anabolism - activation of acetyl-CoA

Answer 7

this is done to malonyl-CoA by acetyl-CoA carboxylase - an essential regulatory enzyme
malonyl-CoA donates carbon atoms to new lipid

Question 8

where is acetyl-CoA carboxylase expressed

Answer 8

liver and adipose tissue

Question 9

function of fatty acid synthase

Answer 9

catalyses the synthesis of saturated long chain fatty acids from malonyl-CoA (provides 2 carbons), acetyl-CoA and NADPH (electron donor);
1. condensation
2. reduction
3. dehydration
4, reduction and release at C-16 (palmitic acid)
further enzymes are required to elongate chain or add unsaturated bonds

Question 10

structure of fatty acid synthase

Answer 10

multi-enzyme complex - single polypeptide chain with 7 distinct enzyme activates
homodimerises through sulfhydryl cross bridges
contains acyl-carrier protein

Question 11

control of fatty acid metabolism

Answer 11

stringently controlled via acetyl-CoA carboxylase
highly responsive to physiological needs - synthesis maximal when carbohydrate and energy are plentiful and fatty acids scarce

Question 12

how does acetyl-CoA carboxylase regulates fatty acid metabolism - fed state

Answer 12

insulin signals the fed state;

stimulates storage of fuels and synthesis of proteins

Question 13

how does acetyl-CoA carboxylase regulates fatty acid metabolism - starved state

Answer 13

glucagon signals the starved state;

epinephrine signals requirement for energy - mobilising glycogen stores

Question 14

what is palmitoyl-CoA

Answer 14

antagonises fatty acid synthesis

abundant when fatty acids are in excess

Question 15

synthesis of triglycerides from fatty acids

Answer 15

requires glycerol-3-phosphate (G3P)
adipose tissue production of triglycerides only during fed state - insulin stimulates adipose tissue uptake of glucose
triglyceride formation involves esterification

Question 16

where is G3P produced

Answer 16

produced by;
liver from glycerol (liver also synthesises phospholipids, cholesterol and lipoproteins)
adipose tissues from glucose