Lipid Synthesis & Degradation Flashcards
what is the role of fats in the body?
- membrane formatin
- uptake of lipid soluble vitamins
- precursors of steroid hormones
- energy store
what is the energy content of fat in comparison to proteins and carbohydrates?
energy content is 2x/g compared to proteins and carbohydrates
when is the synthesis of fat triggered and what is the main source of it?
- when caloric intake > consumption
- cardiac muscle use fats as preferred energy source
- dietary carbohydrate is the most common source bu aa can also be used
what is the structure of fatty acids (FA)?
- chains of methyl groups with a terminal carboxyl group at one end
- id double bonds present, in cis formation
why do humans need to obtain FA in diet?
- humans unable to make double bodes at positions below position 9
- bc they cannot be made in body
where does FA synthesis occur and what does it require?
- in cytosol
- requires acetyl CoA, ATP, NADPH
how does the citrate-malate antipode system work and why do we need it?
- pyruvate is transported from cytosol to inside of mito
- converted to oxaloacetate where acetyl CoA is added to make citrate
- citrate is removed form mito and back into cytosol so acetyl CoA can be released, forming oxaloacetate again
- NADP is added to oxaloacetate to from malate which forms pyruvate when NADPH is removed
- this is done as acetyl CoA cannot pass membrane of mito
what is the first step of FA synthesis?
- acetyl CoA + ATP + HCO3- —-> malonyl CoA + ADP +Pi
- acetyl CoA (C2) has C molecule added by HCO3- with ATP to form malonyl CoA (C3)
- important, irreversible regulatory step activated by citrate and inhibited by palmitic acid
- requires vit B7
what is the structure and function of cholesterol?
- rigid hydrophobic molecule that is insoluble in H20
- important membranen component and precursor of sterols, steroids and bile salts
- transported in circulation as cholesteryl esters
what health issues can cholesterol imbalance lead to?
gallstones and atherosclerosis
describe cholesterol synthesis
-synthesised in ER (w over 30 steps involved)
- starts w activation of acetate in acetyl CoA
- major regulatory step is conversion of 3-hydroxyl-3-methyl-glutaryl CoA (HMG-CoA) to mevalonate
- cholesterol inhibits HMG-CoA reductase
- difficults to remove cholesterol by diet alone
what are the 3 steps of FA degradation?
- mobilisation (in adipocyte)
- activation (in liver cytosol)
- degradation (in liver mito)
what happens in FA mobilisation?
- GPCR activates adenylate cyclase to increase [cAMP] made from ATP, which activates protein kinase
- protein kinase activates triglyceraol lipase
- triglycerol lipase converts triacylglyceril to diacylglyceril
- diacylglycerol is broken down to glycerol and FA
what happens to glycerol formed in FA mobilisation?
- absorbed by liver
1) glycerol phosphorylated to glycerol-3-phosphate
2) glycerol-3-phosphate is oxidised by dihydroxyacetone phosphate
3) dihydroxyacetone phosphate is isomerism to gform glyceraldehyde-3-phosphate (GAP) - most GAP is used in cluconeogenesis and some goes towards glycolysis
what is FA activation?
- FA transported to liver and activated by acyl-CoA synthase in cytoplasm to form fatty acyl-CoA
- fatty acyl-CoA reacts with alcohol carnitine to form fatty acyl-carnitine
- fatty acyl-carnitine is transported across inner mito membrane by translocate
- the fatty acyl-carnitine is broken down and releases acyl to combine with CoA, remaking acyl-CoA
