Lipid Metabolism Flashcards
(23 cards)
What are the three dietary lipids?
Triglycerides = 95%
Cholesterol - don’t get any ATP from it - need to make membranes
Phospholipids - to make membranes
Types of fatty acids in triglycerides?
Saturated FA - no C=C
Mono-unsaturated - one C=C
Polyunsaturated - multiple C=C
Briefly describe lipid digestion
Occurs in the small intestine.
Bile salts emulsify fats to smaller fat droplets - to increase surface area for enzymes to work on
Bile salts and pancreatic lipase and collapse break down triglycerides into 2 fatty acids and monoglyceride
What happens when fatty acids enter the intestinal cell??
They are reformed as triglycerides and packaged with cholesterol, lipoproteins and other lipids to form chylomicrons
Why do fatty acids have to be packaged up?
Because they start to break down cell walls - quite dangerous
How do chylomicrons exit intestinal cell?
They are released into lymphatic system by exocytosis
What does lipoprotein lipase do?
Rips off the lipid component from the chylomicron and these then go to adipose tissues for:
- storage (TG)
- structural (phospholipids)
- oxidation (ATP)
What happens to the rest of the chylomicron after LPL action?
It is transported to the liver
What do lipoproteins do (concerning lipid transport)?
They stop dangerous fatty acids from being free in circulation
Largely in VLDLs then LDL then HDL
Lipoprotein lipase takes the triglycerides away and leaves the cholesterol to be taken to cells
What is beta-oxidation?
The generation of energy (ATP) from fatty acids.
Acetyl CoA is formed (and FADH2 and NADH) which is further oxidised in the TCA cycle and oxidative phosphorylation to get more ATP
Where does beta oxidation occur?
Within the mitochondria which has a double membrane
Fatty acids need a carrier protein to carry them
What carrier protein helps fatty acids over the mitochondrial membrane for beta-oxidation?
Carnitine - an amino acid
- derived from lysine and methionine
- lots in muscle
What enzyme is needed for fatty acid entry to the mitochondrion for beta oxidation?
Carnitine Palmitoyl Transferase
CPT1 and CPT2
How do fatty acids enter the mitochondrion for beta oxidation?
CPT1 (in first membrane) splits carnitine and fatty acyl Co-A into CoA and fatty acyl carnitine
FA carnitine crosses the second membrane
CPT2 then transfers them back to carnitine and fatty acyl CoA which is used for beta oxidation
Regulating factor in beta oxidation?
Activity of the CPT enzymes - especially CPT1
What happens in beta oxidation?
Fatty acyl-CoA is degraded by oxidation at the beta carbon
Fatty acyl chain is reduced by 2 carbons each time
Produces 1 FADH2, NADH and Acetyl CoA each time
Re-enters cycle and chops off 2 carbons each time
What happens to the acetyl CoA?
Further oxidised to get ATP, through the TCA cycle and oxidative phosphorylation
Why are fatty acids such a good source of ATP?
Lots of ATP per molecule vs glucose
Can store TG and lipid droplets together very densely in adipose tissues
How are triglycerides synthesised?
Synthesised from the esterification of three fatty acids and glycerol
Fatty acids:
LPL hydrolyses the FAs in chylomicrons/VLDL - takes away the FA
FAs transported in/out of cell with proteins
Glycerol is obtained from glycolysis
DHAP - G3P stage
Diacylglycerol acyl transferase (DGAT) re-esterifies to triglycerides
What happens in triglyceride breakdown? (lipolysis)
TG is broken down into glycerol and three fatty acids
Enzyme involved = hormone sensitive lipase
Hormone sensitive lipase
Found in adipose tissue (liver also has)
Activated by cAMP-dependent phosphorylation in response to adrenaline in FASTED state
Inhibited by insulin in FED state
Is adipose tissue innervated??
Yes, very highly innervated
Has lots of adrenergic nerves (the autonomic nervous system)
What does lipolysis result in?
Fatty acids transported mainly to muscle (largest tissue) but also other tissues
Glycerol transported to liver for gluconeogenesis to make blood glucose (as stimulated in fasted state remember!!)
