10 - Lipid and Ketone Body Metabolism Flashcards
What is the general structure of a lipid?
- Diverse, contain C,H and O and sometimes P, N
- More reduced than carbohydrates
- Not water soluble
What are the three classes of lipids?
Fatty acid derivatives:
- FA = fuel molecule - TAG = storage molecule
- Phospholipids - Eicosanoids (local mediators)
Hydroxy-methylglutaric acid derivatives:
- Ketone bodies (C4 - water soluble)
- Cholesterol - Cholesterol esters (storage)
- Bile acid and salts
Vitamins:
A,D,E,K essential
How is TAG synthesised and broken down?
- Under hormonal control to be stored in adipose anhydrously as hydrophobic.
Esterification: Insulin
Lipolysis: Glucagon, Cortisol, Adrenaline, GH
Lipolysis during starvation, pregnancy and prolonged exercise
How are triacylglycerols metabolised extracellularly?
- Hydrolysed by pancreatic lipase in SI. Requires bile salts
- Produce FA and Glycerol
Where does B-oxidation not occur?
- RBC as no mitochondria
- Brain as FA can’t pass blood-brain barrier
What happens to glycerol when it has been produced from TAG metabolism?
Goes through blood to liver where it is stored or metabolised
What happens to FA when they have been digested from TAG?
- Converted back to TAG in G.I
- Packaged into lipoproteins called chylomicrons
- Released into circulation by lymphatics and carried to adipose tissue to be stored
- Released by hormone-sensitive lipase
- Carried to consumer tissues by albumin - FA complex
How are fatty acids held in adipose tissue?
- When glucose conc decreases, insufficient glycerol-1-phosphate so fatty acyl-coA cant be converted so FA builds up due to backlog and is released
What is B-oxidation?
Oxidation of fatty acids to release energy, in the mitochondria
What are the two properties of fatty acids?
- Amphipathic
- Saturated/Unsaturated (linolenic acid essential as can’t introduce C double bond after C9)
How are fatty acids catabolised?
- Activated by linking to CoA outside the mitochondria
- Transported via carnitine shuttle through inner mitochondrial membrane as activated FA do not readily cross inner membrane
- Series of oxidative reactions with C2 removed each time and NADH and FADH2 being produced each time
How are fatty acids activated?
Fatty acyl CoA synthase links FA to CoA, using ATP.
How does fatty-acyl CoA get across inner mitochondrial membrane?
- On it’s own cant get across membrane so CAT 1 (carnitine acyltransferase) removes CoA and adds carnitine to produce acyl carnitine
- Acyl carnitine shuttles across carnitine shuttle transporter into mitochondria
- CAT2 adds CoA back and removes carnitine which shuttles back over.
How is carnatine shuttle transporter regulated?
- Controls rate of FA oxidation
- CAT inhibited by biosynthetic intermediate malonyl CoA
- If dect in CAT, will lead to lipid droplets in abnormal places as lipids can’t be broken down
Explain key points of B-oxidation?
- Cycle removing 2C each time
- Oxidation
- Produces NADH and FADH2
- Needs O2
- No ATP synthesis
- Greater yield than glucose as more turns of TCA