Lipid Metabolism Flashcards
List the lipids found in the diet and what they are used for in the body?
Triglycerides: Main lipid.
Cholesterol: For membranes and steroid hormone production. Cannot get energy from cholesterol.
Phospholipid: For membranes.
What kinds of fatty acids are found in triglycerides?
Saturated Monounsaturated (C-C double bond). Polyunsaturated (multiple (C-C double bond).
C-C double bond causes a kink. Loser structure e.g. oils.
What attaches fatty acids to the glycerol molecule in triglycerides?
Ester bonds.
Where does lipid digestion occur?
Via what enzymes?
Small intestine.
Pancreatic lipase and co-lipase: Break down TAG into 2 FA’s and MAG.
Bile Salts are also required to emulsify fats to micelles (tiny fat droplets to increase surface enzymes for enzymes to act).
How are lipids absorbed into cells?
TAG is broken down to MAG + 2FA’s.
They are transported into cells and then repackaged as triglyceride with cholesterol, lipoproteins and other lipids to form chylomicrons.
Chylomicrons enter lymphatic system via exocytosis.
Why must FFA’s be packaged as triglyceride or transported with albumin?
As they act as detergents and can break down cell walls.
How are lipids released from chylomicrons?
Adipose tissue ‘rips off’ triglyceride from the chylomicron using cell surface made from lipoprotein lipase.
This is upregulated in the fed state.
How does adipose use Fatty Acids?
Storage as TAG.
Structural (phospholipid).
Beta Oxidation for ATP.
What is Beta Oxidation?
Where does it occur?
Generates energy from fatty acids.
Fatty acids are added to CoA to give fatty acyl-CoA.
FACoA is degraded by oxidation at the Beta-carbon. Occurs by reducing the fatty acyl chain by 2 carbons each time.
It yeilds FADH2, NADH and acetyl CoA.
Aceytl CoA can be further oxidised in the TCA cycle to yeild ATP.
Occurs in the mitochondria, but must cross the inner mitochondrial membrane. This requires carrier molecule carnitine (high in muscle).
How are Fatty acyl CoA and Carnitine transported across the mitochondrial membranes?
By Carnitine Palmitoyl Transferase.
CPT 1 is on the outer membrane and CPT 2 is on the inner.
It swaps carnitine and FACoA for CoA and FAcarnitine, and back again in the inner membrane.
FACoA can then be used for B-Oxidation.
How is triglyceride synthesised?
Draw diagram of the cell.
Esterification of 3 Fa’s and glycerol.
Lipoprotein Lipase (LPL) hydrolyses TAG in chylomicrons/VLDL.
Diacylglycerol Acyl Transferase (DGAT) re-esterifies to TAG.
The glycerol is formed from glycolysis.
How is triglycerol broken down (lipolysis)?
TAG is broken down to glycerol and 3 FA’s by Hormone Sensitive Lipase (HSL) in adipose cells.
HSL is activated by cAMP-dependant phosphorylation in response to adrenaline in the fasted state. It is inhibited by insulin.
Liberated glycerol goes to the liver.
Liberated FA goes to muscle.
How are Fatty acids synthesised?
Built 2 carbons at a time until 16 carbons.
Regulatory enzymes are Acetyl CoA Carboxylase: Forms Malonyl CoA.
Fatty acid Synthase.
Requires NADPH (from pentose phosphate pathway).
Occurs in cytoplasm.
Uses the vitamin biotin from gut flora.
How are plasma TAG’s (lipoproteins) and FFA (albumin-bound) made?
Dietry lipids.
Fatty acid synthesis.
TAG conversion from adipose.
What are plasma TAG’s (lipoproteins) and FFA (albumin-bound) used fro?
Ketone bodies.
Beta-oxidation.
Phospholipid synthesis.
