Lipid Metabolism Flashcards
(23 cards)
What roles do lipids have?
Cell membranes - cholesterol and phospholipids
Precursors of hormones - cholesterol to steroid hormones
Long term fuels - triglycerides
How is stored triglyceride fat broken down in adipose tissue?
Triacylglcerol - diacylglycerol by triacylglycerol lipase
diacylglycerol - monoacylglycerol by DAG lipase
monoacylglycerol - glycerol by MAG lipase
The free fatty acids release travel in plasma bound to albumin
What is glycerol used for?
Normally used in glycolysis but in liver or starvation it’s converted into glucose by gluconeogenesis
Where does beta-oxidation occur?
In mitochondrial matrix
How is long chain fatty acid activated?
Fatty acyl CoA synthetase converts fatty acid to fatty acid CoA
Uses CoASH and ATP - AMP +PPi
What are the 3 steps of fatty acid oxidation?
Activation - by converting into acyl CoA
Transport - moving acyl carnitine from cytoplasm to mitochondrial matrix
Oxidation - which is a cyclic process until butryryl-CoA is produced
What would an 18 carbon fatty acid produce?
It would go through the cycle 7 times, producing 7 FADH2 and 7 NADH and 8 acetyl-CoA for the TCA cycle
What stimulates fatty acids to be released from adipose tissue?
Adrenaline and glucagon activate lipase enzyme
What regulates fat metabolism?
Activation of lipase enzyme
Speed of carnitine shuttle across mitochondrial membrane
Rate of reoxidation of NADH and FADH2
When does ketogenesis occur?
During starvation or in Type 1 Diabetes
Why does the kidney convert Acetyl-CoA in the liver?
Fatty acid oxidation in the liver leads to more Acetyl CoA than the body can handle so converts extra Acetyl-CoA into ketone bodies (acetoacetate)
What types of cells use ketone bodies?
Most tissues, they convert them back for the TCA cycle but not the brain, liver or red blood cells
Why does the body store fat?
Because it can only store so much carbohydrates in the form of glycerol however ft can be converted into TAG (triacylglycerol)
What do lipoproteins contain?
Varying levels of TAG, cholesterol and its esters, phospholipids and apoproteins/apolipoproteins
What does a chylomicron do?
Largest and lowest density lipoprotein
Transports dietary TAG to the periphery targeting signals like Apo-E
Formed in the intestine
Made of apoB-48
What does VLDL do?
Transport endogenously synthesised fat to periphery
Made of apoB-100
Formed in the liver
What does LDL do?
Main carrier of cholesterol from circulation to tissues including liver
It’s destination targeting signal is apo B-100
Converted from VLDL
What does HDL do?
Transports cholesterol from periphery to liver
Formed in liver
What is familial hypercholesterolaemia?
A genetic disease where people have defective LDL receptors leading to very high levels of LDL cholesterol and early vascular disease
Why is LDL known as bad cholesterol?
High conc. increases the risk of artherosclerosis and coronary heart disease which leads to development of plaques in blood vessels
How do cholesterol plaques develop?
LDL can be oxidised and no longer recognised by B-100 receptors
This is taken by by scavenger receptors in macrophages in arterial walls - leading to blood blocking plaques
What is the structure of a lipoprotein?
Inner core - triglycerides and cholesterol esters
Outer cell - single layer of phospholipids, cholesterol and apoproteins
How is cholesterol synthesised?
Acetyl-CoA + acetoacetyl CoA → HMG-CoA → (HMG-CoA reductase - statins inhibit this enzyme) → mevalonate → cholesterol
