Lipids Flashcards
Name 4 functions of lipids
Stored form of energy Structural element of membranes Enzyme co factors Hormones Vitamins A, D, E, K Signalling molecules
What are TAGs?
Triacylglycerols
Esters of FAs and glycerol
Give some properties of TAGs
Uncharged
Water insoluble
Fuel and insulation
Main dietary lipid
Describe Beta - oxidation
3 stages
Activation - fatty acid activated to form fatty acyl CoA in cytoplasm
Transport by Carnitine Shuttle - fatty acyl CoA is transported from cytoplasm to mitochondria by losing its CoA and binding to a carnitine shuttle (CAT-1)
Degradation - dehydrogenation Hydration Dehydrogenation Thiolysis
What is the main site of the digestion of lipids?
Small intestine.
What are the worst fatty acids?
Trans fatty acids - made from the hydrogenation of vegetable oils e.g margarine. Man made.
What are bile salts?
Act as biological detergents to form emulsions and mixed micelles. Aids digestion of lipids. Derived from cholesterol.
What are TAGs digested into?
Digested by pancreatic lipase in small intestine to form monoacylglycerol + 2 fatty acids.
What are cholesterol esters digested to?
Cholesterol and free fatty acid.
What are phospholipids digested to?
Lysophospholipid and fatty acid.
What happens to the digested lipids?
Form mixed micelles with bile salts. Mixed micelles approach brush border membranes of enterocytes and release lipid products which enter cells by diffusion.
Short and medium chain FA do not require micelles for absorption.
What is Steatorrhea?
Steatorrhea is excess fat in faeces. Stools float due to excess lipid, have an oily appearance and are foul smelling.
What happens to the absorbed fatty acids?
Re-synthesised by packaging them up with apoB-48 ( a soluble protein into Chylomicrons for export. These chylomicrons are then released by exocytosis into lymph, then blood.
What is the function of lipoprotein lipase?
Hydrolyses TAGs in chylomicrons into FA and glycerol.
Primarily found in capillaries of skeletal muscle and adipose tissue.
What can free FA be used for after it has been reabsorbed?
Used as energy or resynthesised an stored as TAG.
What is glycerol used for?
Glycerol is used by the liver to produce glycerol-3-phosphate.
How are FAs released from stored TAG as energy?
Hormone sensitive lipase.
It is activated by phosphorylation in response to epinephrine.
How are free FAs transported through the blood?
In complex with serum albumin.
What are lipoproteins?
Any of a group of soluble proteins that combine with and transport fat or other lipids in the blood plasma.
E.g chylomicrons, LDL, HDL
What does Beta-oxidation produce?
Acetyl CoA and NADH and FADH2 (which are sources of energy) by degrading FAs 2 carbons at a time.
Where does beta-oxidation occur?
Mitochondrial matrix
How is excess Acetyl coA used?
Used to produce ketone bodies which are an energy source during fasting and starvation.
Where are ketone bodies formed?
Liver mitochondrial matrix.
Liver cannot use ketone bodies itself.
Where does fatty acid synthesis occur?
Liver
Lactating mammary gland
Adipose
What metabolic and hormonal signals control the activity of acetyl-CoA carboxylase?
Activated by citrate (signals that there is enough glucose - so make FA)
Deactivated by palmitoyl CoA (enough fatty acid made so halt synthesis).
Insulin activates, glucagon, epinephrine deactivates.
What are some specialised classes of lipid?
Steroid - chemical substances that serve as chemical messengers throughout the body. Cholesterol is the starting point. Precursor to other substances.
Eicosanoids - derived from 20 carbon unsaturated fatty acids. They are synthesised throughout the body.
Name some fates of cholesterol?
Plasma Lipoproteins Bile salts Steroid hormones Membranes Vitamin D
What is the role of statins?
Inhibit HMG-CoA reductase that is essential in cholesterol synthesis
Lower LDL levels
Improve risk of developing cardiovascular disease
What is the role of Eicosanoids?
Signaling molecules derived from omega-3 or omega-6 fatty acids.
Precursors to prostaglandins, thromboxanes, and leukotrienes.
Exert control over inflammation or immunity, and as messengers in the central nervous system.
Short half life.
Give some examples of what eicosanoids regulate?
Inflammatory response (joints, skin, eyes)
Pain & fever (Prostaglandins)
Blood pressure regulation (prostacyclin)
Blood clotting induction (thromboxanes)
Many reproductive functions (e.g. labour induction) & menstrual cramps (prostaglandins)
Sleep/wake cycle
