Lipids Flashcards
Biological functions of lipids
Stored form of energy, steroid hormones, signalling molecules, structural element of membranes
Lipid classes
Fatty acids, triacylglycerol, phospholipids, glycolipid, steroids
Unsaturated fatty acids
One or more double bonds that kink hydrocarbon chain
Saturated fatty acids
Solid, no double bonds
Naming fatty acids
Number of carbons, place of double bond, number of double bonds present
Good fats
High in polyunsaturated fats eg olive oil sunflower oil
Bad fats
High in saturated fats eg beef
Really bad fats
Trans fatty acids (result from hydrogenation of vegetable oil) eg hard margarine
Humans cannot ingest double bonds beyond carbon
9
Omega 3 fatty acids
Derived from linolenic acids as essential fatty acids. Lower cholesterol levels, prevents obesity, reduces inflammation. Found in fish
Omega 6 FA
found in linoleic. Does not have benefits
Essential fatty acid deficiency
Depression, ADHD, scaly dermatitis etc
Triacylglycerols
Esters (neutral uncharged lipids) of fatty acids and glycerol. Major lipid component of adipose tissue. Dietary fuel and insulation
Phospholipids
2 fatty acids and phosphate group, amphipathic, in membrane, help with digestion as they are emulsifiers
What affects the melting points of fatty acids
Number of carbons and degree of unsaturation
Are lipids water soluble
No
What is the main dietary lipid
Triacylglycerol
How are lipids digested
In small intestine. Use of pancreatic enzymes. Promoted by emulsification (dispersion) by bile salts and peristalsis
Bile salts
Biological detergents that form emulsions and mixed micelles, saves lipids coalescing in an aqueous environment. Derivatives of cholesterol
How are triacylglycerols digested
Degraded by lipases to monoacylglycerol and fatty acids
Cholesterol esters are broken down into
Cholesterol and free fatty acid by pancreatic cholesterol esterase
What do products if lipid digestion form and where do they go
Form mixed micelles with bile salts and then approach brush border membranes of enterocytes and release lipid products that enter by diffusion . Only long chain FA need micelles
Gall bladder secretes
Bile
Chylomicrons
Intestinal cells that are packaged with apoB-48 which is a solubilising protein. They are then exported from small intestine by exocytosis into lymph then blood
What happens once chylomicrons reach tissue
- free FA used for energy or reesterified for storage
- if depleted of triacylglycerols they go to liver (chylomicrons remnants)
- lipoprotein lipase found in capillaries of muscle, adipose and skeletal tissue hydrolyse the TAG to fatty acids and glycerol
How are fatty acids release from storage in adipose tissue
By hormone sensitive lipase when it is activated phosphorylation in response to high epinephrine levels
What stops fatty acids from being released from TAG in adipose tissue
When plasma glucose and insulin levels are high and they promote dephosphorylation of lipase
Fatty acids are transported in blood by
Serum albumin ( plasma protein with 2-7 binding sites for FA)
If fatty acids are esterified how are they carried in blood
Lipoproteins
Beta oxidation pathway
Degrades fatty acids two carbons at a time and occurs in mitochrondrial matrix. Produces acetyl CoA and NADH and FADH2
Stages of beta oxidation
Activation of fatty acids in cytosol,
transport into mitochondria by carnitine shuttle,
degradation to two carbon fragments in the mitochondrial matrix- energy!
Carnitine shuttle
Major site of regulation, prevents synthesis and degradation from happening at same time, get it from diet or made from lysine or methionine
4 main steps of metabolism part of B oxidation
Dehydration to produce FADH2
Hydration
Dehydration to produce NADH
Thiolysis (cleaved) to produce acetyl CoA
When fasting/starving/diabetes what happens to acetyl CoA
Not enough oxaloacetate to be used in the citric acid cycle so the acetyl CoA is converted into ketone bodies
Where does ketogenesis occur and why
In liver and because it depends on the activity of rate limiting enzyme HMG CoA synthase which is found in liver (liver cannot use the ketone bodies but it makes them)
Are ketone bodies soluble in blood
Yes. Do not need albumin or lipoprotein
What uses ketone bodies for energy
Cardiac and skeletal muscles, kidney, brain cells
Excessive ketone bodies can cause
Ketonemia, ketonuria, acidemia
Ketone bodies are acidic or alkaline
Acidic
Fatty acid synthesis occurs in cytosol in what tissues/ organs
Liver, adipose tissue, lactating mammary gland
When does citrate shuttle occur
When citrate concentration in mitochondria is high. It allows acetyl CoA to cross membrane from mitochondrion to cytosol
What is the key regulatory enzyme in fatty acid production
Acetyl CoA carboxylase. transfers acetyl coA to TCA
What activates and deactivates Acetyl Coenzyme Carboxylase
citrate activates, palmitoyl CoA deactivates. (Short term) Insulin activates, glucagon and epinephrine deactivates (long term)
What is malonyl CoA
inhibitor of carnitine shuttle. prevents split up of acyl and coA. Substrate that provides the carbon for the formation of palmitate (product of fatty acid synthesis)
