Lipids Flashcards
(42 cards)
Are lipids structurally diverse? are they soluble? what do they contain (element-wise)? Are they more or less reduced than carbohydrates? what does this do to energy released and O2 need?
Lipids are structurally diverse, insoluble in water (hydrophobic), mostly only contain C, H, O, more reduced than carbohydrates = more energy released when oxidised, complete oxidation requires more O2
What are the 3 classes of lipids?
Fatty acid derivatives, Hydroxy-methyl-glutaric acid derivatives, Vitamins
What are the 4 derivatives of fatty acids and what are their roles?
Fatty Acids – Fuel molecules
Triacylglycerols – Fuel storage and insulation
Phospholipids – Components of membranes and plasma lipoproteins
Eicosanoids – Local mediators
What are the 4 derivatives of hydroxy-methyl-glutamic acid and what are their roles?
Ketone bodies (C4) – Water soluble fuel molecules
Cholesterol (C27) – Membranes and steroid hormone synthesis
Cholesterol esters – Cholesterol storage
Bile acids and salts (C24) – Lipid Digestion
What are there 4 fat-soluble vitamins?
A, D, E and K
What is the general structure of a triaglycerols (TAG)?
nb. triaglycerols = triglycerides
Glycerol backbone, 3 fatty acid side chains. connected by ester bonds
What is chemical formula for glycerol and general formula for fatty acids?
glycerol = C3H8O3
Fatty acid = CH3(CH2)nCOOH
What is process for forming/breaking down triaglycerol?
forming = esterification, breaking down = lipolysis
Where are triaglycerols stored and in what form? what is their role? how are they controlled?
Stored in adipose tissue, in anhydrous form, used in prolonged exercise, starvation and pregnancy. storage/utilisation is under hormonal control
How and where are triaglycerols broken down. what else is needed (apart from the enzymes)?
pancreatic lipase in the small intestine to release glycerol and fatty acids. This is a complex process requiring bile salts and a protein factor called colipase
What happens in the small intestine to the glycerol and fatty acids?
recombined and transported as TAG by lipoproteins (chylomicrons)
Where do the lipoproteins carry the TAG to and what happens to the TAG?
Consumer tissues - fatty acid oxidation -> energy
Adipose tissue - stored as TAG
How does TAG in the adipose tissue get used by consumer tissues?
There is hormone-sensitive lipase which becomes more active in the presence of adrenaline/glucagon (less active in presence of insulin). Fatty acids transported by albumin, where it is oxidised to give energy
What is the general formula for Fatty acids?
CH3(CH2)nCOOH where n = 14 - 18
What is the difference between a saturated and a non-saturated fatty acid?
unsaturated has 1 or more double bonds C=C, saturated has none
what is an amphipathic fatty acid?
contains hydrophilic and hydrophobic groups
why are certain polyunsaturated fatty acids essential?
mammals can’t introduce a double bond beyond C9
Where does fatty acid catabolism take place?
in mitochondria
What happens in FA catabolism (in brief)
FA is activated by linking to coenzyme A outside mitochondrion, then transported across inner mitochondrial membrane using a carnitine shuttle, then cycles through sequence of oxidative reactions, with C2 removed every cycle
How is FA activated? give equation
links to coenzyme A by action of fatty acyl coA synthase CH3(CH2)nCOOH + ATP + CoA -> CH3(CH2)nCO-CoA + AMP + 2Pi
Can activated fatty acids cross mitochondrial membrane?
no
How does carnitine shuttle work?
Acyl-CoA binds to carnitine with Carnitine acyltransferase (CAT I), forming Acyl carnitine and CoA (so CoA is reused)
Acyl Carnitine crosses inner mitochondrial membrane via the carnitine shuttle transporter ( carnitine-acylcarnitine translocase)
Acylcarnitine + CoA is converted to acyl-CoA by carnitine acyltransferase II (CAT II) and carnitine is released into cytosol and passes back into inter membrane space to bind with another Acyl-CoA
Is the carnitine shuttle regulated?
yes - so controls rate of FA oxidation
What is the carnitine shuttle inhibited by?
malonyl-coA
