Lipids Flashcards
Fatty Acids
May be saturated (high mp/bad) or unsaturated (low mp/good). Linoleic and linolenic are essential. Hydrogenation of vegetable oils creates trans-fatty acids. All of which are found in the diet.
Triacylglycerol
Uncharged molecules, insoluble in water. Structure; 3 Esters of fatty acids with a glycerol backbone. It is the main form of stored fat which provides fuel and insulation.
Phospholipids
Structure; glycerol with 2 fatty acids. Amphipathic molecules found in cell membranes.
Glycolipids
Lipid plus a carb attached. Used for cell recognition e.g. blood group antigen.
Steroids
Ring structure. Act as chemical messengers e.g. steroid hormones, membrane components like cholesterol.
Lipid digestion
It occurs predominantly in the small intestine but can start in the stomach. Fats mix with bile salts during peristalsis and emulsification to make emulsified fats. These are cleaved by lipases producing monoacylglycerol and 2 fatty acids.
Lipid absorption
The fatty acids and monoglycerol mix with bile salts during emulsion to form mixed micelles. These undergo diffusion through the brush border membrane and release FA and glycerol. The FAs link to creat Triacylglycerol. TAG is converted by the apoB-48 protein to chylomicrons which enter lymph and then the blood. When chylomicrons reach tissue the TAG is released and the chylomicron remnants go to the liver. TAG is broken down by lipoprotein lipase to form free FA (for energy or re-esterified to TAG for storage) and glycerol (used by liver to make glycerol-3-phosphate for glycolysis/gluconeogenesis).
Describe how lipids are transported in the body.
Free FAs are transported through the blood in complex with serum albumin. Most FAs are esterified and are carried in lipoproteins. Lipoproteins are biomolecules which contain lipids bound to proteins allowing fats to move in and out of cells since TAGs and cholesterol esters are insoluble in water. Chylomicrons are rich in TAGs and transport it from the intestine to tissues.
VLDL is TAG rich, liver to tissues.
LDL is cholesterol rich, liver to tissues.
HDL is cholsterol rich, tissue to liver for elimination.
Essential fatty acid
An unsaturated FA that is essential to human health, but cannot be manufactured by the body. Linoleic acid is broken down to linoleic acid and arachidonic acid. Humans can’t produce double bonds beyond C9.
De novo synthesis
The synthesis of free fatty acids in the cytosol of the liver, mammory glands and adipose tissue. There are 2 enzymes; ACC (acetyl CoA carboxylase) (rate limiting) which converts acetyl CoA to malonyl CoA. And fatty acid synthase which is a multicomplex enzyme that has an acyl carrier protein (ACP) arm which holds onto the FA while it is synthesised. It produces a 16C fatty acid. Malonyl CoA is needed to form a high energy C-C bond to form the growing FA.
Differences between synthesis and degradation
Synthesis occurs in the cytosol and requires ACC and FA synthase. The cofactor is ACP and it requires Malonyl CoA and NADPH.
Degradation occurs in the matrix using multiple enzymes. The cofactor is CoA and it requires acetyl CoA, NAD+ and FAD.
B-oxidation
The catabolism of FAs which are degraded 2 Cs at a time. It produces acetyl CoA, NADH and FADH2. It occurs in the mitochodrial matrix.
Sttucture and function of cholesterol
Cholesterol is the starting material for the synthesis of steroid hormones. It is a steroid so contains a ring system structure and is made in the liver. It is found in cell membranes, it’s a precursor to sterol hormones, Vit D and bile acids. It can modify proteins.
Ketone bodies
Ketones are produced in the liver then sent out to other tissues where acetoacetate and B-hydroxybutyrate can be reconverted to acetyl-CoA for use in the CAC. This occurs when glucose is in short supply. They are water soluble. The liver can’t use them.
