Lipids

• Lipids are insoluble in water but soluble in organic solvents such as ethanol. They can exist as fats, oils and waxes.
• They supply twice as much energy as carbohydrates. They also provide body insulation.
• Triglycerides are made up of 3 fatty acid chains attached to a glycerol molecule. The chains attach to the glycerol through a condensation reaction forming an ester bond.
• As there are 3 fatty acids in a triglyceride 3 water molecules are formed. In each triglyceride 3 ester bonds are formed.
• Lipids are made up of carbon, oxygen and hydrogen atoms.
• Saturated fatty acids contain no double bonds between their carbon atoms. This makes them straight and rigid which allows them to pack closely together. This gives them high melting points.
• Unsaturated fatty acids have double bonds meaning they can't line up next to each other and have weak intermolecular bonds and therefore low melting points. The more double bonds the more kinks in the structure.
• Lipids functions are in membranes (phospholipids), energy storage, signaling (glycerophospholipid), fat soluble vitamins and steroid hormones.
• Phospholipids have a hydrophilic head and a hydrophobic tail. This means the heads face outwards towards water, whereas the tails point inwards away from water creating a bilayer.
• Lipids store energy as triglycerides with three fatty acid chains bonded to a glycerol.
• Glycerophospholipids are present mostly in the cell membranes. They serve as an anchor for proteins in cell layers and flag cells.
• Fat soluble vitamins (A, D, E, K) are stored in the body for long periods of time. They pose a greater risk for toxicity when consumed in excess.
• Cholestrol's insoluble so needs to be attached to a protein to be moved around the body, so the body forms lipoproteins.
• High density lipoproteins (HDL) are good and mainly proteins. Transport cholesterol to the liver where it's recycled/excreted reducing total blood cholestrol.
• Low density lipoproteins are bad and mainly lipids. They transport cholesterol from the liver to the blood where it's circulated. They increase the total blood cholesterol.