1.14 Triglycerides, saturated and unsaturated fatty acids

Describe and explain the properties of lipids

• macromolecules that contain carbon, hydrogen and oxygen —→ yet contain a much lower proportion of oxygen and more carbon and hydrogen than carbohydrates, hence they can store more energy per gram - hence, lipids are a more compact way of storing energy

• non-polar and hydrophobic —→ insoluble in water so they cannot form hydrogen bonds with water molecules

• broken down into fatty acids and glycerol

State and explain the function of lipids

• cellular structure - phospholipids needed for the flexibility of cell membranes

• energy storage - fat around major organs and fat under the skin

• insulation - stored under the skin for warmth in mammals / around nerve axons e.g myelin sheath

• protection - fat stored around delicate organs which acts as a shock absorber

• hormone production - oestrogen in girls

Describe, draw and label the formation of trigylcerides

• glycerol and fatty acids join together by forming 3 ester bonds (ester bond is between a hydroxyl group (-OH) on a glycerol molecule and a carboxyl group (-COOH) on a fatty acid

• this is through a condensation reaction called esterification

• 3 water molecules are produced when the triglyceride forms

simple equation:

glucerol + 3 fatty acids —→ triglyceride + 3H₂ O

Describe and draw the structure of a saturated fatty acid

• contain no carbon-carbon double bonds

• the hydrocarbon chain is saturated with hydrogen atoms due to the absence of double bonds

• they form unbranched, linear / straight chains

• hence pack closely together

• stronger intermolecular forces—→ have higher melting points = solids at room temperature

e.g butter

Describe and draw the structure of an unsaturated fatty acid

• monounsaturated : have one carbon to carbon double bond

• polyunsaturated : has more than one double carbon to carbon bond

• lower hydrogen to carbon ratio

• the double carbon to carbon bonds form kinks - the chains are not straight and so cannot pack closely together

• has weaker intermolecular forces —→ liquid at room temperature

e.g oils

Compare the structures of saturated fatty acids and unsaturated fatty acids

both have a hydrocarbon chain

• both are formed from one glycerol and three fatty acids

• both have a -COOH group at one end

• in both the glycerol and fatty acids are held together by an ester bond

• saturated has a higher ratio of H:C atoms than unsaturated

• saturated has no double crabon to carbon bonds whereas unsaturated does

• saturated forms straight chains so can pack closely together whereas unsaturated cannot as they form kinks

State and explain the uses of cholestreol in the body

• function of the cell membrane: phospholids maintain the felxibility of the cell membrane

• synthesis of bile

• hormone production - oestrogen in girls

• insoluble in water - yet needs to be transported by the blood as it is needed to make cell membranes, sex hormones, growth hormones and bile salts

What are liloproteins and state the two types of liloproteins

cholestreol is transported around the body as liloproteins despite being insoluble in water —→ these consist of lipids and proteins

• there are high density liloproteins (HDL) and low density liloproteins (LDL)

Describe and explain the function and properties of high density liloproteins

contain cholestreol, proteins and unsaturated fats —→ consist of double carbon to carbon bonds

• they transport cholestreol to the liver to be broken down - this lowers blood cholestreol by removing the fatty plaques thus reduces artheromas (build up of fatty material in artery walls)

Describe and explain the function and properties of low density liloproteins

contain cholestreol, protein and saturated fat —→ do not consist of any carbon to carbon double bond

• LDL moves cholestreol from the liver into the bloodstream increasing blood cholestreol levels when it is too low

• LDLs bind to receptors on cell surface membrane enabling them to be taken up by the cells that need them and removing cholestreol from the blood

• high levels of LDLs can lead to blockage of membrane receptors, causing blood cholestreol to rise

• high levels also result in artheroma (blockage of artery wall)

increased blood cholestreol

this is because the triglyceride is saturated (does not have carbon to carbon double bonds)

thus the liloprotein is an LDL

liloproteins transport cholestreol

whereby LDL binds to receptors on cell surface membrane