lipids

like carbohydrates

contain C, H, O but in proportion to the C and H they contain much less O

recognise examples of triglycerides and phospholipids

Draw the structural formula for glycerol

General formula for an unsaturated fatty acid

Cn H (2n-2) O2 for one double bond

If there are more than one double bond each extra one removes two more hydrogens

General formula for saturated fatty acids

Cn H2n O2

sollubility

non polar compounds and so are insoluble in water but dissolve in organic solvents such as propanone and alcohols

how are triglycerides formed

by the combination of one glycerol molecule (always the same in a lipid) and three molecules of fatty acids (FA component varies)

how

the FA join to glycerol by condensation reactions: three molecules of water are removed, ester bonds are formed between glycerol and fatty acids

ester bond

an oxygen atom joining two atoms one of which is a carbon atom attached by a double bond to another oxygen atom

phospholipids

each molecule has one end that is soluble in water

explain

one end of the molecule has a lot of oxygen atoms in the glycerol group the phosphate and the choline and this end of the molecule is hydrophilic- polar head of the molecule able to interact with water molecules

whereas

the FA tails dont have any O atoms and dont interact with water so they are hydrophobic- non polar and unable to interact with water molecules

waxes

lipids that melt above 45 degrees

role

they have a waterproofing role in terrestrial organisms in both animals such as the insect exoskeleton and plants in the leaf’s cuticle reducing water loss

phospholipids roles

biological membranes

electrical insulation- myelin sheath that surrounds the axons of nerve cells

triglycerides role 1

thermal insulation- lipids insulate against heat loss when stored under the skin in the cold or heat gain when it is very hot

triglycerides role 2

protection- fat is stored around delicate internal organs such as kidneys protecting against physical damage

triglycerides role 3

metabolic water- produce a lot of it when oxidised

what is metabolic water

water released during chemical reactions in the body

triglycerides role 4

energy reserves in plants and animals because they contain more C-H bonds than carbohydrates

how do you test a sample for lipids

mix the sample with absolute ethanol which dissolves any lipids present and shake it with an equal volume of water

the results

the dissolved lipids come out of the solution because they are insoluble in water forming an emulsion making the sample cloudy white

where does the difference in properties of fats and oils come from

variations in fatty acids

type 1

if the HC chain has only single C-C bonds then the FA is saturated because all the C atoms are linked to the maximum possible number of H atoms

description of saturated FA

the FA chain is a straight zig zag and the molecules can align readily so fats are solid adn they remain solid at body temp

uses

useful for storage in mammals- animal lipids often contain saturated FA’s

type 2

if any C-C bond is not a single bond the molecule is unsaturated. If one C-C double bond is present the lipids are mono unsaturated whereas if there are many C-C double bonds they are polyunsaturated

description of unsaturated lipids

the molecules cannot align uniformly and the lipid doesn’t solidify readily, remain liquid at room temp

uses

oils as they RLART

plant lipids often US and occur as oils such as olive oil and sunflower oil

Need to know how roles of PL and lipids in orgs and cell relate to thier hydrophilic and hydrophobic properties

main causes of heart disease

fatty deposits in the coronary arteries - atherosclerosis AND high BP- hypertension

contributory factors

a diet high in saturated fats

smoking

lack of exercise

aging

lipids role

when food is absorbed at the small intestine lipids and proteins combine to make lipoproteins which travel around the body in the blood stream

diet impact 1

if high in S fats—> LDL low density lipoproteins build up and cause harm, increasing incidence of atheromas in coronary arteries and in other arteries

the harm caused

fatty material- atheroma- gets deposited in the coronary arteries restricting blood flow therefore O2 delivery to the heart which can result in angina

a myocaridal infraction or heart attack occurs if the vessel completely blocked

diet impact 2

if it has a high proportion of US fats the body makes more HDL high density lipoprotein which carries harmful fats away to the liver for disposal

therefore

the higher the ratio of HDL: LDL in a person’s blood the lower the risk of cardio vascular ad coronary heart disease