natural products

Question 1

what are lipids?

Answer 1

lipids is aterm applied to water insoluble natura products isolated from plant and animal cells.

Question 2

what are the two classes they are divided into?

Answer 2

polyketides and polyisoprenes.

Question 3

what are polyketides?

Answer 3

they are 2 carbon units, and are the basis for fats, oils, waxes, prostaglandins, and membrane lipids.

Question 4

what are polyisoprenes?

Answer 4

they are 5 carbon units, and are the basis for fragrant plant perfumes, flavourings and steroid hormones.

Question 5

how are fats and oils made?

Answer 5

a reaction between a glycerol molecule and three fatty acid molecules.

Question 6

how are fatty acid reactions reversed?

Answer 6

hydrolysing the triglyceride with an acid or alkali.

Question 7

what are the effect of double bonds on fats and oils?

Answer 7

trans and cis double bonds cause the chain to become unsaturated.

Question 8

which type of double bond is more disruptive? and why?

Answer 8

cis double bonds are more disruptive as they prevent the chains from packing neatly alongside each other. If the double bonds were trans, far less disruption would be caused.

Question 9

whay are saturated fats typically derived from?

Answer 9

stearic and palmitic acid.

Question 10

what are some features of saturated fats?

Answer 10

long term energy storage (2-3 months).
thermal insulation as subcutaneous fat.
mechanical insulation to protect muscle tissue injury.
echo-location in whales (fat deposits in jaw and head help emit and receive sound).

Question 11

what are some features of unsaturated fats?

Answer 11

contain cis double bonds
healthier as they are easily oxidised
examples- olive oil contains only 10% saturation and corn oil contains 15% saturation
margarine made from vegetable oils; bonds reduced with a hydrogen or platinum catalyst.

Question 12

what is saponification?

Answer 12

if fats are hydrolysed in alkali, then salts of the fatty acids are obtained which can be used as “soaps”.

Question 13

how long ago is saponification thought to have occurred?

Answer 13

600 BC

Question 14

what salts form the basis for domestic soaps?

Answer 14

sodium salts of lauric and myristic acid

Question 15

what is a problem with soaps?

Answer 15

if calcium and magnesium are present in the water, these ions exchange with sodium and potassium and the resulting soaps are insoluble forming scum.

Question 16

why can scum not form a stable micelle?

Answer 16

the calcium stearate has a much greater hydrophobic character, so cannot form a stable micelle.

Question 17

what are detergents?

Answer 17

detergents are similar synthetic molecules that do not form such insoluble salts.

Question 18

what are waxes?

Answer 18

these can be isolated from plant and animal material and are simple monoesters of long chain fatty acids and alcohols. Their natural function is often to act as a waterproof coating for plants and insects (waxes are insoluble in water).

Question 19

why can waxes not become crystalline?

Answer 19

all waxes are mixtures of different chain lengths.

Question 20

what are membrane lipids?

Answer 20

these are very similar to triglycerides, but one of the fatty acid groups is replaced by a different group, usually one that contains phosphoric acid.

Question 21

which is the most common membrane lipid?

Answer 21

the most common type is called “lecithin” or phosphatidylcholine (PC). It occurs in most animal tissues and in egg yolk, wheat germ and soya beans. Typically, R1 is stearic acid (saturated) and R2 is oleic acid (unsaturated). Cephalins, or phosphatidylethanolamines (PE), are very similar.

Question 22

what is the role of membrane lipids?

Answer 22

their major biological role is in the formation of membrane bilayers.

Question 23

membrane structure

Answer 23

membranes are selectively permeable cell barriers with several vital functions.

they compartmentalise various materials and metabolic processes

they support, and provide a suitable environment for the action of, many enzymes, receptors and antigens, each of which can interact with material in the aqueous phase at one or both surfaces

they provide sites of attachment for cytoskeletal elements concerned with cell movement and secretion.

Question 24

what are the classes of lipids?

Answer 24

Glycosphingolipids
Sterols
Phosphosphingolipids
Glyceroglycolipids

Question 25

membrane variety

Answer 25

any biological membrane contains a mixture of the above lipid classes.

there is a wide variation within each class (e.g. in the length, branching and saturation of the fatty acid side chain).

the eventual potential for bio-membrane variation is huge.

some examples contain over 100 chemically distinguishable lipids.

Question 26

what is present in membranes at physiological temperatures?

Answer 26

there is sufficient hydrocarbon chain distortion (as caused by cis double bonds, methyl branches, cyclopropane rings, etc.) for the hydrophobic phase to be fluid rather than gelled.

however, the presence of a lot of cholesterol can restrict the fluidity.

Question 27

what is the consequence of lipid and protein variety?

Answer 27

the consequence of lipid (and protein) variety is that there are many different types of bio-membrane and it is important not to generalise their properties too widely.

Question 28

what impacts membrane dynamics?

Answer 28

their rotational motion

lateral diffusion properties,
flip-flopping from one side of the bilayer to the other

and how they behave as a result of proximity/binding to other lipids and proteins

Question 29

boundary lipids

Answer 29

those that surround membrane-penetrating proteins.
e.g. cytochrome oxidase was found to have a single layer of immobilised lipid surrounding it. in some instances, effects can extend a long way from the protein into the bilayer.

Question 30

lipid phase transitions and separations

Answer 30

when a membrane is cooled, or its composition is changed in a certain way (e.g. increase in lipid chain length and saturation), it passes through a fluid to gel phase change.

this can affect the distribution of proteins in the membrane, making them clump together.

these phenomena may be vital to cell permeability, fusion, aggregation and binding.

Question 31

response of membrane dynamics to presence of added factors

Answer 31

some toxins damage the phospholipids so that they cannot pack together properly and the bilayer is disrupted.

Question 32

Prostaglandins

Answer 32

molecules related to fatty acids that have hormone-like actions in animal tissue.

they have influence over blood clotting, blood pressure, fever, pain, inflammation, the sleep-wake cycle and induction of childbirth.

many of their functions are still unknown.

most are derived from prostanoic acid

Question 33

cyclised polyketides

Answer 33

structurally diverse class of polyketide derivatives that provides numerous clinically effective drugs.

include antibiotics (erythromycin A, rifamycin S), immunosuppressants (rapamycin, FK506), antifungals (amphotericin B), anti-parasitics (avermectin), insecticidals (spinosyn A) and anti-cancers (doxorubicin).

Question 34

production of cyclised polyketides

Answer 34

the polyketide chains are cyclised to produce macrocyclic rings

structural complexity is increased by the frequent presence of multiple chiral centres and by the addition of sugars, methyl and hydroxyl groups