Lipids

Question 1

properties of lipids

Answer 1

insoluble in water and highly soluble in organic solvent

Question 2

are lipids macromolecules?

Answer 2

no. they are unable to form covalent bonds with one another to form larger molecules

Question 3

how to classify lipids?

Answer 3

simple lipids - fatty acids and alcohol (usually glycerol)
compound lipids - fatty acids, alcohol and other groups
lipid derivatives

Question 4

simple lipid definition

Answer 4

alcohol (usually glycerol) linked to one or more fatty acids via ester linkage

Question 5

structure of glycerol

Answer 5

C3H8O3
3 carbon alcohol, each carbon atom bearing an hydroxyl group
soluble in water due to hydroxyl group

Question 6

structure of fatty acids

Answer 6

fatty acids are carboxylic acids, wth carboxyl functional group (COOH) at one end and attached hydrocarbon chain
long carbon skeletons
non-polar C-H bonds

Question 7

why are lipids insol in water

Answer 7

abundance of non-polar C-H bonds makes lipids hydrophobic

Question 8

how can fatty acids defer + explain saturated vs unsaturated fatty acids

Answer 8

1. length of hydrocarbon chain
2. number and locations of double bonds along their carbon skeletons
   - saturated fatty acid -> no double bonds (every carbon maximally bonded to hydrogen atoms)
   - unsaturated fatty acid -> one or more double C=C bonds, kink in its tail

Question 9

explain formation of a glyceride

Answer 9

forms when glycerol linked to one or more fatty acids, resuling in formation of an ester linkage
condensation reaction - formation of ester linkage between a hydroxyl group of glycerol and the carboxyl group of fatty acid, one molecule of water lost

Question 10

types of glyceride

Answer 10

one fatty acid + glycerol - monoglyceride
2 fatty acid + glycerol - diglyceride
3 fatty acid + glycerol - triglyceride (commonly known as fats)

Question 11

properties of a triglyceride + explain

Answer 11

1. melting point of fats increases with hydrocarbon chain length
   - longer the hydrocarbon chains -> more extensive the hydrophobic interactions between the chains -> more thermal energy required to break bonds -> higher melting points
2. melting point of fats decreases as degree of unsaturation of fatty acids tails increases
   - kinks where the double bonds are located prevent the molecules from packing closely -> hydrophobic interactions
   are less extensive -> less thermal energy required to break enough of these interactions to liquefy triglycerides

Question 12

what are hydrophobic interactions

Answer 12

weak bond that exists between hydrophobic molecules,
force of attraction between non-polar molecules.

Question 13

eg of saturated and unsaturated fat

Answer 13

saturated fat -> animal fats, butter, solid at room temp
unsaturated fat -> fat of plant and fish, cooking oil, liquid at room temp

Question 14

structures and functions of triglyceride in animals (5)

Answer 14

1. Structure: lower molecular weight than water per unit volume
   function: less dense than water, fats aid buoyancy of aquatic animals
2. structure: Hydrocarbon tails are non-polar, thus Weak hydrophobic interaction occur between
   triglyceride molecules.
   Function: triglyceride can slide under pressure, adipose tissue around vital organs cushion and protect them against physical impacts
3. structure: C-H bonds are non-polar, triglycerides are hydrophobic. No associated water molecules stored along with triglycerides, and thus triglycerides have no extra weight due to the water of hydration.

function:
- triglycerides do not affect water potential of cells
- absence of water of hydration in triglycerides allows animal’s body mass to be kept to a minimum to facilitate locomotion
- Triglycerides are a good thermal insulator and hence a layer of fat beneath the skin insulates body. (blubber in marine animals)

4. Structure: Triglycerides are highly reduced molecules.
   (two-fold more hydrogen atoms per unit mass than carbohydrates.)
   Function: Triglycerides release more water when they are oxidised during cellular respiration compared to carbohydrates.
   (This water, known as metabolic water, is
   extremely important to desert animals like camels)
5. Structure: triglyceride have higher proportion of C and H atoms compared to O atoms, greater number of carbon atoms per unit mass than carbohydrates
   Function: upon oxidation, triglycerides release larger amount of energy, more efficient energy stores

Question 15

compound lipid

Answer 15

ester of fatty acid and an alcohol phus other chemical groups (eg phosphate and sugar)
e.g. phospholipid, glycolipid

Question 16

phospholipid structure

Answer 16

one glycerol, 2 fatty acids, third OH group of glycerol is joined to negatively charged phosphate group, additional small molecules, usually charged or polar can
be linked to the phosphate group
(REF TO NOTES IMAGE)

Question 17

formation of phospholipid

Answer 17

The two fatty acids are linked to the glycerol by an ester linkage while the phosphate group is linked to the third OH group of the glycerol by a phosphoester linkage

Question 18

properties of phospholipids

Answer 18

1. amphipathic
   - The two fatty acids that comprise the hydrocarbon tails are non-polar and hence hydrophobic
   - phosphate group and its attachments form a polar / charged hydrophilic head that has an affinity for water
2. Three types of lipid aggregates can form when amphipathic phospholipids are situated in
   aqueous environments, aggregates shield the hydrophobic tails from water/ aqueous environment.
   - micelle -> phospholipid monolayer
   - bilayer -> two-dimensional sheet, hydrophilic heads are exposed to the polar exterior and hydrophobic tails are in contact with those of neighbouring molecules, excluded from water in the non-polar interior of the bilayer
   - liposome / vesicle -> formed when lipid bilayer folds back on itself to form a hollow sphere. bilayer sheets avoid exposing their hydrophobic edge regions, achieving maximal stability in their aqueous environment. These bilayer vesicles enclose aqueous solutions, creating a separate aqueous compartment

Question 19

Structure and function of phospholipid

Answer 19

1.structure: Phospholipids are amphipathic molecules, each with 2 non-polar, hydrophobic fatty acids ‘tails’ and a charged, hydrophilic phosphate ‘head’.

Function:
- form a selectively permeable cell membrane, hydrophilic heads are exposed to aqueous medium, hydrophobic tails are in contact with those of neighbouring molecules but excluded from aqueous medium in the non-polar interior of the bilayer -> effective barrier / boundary between cell and its external environment
- Phospholipids form liposome / vesicle when a lipid bilayer folds back on itself to form a hollow sphere.
- Liposomes are used as vesicles for storage and transport of cellular products and digestion of waste (lysosomes).
Liposomes also serve as **vesicles for drug delivery **in humans
- Phospholipids form micelles to transport fats between the gut and body tissues.
- The hydrophilic heads of phospholipids are in contact with the aqueous environment, and the hydrocarbon tails are restricted to the water-free interior of the micelle

2. Structure: Hydrophobic interactions exist between fatty acids tails.
   Function: The integrity of the membrane bilayer / liposomes / vesicles / micelles is maintained due to large number of interactions. Individual hydrophobic interactions are weak, permitting lateral movement of phospholipids -> membrane fluidity

3 Structure: Most phospholipids contain choline.
Function: represent a large proportion of the body’s store of choline. Choline is important for the synthesis of acetylcholine, a neurotransmitter.

Question 20

glycolipids structure

Answer 20

composed of glycerol, 2 hydrophobic hydrocarbon tails, and.a polar, short carbohydrate chain with no phosphate

Question 21

formation of glycolipid

Answer 21

short carbohydrate chain joined to glycerol’s OH group by glycosidic bond, which is a covalent bond

hydrocarbon tails joined to glycerol’s OH group by ester bond during condensation reaction

Question 22

structure and function of glycolipid

Answer 22

1. structure: carbohydrate chain attached to glycerol
   Function: Found at the cell surface membrane facing the exterior environment. It serves as a marker that distinguishes one cell from another in cell-cell recognition as cells recognise other cells by binding to these carbohydrate chains.
   It is also involved in cell-cell adhesion as a result of this binding in tissue formation
2. structure and property: hydrophobic interactions exist between fatty acid tails
   function: hydrophobic interactions anchor entire glycolipids at cell surface membrane

Question 23

structure of cholesterol

Answer 23

cholesterol is a lipid derivative

cholesterol possesses a carbon skeleton made up of three fused six-membered and one five-membered ring

Question 24

function of cholesterol

Answer 24

regulates membrane fluidity, precursor for synthesis of bile acids, steroid hormones such as estrogen and testosterone and vitamin D

Question 25

emulsion test

Answer 25

principle: lipids soluble in organic solvents such as alcohol but not in water, which which they form emulsions on vigorous shaking method: add 2cm3 of absolute ethanol and mix well. decant ethanol into another test tube containing equal volume of water observation: lipid is present, it dissolves in ethanol to form a clear solution, which then forms an emulsion with water. If lipid is absent, a clear solution is still formed with ethanol, which remains clear when added to water.