Topic 1: Lipids

Question 1

what are lipids?

Answer 1

large biological molecules, does not include true polymers due to inability to form covalent bonds with e/o to form larger molecules

Question 2

why are lipids not macromolecules?

Answer 2

generally not big enough

Question 3

why are lipids large biological molecules that does not include true polymers?

Answer 3

• unable to form covalent bonds with one another to form larger molecules

Question 4

what are some substances that are categorised as lipids?

Answer 4

fats (triglycerides), phospholipids, glycolipids, sterols

Question 5

why are fats (triglycerides), phospholipids, glycolipids and sterols categorised as fats?

Answer 5

• insolubility in water due
  high solubility in non-polar solvents

Question 6

a) function of phospholipids and sterols?
b) function of other lipids

Answer 6

a) major structural elements of biological membranes
b) present in relatively small quantities, play crucial roles as enzyme cofactors, electron carriers, light absorbing pigments, hydrophobic anchors for proteins, emulsifying agents in digestive tract, hormones and intracellular messengers

Question 7

what can lipids be further classified into?

Answer 7

• simple lipids
• compound lipids
• lipid derivatives

Question 8

simple lipids consists of…?

Answer 8

an alcohol (usually glycerol) linked to 1 or more fatty acids via an ester linkage

ie triglyceride

Question 9

what are compound lipids

Answer 9

esters of fatty acid(s) and an alcohol and other chemical group like phosphate or sugar
- phospholipids / glycolipids

Question 10

what is the a) structure and b) properties of glycerol

Answer 10

a)
- has mol formula of C3H8O3
- 3 carbon alcohol, each carbon bears an OH group

b)
- soluble in water due to polar OH- group

Question 11

what is the a) structure of fatty acids and b) properties of fatty acids

Answer 11

a)
- carboxylic acids made up of acidic carboxyl (COOH) func. group at one end and a hydrocarbon chain
- posses long hydrocarbon skeletons (btwn 12-20 carbons)
- each carbon is joined to hydrogen atoms

b)
- hydrophobic due to non-polar C-H bonds

Question 12

how can fatty acids differ?

Answer 12

1. length of hydrocarbon chain
2. number and location of double bonds along the carbon skeleton

Question 13

what is the difference between saturated and unsaturated fatty acids?

Answer 13

• saturated fatty acids have no carbon double bonds
• unsaturated fatty acids have 1 or more C=C bonds and a kink appears wherever the double bond occurs

Question 14

how is glyceride formed?

Answer 14

1. glycerol linked with one or more fatty acids
2. forms an ester linkage between the hydroxyl and carboxyl grou
3. one molecule of water is lost

*one linkage of alcohol to fatty acid = monoglyceride
* two linkage = diglyceride
* three = triglyceride (termed as fats)

Question 16

what affects the properties of triglyceride ?

Answer 16

• chain length and degree of saturation of fatty acids via

Question 17

how does hydrocarbon chain length affect the melting point of fats

Answer 17

• longer the chain length = more extensive hydrophobic interactions between the chains
• hence more thermal energy required to break the bonds

Question 18

what are hydrophobic interactions

Answer 18

• a weak bond between hydrophobic molecules
• a force of attraction between non-polar molecules

Question 19

how does saturation of fatty acids affect the melting point of fats

Answer 19

• less saturated = less closely packed molecules due to the kink where the C=C bonds occurs
• when fatty acid tails are less closely packed, hydrophobic interactions = less extensive
• hence less thermal energy needed to break enough interactions to liquefy the fats (triglyceride)

Question 20

what are the 5 structures of triglycerides and their respective adaptations?

Answer 20

1. higher proportion of C and H atoms compared to O atoms
- greater no. of C atoms compared to that of carbohydrate
- when oxidised, releases larger amounts of energy
- 1g of fat releases more than x2 of energy than 1g of carbohydrate
HENCE: more efficient energy stores than carbo.

2. highly reduced molecules
- contains two fold more H atoms/unit mass than carbo.
HENCE: releases more H2O upon oxidation during cellular respiration than carbo.
- said H2O = metabolic H2O = important for animals like camels

3. C-H bonds are non-polar = triglyceride is hydrophobic
- no associated H2O molecules stored alongside triglyceride
- no extra weight due to absence of H2O of hydration
~ absence of H2O of hydration keeps body mass at a minimum to facilitate locomotion
HENCE: does not affect WP of cells when stored in large amounts
HENCE: also good thermal insulators = help animals living in cold climate

4. Hydrocarbon tails are non-polar
- weak hydrophobic interactions between fat molecules
HENCE: slide under pressure
* Adipose tissues found around vital organs will protect and cushion physical impacts against vital organs

5. Lower molecular weight than water/unit volume
- less dense than water
HENCE: aids in buoyancy = helps aquatic animals

Question 21

function of phospholipids?

Answer 21

• construction of cell membrane
• to enclose all cells and their internal organelles

Question 22

structural component of phospholipids?

Answer 22

• consists of one glycerol, 2 fatty acids and the third OH group of glycerol usually joined to negatively charged phosphate group
• additional small molecules (charged or polar) can be linked to phosphate group to form variety of phospholipids

Question 23

how are phospholipids formed?

Answer 23

• 2 fatty acids linked to one glycerol via ester linkage
• phosphate linked to third OH group of glycerol via phosphoester linkage

Question 24

what are the properties of phospholipids/ compound lipids

Answer 24

ambivalent behaviour towards H2O
- fatty acids have hydrocarbon tails which are non-polar
SO: hydrophobic and can only form bonds with hydrophobic molecules or among themselves
- phosphate group and its attachments form a polar/ charged hydrophilic head which has an affinity for water
HENCE: since it has both phobic and phillic regions, it is amphipathic

Question 25

what are the 3 types of lipid aggregates that form when amphiphatic phospholipids are situated in aq environments ?

Answer 25

**1. Micelle** - small spherical droplet - phospholipids monolayer - head out , contact with aq environment - tail in, not in contact with **2. Bilayer ** - 2 monolayer combine and form a 2D sheet - heads out, contact with aq environment - tails in contact with neighbouring molecules but excluded from H2O non-polar interior **3. Liposome** - when lipid belayer folds back on itself - forms a hollow sphere - avoid exposing the hydrophobic edge regions to the aq environment SO: achieve max stability in sq environment - enclose aq solutions SP: forms separate aq compartment

Question 26

relate the structure of phospholipids to its functions

Answer 26

**1. phospholipids are amphiphatic** - 2 non-polar hydrophobic fatty acid “tails” and a charged hydrophilic phosphate “head” HENCE: 3 lipid aggregates a. Micelle - transport fats between gut and body tissues b. Bilayer - selectively permeable cell membrane - effective barrier between the aq/external environment and the cell c. Liposome/Vesicles - used for storage and transport of cellular products ie proteins and lipids - used for drug delivery in humans - used for digestion of waste (lysosomes) **2. Hydrophobic interactions between fatty acid tails** - integrity of the membrane (?) of the lipid aggregates is maintained due to the large number of interactions - weak individual hydrophobic interactions allow for lateral movement = membrane fluidity **3. Most phospholipids contains choline** - choline it’s important for the synthesis of acetylcholine, a neurotransmitter

Question 27

what are the structural components of glycolipids and how is it formed?

Answer 27

- 2 hydrophobic fatty acid tails - polar short hydrocarbon chain (<15 sugar residues) - no phosphate short carbohydrate chain joined to glycerol OH group by glycosidic bond which is a covalent bond

Question 28

relate the structure of glycolipids to their functions

Answer 28

trick : interactions follow after attraction **1. carbo. chain attached to a glycerol** (attraction) - faces the exterior environment on the cell surface membrane - serves as a marker for cell-cell recognition and cells can recognise each other by binding to the carbohydrate chains - involved in cell-cell adhesion (TBC TBC) **2. hydrophobic interactions between fatty acid tails ** (interaction) - anchors the entire glycolipids to the cell surface membrane

Question 29

what do derived lipids include? (the most important one in syllabus)

Answer 29

steroid cholesterol

Question 30

structure of cholesterol ?

Answer 30

posses a carbon skeleton made up of 3 fused 6-membered and 1 5-membered ring

Question 31

function of cholesterol ?

Answer 31

- regulate membrane fluidity - serve as a precursor for synthesis of bile acids, steroid hormones and vitamin D

Question 32

what is the principle of the emulsion test

Answer 32

lipids are soluble in organic solvents such as ethanol but not in water, which they would form emulsions upon vigorous shaking

Question 33

what is the method of the ethanol emulsion test?

Answer 33

1. add 2cm3 of ethanol to sample, mix well 2. decant ethanol into another test tube containing equal volume of water if lipid present: emulsion is observed - lipid dissolves in ethanol to form a clear solution which forms emulsion with water if lipid absent: solution remains clear - a clear solution still formed with ethanol which remains clear when added to water