LIPIDS 🍔

Question 1

Types of lipids

Answer 1

Triglycerides, phospholipids, glycolipids, sterols

Question 2

Simple lipids

Answer 2

fatty acid and an alcohol(usually glycerol)

Question 3

Compound lipids

Answer 3

fatty acid + an alcohol + other groups

Question 4

Structure of triglyceride + properties of the components

triglyceride=fats

Answer 4

Glycerol - C₃H₈O₃
- polar due to -OH group
- soluble in water

3 fatty acid/long hydrocarbon chain - carboxyl group(-COOH) and an attached hydrocarbon group
- insoluble in water/hydrophobic due to abundance of non-polar C-H bonds
- Saturated: no double bonds, maximal number of hydrogen bonds bonded per C atom
- Unsaturated: double bonds and kink occurs at every double bond
- Acidic in water: presence of carboxyl group, leading to formation of H+ ions in water

❌fatty acid chain
✔fatty acid

Question 5

Process of formation of triglyceride

Answer 5

1. condensation reaction
2. formation of ester linkage between OH group of glycerol and COOH group of fatty acid
3. with loss of one water molecule per ester linkage formed
   5.one glycerol + three fatty acid = triglyceride

Question 6

Hydrolysis of triglyceride

Answer 6

1. addition of one water molecule
2. Breaking of ester linkages
3. Release of glycerol and fatty acids

Question 7

Properties of triglycerides

Answer 7

non-polar/insoluble in water/hydrophobic: abundance of non-polar C-H bonds in hydrocarbon tail

melting point increases as hydrocarbon chain length increases:
- increase length, hydrophobic interactions become more extensive between chains
- more thermal energy required to break enough hydrophobic interactions to liquefy the triglyceride
- melting point increases

Melting point decreases as degree of unsaturation increases/as number of double bonds in fatty acid increases
- kinks in double bonds prevent molecules from packing closely
- less closely packed, hydrophobic interactions less extensive
- less thermal energy required to break enough hydrophobic interactions to liquefy the triglyceride
- melting point decreases

Question 8

Adaptations of triglycerides

Answer 8

higher proportion of C and H atoms to O atoms/greater number of carbon atoms per unit mass: release a larger amount of energy upon oxidation, more efficient energy stores
1. highly reduced molecules: release more metabolic water when oxidised, crucial for desert animals

C-H bonds non-polar and hence triglycerides are hydrophobic, no associated water molecules stored along with triglyceride
1. no extra water weight due to water of hydration
2. does not affect water potential of cells when stored in large amounts
3. fulfils requirement for an animal’s body mass to be kept to a minimum to facilitate locomotion

Good thermal insulators
1. layer of fat(subcutaneous fat) beneath skin insulates the body

Hydrocarbon tails are non-polar, weak hydrophobic interactions between triglyceride molecules
1. can slide under pressure
2. adipose tissue containing fats around vital organs can help cushion and protect vital organs against physical impacts

Lower molecular weight than water**(less dense than water) **
1. aid buoyancy of aquatic animals

Highly reduced molecule: a molecule that has a lot of hydrogen atoms compared to oxygen atoms, or that has many carbon-hydrogen bonds/low oxidation state -> reducation is gain of hydrogen

Question 9

Main functions of triglycerides

Answer 9

1. long-term energy storage
2. protection
3. insulation
4. lubrication
5. hormone precursors(hormones formed from these lipids)
6. key components of cell membrane

Question 10

Structure of a phospholipid(a COMPOUND lipid)

Answer 10

one glycerol + 2 fatty acids + negatively charged phosphate group:
1. 2 OH groups joined to one fatty acid each by ester linkage
2. 1 OH group joined to negatively charged phosphate group by phosphoester linkage

Question 11

Properties of phospholipids

Answer 11

Ambivalent behaviour towards water/amphiatic
1. two fatty acids that comprise the hydrocarbon tails are non-polar and hence hydrophobic, form bond with hydrophobic molecule or among themselves
2. phosphate group and its attachment form a polar/charged hydrophilic head that has affinity for water

Three types of lipid aggregates:
1. Micelle
2. Bilater
3. Liposome/vesicle

Question 12

Structure and function of phospholipids

Answer 12

Amphiatic molecules
1. Form a selectively permeable cell surface membrane, forming an effective barrier/boundary between cell and external environment
* phosphate head face outwards towards aqueous environment
* hydrophibic hydrocarbon tails face inwards away from aqueous environment
2. Form liposomes which are used as vesicles for storage and transport of cellular products, digestion of waste, drug delivery
3. Form micelles for transport of fats between gut and body tissue

Hydrophobic interactions exits between fatty acids tails
1. large number of interactions allows maintenance of intergrity of membrane bilayer
2. individual interactions are weak, permitting lateral movement of phospholipids, allowing for membrane fluidity

Most phospholipids contain choline
1. represent a large proportion of body’s store of choline
2. choline is important for the synthesis of acetylcholine, a neurotransmitter

Question 13

Structure + function of glycolipids

Answer 13

2 hydrophobic hydrocarbon tails + + glycerol + a polar, short carbohydrate chain with no phosphate

short carbohydrate joined to glycerol’s -OH group by glycosidic bond, which is a covalent bond
1. found at cell surface membrane facing exterior environment
2. marker that distinguishes one cell from another in cell-cell recognition. cells recognise other cells by binding to these carbohydrate chains

hydrophobic interactions exist between fatty acids tails
1. anchors entire glycolipids at cell surface membrane

Question 14

Cholestrol
- components
- function

Answer 14

Components: three fused six-membered and one five membered ring
Function:
- regulate membrane fluidity:
1. rigid steroid rings interferes with motions of hydrocarbon chains of phospholipids due to van de Waals interactions, enhances mechnical stability of cell surface membrane
2. at high temperatures, cholestrol restricts movement of phospholipids by distrupting motions of the hydrocarbon chains, leading to decreased membrane fluidity
3. at low temperatures, cholestrol prevent the hydrocarbon chains from packing too closely together, decreasing the tendency of the membrane to solidify, leading to decreased membrane fluidity
- precursor for synthesis of bile acids, steroid hormone and vitamin D

Question 15

Emulsion test - test for lipids

Answer 15

Method:
1. Add 2cm3 of absolute ethanol to sample and mix well - lipids solube in organic solvents
2. decant ethanol into another test tube containing an equal volume of water

Interpretation of results:
- Present: lipid dissolves in ethanol to form clear solution which forms emulsion with water
- Absent: clear solution still formed with ethanol, reamins clear when added to water