Lipid structure and function

Question 1

What are lipid biological functions (6)

Answer 1

1. long term energy storage - metabolised to produce ATP
2. a component cell membranes - form lipid bilayer
3. Insulation
4. act as hormones - chemical messengers to regulate cellular processes
5. Protection
6. transmission of nerve impulses

Question 2

What are lipids (4)

Answer 2

1. Small, naturally occurring molecules
2. Limited solubility in water
3. Extracted with non-polar organic solvents
4. Examples: fats, oils, waxes, vitamins, hormones, cell membrane components

Question 3

What is are the classification of lipids (2)

Answer 3

1. No ester linkages - can he hydrolysed (fats & waxes)
2. Have ester linkages - cannot be hydrolysed (cholesterol & steroids)

Question 4

What are triglycerols (4)

Answer 4

1. triesters of glycerol with three long-chain carboxylic acids (fatty acids)
2. Fatty acids are generally unbranched with 12-20 saturated/unsaturated carbons
3. Double bond(s) usually have cis geometry
4. Animal fats and vegetable oils most abundant

Question 5

What are cis-trans isomers (3)

Answer 5

1. Isomers = same molecular formula, different arrangement
2. Cis = methyl on same side of double bond
3. trans = methyl on different side of double bond

Question 6

What is the composition of lipids (2)

Answer 6

1. Made up of glycerol and fatty acids held together by ester binding
2. undergo hydrogenation reactions to from glycerol with OH groups and Carboxylic acids with the COOH group.

Question 7

What are fatty acids (6)

Answer 7

1. Generally unbranched
2. Contain even number of carbon atoms
3. Double bonds usually have cis geometry
4. More than 100 different fatty acids
5. exist as anions (negatively charges species)
6. anions are amphipathic (two opposing polarities within the same molecule)

Question 8

How are fatty acids used to build up the cell membrane (3)

Answer 8

1. Fatty acid anions are amphipathic (two opposing polarities within the same molecule)
2. The carbon chain is a non-polar = hydrophobic tail
3. The COO- is polar = hydrophilic head

Question 9

How do you make fatty acids soluble (2)

Answer 9

1. react the fatty acid with a base changing it to an ionic compound which can dissolve in water, changing its solubility properties.
2. stearic acid + NaOH → sodium stearate + H2O

Question 10

Why do unsaturated fatty acids generally have lower melting points than saturated fatty acids? (4)

Answer 10

1. Unsaturated fatty acids have lower melting points because their double bonds create bends in the chain, which prevent tight packing.
2. bends lead to weaker intermolecular forces, so they melt more easily.
3. In contrast, saturated fatty acids have straight chains that pack tightly
4. straight chains result in stronger forces and higher melting points.

Question 11

What affects the melting point of fatty acids (2)

Answer 11

1. Carbon chain length - more carbons = higher melting point (more intermolecular forces)
2. Degree of unsaturation - unsaturated = higher melting point, pack tightly together forming a lattice

Question 12

What is Catalytic hydrogenation (3)

Answer 12

1. Used to reduce double bonds using hydrogen (H₂)
2. Can change liquid into a saturated solid
3. Some double bonds can react with the catalyst changing the geometry of the double bond from cis → trans

Question 13

What happens if fats contain trans double bonds (4)

Answer 13

1. Hydrogenated fats from catalytic hydrogenation
2. Negative health effects
3. Lower good cholesterol
4. Cardiovascular disease

Question 14

What are waxes (6)

Answer 14

1. Mixtures of esters of long-chain carboxylic acid and long-chain alcohols
2. Carboxylic acid = usually even numbers of C (16-36)
3. Complex alcohol = usually even number of C atoms (24-36)
4. Have protective function - preventing water loss
5. Insoluble in water
6. Soluble in non-polar solvents

Question 15

What are phospholipids (5)

Answer 15

1. Diesters of phosphoric acid (H3PO4)
2. glycerophospholipids or sphingomyelins
3. C1 fatty acid - saturated
4. C2 fatty acid - unsaturated
5. C3 phosphate bonded to an amino alcohol

Question 16

What are amino alcohols (2)

Answer 16

1. Choline
2. ethanolamine

Question 17

What are Glycerophospholipids (4)

Answer 17

1. glycerol linked to 2 fatty acids and 1 phosphoric acid
2. Major component of cell membrane (40%)
3. Most important = lecithins and cephalins
4. Lecithins = choline attached to phosphate
5. Cepthalins = ethanolamine attached to phosphate

Question 18

What is the structure of lecithins (4)

Answer 18

1. Glycerol - 3-carbon alcohol
2. C1 = fatty acid chain (Saturated)
3. C2 = Fatty acid chain (Unsaturated)
4. C3 = phosphate + amino alcohol (choline)

Question 19

What do lecithins do (2)

Answer 19

1. Transfer fats
2. Reduction of cholesterol

Question 20

What is the structure of Cephalins (4)

Answer 20

1. Glycerol - 3-carbon alcohol
2. C1 = fatty acid chain (Saturated)
3. C2 = Fatty acid chain (Unsaturated)
4. C3 = phosphate + amino alcohol (ethanolamine)

Question 21

What do cephalins do

Answer 21

accelerate blood clotting

Question 22

What is the structure of the cell membrane (3)

Answer 22

1. Phospholipid bilayer
2. Hydrophobic tail = long non-polar hydrocarbon chain
3. Hydrophilic head = polar, carboxylic anion region (glycerol back-bone + phosphate + amino alcohol)

Question 23

What are Sphingomyelins (5)

Answer 23

1. Spingosine backbone not glycerol backbone
2. Spingosine = larger nitrogen-containing alcohol backbone
3. In plant and animal cell membrane
4. Abundant in brain and nerve tissue
5. component of myelin sheath for insulation of nerve cells

Question 24

What is the structure of Sphingomyelins (3)

Answer 24

1. Alcohol, amino, alcohol, unsaturated hydrocarbon chain
2. Hydrophobic tail = alcohol backbone + amine + fatty acid
3. Hydrophilic head = phosphate + choline