Lipid structure and function Flashcards
1
Q
What are lipid biological functions (6)
A
- long term energy storage - metabolised to produce ATP
- a component cell membranes - form lipid bilayer
- Insulation
- act as hormones - chemical messengers to regulate cellular processes
- Protection
- transmission of nerve impulses
2
Q
What are lipids (4)
A
- Small, naturally occurring molecules
- Limited solubility in water
- Extracted with non-polar organic solvents
- Examples: fats, oils, waxes, vitamins, hormones, cell membrane components
3
Q
What is are the classification of lipids (2)
A
- No ester linkages - can he hydrolysed (fats & waxes)
- Have ester linkages - cannot be hydrolysed (cholesterol & steroids)
4
Q
What are triglycerols (4)
A
- triesters of glycerol with three long-chain carboxylic acids (fatty acids)
- Fatty acids are generally unbranched with 12-20 saturated/unsaturated carbons
- Double bond(s) usually have cis geometry
- Animal fats and vegetable oils most abundant
5
Q
What are cis-trans isomers (3)
A
- Isomers = same molecular formula, different arrangement
- Cis = methyl on same side of double bond
- trans = methyl on different side of double bond
6
Q
What is the composition of lipids (2)
A
- Made up of glycerol and fatty acids held together by ester binding
- undergo hydrogenation reactions to from glycerol with OH groups and Carboxylic acids with the COOH group.
7
Q
What are fatty acids (6)
A
- Generally unbranched
- Contain even number of carbon atoms
- Double bonds usually have cis geometry
- More than 100 different fatty acids
- exist as anions (negatively charges species)
- anions are amphipathic (two opposing polarities within the same molecule)
8
Q
How are fatty acids used to build up the cell membrane (3)
A
- Fatty acid anions are amphipathic (two opposing polarities within the same molecule)
- The carbon chain is a non-polar = hydrophobic tail
- The COO- is polar = hydrophilic head
9
Q
How do you make fatty acids soluble (2)
A
- react the fatty acid with a base changing it to an ionic compound which can dissolve in water, changing its solubility properties.
- stearic acid + NaOH → sodium stearate + H2O
10
Q
Why do unsaturated fatty acids generally have lower melting points than saturated fatty acids? (4)
A
- Unsaturated fatty acids have lower melting points because their double bonds create bends in the chain, which prevent tight packing.
- bends lead to weaker intermolecular forces, so they melt more easily.
- In contrast, saturated fatty acids have straight chains that pack tightly
- straight chains result in stronger forces and higher melting points.
11
Q
What affects the melting point of fatty acids (2)
A
- Carbon chain length - more carbons = higher melting point (more intermolecular forces)
- Degree of unsaturation - unsaturated = higher melting point, pack tightly together forming a lattice
12
Q
What is Catalytic hydrogenation (3)
A
- Used to reduce double bonds using hydrogen (H₂)
- Can change liquid into a saturated solid
- Some double bonds can react with the catalyst changing the geometry of the double bond from cis → trans
13
Q
What happens if fats contain trans double bonds (4)
A
- Hydrogenated fats from catalytic hydrogenation
- Negative health effects
- Lower good cholesterol
- Cardiovascular disease
14
Q
What are waxes (6)
A
- Mixtures of esters of long-chain carboxylic acid and long-chain alcohols
- Carboxylic acid = usually even numbers of C (16-36)
- Complex alcohol = usually even number of C atoms (24-36)
- Have protective function - preventing water loss
- Insoluble in water
- Soluble in non-polar solvents
15
Q
What are phospholipids (5)
A
- Diesters of phosphoric acid (H3PO4)
- glycerophospholipids or sphingomyelins
- C1 fatty acid - saturated
- C2 fatty acid - unsaturated
- C3 phosphate bonded to an amino alcohol
16
Q
What are amino alcohols (2)
A
- Choline
- ethanolamine
17
Q
What are Glycerophospholipids (4)
A
- glycerol linked to 2 fatty acids and 1 phosphoric acid
- Major component of cell membrane (40%)
- Most important = lecithins and cephalins
- Lecithins = choline attached to phosphate
- Cepthalins = ethanolamine attached to phosphate
18
Q
What is the structure of lecithins (4)
A
- Glycerol - 3-carbon alcohol
- C1 = fatty acid chain (Saturated)
- C2 = Fatty acid chain (Unsaturated)
- C3 = phosphate + amino alcohol (choline)
19
Q
What do lecithins do (2)
A
- Transfer fats
- Reduction of cholesterol
20
Q
What is the structure of Cephalins (4)
A
- Glycerol - 3-carbon alcohol
- C1 = fatty acid chain (Saturated)
- C2 = Fatty acid chain (Unsaturated)
- C3 = phosphate + amino alcohol (ethanolamine)
21
Q
What do cephalins do
A
accelerate blood clotting
22
Q
What is the structure of the cell membrane (3)
A
- Phospholipid bilayer
- Hydrophobic tail = long non-polar hydrocarbon chain
- Hydrophilic head = polar, carboxylic anion region (glycerol back-bone + phosphate + amino alcohol)
23
Q
What are Sphingomyelins (5)
A
- Spingosine backbone not glycerol backbone
- Spingosine = larger nitrogen-containing alcohol backbone
- In plant and animal cell membrane
- Abundant in brain and nerve tissue
- component of myelin sheath for insulation of nerve cells
24
Q
What is the structure of Sphingomyelins (3)
A
- Alcohol, amino, alcohol, unsaturated hydrocarbon chain
- Hydrophobic tail = alcohol backbone + amine + fatty acid
- Hydrophilic head = phosphate + choline
