lipids

Question 1

formation of triglycerides

Answer 1

1 fatty acid attached to each OH of glycerol = 3 fatty acids per triglyceride

1. An ester * linkage is formed between a hydroxyl group (-OH) of a glycerol molecule and a carboxyl group (-COOH) of a fatty acid chain;
   - H atom loses from hydroxyl grp of glycerol, OH lost from COOH of fatty acid chain
2. via a condensation reaction* whereby a molecule of water* is removed; (hence per triglyceride, 3 water molecules are removed)

Question 2

Properties of fatty acids

Answer 2

1. Long non polar hydrophobic hydrocarbon chains with carboxyl (-COOH) group at one end of the chain
2. when ionized in water, has charged COO- group which can interact with water
   = short fatty acids are soluble in water;
3. non-polar hydrophobic hydrocarbon chains increases in length= fatty acid unable to interact with water = decreases solubility
4. Weak acid: dissociates partially in water to give a low conc of H+ ions

Question 3

Properties of glycerol

Answer 3

1. Hydroxyl group on each carbon in glycerol can interact with water = soluble in water

Question 4

how can lipids be classified at room temp

Answer 4

1. fats: fatty acid of lipid is saturated = contains only C-C and C-H = particles closely packed to one another = solid state
2. oil: fatty acid of lipid is unsaturated = contains one or more C=C bond = causes kinks to occur = kinks precent fatty acid chains from being closely packed = liquid state

Question 5

functions of triglyceride

Answer 5

1. energy storage
2. produces metabolic water: H and O atoms from oxidation forms water
3. cushions and protects internal organs
4. subcutaneous fat provides thermal insulation
5. lipids are less dense than water, improve buoyancy in marine animals

Question 6

how can lipids release more energy than carbohydrates

Answer 6

1. for an equivalent mass of carbohydrates, triglycerides contain more hydrogen atoms and carbon atoms and less oxygen atoms per gram = more energy in form of ATP released during oxidation
2. lipids are hydrophobic = compact energy store = have higher energy density (pack more energy within a molecule)

Question 7

structure of phospholipid

Answer 7

1. made up of a glycerol* backbone joined to two non-polar,hydrophobic hydrocarbon tails* and a negatively charged, hydrophilic, phosphate*
   group;
2. The non-polar, hydrophobic hydrocarbon tails phospholipids are linked to the glycerol backbone via ester* linkages;
3. The charged, hydrophilic phosphate head is linked to the glycerol backbone via a
   phosphoester linkage*;
4. Phospholipids may contain a nitrogen-containing choline attached to the phosphate
   group;

Question 8

how is phosphodiester bond formed

Answer 8

OH atoms removed from phosphoric acid, H atom lost from glycerol = phosphodiester bond formed between glycerol and phosphoric acid with formation of water molecule

Question 9

properties of phospholipids

Answer 9

1. amphiatic: non polar hydrocarbon tails are hydrophobic, negatively charged phosphate head is hydrophillic (can interact with water)
2. will self-assemble into p/lipid bilayer/micelle when placed in aqueous solution (hydrophobic hydrocarbon tails form hydrophobic core, hydrophillic phosphate heads face exterior)

Question 10

properties of steroids (cholesterol)

Answer 10

1. slightly amphiatic: has hydrophillic hydroxyl group and hydrophobic ring structure
2. OH- of cholesterol aligns with phosphate heads = interact via hydrophillic interactions
3. remaining hydrophobic ring structure tucked into hydrophobic core = interact via hydrophobic interactions

Question 11

functions of cholesterol

Answer 11

1. regulates membrane fluidity:

a. prevents the membrane from being overly fluid at warmer temperatures = cholesterol’s rigidity restricts phospholipids’ lateral movement
b. prevents membrane from being overly firm at lower temperatures = cholesterol
prevents the close packing of phospholipids = prevents membrane’s solidification/crystallization

2. helps to anchor / secure proteins in the membrane;
3. provides mechanical stability = forms weak hydrophobic interactions with neighbouring hydrocarbon chains of phospholipids

Question 12

how to test for lipids

Answer 12

Process
(if sample is solution) add 2cm3 of ethanol to 2 drops of sample, let stand, decant into test tube with water
(if sample is solid) crush sample, add 2cm3 of ethanol, mix and let stand, decant into test tube with water

results:
white emulsion formed in water = fat present
solution remains clear = fat absent

rationale:
fats do not dissolve in water (only organic solvents like ethanol) = forms emulsion