Lipids

Question 1

What are lipids?

Answer 1

Diverse group
Oily, greasy, waxy, heterogeneous substances in biosphere
C, H, O constituents but H and O are never in a 2:1 ratio

Question 2

Solubility of lipids

Answer 2

Long alkyl chains make lipids non polar and hydrophobic (insoluble in water) and also make the structure complex but they are soluble in some organic solvents such as benzene, ether, chloroform

Question 3

Essential fatty acids

Answer 3

Linoleic acid (18:2)
Linolenic acid (18:3)
Arachidonic acid (20:4)

Question 4

Non essential fatty acids

Answer 4

Palmitic acid (16:0)
Stearic acid (18:0)
Oleic acid (18:1)

Question 5

Saturated fatty acids

Melting point

Answer 5

Palmitic acid
CH3-(CH2)14-COOH

Stearic acid
CH3-(CH2)16-COOH

Increased melting point of liquid

Question 6

Unsaturated fatty acids

Melting point

Answer 6

Oleic acid
CH3-(CH2)7-CH=CH(CH2)7COOH

Linoleic acid
CH3(CH2)4CH=CHCH2CH=CH(CH2)7CO
OH

Linolenic acid
Arachidonic acid

Decreases melting point

Question 7

Fats and oils

Answer 7

Fats - high mp; solids at room temp
Butter, ghee

Oils - low mp, liquids/oils at room temp
Gingelly oil, sunflower oil

Question 8

Simple lipids

Answer 8

1. Neutral lipids - tri and diacylglycerol
2. Wax - single fatty esters of monohydric alcohol
   Cerumen (ear wax)
   Lanolin (wool fat)
   Bees wax - palmitic acid (C16H32O2) and myricyl alcohol (C30H61OH)
   Also called hexocosyl palmitate, secreted by worker bees
   Wax-D - bacteria that causes tuberculosis and leprosy

Question 9

Conjugated/conpound lipids

Answer 9

1. Phospholipid - glycerol+ PO4 group attached to outer OH, 2 fatty acid joined to other 2 OH, nitrogen containing choline attached to PO4
   Lecithin(cell membranes and lung surfactant)
2. Sphingolipids - conjugate of amino acid (sphingosine) plus 1 fatty acid plus one sugar or phosphate group
   Present on surface of RBC (glycolipid): cerebroside/gangioside
   Form myelin sheath - sphingomyelin
3. Lipoprotein- lipids and proteins
   Membrane composed of lipoproteins
4. Chromolipid - pigments like carotenoids
   Carotene, Vitamin A

Question 10

Derived lipids

Answer 10

Steroids - no fatty acids but similar properties, 4 fused C rings
cholesterol derived from acetic acid, synthesised in liver -
used in production of bile salt and vitamin D,
essential conponent of animal plasma membrane/biomembrane and
precursor of all steroid hormones