Lipids and proteins
Lipids:
-
Organic compounds.
Composed of C, H, and O.
Building units are Glycerol & fatty acids.
Linkage: ester bonds.
Classified into: simple, compound and derivatives.
1. Simple lipids:
One molecule of glycerol & 3 fatty acids → one molecule of triglyceride ( lipid
molecule) & 3 molecules of water.
Examples: Fats & waxes.
2. Compound lipids:
Simple lipid + new compound or ion.
Examples: phospholipids ( phosphorus + lipids).
Glycolipids ( glucose + lipids).
3. Derivatives:
Lipids derived from simple or compound lipid.
Examples: Glycerol & steroids.
- Identification of lipids:
Add 1 ml of Sudan III dye & 1ml oil, then shake vigorously and observe.
You will notice that the two layers of sudan III and oil mix together to form one layer.
Shake vigorously
Like dissolves like: Organic compounds dissolve other organic compounds, while
inorganic compounds dissolve inorganic compounds.
- Lipid solubility:
To 1ml oil on a test tube, add 2ml of ether, acetone, CCl4, alcohol & water separately,
and then watch the result.
Shake
The order of solubility of the above compound is as follows:
Ether > Acetone > CCl4 > Alcohol & no solubility for oil in water.
Protein:
-
Organic compounds composed of C, H, O, and N.
Polymer of amino acids connected by “peptide bond”.
Amino acids differ from each other by the R- group.
Examples: If the R- group is:
H: the amino acid called glycine.
CH2SH: the amino acid called cystine.
- Protein coagulation:
Proteins which are soluble in water have globular structure, folded form of the protein;
tend to become linear when they are exposed to heat or some organic solvents, which
break down the hydrogen bonds between protein chains.
a) By heat:
Heat
Egg albumin
coagulated protein
b) By organic solvents:
By adding few drops of the following organic solvents into 2 ml of egg albumin.
( few drops of 95% alcohol, CuSO4, HCl, TCA or H2O)
Egg albumin
Coagulated protein
-Color tests of protein:
a) Xanthoproteic test:
Add 3 ml egg albumin into 1.5 ml HNO3, warm on direct flame and the add excess
amount of NH4OH until orange color appears.
Heat over direct flame
Add excess NH4OH
b) Ninhydrin test:
Add 2ml Ninhydrin reagent into 2 ml egg albumin.
Boil