Biological molecules flashcards

4.1 Biological molecules

Elements in carbohydrates, fats and proteins

Carbohydrates and fats: C, H, O. Proteins: C, H, O, N (some also S). Only proteins contain nitrogen.

Starch, glycogen and cellulose are made from…

Glucose. Starch is a store in plants, glycogen a store in animals and fungi, cellulose forms plant cell walls.

Building blocks of proteins, and of fats and oils

Proteins: amino acids. Fats and oils: fatty acids and glycerol.

Iodine test for starch

Add iodine solution. Orange-brown → blue-black if starch is present.

Benedict's test for reducing sugars

Add Benedict's solution and heat in a water bath (about 80 °C). Blue → green, yellow, orange or brick-red. The further along, the more reducing sugar.

Biuret test for protein

Add biuret solution and mix (no heating). Blue → purple if protein is present.

Ethanol emulsion test for fats and oils

Shake the food with ethanol, then pour into water. A cloudy white emulsion shows fat or oil. (Ethanol first, water second; ethanol is flammable.)

DCPIP test for vitamin C

Add the food solution drop by drop to DCPIP: blue → colourless. The smaller the volume needed to decolourise it, the more vitamin C.

Structure of DNAExtended

Two strands coiled together to form a double helix. Each strand contains bases. Bonds between pairs of bases hold the strands together. A pairs with T; C pairs with G.

In a DNA sample 15% of the bases are A. What percentage are C?Extended

T = 15%, so A + T = 30%. C + G = 70%, so C = 35%.