Question

What are nucleic acids? Explain the difference between DNA and RNA and state their two important biological functions.
OR
How can vitamins be classified? Write the name of a fat soluble vitamin. Which vitamin is responsible for blood clotting?

Hint:

For Option 1, recall that a nucleotide is base plus sugar plus phosphate, and that DNA has deoxyribose and thymine while RNA has ribose and uracil. For Option 2, classify vitamins by their solubility and remember that Vitamin K aids blood clotting.

Answer 1

Option 1:
Step 1: What are nucleic acids? Nucleic acids are long-chain biomolecules (polynucleotides) found mainly in the nucleus of living cells. They are polymers made of repeating units called nucleotides. Each nucleotide is built from three parts: a nitrogen-containing base, a pentose sugar and a phosphate group. The two nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
Step 2: Difference between DNA and RNA.
(a) Sugar: DNA contains 2-deoxy-D-ribose, whereas RNA contains D-ribose.
(b) Bases: DNA has adenine, guanine, cytosine and thymine, while in RNA thymine is replaced by uracil (adenine, guanine, cytosine and uracil).
(c) Structure: DNA is a double-stranded helix, whereas RNA is usually single-stranded.
(d) Occurrence and role: DNA is the store of genetic information, while RNA mainly takes part in protein synthesis.
Step 3: Two important biological functions.
(i) DNA is responsible for heredity, that is, the transfer of genetic characters from one generation to the next through the process of replication.
(ii) Nucleic acids (acting through the different RNA molecules) control the synthesis of proteins in the cell.

Option 2:
Step 1: Classification of vitamins. On the basis of their solubility, vitamins are divided into two groups.
(a) Fat-soluble vitamins: vitamins A, D, E and K. They dissolve in fats and oils and are stored in the liver and in adipose (fat) tissue.
(b) Water-soluble vitamins: the B-group vitamins (B₁, B₂, B₆, B₁₂ and others) and vitamin C. They dissolve in water, are not stored in the body and must be supplied regularly through the diet.
Step 2: A fat-soluble vitamin. Example: Vitamin A (retinol). Vitamins D, E and K are also fat soluble.
Step 3: Vitamin responsible for blood clotting. Vitamin K is responsible for the clotting (coagulation) of blood.