Vitamins, Nucleic Acids and Hormones: Quick Revision

A brief note on Vitamins, Nucleic Acids and Hormones. Read it before a test. Try each question at the end before you open its answer.

Vitamins

• Fat-soluble: A, D, E and K. They are stored in the liver and fat. Water-soluble: the B group and C. They are not stored, except B12.
• A: night blindness. D: rickets. E: fragile red blood cells. K: slow clotting. B1: beri-beri. B2: cheilosis. B6: convulsions. B12: pernicious anaemia. C: scurvy.
• Vitamin B12 contains cobalt, and vitamin C is a reducing agent that reacts 1 : 1 with iodine.

Nucleic acids

• Nucleoside = base + sugar. Nucleotide = base + sugar + phosphate. A nucleotide is joined to the next by a 3' to 5' phosphodiester linkage.
• DNA: 2-deoxyribose, with A, G, C and T. RNA: ribose, with A, G, C and U. Purines are A and G. Pyrimidines are C, T and U.
• Double helix: two antiparallel strands, A with T (2 hydrogen bonds), G with C (3). Chargaff: A = T and G = C.
• B-DNA: 0.34 nm between pairs, about 10.5 pairs and 3.57 nm per turn, about 2 nm wide.
• A codon is 3 bases. There are 64 codons, 3 of them stop signals. A strand of $n$ nucleotides has $n - 1$ linkages.

Hormones

• Steroids (testosterone, cortisol) are fat-soluble and act inside the cell. Peptides (insulin, 51 amino acids) bind a receptor on the surface. Amino acid derivatives are adrenaline and thyroxine (four iodine atoms).
• Insulin lack gives diabetes. Iodine lack gives goitre.

A worked example

Count the hydrogen bonds in a duplex with 10 base pairs, 4 of which are G-C pairs.

1. A-T pairs. $10 - 4 = 6$.
2. Bonds. $6 \times 2 + 4 \times 3 = 12 + 12 = 24$.

Practice with new numbers

A program to try

Mistakes to avoid

• Mixing up the vitamins and the diseases. Scurvy is C, rickets is D, beri-beri is B1.
• Putting thymine in RNA.
• Pairing A with G. A pairs with T, and G with C.
• Counting stop codons as amino acids.

Check yourself

1. Which vitamin contains cobalt?

2. If a DNA sample is 35% adenine, what percentage is cytosine?

3. How many phosphodiester linkages are in a strand of 10 nucleotides?

4. Is thyroxine a steroid?

Sources

• Nelson and Cox, Lehninger Principles of Biochemistry, 8th edition, Chapters 8 and 10.
• NCERT Chemistry for Class 12, Part II, the chapter Biomolecules.
• OpenStax, Organic Chemistry, Chapter 28.