Question

Given above is a diagram of a double helical structure of DNA. [5]
i) Name the four nitrogenous bases that form a DNA molecule.
ii) Name the bond which attach two nitrogenous base together.
iii) If nitrogenous bases forms the rungs of this ladder like structure then what forms the sides of this double helical structure?
iv) Name the unit of heredity.
--------------------------------------------------

Answer 1

Answer:

1. The four nitrogenous bases present in DNA are adenine (A), guanine (G), cytosine (C) and thymine (T). In RNA, the only differing nitrogenous base is uracil (U) (which replaces thymine in DNA and differs thymine only by the missing methyl group at carbon 5 of the pyrimidine ring).
2. The nitrogen bases are held together by hydrogen bonds: adenine and thymine form two hydrogen bonds; cytosine and guanine form three hydrogen bonds.
3. The nitrogenous bases point inward on the ladder and form pairs with bases on the other side, like rungs. Each base pair is formed from two complementary nucleotides (purine with pyrimidine) bound together by hydrogen bonds. The base pairs in DNA are adenine with thymine and cytosine with guanine.
4. Genes are the units of heredity and are the instructions that make up the body's blueprint. They code for the proteins that determine virtually all of a person's characteristics. Most genes come in pairs and are made of strands of genetic material called deoxyribonucleic acid, or DNA.