Question

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8. (10 pts) Structure of DNA a) List 6 structural characteristics of DNA. b) List three structural differences between DNA and RNA.

Answer 1

8a)

Cells contain two types of nucleic acids called deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). All the cells of higher organisms contain both these nucleic acids.

Nucleotide is a 3 subunit molecule containing pentose sugar, nitrogen base reacting with a phosphate group. Nucleotide is the building block of nucleic acids the DNA and RNA.

The DNA is a macro molecule containing four types of nucleotides with the bases, adenine (A), guanine (G) the purines; cytosine (C) and thymine (T) the pyrimidines.

In a DNA molecule the amount of A = T and the amount of G = C.

The DNA molecule has double helix structure and it was proposed by Watson and Crick.

The DNA structure contains the deoxyribose sugar and phosphate molecules bonded together. The sugar and phosphate groups are held by phosphoester bond. The nitrogen bases, sugar and phosphate groups in anucleotide are held by covalent bonds.

The nitrogenous bases are held by hydrogen bonds. Each base, pairs with a complementary base.

The two strands are antiparallel and run in opposite directions means from 5'$\rightarrow$3' and 3'$\rightarrow$5'.

There are about 10.5 bases per turn and the pitch of helix is 33.2$\AA$.

b)

DNA contains deoxyribose sugar while RNA contains ribose sugar.

DNA is double stranded while RNA is single stranded (exception is observed in some viruses containing double stranded RNA).

DNA contains pyrimidine thymine pairs with purine Adenine. RNA contains pyrimidine Uracil instead of thymine and it basepairs with Adenine.

guanine C > cytosine - adenine T thymine ..hydrogen bonds S deoxyribose sugar P- phosphate group