Watson and crick model of Dna

Double helical structure of Dna

Watson and Crick showed that each strand of the DNA molecule was a template for the other.

• DNA  consist of two  strands coiled around each other to form a double helix.. (polynucleotides) Each nucleotide is composed of a nitrogen base—either cytosine (C), guanine (G), adenine (A), or thymine (T in DNA), uracil(U in RNA) ,a sugar moiety (Deoxyribose ribose sugar in DNA,Ribose sugar in RNA) and a phosphate group.

• Nucleotides pair in a specific way - called the Base-Pair Rule Adenine pairs to Thymine(A=T) Guanine pairs to Cytosine(C=_G)

• The diameter of the alpha helix structure of DNA is 2nm.

•  DNA strands run in  antiparallel direction. (parallel, but in opposite directions).5'-3' and another 3'-5'.
•  B-DNA, the most common double helical structure, the double helix is right-handed with about 10–10.5 base pairs per turn.
• The double helix structure of DNA contains a major groove and minor groove. In B-DNA the major groove is wider than the minor groove.
• The pitch of the helix is 3.4nm /turn.
• Dna has deoxyribose sugar which makes it stable towards hydrolysis .

Q.1 During replication in S phase of cell cycle DNA is duplicated but what happens to the chromosome no.?
Ans. The chromosome no. remains same

Q2. Chirality of DNA is due to:

  a. The bases 

  b. Base stacking

  c. Hydrogen bonds between bases

  d. Deoxyribose

Ans: d – Deoxyribose

Biomolecules like DNA, proteins, amino acids and sugars are chiral molecules.

3.What is the nature of DNA backbone? 

a. hydrophobic 

b. hydrophilic 
C. Neutral
D. None of the above
Ans.  B

Thank you for visiting my blog.Please feel free to share your comment on this article ,Please subscribe and share the articles to get more such articles.