Question

1. Name the three components of a DNA nucleotide. Explain how the DNA double helix is formed including the Base Pairing rules and the Antiparallel structure.

Answer 1

DNA is deoxy-ribonucleicacid, a nucleotide which is formed by 3 components
1. Nitogeneuous base- In DNA, bases are(A) Adenine, (T) Thymine, (G) Guanine and (C) Cytosine
2. Pentose sugar which is a deoxyribose sugar
3. Phosphate group
DNA stores the genetic information required for the expression of genes.

Formation of DNA double helix:
DNA is a double stranded structure in the form of helix thus termed as double helical structure.
Backbone of DNA is made up of sugar and phosphate group.
Nitrogeneous bases are stacked inside of DNA in the form of staircase.
The bases are joined together via Hydrogen bonds
Adenine is paired with Thymine with two hydrogen bonds
Guanine is paired with cytosine with three hydrogen bonds
Also, the two strands of DNA are always antiparallel that is they have the opposite polarity. Which means if one strand has direction from 3'- 5' end then the other strand will be in opposite direction and will have the polarity from 5'-3' direction.
The DNA to be antiparallel is important for replication of DNA

Base pairs:
In DNA, there is complementary base pairing that always occurs between a purine( Adenine and Guanine) and a pyrimidine(Thymine and Cytosine)
That is Adenine pair up with Thymine
Guanine pair up with cytosine
Thus this rule of base pairing is termed as complementary base pairing.
DNA strand are always complementary to each other. If one DNA strand have sequence of GTACGT then other strand will have sequence complementary to it thus it will be CATGCA.

Antiparallel Strands
The two strands of DNA are always antiparallel to each other
Two strands run in opposite direction, if one strand having the direction from 5'-3' then the other complementary strand will have direction from 3'-5' end.