Structure of DNA

1.

Sugar-Phosphate Backbone • Each strand is made of nucleotides, and each nucleotide contains a phosphate group, a deoxyribose sugar, and a nitrogen base. • The phosphate of one nucleotide is connected to the deoxyribose sugar of the next nucleotide by a covelant bond. • These sugar and phosphate groups form the backbone of the DNA strand.

2.

Nitrogen Bases and Hydrogen Bonds • The nitrogen bases (Adenine, Thymine, Cytosine, and Guanine) are found in the centre of the molecule. • Adenine (A) always pairs with Thymine (T) using two hydrogen bonds. • Cytosine (C) pairs with Guanine (G) using three hydrogen bonds. • These hydrogen bonds hold the two strands together.

3.

Antiparallel Strands • The two strands of DNA run in opposite directions. • One strand runs from 5′ (five-prime) to 3′ (three-prime), and the other runs 3′ to 5′. 3

• The 5′ end has a phosphate group, while the 3′ end has a hydroxyl (-OH) group on the sugar. • This directionality is important for processes like DNA replication and transcription.

4.

Double Helix Shape • The DNA is twisted into a helix, giving it stability and compactness. • The twisting protects the genetic code stored in the sequence of nitrogen bases.