The Structure of DNA

DNA DNA (deoxyribonucleic acid) is found in the nuclei of all cells. It is the DNA that carries the genetic information which will determine all your characteristics (hair color, shape of nose, etc.) Every person’s DNA is different, except for identical twins.

DNA is composed of: 5 carbon sugar, deoxyribose phosphate group 4 different nitrogenous (nitrogen- containing) bases S P

Sugar and phosphate group

Nitrogenous Bases Purines (double ring)Pyrimidines (single ring) adenine (A) guanine (G) thymine (T) cytosine (C)

Purines

Pyrimidines

Each DNA unit is called a nucleotide. A nucleotide consists of one phosphate group, one deoxyribose molecule, and one of the four bases.

Watson and Crick James Watson and Francis Crick discovered the structure of DNA in It has been termed the discovery of the century. They determined its shape is a double helix (like a spiral staircase)

Watson and Crick

The Double Helix The sugars and phosphate groups are bonded together to make up the backbone of the DNA molecule. This is like the handrails of the spiral staircase. The bases bond to each other in pairs and make up the internal structure of the molecule. This is like the rungs or steps of the spiral staircase.

DNA Double Helix

Adenine always bonds to Thymine. AT CG Cytosine always bonds to Guanine.

DNA Double Helix

Bases are held together by weak hydrogen bonds. Adenine always bonds to thymine with 2 hydrogen bonds. AT CG Cytosine always bonds to guanine with 3 hydrogen bonds.

DNA Double Helix

The two strands of the DNA molecule are complementary – the sequence of bases along one strand automatically determines the matching bases on the other strand because of the rules of base pairings (A-T, C-G). If all the DNA in your body were uncoiled and stretched out, it would reach to the sun and back ~3000 times!!!