The Structure of DNA

The Structure of DNA

DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost

all other organisms. Nearly every cell in a person's body has the same DNA. Most DNA

is located in the cell nucleus (it is called nuclear DNA), but a small amount of DNA

can also be found in the mitochondria (U.S. National Library of Medicine, 2009). A

DNA molecule consists of two chains of nucleotides (polymers of nucleic acid each

composed of a phosphate, a five carbon sugar, and a nitrogenous base) that spiral to form

the double helix shape. The nucleotides that forms the DNA structure are organized so

their sugar-phosphate components face the outside and form the backbone of the

structure, whereas the nitrogenous bases face inward. These bases are not all the same,

there are four types in DNA: Adenine, Thymine, Guanine and Cytosine.

Animation of the structure of a section of DNA. Th...

English: The structure of DNA showing with detail ...

From left to right, the structures of A-, B- and Z...

When the two

chains of DNA come together to form a helix the bases of one strand bond with the bases

of the other with Adenines only bonding with Thymines and Guanine only binding with

Cytosines. DNA molecules are basically long strands of nucleotides. Groups of

nucleotides are called genes. Therefore, each DNA molecule consists of hundreds or

thousands of genes, each occupying a different section of the strand and genes are

grouped into chromosomes (Miko, 2008). Humans have 46 chromosomes, or other

words 23 pairs of chromosomes.

By the 1940s scientists knew that chromosomes carry the hereditary material.

They knew that chromosomes contained nucleic acids DNA (deoxyribonucleic acid) and

protein. They knew that proteins were complex macromolecules that were very variable

and functionally specific whereas DNA appeared to be a much simpler molecule about

which little was known, but people figured it wasn't variable enough to be...