The discovery of DNA - Essay Example

DNA DNA or deoxyribonucleic acid is a chain of nucleotide units consisting of a nitrogenous base, a deoxyribose sugar and a phosphate. There are 2 types of nitrogenous bases, namely, pyramidine and purine. In DNA, the pyramidines are cytosine and thymine and the purines are guanine and adenine. Each nitrogenous base is connected to a molecule of deoxyribose sugar to form a nucleoside. Each nucleoside is joined to a phosphate group to form a nucleotide. Repeating units of nucleotides form DNA. The structure of DNA is double helix.

The edges on the outer side are formed by alternating phosphate groups and deoxyribose sugar molecules. The two strands of the helix run in opposite directions (1 “up” and 1 “down”). The inner edges of the helices are formed by the nitrogenous bases and they run in pairs. Adenine pairs with thymine with 2 hydrogen bonds and cytosine pairs with guanine with 3 hydrogen bonds (Murray et al, 2007). Though this can dictate side-to-side pairing, there is no clue about the order along the molecule.

According to Watson and Crick, the variety in genetic code can be due to the variability along the molecule. DNA replicates itself through ‘semi-conservative’ replication. The DNA molecule first unzips and new matching bases are added to create new molecules of DNA. Thus each new molecule of DNA has one ‘old’ strand and one ‘new’ strand (Murray et al, 2007). Figure: 1. Helical structure of DNA (Biology education, 1996). The discovery history of DNA can be dated back to 1870s and 1890s when mitosis and meiosis were discovered.

In 1928, Frederick Griffiths experiment on pneumonia bacteria and mice hinted that DNA was the genetic code material. In 1952, Alfred Hershey and Martha Chase performed an experiment on viruses and hinted that viral genetic code material was DNA and not protein capsid. In the early 1950s, Rosalind Franklin attempted to figure out the structure of DNA using bouncing back of X-rays but failed. However, she had some photographs of DNA crystallography and from these photographs, James Watson and Francis Crick determined that the structure of DNA was double helix.

The duo received Nobel prize for this in 1962 (Biology education, 1996). DNA is present in the chromosomes of most of the living beings. The human genome approximately has 3 billion base pairs of DNA which are arranged in the 23 pairs of chromosomes. Sequence pieces of DNA form genes which carry vital information. The genetic information is achieved by complementary base pairing. Transmission, transcription and translation are the steps involved in transmission of genetic information. Currently, DNA is used in the field of genetic engineering for the treatment of many diseases (Murray et al, 2007).

ReferencesBiology Education (1996). DNA Structure and Function. Retrieved Feb 27, 2009 from http://biology.clc.uc.edu/courses/bio104/dna.htmMurray, R.K., Granner, D.K., Mayes, P.A., and Rodwell, V.W. (2007). Harper’s Biochemistry. McGraw Hill: Singapore.