DNA

From ArticleWorld

DNA or deoxyribonucleic acid is a nucleic acid that contains the hereditary information for all cellular forms of life as well as the majority of viruses. DNA encodes in its nucleotides the sequence of amino acids for the synthesis of proteins. DNA is normally found in the cell nucleus but for simpler cells it is usually located within the cell's cytoplasm and not separated within a nuclear membrane. Some cell organelles such as the chloroplast and the mitochondria carry DNA.

DNA is replicated during cell division and can be passed along to offspring during reproduction. It is known that mitochondrial DNA comes only from the mother and the male Y chromosome only originates from the father. The offspring will inherit its DNA from both parents. This is done with the inheritance of twenty-three chromosomes from each parent in addition to the mitochondrial DNA from the mother. These combine to form the DNA of the zygote.

Structure

DNA is not one molecule but rather two polynucleotide strands bonded together by hydrogen bonds in a double helix. The strands are complementary to each other and composed of nucleotides of which there are four types each composed of a sugar, phosphate and a base. These are identified according to their base types which are adenine (A), cytosine (C), guanine (G) and thymine (T). In the pairing up of the strands each base can only pair with one single other base. This is done in the following combinations: A+T, T+A, C+G and G+C. This structure of DNA allows for a simple method of replication. This involves the DNA being unzipped down the middle and the single strands being exposed to the four bases and using an enzyme the correct complimentary bases being paired with the original strand.

Applications

DNA has found applications in forensic science and crime as well as in historical and anthropological studies. DNA is used to identify criminals by a process called genetic fingerprinting where it is possible to identify individuals by blood, semen, skin or hair left at the scene of crimes.

As DNA is found to mutate over time this gives evidence as to the processes that have occurred in the past. This information is also useful to evolution where the DNA of different species may be compared to establish relationships.