Deoxyribonucleic acid, which is commonly known by its acronym DNA, is the hereditary material in humans and almost all other living organisms. It was discovered by Friedrich Meischer in 1869. It is a linear polymer that is located in the cell nucleus (nuclear DNA) and is protected by the nuclear envelope. However, some of it can be found in the mitochondria (mitochondrial DNA). Nearly every cell in the human body has the same kind of DNA. Its function is to encode information. It encodes all of the sequences of all of the proteins that an organism needs to live. It is an extremely long polymer therefore a single molecule of it encodes all of the information necessary to produce thousands of proteins. Information in DNA is stored as a code made up of four chemical bases: the purine bases, adenine (A) and guanine (G) and the pyrimidine bases, cytosine (C) and thymine (T). It may contain more than 200 million nucleotide base and more than 99% of all these bases are the same in all human beings. DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. Together, a base, sugar, and phosphate are called a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a double helix. The complementarity of the two strands with strict adherence to the A to T and G to C pairing rules – is the basis for replication of the genes. The two strands separate during replication, and each serves as a template for the synthesis of a new complementary strand.
James Watson, Francis Crick and also Rosalind Franklin are the scientists who discovered that DNA was the carrier of the information needed to make all the proteins in the body. They formulated the ‘central dogma’ that paved way to modern molecular biology. It stated that DNA can be copied to make more DNA, copying all the information in the original. The information in DNA can also be transcribed into RNA, which then directs the production of a protein whose sequence of amino acids is determined by the sequence of nucleotides in the DNA (and RNA). Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. The information flow is always either DNA to DNA or DNA to RNA to protein.
Mitochondrial DNA also plays a very important part in this information flow. It contains thirty seven genes, all of which are essential for normal mitochondrial function. Thirteen of these genes provide instructions for making enzymes involved in oxidative phosphorylation. The twenty four remaining genes provide instructions for making molecules called transfer RNAs (tRNAs) and ribosomal RNAs (rRNAs), which are chemically related to DNA. These types of RNA help assemble protein building blocks (amino acids) into functioning proteins.
The discovery of DNA function and structure is one of the most important contributions to science and has enabled scientists and clinicians to better understand the physiology of the human body.
admin January 16th, 2014
Posted In: Handbook