What is DNA?
Human characteristics such as eye, hair and skin colour are all determined by a person's DNA. DNA stands for deoxyribonucleic acid, and it is a very large and complex molecule which is found in the cells of all organisms. It is a vital component of life, as it contains all an organism's hereditary information, as well as all the information necessary for the organism to grow, develop, thrive and survive; it not only determines what an organism will look like, but also the way it is designed and the activities that it undertakes.
It was first observed by Swiss biochemist Frederich Miescher in the late 1800s, but it took scientists almost a century to decipher its structure. Since its discovery, scientists are constantly discovering more about this extremely important molecule, resulting in a long and decorated history. Most DNA is located the the nucleus of cells, and is thus referred to as nuclear DNA. However, a small amount of DNA also exists in the mitochondria of complex organisms such as humans. Sections of DNA molecules make up genes. These are the basic physical and functional unit of genetics, and act as instructions to make proteins. The size of a gene varies greatly, ranging between 1 000 - 1 000 000 bases in humans. However, they only account for 1% of DNA sequence - the rest regulates the protein. They consist of three types of nucleotide sequences: - Exons - these are coding regions and contain genetic coding for protein synthesis. - Introns - these are non-coding regions and do not contain any genetic information. - Regulatory sequences - these determine when, where and how much of a protein is made. DNA exists as extremely long strands of genetic material; DNA in humans is approximately 2-3M long. In humans, there are a total of 46 strands of DNA (23 pairs - one from each parent). In order to fit all these molecules into the nucleus, each DNA molecule is tightly coiled and bound to special proteins known as histones. This process is known as DNA packaging - fitting DNA into compact forms. During, DNA molecules are wrapped, looped and coiled around histones. These provide structural support and also aid in controlling the activities of the genes. A single strand of DNA wraps around a cluster of these proteins to form a structure known as a nucleosome. Several nucleosomes are packed together to form a highly coiled structure known as a chromosome. This condensation and cell packaging occurs just before a cell undergoes division, and makes the chromosomes more visible. The chromosomes then take part in either meiosis or mitosis, and exact copies of these chromosomes are distributed into daughter cells, thus carrying on genetic material. |