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Friday, September 16, 2016
Deoxyribonucleic acid or DNA
Deoxyribonucleic acid or DNA is a molecule that contains the instructions an organism needs to develop, live and reproduce. These instructions are found inside every cell, and are passed down from parents to their children.
DNA is made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C). The order of these bases is what determines DNA's instructions, or genetic code. Similar to the way the order of letters in the alphabet can be used to form a word, the order of nitrogen bases in a DNA sequence forms genes, which in the language of the cell, tells cells how to make proteins. Another type of nucleic acid, ribonucleic acid, or RNA, translates genetic information from DNA into proteins.
The entire human genome contains about3 billion bases and about 20,000 genes.
DNA:Deoxyribonucleic acid. One of two types of molecules that encodegeneticinformation. (The other isRNA. In humans DNA is the genetic material; RNA is transcribed from it. In some other organisms, RNA is the genetic material and, in reverse fashion, the DNA is transcribed from it.)
DNA is a double-stranded molecule held together by weak hydrogen bonds between base pairs of nucleotides. The molecule forms a double helix in which two strands of DNA spiral about one other. The double helix looks something like an immensely long ladder twisted into a helix, or coil. The sides of the "ladder" are formed by a backbone of sugar and phosphatemolecules, and the "rungs" consist of nucleotide bases joined weakly in the middle by the hydrogen bonds.
There are four nucleotides in DNA. Each nucleotide contains a base: adenine(A), guanine (G), cytosine (C), or thymine (T). Base pairs form naturally only between A and T and between G and C so the base sequence of each single strand of DNA can be simply deduced from that of its partner strand.
The genetic code in DNA is in triplets such as ATG. The base sequence of that triplet in the partner strand is therefore TAC.
The first proof that DNA was the hereditary material was provided in 1944 by Oswald Avery, Maclyn McCarty and Colin MacLoed. The double helical structure of DNA was discovered in 1953 by James D. Watson and Francis H.C. Crick with the invaluable collaboration of the X-ray crystallographer Rosalind Franklin. Watson and Crick shared the 1962 Nobel Prize in Physiology or Medicine with Maurice H.F. Wilkins.