Dna - the Molecule, Expand

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DNA - the molecule, expand Deoxyribonucleic Acid, DNA is the genetic code in most human cells. It codes for all structures and functions within a living body. DNA has a double strand helix structure. The two strands are made up from a sugar-phosphate backbone with a base pair in the middle. These bases are, C G T A each base has a complimentary base e.g. C pairs with G and T pairs with A, these base pairs join in the centre of the two strands by hydrogen bonding. DNA is split into triplet codes of 3 bases, chromosomes which are long strands of DNA highly coiled which contain thousands of genes, these appear in sex cells and before a cell replicates. For DNA to be in every cell of the body it has to be replicated as the parents sex cells cannot hold all the DNA for every cell in the organism, but the parents sex cells do hold all the information for every cell in the offspring. DNA replication takes place in every nucleus in several stages. Firstly an enzyme called DNA helicase unwinds the two strands in the helix and the enzyme breaks the hydrogen bonds between the bases to make two separated strands. Primers are then added to the strands which indicate to a second enzyme DNA polymerase where to begin copying. The Polymerase enzyme attaches to the strand at the primers and then moves along the strand catalysing the addition of new complementary nucleotides to complete the new strand. The new strand will be exactly the same as the first as the bases haven’t changed order. DNA is used in the body to make proteins, chains of amino acids which make structures used by the body. For example Haemoglobin is a quaternary protein. Proteins are made in a multi stage process involving several enzymes and parts of the cell. Firstly a stage called transcription occurs, this is where DNA helicase again splits the two strands of DNA in the double helix and then RNA

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