Dna and Transfer of Information

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DNA and the transfer of information DNA or deoxyribose nucleic acid is present in all cells. It carries the instructions for its correct functioning. DNA is a polynucleotide made up from nucleotides which contain the bases adenine, thymine, cytosine and guanine. It is a double stranded molecule which coils to create a double helix. DNA nucleotides consist of three components, a phosphate group, a deoxyribose pentose sugar and an organic nitrogenous base, FIGURE 1. The organic bases fall into two groups. These groups are the purines and the pyrimidines. Purines have a double ring structure and are the bases adenine and guanine and pyrimidines have a single ring structure and are the organic bases thymine and cytosine FIGURE 2. DNA is a stable double stranded molecule consisting of two polynucleotide chains that carry the genetic code. When the nucleotide chains are joined they bind with hydrogen bonds, a purine always bonds with a pyrimidine. Therefore adenine always pairs with thymine and cytosine always pairs with guanine. These are known as complementary base pairs and they are held together by hydrogen bonds, 2 between adenine and thymine and 3 between cytosine and guanine. These hydrogen bonds form as oxygen and nitrogen atoms in the bases carry a slightly negative charge and the hydrogen’s carry a positive charge and this difference in charges causes an attraction which makes up the hydrogen bonds. DNA consists of two antiparallel strands and it twists to form a double helix. Each base pairing causes a twist with one complete turn happening every 10 bases. FIGURE 3 A gene is a section of DNA that contains coded information in the form of a specific sequence of bases. The bases code for the sequence of amino acids that make up polypeptides. Genes occupy fixed positions on particular strands of the DNA. The position of the genes on the chromosome is called

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