DNA Structure
Deoxyribonucleic acid is a linear polymer of up to a hundred million monomer units (nucleotides). DNA contains only four different nucleotides. A nucleotide has only three parts, a phosphate group, 2-Deoxyribose, and an organic base. The structures of 2-Deoxyribose and of the bases are shown below. A purine has a pair of fused rings; a pyramidine has only one ring. Both purines and pyramidines are heterocyclic, i.e. the rings are built from more than one type of atom. The N atoms are not protonated at neutral pH, but the nucleotides have acidic character due to the phosphate which dissociates and becomes negatively charged. The 1 or 9 nitrogen of the base is attached to the 1` carbon of the deoxyribose. The 5` hydroxyl group of the deoxyribose forms an ester bond to the phosphate group. from essaybank.co.uk When nucleotides polymerise to form nucleic acids, the 3` hydroxyl group of the deoxyribose of one nucleotide forms a phosphodiester bond to the phosphate of another nucleotide, eliminating a molecule of water.
Bent DNA is important because it accommodates binding proteins. s a single DNA strand is a phosphate- deoxyribose polymer with purine and pyramidine bases as side groups. Like a polypeptide, a nucleic acid strand has a chemical orientation: the 3` end has a free 3`hydroxyl group, the 5` end has a free 5` hydroxyl or phosphate group. DNA does not normally exist as a single strand, it has a tendency to associate with another, complementary strand. The strands wind together through space in a helical fashion which is described as a double helix. The two sugar-phosphate backbones are on the outside of the double helix, and the bases project into the interior. The adjoining bases in each strand stack on top of one another in parallel planes. The orientation of the two strands is antiparallel (their 5` > 3` are opposite); they are held together by the cooperative energy of many hydrogen bonds in addition to hydrophobic interactions. The opposite strands are held in precise position by a regular base pairing between the two strands. A is paired with T by two
Some common words found in the essay are:
SEQUENCES DNA, DNA Deoxyribonucleic, DNA DNA, Cellular DNA, Bent DNA, Circular DNA, double helix, hydrogen bonds, purine pair, , paired hydrogen bonds, purine pair pyramidine, left handed, hydroxyl deoxyribose, bond phosphate, pair pyramidine, dna strand, natural dna, base pairs,
Approximate Word count = 725
Approximate Pages = 3 (250 words per page double spaced)
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