DNA and Proteins.
The structure of DNA is illustrated by a right-handed double helix, with about 10 nucleotide pairs per helical turn. Each spiral strand, composed of a sugar phosphate backbone and attached bases, is connected to a complementary strand by hydrogen bonding (non- covalent) between paired bases, adenine (A) with thymine (T) and guanine (G) with cytosine (C).
Adenine and thymine are connected by two hydrogen bonds (non-covalent) while guanine and cytosine are connected by three.
DNA structure has two helical chains each coiled round the same axis. Both chains follow right-handed helices. The two chains run in opposite directions. The bases are on the inside of the helix and the phosphates on the outside.
DNA is a polymer. The monomer units of DNA are nucleotides, and the polymer is known as a "polynucleotide." Each nucleotide consists of a 5-carbon sugar (deoxyribose), a nitrogen-containing base attached to the sugar, and a phosphate group.
There are four different types of nucleotides found in DNA, differing only in the nitrogenous base. The four nucleotides are given one-letter abbreviations as shorthand for the four bases.
There are only four DNA bases, but there are 20 amino acids that can be used for proteins, Proteins are molecules composed of amino acids linked together in a particular order specified by a gene's DNA sequence. Proteins perform a wide variety of functions including serving as enzymes, structural components or signalling molecules. So, groups of three nucleotides form a word (codon) that specifies which of the 20 amino acids goes into the protein (a 3-base codon yields 64 possible patterns (4*4*4), which is more than enough to specify 20 amino acids. Because there are 64 possible codons and only 20 amino acids, there is some repetition in the genetic code. Also, the order of codons in...