1 - DNA, Gene Structure, and DNA Replication

Abstract

Genetic information is determined by the sequence of nitrogenous bases in one of the strands, with a three-base (triplet) codon designating an amino acid. The genetic code is degenerate, which means that more than one codon specifies most amino acids. The genetic information is expressed when deoxyribonucleic acid (DNA) is transcribed into messenger ribonucleic acid (mRNA), which is then translated into polypeptides. Efficient and accurate replication of DNA must occur at each cell division, or the cell or the organism may not survive. DNA replication is semiconservative, which means that one of the nucleotide strands of each new DNA molecule is new and the other is old in each cell generation. The new DNA strand is complementary to the parental (or template) strand. DNA replication occurs in one direction only and thus replication takes place differently on the two antiparallel strands. Replication on a “leading strand” can occur in a continuous manner, while on the “lagging strand,” DNA replication occurs in short segments (Okazaki fragments). Although DNA replication is usually highly accurate, errors in DNA replication or mutations can result from duplications, deletions, inversions, and translocations of nucleotides that may affect the functioning of the resultant polypeptide. New combinations of genes can occur through recombination during meiosis.