Chapter 5. Replication & Recombination Aala A. Abulfaraj

DNA Replication Is Semiconservative Semiconservative replication: DNA replication is done by separation of the strands of a parental duplex Each strand then acting as a template for synthesis of a complementary strand. The sequences of the daughter strands are determined by complementary base pairing with the separated parental strands.

Replication of The DNA Replication of DNA is undertaken by a complex of enzymes that separate the parental strands and synthesize the daughter strands. Denaturation – In DNA, this involves the separation of the two strands due to breaking of hydrogen bonds between bases. Renaturation – The reassociation of denatured complementary single strands of a DNA double helix. Polymerases Act on Separated DNA Strands at the Replication Fork

FIGURE: The replication fork Replication of The DNA The replication fork is the point at which the parental strands are separated. The enzymes that synthesize DNA are called DNA polymerases. Polymerases Act on Separated DNA Strands at the Replication Fork FIGURE: The replication fork

Replication of The DNA Nucleases are enzymes that degrade nucleic acids; they include DNases and RNases and can be categorized as endonucleases or exonucleases. FIGURE : An endonuclease cleaves a bond within a nucleic acid FIGURE : An exonuclease removes bases one at a time

DNA Recombination Genetic recombination: A process by which separate DNA molecules are joined into a single molecule, due to crossing-over event This cross -over produces a new combination of alleles Recombination Occurs by Physical Exchange of DNA resulting in the exchange of genes between the two homologous chromosomes

DNA Recombination Recombination occurs by a breakage and reunion The frequency of recombination between two genes is proportional to their physical distance. Recombination between genes that are very closely linked is rare. For genes that are very far apart on a single chromosome, the frequency of recombination is not proportional to their physical distance because recombination happens so frequently

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