Zoo342 Molecular biology Lecture 2 DNA replication DNA

Zoo-342 Molecular biology Lecture 2 DNA replication

DNA replication v DNA replication is the process in which one doubled-stranded DNA molecule is used to create two double-stranded molecules with identical DNA sequences. v DNA replication occurs during the S phase of the eukaryotic cell cycle.

Three alternative models for DNA replication

Initiation of DNA replication in prokaryotes and eukaryotes v Each mammalian chromosome is composed of many replication sites or origins of replication (replicons). v The Escherichia coli (prokaryotes), chromosome is composed of only one replicon.

Initiation of DNA replication

DNA replication fork v Helicase unwind the double-stranded DNA helix and single-strand binding proteins (ssb protein) react with the single-stranded regions of the DNA.

Differences between DNA replication in prokaryotes and eukaryotes Site of DNA replication The number of origin replication (replicon) The number nucleotides Prokaryotes Eukaryotes In the cytoplasm In the nucleus One Several (many) of in the number of 100 -200 nucleotides replicon The replication forks Two Each replicon is formed of approximately 150 nucleotides Many Leading strand is synthesized by DNA Types of DNA polymerase Leading and lagging strands synthesize by polymerase delta (δ), while lagging DNA polymerase III strand is synthesized by DNA polymerase alpha (α). Size of fragments Okazaki Large, approximately 1500 nucleotides Short, approximately 150 nucleotides

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