DNA复制-第一讲课件.pptVIP

免疫学信息网 * Electron Microscopy of replicating DNA reveals replicating bubbles. How does one prove bidirectional fork movement? Pulse with radiolabeled nucleotide; chase with cold nucleotide. Then do autoradiography DNA Replication DNA replication is semi-conservative, one strand serves as the template for the second strand. Furthermore, DNA replication only occurs at a specific step in the cell cycle. The following table describes the cell cycle for a hypothetical cell with a 24 hr cycle. Stage Activity Duration G1 Growth and increase in cell size 10 hr S DNA synthesis 8 hr G2 Post-DNA synthesis 5 hr M Mitosis 1 hr DNA replication has two requirements that must be met: 1. DNA template 2. Free 3 -OH group DNA Replication DNA replication is semi-conservative, one strand serves as the template for the second strand. Furthermore, DNA replication only occurs at a specific step in the cell cycle. The following table describes the cell cycle for a hypothetical cell with a 24 hr cycle. Stage Activity Duration G1 Growth and increase in cell size 10 hr S DNA synthesis 8 hr G2 Post-DNA synthesis 5 hr M Mitosis 1 hr DNA replication has two requirements that must be met: 1. DNA template 2. Free 3 -OH group Proteins of DNA Replication DNA exists in the nucleus as a condensed, compact structure. To prepare DNA for replication, a series of proteins aid in the unwinding and separation of the double-stranded DNA molecule. These proteins are required because DNA must be single-stranded before replication can proceed. 1. DNA Helicases - These proteins bind to the double stranded DNA and stimulate the separation of the two strands. 2. DNA single-stranded binding proteins - These proteins bind to the DNA as a tetramer and stabilize the single-stranded structure that is generated by the action of the helicases. Replication is 100 times faster when these proteins are attached to the single