DNA-replication@生物化学精品讲义.pptx

Happy Birthday,Double Helix DNA ReplicationBackground Information Watson CrickGeneral Features 1) Many enzymes and proteins are required 2) Template dNTPs/Mg 2+ are required 3) Semi-conservative A key experiment designed by M. Meselson and W. F. Stahl （1958） 4) DNA Unwinding is necessary 5) A Primer with a free 3 -OH group is required 6) Only in the 5′→3′direction 7) Specific Origin of Replication-Ori C and ARS (Autonomously Replicating Sequence） Three Common Features of Replication Origins 8) Bi-directional (With some exceptions) 9) Semi-discontinuous Replication fork ， Leading strand , Lagging strand and Okazaki fragments 10) Highly processive , Highly ordered and Extremely accurate Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid (Nature, April 25, 1953. volume 171:737-738.) The novel feature of the structure is the manner in which the two chains are held together by the purine and pyrimidine bases... The (bases) are joined together in pairs, a single base from one chain being hydrogen-bonded to a single base from the other chain, so that the two lie side by side...One of the pair must be a purine and the other a pyrimidine for bonding to occur. ...Only specific pairs of bases can bond together. These pairs are: adenine (purine) with thymine (pyrimidine), and guanine (purine) with cytosine (pyrimidine). ...in other words, if an adenine forms one member of a pair, on either chain, then on these assumptions the other member must be thymine; similarly for guanine and cytosine. The sequence of bases on a single chain does not appear to be restricted in any way. However, if only specific pairs of bases can be formed, it follows that if the sequence of bases on one chain is given, then the sequence on the other chain is automatically determined. ...It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material. The structure itself suggested that