生物化学IILectureDNARNAProteinmetabolism.pptVIP

Nucleic acids and protein synthesis Central dogma of molecular genetics DNA as the genetic material Experiments that proved this DNA replication Meselson-Stahl experiment: semi-conservative replication Process of replication: DNA polymerase, Okazaki fragments Transcription (TS) RNA pol Translation tRNA’s, triplet code Wobble hypothesis Ribosomes Steps: Activation, initiation, elongation, termination Exonucleases and endonucleases ? biotechnology industry Post-translational modification Nucleic acids DNA as genetic material DNA is the genetic material *** DNA is used as a template (or blueprint) for the synthesis of large molecules How did we determine that DNA is the genetic material? Two experiments: Avery-McLeod-McCarty experiment (1944) Hershey-Chase experiment (1952) Avery-Mcleod experiment Studied a virulent strain of bacteria: pneumococcus Live encapsulated pneumococcus ? inject mouse ? dead mouse Live nonencapsulated pneumococcus ? inject mouse ? live mouse Live encapsulated pneumococcus ? HEAT ? heat-killed encapsulated ? inject mouse -? live mouse Live non-encapsulated pneumococcus + heat-killed encapsulated ? inject mouse ? dead mouse Live non-encapsulated + DNA from heat killed encapsulated ? bacteria were transformed ? turned into encapsulated live ? inject mouse ? dead mouse Avery-Mcleod experiment They showed that DNA extracted from the virulent strain could transform the non-virulent strain Suggested that DNA was carrying genetic info. Doubts: Their DNA contained protein as well Or possible that non-virulent strain was just “resurrecting” the dead virulent strain Hershey-Chase experiment Studied a bacteriophage (T2) that infects E. coli Conclusion: DNA alone was sufficient to carry all of the necessary genetic information Original theories of DNA replication Replication occurs in a conservative, semi-conservative, or dispersive fashion Which is it? Semi-conservative How do we know this? Meselson-Stahl experiment Meselson-Stahl experiment 19