Introduction to bacteria
Haploid organisms – small circular genomes, (E. coli 4.5 X 106 bp.)
Rapid growth (E. coli 20 minutes per generation; therefore, 1 cell to 1,000,000 in less than 7 hr.)
Grow to high population density – liquid ~109- 1010 at saturation,
Several features of bacterial genetics are particularly useful
in the study of genetics in general. Since most genetic alterations are subtle (细微的) and rare, bacteria offer advantages such as:
(1)Bacteria contain a single genome per cell so analysis is not complicated by multiple gene copies (2) Fast growth rates ---> rapid results. In higher organisms results of genetic experiments need years. With bacteria results can be obtained in days . (3) Enormous numbers of offspring; even the most improbable events can occur at significant rates.
Proof that DNA is the genetic material
四个实验
?The observation that something in heat-killed virulent (毒力的) bacteria can transform avirulent bacteria to the virulent phenotype formed the basis for one of the first demonstrations that DNA is the genetic material.
Proof that DNA is the genetic material
?Destroying the DNA in the heat killed bacteria eliminated the transforming activity.
上页的d实验
DNA is the Chemical Agent Responsible for Transformation ?In 1944, O. Avery, C. MacLeod, and M. McCarty provided strong evidence that bacterial transformation is mediated by DNA. ? Proteins were destroyed using proteases.
?RNA was destroyed using RNase. ?DNA was destroyed using DNase.
–Only the DNase treatment destroyed the transform the bacteria.
Avery OT
MacLeod CM
ability of the extract McCarty M
to
细胞生物学英文课件-61 转化
