2.T2噬菌体的侵染实验 1952年Hershey 的实验： Protein coat is DNA is labeled labeled specifically with 35S specifically with 32p Attachment of phage to host cel Removal of phage coats by blending Removal of phage coats by blending 3 plus unlabeled DNA 3 (a) (b) Figure 2.4 The Hershey-Chase experiment.Phage T2 contains genes that allow it to replicate in E.coli.Since the phage is composed of DNA and protein only.its genes must be made of one of these substances.To discover which,Hershey and Chase performed a two-part experiment.In the first part(a).they labeled the phage protein with 3S(blue).leaving the DNA unlabeled(black).In the second part(b).they labeled the phage DNA with 32P (red).leaving the protein unlabeled(black).Since the phage genes must enter the cell.the experimenters reasoned that the type of label found in the infected cells would indicate the nature of the genes.Most of the labeled protein remained on the outside and was stripped off the cells by blending(a). while most of the labeled DNA entered the infected cells(b).The conclusion was that the genes of this phage are made of DNA.2．T2噬菌体的侵染实验 1952年 Hershey 的实验：