Question

Okazaki fragments form on the

		the lagging strand
		mismatched DNA
		the 3' end of a polymerizing strand of DNA
		RNA
		the leading strand

What did the Hershey-Chase experiment demonstrate, does not enter the bacterium? In other words, what was demonstrated NOT to enter the bacterium?

Answer 1

Okazaki Fragments are the short sequences of DNA always formed on/present on the lagging strand of the DNA. Since we know that the synthesis of the daughter strand of the DNA is from 5'to 3' direction the leading strand synthesis takes place in the 5' to 3' direction whereas the DNA polymerase has to also synthesize the daughter strand on the antiparallel strand i.e the lagging strand. So imagining a replication bubble where there are forks at both the ends the direction of the synthesis is supposed to be 5' to 3'.

The helicases will come and unzip the parental double strand and the polymerase will elongate the daughter strands, Understand that the DNA parental strands are antiparallel to each other so if one strand runs from 3' to 5' its complementary strand runs in 5' to 3' direction. Each of these strands acts as templates to grow the daughter strands once the replication bubble is formed. Now the daughter strand forming on 3' to 5' parental strand will be a leading strand whose synthesis has to be taken place in 5' to 3' direction. There is no issue with the elongation of this strand as the DNA polymerase just has to add bases. The catch is, in the same replication bubble there is 5' to 3' parental strand whose daughter strand shall be of 3' to 5' direction but according to the elongation rules it should be from 5' to 3' so here come the Okazaki fragments into the picture so that the direction of the replication could be maintained and later these fragments are joined by the enzyme ligase.

So the correct option should be 1st.

The Hershey & Chase Experiment

The Hershey & Chase Experiment was performed to demonstrate that it is DNA, not the Protein which is the Genetic Material in the Cell. Alfred Hershey and Martha Chase performed the experiments on the life cycle of T2 bacteriophages by radiolabelling their protein and genetic material. Radioactive Phosphorus-32 was used to label the DNA since the phosphorus is found specifically in the nucleic acids whereas radioactive sulfur-35 was used to label the protein of the T2 phages. It is known that the bacteriophage attack a bacterial host in order to complete their life cycle and the mode of entry of a phage inside the host is through transduction. So the rationale of the experiment was that if  Phosphorus-32 is detected inside the bacterium it will indicate that the genetic material is in fact DNA whereas the presence of radioactive sulfur-35 will indicate it is the protein that is the genetic material. The experiment was performed where the radiolabelled T2 Phages were allowed to transduce the bacterial cells & it was demonstrated that most of the radioactive sulfur-35 is outside the cell which means the protein arent getting inside the bacterial cells in order to complete the lifecycle of the T2 phage. Although, this radioactive phosphorus-32 was found incorporated inside the bacterial cells depicting that it is DNA which is the actual genetic material.