Question

1. The experiments that clearly showed that DNA from every organism studied had an amount of adenine equal to the amount of thymine and a cytosine content equal to the content of guanine were conducted by:

a.   E. M. Sutton.

b.   Cohen and Boyer.

c.   Hershey and Chase.

d.   Erwin Chargaff.

e.   Rosalind Franklin.

2. A quiescent (non-dividing) human cell is most likely (or most correctly described as being) in:
   1. G1.
   2. S phase.
   3. G0
   4. M phase.
   5. cytokinesis.

3. Who utilized the process of transformation, as originally demonstrated by Frederick Griffith, to provide the first solid evidence suggesting that DNA was the genetic material of living systems (in this case bacteria)?
   1. Messelson and Stahl
   2. Thomas Morgan
   3. Erwin Chargaff
   4. Hershey and Chase
   5. Avery, McCarty and Macleod

4. The two strands of a DNA helix are initially separated during the process of DNA replication by:

1. DNA polymerase I.
2. DNA polymerase III.
3. a topoisomerase.
4. primase.
5. a helicas

5. To avoid problems associated with gene dosage issues (noting that males are XY), human XX females convert one X chromosome into a/an:
   1. Barr body.
   2. centromere.
   3. centrosome.
   4. telomere.
   5. balanced translocation.

Answer 1

1.By an experiment Erwin Chargaff showed that percentage of adenine is always equal to percentage of thymine and Percentage of guanine is equal to percentage of cytocine. This also shows that purines always pair with pyrimidines.

2.A quiescent or nondividing human cell is most likely to be in G0 stage. This is the resting phase of cell cycle where cell try to accumulate sufficient cytoplasm to nourish the cell. Once a cell enter into this stage either undergo for differentiation or enter to cell cycle when required.

3.Avery, McCarty and Macleod use the Griffith experiment to prove that DNA is the genetic material. They performed this experiment in biochemical basis. They digested different components of bacterial cell with respective digestive enzymes and showed that only when DNA get digested in that case transformation is not possible. This experiment also known as biochemical assay of transformation.

4. During DNA replication the two strands of DNA initially separated by the action of a helicase. It is a hexameric protein.It requires ATP for it's action.

5.To avoid dosage problem the X choromosome of human female undergo inactivation. That is called as Barr body. This process also called as dosage compensation. By staining a female cell if we observe it under compound microscope it appears as a black dot which remain stick to the nuclear membrane.