21. The overall conclusion of the Hershey-Chase experiment was that

A. DNA was responsible for heredity
B. proteins and DNA were responsible for heredity
C. the ratio of Adenine to thymine was always the same
D. phage DNA was similar to bacterial DNA

22. A cesium chloride will separate DNA molecules by

A. absorption
B. resorption
C. density
D. adhesion

23. If one cell has AT contents 40%, what will be the percentage of Guanine residue?

A. 60%
B. 15%
C. 30%
D. Guanine residue can not be calculated

24. Which of the following enzyme adds complementary bases during replication?

A. Helicase
B. Synthesase
C. Replicase
D. Polymerase

25. Which DNA polymerase removes RNA primers in DNA synthesis?

A. Polymerase I
B. Polymerase II
C. Polymerase III
D. none of these