DNA Experiments

Question 1

What was the key discovery from Griffith’s Transformation Experiment (1928)?

Answer 1

Harmless bacteria can acquire genetic material from dead virulent cells — showing a “transforming principle” exists

Question 2

What molecule did Griffith’s experiment imply carried genetic information?

Answer 2

A transferable substance later identified as DNA

Question 3

What did Avery, MacLeod, and McCarty (1944) show about the transforming principle?

Answer 3

Transformation was prevented only when DNA was destroyed — proving DNA is the hereditary material

Question 4

What was the goal of the Hershey–Chase experiment?

Answer 4

To determine whether DNA or protein carries genetic information in viruses

Question 5

How did Hershey and Chase label DNA and protein in bacteriophages?

Answer 5

DNA with ³²P, protein with ³⁵S

Question 6

What did Hershey and Chase find inside infected bacteria?

Answer 6

³²P-labeled DNA entered the cells — confirming DNA is the genetic material

Question 7

What do Chargaff’s Rules state?

Answer 7

In any DNA sample, A = T and G = C

Question 8

Why were Chargaff’s Rules important?

Answer 8

They revealed base pairing regularity, key to the double helix model

Question 9

What did Watson and Crick discover about DNA structure?

Answer 9

DNA is a double helix with antiparallel strands and complementary base pairing (A–T, G–C)

Question 10

What was the Meselson–Stahl experiment designed to test?

Answer 10

How DNA replicates — conservative, semi-conservative, or dispersive

Question 11

What result supported semi-conservative replication in the Meselson–Stahl experiment?

Answer 11

One intermediate band after 1 generation; one light + one intermediate band after 2 generations

Question 12

Why is DNA replication described as semi-conservative?

Answer 12

Each new DNA molecule has one old (parental) and one new (daughter) strand