Meselson and Stahl's experiments- lqc 4b

Question 1

What were the three ways hypothesised that DNA could replicate by?

Answer 1

1. Fragmentary
2. Semi-conservatively
3. Conservatively

Question 2

how were bacterial cells grown in the first tube during semi-conservative replication

Answer 2

Bacterial cells were grown for many generations in a growth medium containing heavy nitrogen (15N)

Question 3

what was observed in the first tube during semi-conservative replication

Answer 3

One single band of heavy DNA was observed at the bottom of the tube

Question 4

what happened when the bacterial cells were transferred to a second tube in semi-conservative replication

Answer 4

The bacterial cells were then transferred to a growth medium containing light nitrogen (14N) and allowed to undergo two cycles of replication

Question 5

how was dna extracted during semi-conservative replication

Answer 5

DNA was extracted and separated by the process of centrifugation
after one and two cycles of replication

Question 6

when was the dna extracted during semi-conservative replication

Answer 6

DNA extracted after one cycle of replication gave one band of medium/intermediate (density)

Question 7

what happens to the dna after its been extracted for a second time during semi-conservative replication

Answer 7

DNA ( middle of the tube)

Question 8

what happens when DNA extracted after two cycles of replication gave two bands DNA

Answer 8

one band of medium DNA ( middle of the tube) and one band of light DNA ( top of the tube)