Semi-conservative replication

Question 1

what experiment did Meselson and Stahl perform

Answer 1

1. the grew E.coli in a medium that contained only the heavy isotope of nitrogen called N15
2. at the start of the experiment all the DNA nucleotides in the E.coli was made up of N15 so was heavier than normal DNA
3. they then transferred the bacteria into a medium containing only N14 sp from that point onwards any new nucleotides would be made of N14 and so lighter
4. they allowed the bacteria to replicate one and then removed and centrifuged their DNA
   5.DNA in the middle of the tube were a mix of light and heavy DNA and so proved DNA used Semi- conservative replication

Question 2

what is Semi-conservative replication

Answer 2

each newly synthesised DNA molecule has one strand from the old DNA molecule and one newly synthesised strand