DNA replication Flashcards
why does DNA replicate itself
so that each new cell has a full amount of DNA
what’s semi conservative replication
the process of how DNA replicates itself
what’s the first step of DNA replication
the enzyme DNA helicase breaks the hydrogen bonds between the bases on the two polynucleotide DNA strands. This makes the helix unwind to form two single stands
what’s the second step in DNA replication
each original strand acts as a template for a new stand
complementary base pairing means that free floating DNA nucleotides are attached to their complementary exposed bases
what’s the third step in DNA replication
condensation reactions join the nucleotides of the new strand together
this is catalysed by the enzyme DNA polymerase
hydrogen bonds form between the bases on the original and new stand
each new DNA molecule contains one strand from the original DNA molecule and one new strand
what’s the difference in the ends of the stands in DNA
one is called the 3 prime and the other is 5 prime
what does DNA polymerase do in DNA replication
the active site of DNA polymerase is only complementary to the 3’ end of the NEWLY forming DNA strand
who determined the structure of DNA
Watson and Crick
explain Meselson and Stahl’s experiment step 1
two isotopes of nitrogen, heavy nitrogen and light nitrogen
two samples of bacteria were grown, one was in a nitrogen broth containing light nitrogen and one in a broth of heavy nitrogen, as the bacteria reproduced they took up the light/heavy nitrogen from the broth to help make nucleotides for new DNA. Nitrogen became part of the bacteria’s DNA
explain Meselson and Stahl’s experiment step 2
a sample of bacteria was taken from each batch of bacteria and was spun in a centrifuge the heavy nitrogen settled lower than the light nitrogen
explain Meselson and Stahl’s experiment step 3
the bacteria grown in the heavy nitrogen broth were taken out and put in the broth containing only light nitrogen. they were left for one round of DNA replication and then spun in the centrifuge
explain Meselson and Stahl’s experiment step 4
the DNA settled in the middle showing that the DNA molecules contained a mixture of heavy and light nitrogen showing us that the replication is semiconservative
