experiment supporting DNA replication and history Flashcards
first 3 theories as to how DNA replicates
1) Conservative- DNA molecule copied to make a new molecule
1) Dispersive - DNA cut at various points each of which get copied and reattach to make 2 new DNA molecules
2) Semi- conservative - 2 DNA strands separate and act as a template for new ones
Who conducted the experiment to prove a semi-conservative replication model
-Meselson and Stahl
Outline the experiment of the semi-conservative model
-used bacteria as easily grown
-first, grew bacteria in a 15N medium
-after 14 gens, most DNA was heavy as it was grown in this medium
-Bacteria transferred to medium with 14N isotope and undergo one replication- centrifuged
-the F1 gen of 15N and 14N settled halfway down- shown its half heavy and half light
-in the F2 and F3 gen, lighter band of 14N also formed bc growth medium was entirely 14N so DNA continued to replicate this as it was replicating
how did the experiment disprove the dispersive model
-not in line as after 2 cell divisions, should contain a mix of heavy and light, not a band of light DNA
how did the experiment disprove the conservative model
-In the first centrifuge after the 1st replication in 14N, if it was conservative half should have been all light and half should have been all heavy rather than one half light half heavy strand
why did they centrifuge
-so can separate things due to their weight
how does the experiment prove semi-conservative
-as there was a light band and a mixed one because the light+ heavy DNA turned into (light + light) and (heavy + light)
when do mutations occur
-when the wrong nucleotide may be inserted in the sequence
what is it called when the wrong nucleotide is inserted into the sequence
-point mutation
what stops mutations
-proof reading enzymes edit out many incorrect nucleotides
why are some mutations harmful
-produce different versions of a gene/ allele
-resulting in abnormalities of a phenotype
