Meselson and Stahl Flashcards
What does replication mean?
A general term that means repetition. In DNA replication, an exact copy of the DNA is made prior to cell devision.
What is the semi conservative model?
In DNA replication, each of the two resulting DNA molecules contain one ‘old’ (conserved) strand and one ‘new’ strand
What is the dispersive/fragmentary model?
All DNA strands are made up of a mixture of original parent DNA nucleotides and new nucleotides.
What is the conservative model?
One DNA molecule has 2 original parent DNA strands and the other has 2 ‘new’ strands
What were the stages of the Meselson and Stahl experiment (first stage)
First, bacteria is cultured in a medium containing a HEAVY isotope of Nitrogen (15N)
What were the stages of the Meselson and Stahl experiment (stage 2)
Bacteria is transferred to a medium containing elemental nitrogen (14N)
What were the stages of the Meselson and Stahl experiment (stage 3)
DNA is centrifuged after the first replication
What are the predictions after the first replication of the Meselson and Stahl’s experiment?
CONSERVATIVE: one light
one heavy
SEMI - CONSERVATIVE: 2 medium (one stand of parent and one strand of new DNA)
DISPERSIVE: 2 medium (both made of of fragments of original and new DNA)
Which theory was disproved after the first replication (Meselson and Stahl)?
After one replication, there was a band of MEDIUM DNA. This disproved the CONSERVATIVE replication of DNA, because if this was true, then there would be a band of heavy and light DNA, not a band of medium DNA.
What were the stages of Meselson and Stahl’s experiment (stage 4)?
To find out if it was fragmentary or semi - conservative, they centrifuged the DNA sample a second time after the second replication.
What are the predictions after the second replication of the Meselson and Stahl’s experiment?
SEMI - CONSERVATIVE: a band of light and a band of medium DNA
FRAGMENTARY: only a band of medium DNA
Which theory was disproved after the second replication (Meselson and Stahl)?
They found after the second replication, that there was a band of light and medium DNA. This disproves the FRAGMENTARY DNA replication theory as, if it was always a mix of light and heavy DNA there would only be a band of medium DNA.
