DNA replication Flashcards
The semi conservative replication of DNA ensures…
genetic continuity between generations of cells
Why is DNA replication described as ‘semi conserved’?
When DNA is replicated it forms daughter DNA: one strand is from the parental DNA and one strand is newly synthesised
Where does DNA replication occur?
In the nucleus
In what part of the cell cycle is DNA replicated?
The S-phase
How is DNA replicated?
1) DNA helicase breaks the hydrogen bonds between complementary bases causing the double helix to unwind
Each of the separated strands act as a template
2) Free floating nucleotides will attract to their complementary base pairs on the template strands
3) The adjacent nucelotides are joined together via condensation reactions, forming phosphodiester bonds
DNA polymerase catalyses these condensation reactions
4) Two new sets of daughter DNA are formed
What is the role of DNA helicase in DNA replication?
DNA helicase catalyses the reactions that breaks hydrogen bonds between complementary bases
What is the role of DNA polymerase in DNA replication?
- Catalyses the condensation reactions that form phosphodiester bonds between adjacent DNA nucleotides in the 5’ to 3’ direction
- A polynucleotide is formed
What is the role of DNA ligase in DNA replication?
Catalyses the reaction that joins two nucleic acid fragments
Which direction are nucleic acids synthesised?
5’ to 3’
What did Watson and Crick discover with the help of Rosalind Franklin’s research on x-ray diffraction?
The structure of DNA
What did Watson and Crick hypothesis about DNA?
That DNA must replicate conservatively or semi-conservatively
Who are Meselson and Stahl and what did they do?
Two scientists who conducted an experiment to see whether DNA is replicated conservatively or semi-conservatively
What did Meselson and Stahl find?
That DNA replication is semi-conserved
- This proved Watson and Crick’s hypothesis
State the 4 steps and results of Meselson and Stahl’s experiement into DNA replication
Generation 0
Bacteria grown in a medium containing 15N
- 100% of DNA is 15N 15N
Generation 1
Bacteria grown in a medium containing 14
- 100% of DNA is 14N 15N
Generation 2
Bacteria grown in a medium containing 14N
- 50% of DNA is 14N 15N
- 50% of DNA is 14N 14N
Generation 3
Bacteria grown in a medium containing 14N
- 75% of DNA is 14N 14N
- 25% of DNA is 14N 15N
