Semi-Conserveative replication Flashcards
What is semi-conservative DNA replication?
-For when new body cells are created, DNA must be replicated before mitosis for each daughter cell -> Identical copies for each
-Each cell has some proteins and carry out the same roles -> Characteristics
What does semi-conservative replication make?
New DNA molecule that is half of the original and half the new where the original strand acts as a template
Steps for semi-conservative replication
1) Two strands in double helix are separated by breaking the hydrogen bonds between bases, which is catalysed by DNA helicase
2) Each strand acts as a template which free nucleotides are attracted to their complementary based on the exposed strand hydrogen bonds form between the pairs
3) DNA polymerase joins adjacent DNA nucleotides on the new strand through condensation reactions forming phosphodiester bonds
4) Results in 2 DNA molecules containing one strand of new DNA and one strand of original DNA
What is DNA polymerase specific to?
DNA polymerase has a specific complementary active site to the 5’ end (phosphate group) of incoming free nucleotides and the 3’ end of the (OH of deoxyribose sugar) of the new strand
What is the purpose of DNA polymerase?
Catalyses a condensation reaction which forms phosphodiester bonds between last DNA molecule in developing 3’ and incoming 5’. Synthesises strand in 5’-3’ direction
What are the other models of DNA replication?
Conservative, semi-conservative and dispersive replication
What is the Meselson Stahl experiment?
Involved labelling the radioactive of DNA and then looking to see how the DNA is distributed in subsequent cell generations
What is the Meselson Stahl experiment based on?
All bases containing nitrogen, two isotopes n14 which has fewer neutrons so less dense and n15 which has more neutrons so more dense, bacteria take up nitrogen from their environment to make new DNA nucleotides during replication
Generation 0:
Bacteria in a medium of n15 so only n15 DNA. 1 band settles at the bottom of tube -> because it’s more dense
Generation 1:
Generation 0 (n15) DNA put in n14 medium. 1 band settles in the middle containing n14 and n15. Semi-conservative replication has occurred
Generation 2:
Generation 1 (n15 and n14) put in n14 medium. 2 bands = 1st in the middle and 2nd at the top made up of only n14
What happens in each generation of replication?
More n14 only DNA is made
