DNA Replication Flashcards
Describe how semi conservative replication happens
1) DNA helicase (enzyme) breaks down hydrogen bonds that join bases together which cause the 2 strands of DNA to separate
2) free DNA nucleotides are attracted to exposed bases and pair up forming hydrogen bonds between complementary bases
3) nucleotides are joined together via DNA polymerase to join adjacent nucleotides together by condensation reaction, forming phosphodiester bonds
4) 2 identical molecules of DNA are formed each molecule retains half of the original strand
What was Watson and Crick’s hypothesis
Their is either semi conservative replication or conservative replication
Define conservative replication
Original DNA remain intact and 2 new synthesised strands of DNA join together
Define semi conservative replication
Each replicated DNA molecule contains 1 strand of the original DNA and 1 strand of the newly synthesised DNA
What does Meselon and Stahl’s experiment prove
Semi conservative replication
What does it mean when DNA bases are nitrogenous
Contain nitrogen
Key facts about semi conservative experiment
- nitrogenous bases contain nitrogen
- Nitrogen has 2 isotopes = 14N 15N
- bacteria takes in nitrogen isotopes to make new DNA nuceolutides
- DNA can be spun in a centrifuge to confirm density
What does it mean when bacteria takes in a specific nitrogen isotopes
Bacteria grown in a medium containing 15N will have DNA which only contains this isotope
After being spun in then centrifuge what is the density if DNA settles lower
More dense
After being spun in then centrifuge what is the density if DNA settles higher
Less dense
In G0 what medium is bacteria grown in
15N
In G0 where did the DNA settle and what did this mean
DNA settles at the bottom meaning 100% of the DNA is 15N 15N
In G1 what medium is bacteria grown in
14N
In G1 where does the DNA settle and why
DNA has settled slightly higher means 100% DNA 15N 14N
In G2 what medium is the bacteria grown in
14N
