DNA lecture 1 Flashcards
What did Watson and Crick Propose
Semi-conservative replication.
- Parent strand
- Daughter strand
Hybrids of the new and old strand
Who proved the Watson and Crick hypothesis?
Messelson and Stahl who conducted an experiment using radioactive nitrogen taken up within Ecoli.
What did the experiment involve?
Centrifuged the Ecoli bacteria and then measured the density of the resulting DNA strands. Radioactive 15N has a greater density and would sink to the bottom of the test tube.
Then would compare by the degree of sinking within the test tube:
- Parent strand vs Daughter Strand vs Hybrid strand
What determines where DNA replication occurs in eukaryotic cells?
The origins of replication
What is involved within DNA replication
To antiparallel complementary DNA strands
What determines the direction of the DNA strands?
Sugar in the carbons - exposed 3` OH group
What initiates DNA replication
DNA polymerase III = polymerisation of nucleotides
What does DNA Polymerase III require?
4 dNTPs, template strand & primer with 3` OH group
What makes RNA Primers
RNA Primase/ polymerase
What direction is complementary DNA strands synthesised in
5 to 3
What direction do the DNA enzymes move in?
3 to 5
Does one or both strands act as templates
Both strands behave as templates
What are two important components of semi-conservative replication
Bidirectional and simultaneous DNA replication
What do we need to overcome in DNA replication synthesis
The need for complementary strands to be made 5` to 3. We overcome this through discontinuous synthesis.
What is it easier to make a complementary DNA strand for: leading or lagging strand
Leading strand = continuous synthesis
What are the DNA fragments called that are made in discontinuous DNA synthesis
Okazaki fragments
How did we prove the Okazaki fragments presence?
Okazaki used H3-dnTP (ie radioactive) which was incorporated into the presence of the DNA for 5 second pulses. Break up strands and found more H3 in continuous strand of leading strand and less in the lagging strand during discontinuous synthesis in DNA replication.
What does helicase do
Unwinds DNA double helix by breaking double bonds between complementary DNA base pairs
What form of DNA polymerase is responsible for exonuclease activity?
DNA Polymerase I
What does DNA polymerase I do?
locates and removes RNA primers
What does DNA ligase do?
Adds phosphate into the gaps of the phosphate sugar backbones, where the RNA primers originally where.
What does RNA Primers initiate?
DNA replication
What do we call the protein complex of DNA replication
Replisome
What determines the origin of replication
Regions where there are lots of adenine and thymine nitrogenous bases = 2 hydrogen bonds and therefore easier to separate.
Does proof reading occur
Yes
Number of template strands
2
Size of templte
Whole strand of complementary DNA
Products
DNA
Nucleotide substrate
dNTPs
