Lecture 4 Flashcards
Who discovered Nucleic acid?
Friedrich Miescher.
What type of experiment did Griffith undertake in 1928?
Using which microorganisms?
Transformation experiments with lethal and non-lethal Streptococcus pneumoniae.
What letters represent benign and virulent S. pneumoniae?
R = benign. S = virulent.
What did he find?
Heat killed S form + R form caused mice to die. Blood contains live pathogenic S. pneumoniae.
What did Griffith’s experiment mean?
Must be a ‘transforming principle’.
What did Avery, McLeod and MacCarty do in 1944?
Establish chemical properties of ‘transforming principle’.
What are the chemical properties of the transforming principle?
Resistant to proteases - not protein, lipases, ribonucleases - so not protein, lipid or RNA.
Ethanol insoluble - not carbohydrate.
High molecular weight - like DNA.
Positive reaction to Dische test for DNA.
What is Chargaff’s rule, and what does it provide evidence of?
A=T, (1:1)
G=C. (1:1)
Evidence of DNA.
What is a bacteriophage?
Type of virus composed of DNA and protein which infects bacterial cells.
What did the Hershey-Chase experiment show?
Bacteriophage injects DNA into bacterial cell.
How was the Hershey-Chase experiment performed?
- B’phage protein labelled with 35S, mixed with E.coli.
Most of the radioactivity ended up in supernatant. - B’phage DNA labelled with 32P.
Most of the radioactivity in the pellet.
What happens at the end of a bacteriophage infection?
New generation of virus particles burst from host cell.
What method did Watson and Crick use for developing their model for the double Helix?
Trial and error, and 2 purines too wide, and 2 pyrimidines too narrow.
How many H bonds in A-T?
2.
How many H bonds in G-C?
3.
Are DNA strands parallel or anti-parallel?
Anti-parallel.
What did Watson and Crick suggest regarding replication? What type of replication did they discover therefore?
Each strand can act as a template for synthesis of a new complementary strand.
Semi-conservative replication.
What other scientists supported the semiconservative model besides W&C? What did they do in their experiment?
Matthew Meselson and Franklin Stahl.
Labelled old nucleotides with heavy isotope of Nitrogen. Any new nucleotides labelled with lighter isotope.
1st replication produced band of hybrid DNA, eliminating conservative model.
2nd replication produced both light and hybrid DNA, eliminating dispersive model, supporting semiconservative.
What end must DNA polymerase add nucleotides to?
3’ OH end.
Where does replication begin on the chromosome?
Many sites simultaneously, on both sides of DNA.
What are the front and back of synthesising DNA strands called?
Leading and lagging respectively.
What does synthesis of the lagging strand require?
Synthesis of multiple short fragments (Okazaki), then joined together.
What synthesises a new primer during DNA replication?
Primase.
What 6 proteins and enzymes contribute to DNA replication?
Helicase, Single-strand binding proteins, Primase, DNA polymerase III, DNA polymerase I, DNA ligase.
