3 DNA Structure And Replication Flashcards
(40 cards)
What was Griffith’s experiment - give a summary of the steps and findings
- He used Streptococcus pneumonia = two strains — rough and smooth and injected the two strains into different mice
- rough strain= killed mice
- smooth strain = mice lived
- heat killed smooth strain = mice lived
- rough strains and heat killed smooth strain = mice died
- therefore, there suggested there was a transforming agent being transferred
- we know now the transforming agent was DNA
Which strain of S. pneumonia is virulent (in Griffiths experiment)
Smooth strain. ( it has a capsule around it which protects it from our immune system and is therefore virulent)
Which strain of S.pneumonia is nonvirulent
Rough strain
What was Avery’s experiment
He broke down smooth bacteria into different component and injected each with rough strain
- only DNA from smooth strain caused pneumonia
What did Hershey and Chase find
Confirmed the role of DNA - concluded that it has genetic material
Give a summary of Hershey and Chase’s experiment
- had two batches of bacteriophage
- one batch = sulphur radioactively only labels phage proteins
- other batch = phosphorous only radioactively labels phage DNA
- each batch infected different cultures of bacteria
- cultures filtered, centrifuged
- only phosphorous found in Pallat, sulphur in supernatant
- therefore, DNA was injected into bacteria
What were Chargaffs findings
found ratio of A:T & C:G was same in each species – but variation between species
What were some of Watson and Cricks findings
- DNA has a double helical structure
- each strand of DNA acts as a template for new strand
What is a nucleotide in DNA made of
Deoxyribose sugar
Base
Phosphate
Which bond links the sugar to phosphate molecule
Phosphodiester bond
What is the sugar phosphate backbone made of
Deoxyribose sugar and phosphate
What is DNA coiled around
Histone
Which genes are more loosely coiled - active or silent?
Active genes
What is chromatin
DNA coiled around histone - efficiently packages DNA to take up less volume
What is Meselson and Stahl’s experiment
- Grew E.coli in a medium containing heavy n15
- Bacteria took this up and used to to make new DNA
- this bacteria was added to a n14
- 1st generation = Hybrid of light and heavy DNA
- 2nd generation = some hybrid, some only consisted of n14
— EVIDENCE for semi- conservative replication
Which enzyme unwinds the two strands of the DNA
DNA helical
How does DNA helical separate the two strands
By breaking hydrogen bonds
What do single strand binding proteins do
Stabilise the denatured DNA to prevent it from winding back up into a double helix
Which enzyme synthesises a shirt RNA primer for the start of replication
DNA primase
Give a summary of the steps in DNA replication in prokaryotes
- initiates at origin of replication
- DNA helical unzips the two strands
- leading strand:
—Primer binds to end
— DNA polymerase binds and goes along adding new complementary bases in 5’ to 3’ direction - lagging strand:
— Several RNA primers bind to different points of the strand
— chunks of DNA are added = Okazaki fragments - exonuclease strips away the primers
- DNA polymerase III fills in the gaps left when primers are removed
- new strand is proofread
- DNA lipase seals fragments
- new DNA winds up into a double helix
Role of exonuclease in DNA replication
Strips away the primers
Why is DNA replication semi-conservative
Each new DNA molecule made consists of one new and one old chain strand
What is the direction of growth of the leading strand
5’ to 3’ (read up write down)
Top strand is always 5’ at the beginning = leading strand
Which enzyme is used to seal the gaps between the Okazaki fragments in DNA replication
DNA ligase
