4 Nucleic acids and replication Flashcards
DNA structure
Purines - A/G (1 ring)
Pyrimadines - C/T/U (2 rings)
Phosphodiester bonds between phosphate group and deoxyribose of another
DNA helix is a right handed helix
DNA as genetic material
Griffiths (1928)
Avery, MacLeod and McCarty (1944) - by purifying this material it was the nucleic acids doing this rather than the protein
Hershey and Chase (1952) - experiment below (showed that it’s the DNA gets passed down as genetic material
Sulfur vs phosphorus labelling
After centrifugation
Only phosphorus in cells
X-ray diffraction (photo 51)
Helical structure - repeat at 0.34 and 3.4 nm / 2nm wide
Phosphates on outside
2 strands
What did Chargaff discover
Complimentary base pairing
What did Watson and Crick discover
Double helix (using photo 51)
RNA world and ribozymes
The proposition that RNA predated DNA (and protein) in evolution
RNA could carry information and replicate itself
Modern RNA can catalyse chemical reactions (ribozymes)
Is involved in all stages of protein synthesis
Why DNA evolved from RNA
RNA - unstable (2’ hydroxyl makes it unstable especially in alkali conditions) - so the loss of thos results in a more stable molecule
Cytosine —> uracil and thymine (by deamination) - cytosine is not very stable and overtime converts into uracil - problem in information carriage because impossible to tell which uracil’s were initially cytosines
Use of uracil gycosylate
Semi-conservative replication
Meselona= and Stahl (1958) —> both strands act as template
Always adding onto the 3’ end (5’—>3’)
Synthesis require = primers - RNA polymerase makes primer (caalled perimase)
DNA polymer extends primer
Problem of antiparellel DNA
When making replication form because DNA always synthesised in same direction (5’—>3’) enzyme only works in 1 direction (anti-parallel strand has to be synthesised backwards)
Problem with the helix
Twisting in the strands
Topoisomerase - only use of it is because DNA is helical
