Biology 1202B Lecture Notes - Covalent Bond, Nucleoside Triphosphate, Hydroxy Group

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12 Feb 2014
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DNA Replication
DNA is replicated semi-conservativley – Meselson and Stahl used two different isotopes
for Nitrogen ( N15 & N14) and added E. Coli to the medium
- the lighter band is higher up and the darker band lower down
- isolates DNA  see how the DNA settles
- exam question – what would the other two options (conservative and dispersive)
results look like?
DNA polymerase adds bases to 3’ Hydroxyl group but synthesizes 5’-3’
Nucleoside triphosphate pairs – carbon sugar, phospahate group and a nucleotide base
- only complimentary base will be able to join in
Phosphodiester linkage produces energy to break the covalent bond
Hydrogen bongs need to be strong enough to keep the helixes together but weak
enough to be broken apart for replication
Bacterial polymerase—a clamp holds the DNA in place to allow more efficient/faster
replication
- if the clamp was not there, polymerase would polymerize and then disassociate making
the process very slow
Initiation of DNA replication:
- starts off with an origin of replication – various binding protiens (cascade of molecules
will start to process)
- helicase  unbinds the helix of DNA – energy dependant (hydrolyzed ATP)
- single stranded binding proteins – proteins that bind to the individual strand to prevent
it from becoming double stranded again
- topoisomerase – nixes the backbone allowing it unwind releasing/relieving tension on
the helixes
- RNA primase – recognizes origin of replication and lays down RNA primer (3’) –
attaches to clamp and starts putting bases down
- polymerase – put down a new nucleotide bas at 3’ OH
Elongation – a continuous and lagging strand
Exonuclease – removes nucleotides
Telomerase – synthesizes nucleotides from 5’- 3’
RNA enzyme built in – recognizes sequence at the end b/c highly repetitive
Mice experiment
- no telomerase = shorter life span but less cancer
- excessive telomerase = longer life but increase cancer