Lectures 16-23 Flashcards
Polycistronic
More than one gene can be encoded. Prokaryotic mRNA is often polycistronic.
DNA structure
10 bps or 34A /turn, 20A diameter.
DNA polymerase types and function.
I: Kornberg Enzyme- involved in DNA excision repair of UV damage.
II
III: can polymerize up to 30,000 nucleotides/minute.
All 3 of the DNA polymerases require a preexisting polynucleotide chain on to which to add mononucleotides on the 3’-OH end.
DNA replication occurs in what direction? Why?
5’->3’
Because it cannot do a nucleophile attack in the 3 to 5 prime direction.
DNA Replication is___(3 things)…
Semiconservative (Mendelsson/Stahl 1958), bidirectional, and starts at the oriC.
RNA Polymerase
Contains a, B, B’, sigma. These all comprise the haloenzyme.
Bac: 1 type w/ 6 subunits
Arc: several types w/ 8-12
Euk: several types w/ 12-14 su
Sigma Subunit
Initiation factor, dissociates once polymerization begins.
tAKES PART IN Nitrogen met, Flagellum syn, Aand pathogenic.
mRNA
5% of total RNA.
Translation of mRNA rarely starts exactly at one end of the mRNA molecule and proceeds to the other end. Instead it may begin 100’s of nucleotides in from the 5’-P terminus. This untranslated region is called the leader, (5-20 bases usually). The polycistronic mRNA usually contains spacer sequences 10 bases long which separate the coding sequences.
rRNA
70S-> 50S (23S+5S) +30S (16S)
16S pairs w/ initiation sequence on mRNA and positions the mRNA on the ribosome.
23S is the peptidyl transferase (assc w/ peptide bond formation)
tRNA
3 loops:
anticodon-recognition at the ribosome, matches up w/codon.
dihydrouridine + pseudouridine: binding of ribosome and aminoacyl-tRNA synthetase
Termination of Transcription
Rho Independent- when RNA polymerase synthesizes poly U seq
Rho dependent- rho binds to RNA and cataches polymerase at a terminator where it unwinds the RNA-DNA hybrid.
Promotor for RNA synthesis
Pribnow box- TATAAT- 10 SEQ
TTGACA- 35 SEQ
Stop/Start Codons
Stop UGA UAG UAA
Start AUG GUG (METHIONINE)
