October 10 Notes

Transcription and translation of a gene occur simultaneously
As a gene is being transcribed, that mRNA starts being translated, even before transcription is finished

I. Bacterial vs. Eukaryotic genetic
a. Chromosome shapes

  1. eukaryote - linear DNA
  2. Prokaryote- circular DNA

DNA polymerrase can't copy DNA without a swatch of DNA (or RNA) called a primer
exceptions: some spirochetes have linear chromosomes -repair to shortening ends of chromosomes by telomerase
-linear chromosomes loses swatch size of primer every time they are copied, where as circular chromosomes do not.

b. mRNA splicing -DNA polymerase can not start replicating DNA w/o swatch called a primer.
Ribonucleases cut transcribed RNA's into correct bits for translation
Processing of tRNA and rRNA transcripts also relies on ribonucleases

i. Eukaryotic introns and exons
Eukaryotic genes contain
Introns-spacer regions, trans scribed but not translated, they don't code for proteins. Intros must be spliced out and patched up by ribonuclease before translation
Exons-do code for proteins

ii. Bacterial operons
An operon is a set of genes with related functions that are all transcribed together as a set, then they are spliced into seprate peices. mRNA's translated seperately

c. Finding new bacteral genes by searching for open reading frames (OPRF's)
To find new bacterial genes, look for promoter-ish sequence on DNA, then look for genes.

II. Programmed ribosomal frameshifting goes beyond viruses, Dinnman 2007:
-Ability of a single mRNA by encoding many proteins because the mRNA include sequences which allow rRNA to shift 1 position
-this is not an example of frameshift mutation in DNA
-new reading frame for mRNA
-ex: E. Coli Release Factor 2 gene
*one reading frame - RF2 being translated
*other reading frame - different protein
ex.: prfB: codes for RF2
RF2 : binds to UGA codon
1. Gene prfB is transcribed
2. prfB mRNA is translated *rRNA bind to Shine-Dalgarno Sequence
*reaches AUG (start codon)
*translation; then ribosome reaches UGA
3. If low concentration of RF2 in cell, rRNA can't be released from mRNA at UGArRNA backs up, binds to Shine-Dalgarno sequence
4. Then rRNA translates in new reading frame, until reaches UAA (recognized by RF1)
resulting protein is RF2

  • promoter sequence-start of transcription
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