Midterm 1 Flashcards
RNA polymerase
enzyme that reads DNA template strand 3’-5’ and generates mRNA 5’-3’
where does RNA polymerase bind?
to the -35 and -10 sites
transcription starts at the +1 site
Shine-Delgarno (SD) Sequence
sequence in bacteria that binds ribosomes for translation. this sequence is not translated.
located after the +1 site and before the AUG/ATG start codon.
Consensus SD Sequence
AGGAGGU (typically 5-15 nucleotides upstream of the start codon)
Operon
a transcriptional unit defined by a promoter and terminator. can contain more than one gene = “polycistronic operon”
Terminator sequence
GC rich region that forms a hairpin, followed by a stretch of As or Ts
Missense mutation
change in bp leading to different amino acid
- little effect to total loss-of-function
Nonsense mutation
change in bp that causes a new stop codon (causes premature termination of protein)
- usually loss-of-function
frameshift mutation
gain or loss of one or more bps
-usually loss-of-function
average mutation rate in prokaryotes
10^(-10) = 1 mutation/2000 cells
how do we generate mutations for Forward genetics?
Transposon mutagenesis
Chemical mutagenesis
Selection
when individuals lacking the phenotype of interest (including WT) are killed and ONLY mutants of interest grow (“are selected for”) and the mutation is typically gain-of-function
- antibiotic resistance
- phage resistance
Screen
individuals are examined to identify those mutants with the phenotype of interest. Large number of individuals are screened, typically contains loss-of-function or change-in-function mutations.
- auxotrophy
- cell cycle mutants
define Auxotroph
organisms or bacteria that lost the ability to synthesize certain substances required for their growth (usually due to mutation)
- bacteria that can no longer synthesize histidine (cannot grow unless on media with histidine provided)
library size
of mutants to screen when looking for a certain gene through mutagenesis
