chapter 10 micro exam 2 transcription

what is gene expression

the flow of genetic information

how does gene expression work

DNA (and RNA sometimes) encode genes

• transcription yields a RNA copy of specific genes

• translation uses information in mRNA to synthesize polypeptides

  • does this by using tRNA and rRNA

what is RNA

polymer of nucleotides

• contains bases A, G, C, and U (replaced T)

what sugar is used in RNA

ribose

what sugar is used in DNA

deoxyribose

what are most RNA molecules like

single stranded

• often fold and have regions of base pairing

what are the 3 classic types of RNA that differ in function, site of synthesis (eukaryotes), and in structure

messenger RNA → mRNA

transfer RNA → tRNA

ribosomal RNA → rRNA

how is RNA produced

from DNA through transcription

• catalyzed by RNA polymerase

  • produces copy of only one DNA strand

what are the 3 stages of RNA transcription

RNA polymerase binds to promoter region near the beginning of the gene

elongation then occurs generating a complementary RNA copy

termination occurs when the RNA polymerase releases the new RNA molecule

what can the gene be generally defined as

basic unit of genetic information

• nucleic acid sequence that encodes a polypeptide, tRNA, and rRNA

  • linear sequence of nucleotides with a fixed start and end point

what is the 2nd way a gene can be defined

as a protein coding open reading frame

• string of codons that can be translated to give a protein gene product

what is the promoter region

site where RNA polymerase binds to initiate transcription

• it is not transcribed

what are the 2 characteristic features of the promoter

6 conserved bases located at position -35

TATAAT related sequence at -10 referred to as pribnow box

what is the first nucleotide in the mRNA numbered as and what would be the one preceding it be numbered

+1, -1

what is the typical range for bacterial promoters found to be in

+1 to -35
-10 and -35 are very common

what does the primary rRNA transcribe

precursor that is processed into multiple RNA products

• same thing for primary tRNA transcripts → tRNA products q

what is the typical initiation codon

AUG

what are the 3 termination codons

UAA,UAG,UGA

what is the core enzyme of RNA polymerases composed of

5 polypeptide subunits

• a2BB’w

  • catalyzes RNA synthesis

what is Rifampin and what does it do

antibiotic that inhibits activity of RNA polymerase by binding to the B subunit

what does the sigma factor do in RNA polymerase

no catalytic activity

• helps core enzyme locate and recognize the start of genes

what is a holoenzyme

core enzyme + sigma factor

• only this can begin the transcription of RNA

what does RNA polymerase do after binding

unwinds the DNA

what is produced after the RNA polymerase unwinds the DNA during transcription

transcription bubble

• moves with polymerase as it transcribes mRNA from template strand

  • within bubble temporary RNA:DNA hybrid is formed

how does Rho independent bacterial transcription termination

transcribed RNA contains hairpin (multiple GC base pairs followed by a stretch of U)

• referred to as the stem

polymerase pauses at the hairpin and eventually falls off template

why does the polymerase fall off the template at the hairpin

bc the U stretch in the template is too weak of an interaction to keep the polymerase from falling off

how does the rho dependent bacterial transcription termination work

terminator region pauses transcription at stem loop (no U stretch)

rho factor (protein) binds to nascent transcript at rut site and moves from 5’ → 3’ on the transcript until it encounters polymerase paused at terminator

• unwinds the RNA:DNA duplex and causes polymerase dissociation