Molecular and Cellular Biology, Lecture 6: Bacterial Transcription

Direction of RNA and DNA synthesis

5' to 3'

template strand

The DNA strand that provides the template for ordering the sequence of nucleotides in an mRNA transcript.

sense strand

Matches RNA strand except for Uracil (RNA product is identical to sense strand expect U instead of T)

regulatory sequence

site for the binding of regulatory proteins, influence the rate of transcription, can be found in a variety of locations

promoter

site for RNA polymerase binding; signals the beginning of transcription

terminator

signals the end of transcription, polymerase unbinds

ribosome binding site

Site for ribosome binding; translation begins near this site in the mRNA. In eukaryotes, the ribosome scans the mRNA for a start codon.

start codon (AUG)

Specifies first amino acid in a polypeptide

Codon

3 nucleotide sequence within mRNA that specify particular amino acids, determine amino acids within polypeptide

Stop codons (UAA, UAG, UGA)

specifies end of polypeptide synthesis

polycistronic

mRNA codes for more than one protein. Found mainly in Prokaryotes.

transcriptional start site

site at which transcription begins, always adenine, included in RNA

-10 sequence

TATAAT; about 10 bp upstream of the start site; easier to be separated

-35 sequence

Consensus sequence (TTGACA) found in many bacterial promoters approximately 35bp upstream of the transcription start site.

sigma factor

controls the binding of RNA polymerase to the promoter

Rho-dependent termination

Rho protein recognizes cut sequence on mRNA, catches RNA pol due to RNA pol pausing due to stem loop forcing RNA pol to detach from DNA

Rho-independent termination

stem loop causes RNA pol to pause, NusA protein stabilizes pause causing RNA pol to detach from DNA

regulated genes

genes whose activity is controlled in response to the needs of a cell or organism

constitutive genes

genes that are expressed all the time

repressor protein

a protein that inhibits genes from being expressed, binds to DNA and inhibits transcription

activator protein

positive control, bind to DNA and increase transcription

small effector molecules

regulate gene transcription by binding a regulatory protein.

inducer

A small molecule that binds to a repressor protein changing the repressor's shape so that it cannot bind to DNA, allowing polymerase to bind

co-repressor

a small molecule that cooperates with a repressor protein to switch an operon off, blocking transcription, blocking polymerase

Inhibitor

inhibits activators, activator can no longer recruit polymerase for transcription

operon

a group of genes that operate together under one promoter