Lecture 5: Prokaryotic Gene Regulation- Lac Operon Flashcards
Transcriptional regulation in bacteria is relatively simple because it
involves a single activator or repressor protein
Transcriptional regulation in eukaryotes is complex because (3)
- More complex transcriptional regulation: Multicellular eukaryotes use transcriptional regulation to create different cell types
- RNA processing of eukaryotic mRNA: extensive processing of eukaryotic mRNA
- Nuclear membrane: In eukaryotes, transcription and translation take place in different cellular compartments (transcription in nucleus, translation in cytoplasm)
Prokaryote have a —- of RNA polymerase
single type
RNA polymerase
Structural
composed of a 5-subunit core plus a subunit called sigma factor.
Sigma factor
Positions RNA polymerase corectly at the promotor and after transcription is initiated. sigma factor leaves. Some sigma factor recognize promotors of genes required for growth in high heat while others for nitrogen saturation
Factor independent termination
GC rich DNA followed bu an A rich stretch causes RNA polymerase to release from the DNA template. Forms hairpin loop followed by bunch of UUUU mrna. Very unstable and polymerase try to stable by stoping but hairpin makes it fall off.
Rho dependent termination
Rho factor recognize a C-rich sequence of RNA and climbs up to release RNA polymerase (stopped at terminator) from the DNA template.
Promotor
DNA sequence where RNA polymerase binds to initate transcription
Activator
What it is
Protein bringing the RNA polymerase closer to the promotor
Repressor (2 types)
Protein blocking RNA polymerase from binding to the promotor or blocking it from moving along the DNA
Allosteric effectors
Small molecules that bind to the allosteric site of regulatory proteins
Effector binds which allows the activator to
Bind at the activator binding site
Operon (4)
What it isx2+genes+product
- Linked genes under the control of a single promotor
- Functionally related genes (ex: all involved in lactose metabolism)
- Genes are transcribed onto a single mRNA molecule
- Either all or none of the gene products will be synthesized
Lac Operon (2)
WHat it is+ ecoli
- Operon required for the transport and metabolism of lactose
- Ecoli use glucose as their source of Carbon and energy but can use lactose when glucose is carce in the environment.
When lactose is present, Ecoli …
expresses the enzyme: B-galactosidase
Permease (Y)
Transports lactose into the cell
Beta-galactosidase (Z)
Modifies lactose into allolactose and cleaves lactose
I gene
encodes the repressor (Protein that can then bind to the operator)
Talk about the location of the I gene
it can be far away fro the lac operon or near, the location isnt important because only the protein that it encodes is important (free to float in cell)
Trans-acting
Affect gene expression of distant genes (on DNA other than where the trans-acting factor is encodoes)- in addition to nearby genes
Far away gene, nearby gene, gene on same DNA, on different DNA
Cis-acting
Affect gene expression of nearby genes (only genes on the sane piece of DNA as the cis-acting factor is found)
Affect nearby gene or gene on the same piece of DNA
Lac operon expression is regulated by both
negative regulation and positive regulation
Negative regulator
involves a repressor -> turning the lac operon ON/OFF
Positive regulation
involves an activator -> fine tuning expression levels from the Lac operon
Z and Y enzymes
get expressed at the same time and at the same level since they are on the same piece of mRNA
P-
RNA plymerase cannot bind to the promotor
Z-
Inactive Z
Oc
Cannot bind to operator