Biol121 Lecture 12 Molecular regulation Midterm 2 Review

Molecular Regulation

Bacteria has to be able to handle other metabolic processes, so controlling gene expression at many levels-->Transcriptionally, Post-transcriptionally, Translationally, Post translationally helps in not making unneeded proteins

Housekeeping proteins

On all the time, since they are always required for microbial/bacterial growth. If you already have something, you don't need to to make it and genes turn off.

Regulatory proteins/Trasncription factors

Alter gene expression to help a cell repsond to changing conditions inside and outside of the cell.

A reminder: Operon

Functioning Unit of DNA, containing a cluster of genes under the control of a single promoter

Another reminder: Regulon

A set of genes or operons all regulated by the same transcription factor

Repressor

Bind to regulatory sequences in DNA, prevent transcription of target genes

Activators

Bind to regulatory sequences in DNA, and stimulate transcription of target genes.

Repressor Type 1(Inducible)

One type: Binds operator DNA by itself, and prevents transcription, and inducer must be present to bind repressor and express target gene(induction)

Repressor Type 2(Corepression)

Does not bind well to operator unless a corepressor is bound when the corepressor dissapear, target gene can be expressed(derepression)

Activator

Binds to promoter, note the difference, repressors bind to operators and activators bind to promoter/close to promoter, can interact with RNA polymerase nearby to initiate transcription. some activators require an inducer to bind DNA activator sequences.

The E. Coli Lac operon(Inducer example)

Important genes:

LacZ, B-galactoZidase->Cleaves bonds, or can alter lactose to produce allolactose

LacY-Lactose permease->allows permeability of membrane to lactose(Y in LacY stands for yes, you may pass-->stupid mnemonic)

Need both to digest lactose

LacI

The Lactose repressor which binds to the operator region, at a specific DNA sequence, in this case, LacO. (LacI-->The I stands for inhibit, mnemonic)

Allolactose(Inducer)

At low concentrations, B-galactosidase makes allolactose, binds to LacI, reducing it affinity to operator, allowing it to turn on. (Allolactose-->AlloWlactose , ok I'll stop)

Catabolite repression

An operon enabling the catabolism of one nutrient repressed by presence of more favorable nutrient(In E. Coli, glucose is preferred over lactose)

Activation of lac operon

Requires presence of cyclic AMP, and recpetor protein CRP, binds to promoter, and interacts with RNA polymerase to increase rate of transcription initiation

Phosphotransferase system

Acts as a sensor for glucose levels, Phosphates transferred to glucose to maintain concentration gradient, phosphates necessary for IIA to make adenylate cyclase which creates cAMP is "Stolen".

No glucose, PTS members phosphorylated, cAMP can activate lac operon

(Not sure if this is scientifically accurate, but you can think of glucose as stealing phosphates, to maintain concentration gradient)

Glucose catabolite repression(Lactose exclusion)

Glucose transport by PTS Inhibits LACY permease activity, lactose cannot pass through cell,

Extra info(may help you remember)-->results in dephosphorylation of a complex that then binds to lacy preventing its transcription