General Characteristics of proteins that regulate transcription by binding DNA.

-mRNA has short life spans, prevents unneeded proteins 

-interactions will small molecules, can change conformation of regulatory protein

-DNA-binding proteins interact with DNA in specific-manner(motif)

-Major Groove of DNA is the main site of protein binding

-Homodimeric proteins, interact with inverted repeats of dNA 

how prokaryotes respond to the presence of other cells in their vicinity (chemically)

·      Each bacterial species has an Autoinducer molecule in charge of quorum sensing

o   Diffuses freely across the cell envelope

o   Reaches high concentrations inside cell only if many cells are near

o   Binds to specific activator protein and triggers transcription of specific genes

1. Luxl protein synthesizes a homerserine lactone QS signal 

2. a signal diffuses down a concentration gradient to the extracellular millieu 

3. as cell density increases, the concentration of signal increases

4. as a threshold concentration, the LuxR protein binds the signal and activates expression of QS regulon, including the lux operon

o   mutations that change only one base pair, this can lead to single amino acid change in a protein, an incomplete protein, or change at all

Silent mutation

§  does not affect amino acid sequence

Missense mutation

§  amino acid changed; polypeptide altered (may not lead to a phenotypic change)

Nonsense mutation

§  codon becomes stop codon; polypeptide is incomplete

What is a mutagen? 

chemical, physical, biological agents that increase mutation rates 

Examples of mutagens

o   DNA Repair

What is the Ames test, and how does it work? 

·      Generates diversity among bacterial populations

Name and briefly describe the three mechanisms for horizontal gene transfer in bacteria. 

·      Conjugation- plasmids transfer DNA from cell to cell

 Describe Griffith’s experiment that identified the “transforming principle.”

·      Live R cells + DNA from S cells = live S cells

"TRANSFORMING PRINCIPLE"= DNA

Contains DNA or RNA genome, that replicates inside cells 

Small genomes than prokaryotes 

Lytic pathway

o   Cell lyses, relasing phage virions

Temperate phage: uses both lysogenic and lytic pathways ­

Describe the process of F plasmid transfer from a donor cell to a recipient cell. 

Operon: 

cluster of genes arranged in a linear fashion whose expression is under control of a single promotor

·      Transcription is physically blocked when repressor binds to operator

Regulon: 

multiple operons controlled by the same regulatory protein

Induced Mutation

-DNA replication errors

Spontaneous Mutation

-DNA Polymerase errors during DNA replication

Possible fates of transferred DNA

·      It may recombine with the host genome

Basic phases of viral replication

5.     Release of mature virions from the cell.

Lysogeny: 

A state in which lytic events are repressed. Viruses capable of entering the lysogenic state are called temperate viruses 

Prophage: 

During lysogeny the virus genome becomes a prophage, either by integration into the host chromosome or by replicating like a plasmid in step with the host cell.

Generalized Transduction: 

DNA derived from virtually any portion of the hose genome is packaged inside the mature virion
·      Defective virus partical incorporates random fragment of the cell’s chromosome, instead of phage DNA

·      Both temperate and virulent phage can DO THIS

Specialized transduction: 

-DNA from a specific region of the host chromosome is integrated directly in the virus genome

·     - Transducing efficiency can be high

Conjugation (mating)– 

mechanism of genetic transfer that involves cell-to-cell contact