Bacterial and Viral Genetic Systems (7)

Bacteria and virus model systems contributions to genetics

1. Gene regulation
2. Molecular biology and biochemistry of genetic processes (replication, transcription, translation, recombination)
3. Gene structure and organization in bacteria
4. Workhorse of recombinant DNA
5. Gene mutations

Advantages of using bacteria and viruses for genetic studies

1. Reproduction is rapid
2. Many progeny
3. Genomes are small

Bacteria growth is ...

Colonal - allows the isolation of clones of cells

Replica plating

Rubber stamp of petri plate to inoculate plates with different nutrients

Bacteria cells contain ...

A single circular chromosome - some have small, extra chromosomal DNA (plasmids)

Bacterial genomes typically have ...

One origin of replication - bidirectional

Plasmids can encode ...

A variety of different information

Plasmid genomes typically have ...

Multiple origins of replication + an origin of transfer

Plasmids replicate ...

Independently, but in a fashion similar to that of the bacterial chromosome

Mechanisms of horizontal transfer of Genetic Traits

1. Transformation - uptake of “naked” DNA directly from the environment
2. Transduction - phage-mediated transfer of DNA
3. Conjugation - transfer via cell-to-cell contact; pilus mediated

Who demonstrated genetic exchange in 1946?

Joshua Lederberg and Edward Tatum

Prototrophs

Can make essential nutrients they need to survive

Auxotrophs

Can't make essential nutrients they need to survive

Who shows Lederberg that exchange requires cell-to-cell contact?

Bernard Davis

During bacterial conjugation, what connects the two cells?

Sex pilus

Replication is initiated at...

oriV

What do insertion sequences (IS3 and IS2) do?

Control insertion into the bacterial chromosome and exertion from it

What genes does a cell need to be a donor?

Tra genes

What are the F factor characteristics and role of F+ cells?

Present as separate circular DNA and is a Donor

What are the F factor characteristics and role of F- cells?

Absent and Recipient

What are the F factor characteristics and role of Hfr cells?

Present, integrated into bacterial chromosome and is a high-frequency donor

What are the F factor characteristics and role of F' cells?

Present as separate circular DNA, carrying some bacterial cells and is a donor

Conjugation between F+ and F-

Two F+ cells (F- becomes F+)

Conjugation between Hfr and F-

One Hfr cell and one F- (no change)

Conjugation between F' and F-

Two F' cells (F- becomes F')

Who used interrupted conjugation to map bacterial genes?

Jacob and Wollman

Transfer times indicate ...

The order and relative distances between genes (can be used to construct genetic map)

Arrowheads on the plasmid indicate ...

The origin and direction of transfer

R plasmids are ...

Conjugative plasmids that carry antibiotic resistance genes

Transformation occurs via ...

The uptake of naked DNA

The rate of cotransformation is ...

Inversely proportional to the distances between genes

Bacterial viruses (bacteriophage) offer ...

A mechanism for the transfer of DNA between bacterial cells

What are plaques?

Clear patches of lysed cells on a lawn of bacteria

Who showed that not all genetic exchange requires direct contact?

Lederberg and Zinder

What are the alternative life cycles of bacteriophages?

Lytic and Lysogenic

What is generalized transduction?

Any DNA from the donor can be transferred into to new bacteria

What is specialized transduction?

Only special genes which are nearby the integration type are transferred