biol 282 chapter 6

What is bacteria’s primary source of genetic variation?

Spontaneous mutation.

Prototrophs

Bacteria that are wild-type for all growth requirements and can grow on minimal media.

Minimal media

The simplest set of chemicals needed for an organism to grow and survive, usually only wild-type organisms can grow on it.

Auxotrophs

Bacteria that have undergone mutation and lost the ability to synthesize one or more organic components, can usually grow on complete media.

Lag phase

The period where the bacteria growth curve is constant as the bacteria get use to the new enviornment.

Log phase

The period on the curse where the bacteria is beginning to grow and multiply.

Stationary phase

The period on the curve where the number of bacteria is now constant after mutliplying.

What is important to remember when mapping bacterial genes?

The transfer is unidirectional and no complete diploid stage is formed.

Conjugation

A process in which there is unidirectional transfer of genetic information through direct cellular contact between a donor bacterial cell and a recipient bacterial cell.

Pilus

The physical bridge that joins the cells during conjugation.

F+ cells (donors)

Contain a fertility factor (F factor) that confers the ability to donate DNA during conjugation.

F- cells (recipient cells)

Cells that recieve the DNA to become F+ cells.

Fertility (F) factor

A plasmid, circular, double-stranded DNA molecule that is extrachromosomal and replicated independently of the host chromosome. Also contains the origin, the point where DNA transfer to the recipient begins.

Hfr cells

They are a special class of F+ cells and orginate by a rare crossover event in when the F factor intergrates into the bacterial chromosome.

F’ State and Merozygotes

Cells where the F factor is excised form the chromosome of an Hfr strain and is not partially diploid.

Transformation

Small pieces of extracellular DNA are taken up by a living bacterial cell and integrated stably into the chromosome. There does not have to be direct contact.

What can transformation be used for?

Helps determine whether genes are close to one another on the single chromosome and the order and distance of genes.

What happens if two genes are far apart on a donor chromosome?

They will always be found on different DNA fragments.

Transduction

Process by which bacteriophages transfer genes from one bacterium to another.

Bacteriophages (phages)

Viruses that infect bacteria.

How do bacteriophages infect?

They inject their DNA into a host bacterium.

Lytic cycle

Phage reproductive cycle that culminates in the death of the host cell.

Lysogenic cycle

Part of the phage cycle where the phage genome is replicated without destroying the host cell.

General transduction

Phages will infect a bacteria and then take in its DNA and then the cell will lyse and release these new transducing phages will infect a new bacteria and replace its DNA with the one it got from the previous cell.