topic16 prokaryotic genetics

Question 1

sexual reproduction

Answer 1

1. transformation
2. transduction
3. conjugation

Question 2

asexual reproduction

Answer 2

binary fission

Question 3

advantages of working with bacteria

Answer 3

-very fast generation time
-can work with v large numbers in a small space (white spot can be one colony and each colony has billions of cells)
-this means we can study very rare events eg. an event that occurs in 1/100000000000 divisions can then happen hundreds of times in one pertri dish in one day

Question 4

is there meiosis in proks

Answer 4

no, rmb proks only have 1 circular chroms and sometimes small plasmids (they arent diploid)

Question 5

plasmid

Answer 5

a circular extrachromosomal dna molec occuring free in cytoplasm and capable of autonomous replication using alrd existing cellular enzymes
-Plasmids have specific sequences called origins of replication (ori), which act as starting points for replication.
-These sequences allow plasmids to self-replicate, ensuring their propagation in daughter cells during cell division.

This autonomy is crucial for plasmids because it enables them to be maintained in the cell as separate, functional genetic elements, often carrying genes that provide advantageous traits (e.g., antibiotic resistance).

“plasmids aint pussies!”

Question 6

binary fission

Answer 6

1. replication of dna
2. cell growth and each dna moves to poles
3. septum forms then cytokenisis

Question 7

mediums in bacterial growth (in petri dish)

Answer 7

-either in a liquid medium or semisolid agar surface
-minimal medium consists of only an organic carbon source like glucose or lactose and various inorganic ions like na+,k+,mg2+ etc. the bacterium
-complete medium is completed with amino acods

Question 8

bacterial sex is ____ in that it does not involve gamete fusion or reproduction

Answer 8

unidirectional

Question 9

conjugation

Answer 9

-donor forms a sex pilus, attaches to recipient. copy of plasmid or even parts of the chromosome can be transfered. then the recipient synthesizes a complimentary strand

Question 10

transformation

Answer 10

where a cell picks up dna segments from environment, and through homologous recombination/cross over events the dna is transformed (incorporate peices of it into its genome)

“transForm the dna by Fragments”

Question 11

transduction

Answer 11

bacteriophage transfers some dna from pervious host to recipient host cell. phages normally only carry their own dna but sometimes they accidentally pick up bacteria dna when they replicate in ahost and then when they go to a new host it goes to that host.

Question 12

horizontal/lateral genetic transfer

Answer 12

eg) the three forms of sexual reproduction.
-Transfer of genetic information from a donor organism to a recipient organism that is not its offspring
-made possible by mobile genetic elemnts like plasmids, transposons (jumping genes; move from one location to another in genome) and bacetriophasges
- acquisition of antibiotic resistivity by bacteria is a result of horizontal gene transfer

Question 13

vertical gene transfer

Answer 13

This is in contrast to the transfer from parent to offspring, which is
referred to as vertical gene transfer
– Transfer of genetic information between members of same species

Question 14

discovery of conjugation in bacteria

Answer 14

joshua lederberg and edward tatum in 1946. they showed e coli intered a sexual phase during which it could share genetic info.

Question 15

initial experiment with e coli

Answer 15

two auxotrophs in complete mediums (strain A
required methionine (met) and biotin (bio) in order to grow, whereas strain B required threonine (thr), leucine (leu) and thiamine (thi)). then when theyre both put in one petri dish in a minimal medium, phototrophs grew
-researchers assumed that any prototrophs recovered must have arisen as a result of some form of genetic exchange and recombination between the two mutant strains. ofc no growth in controls (minimal mediums with aux a an aux b on two seperate dishes)

Question 16

F+ cells vs F- cells

Answer 16

F+ (fertility)=serves as dna donors
F-=recipients and they recombine chromosomal material with part of their own chrom

Question 17

What was the David U-tube experiment?

Answer 17

In 1950, Bernard Davis designed the David U-tube with a glass filter to study genetic transfer between F+ and F- cells. The filter allowed medium to pass but not bacteria. No prototrophs were found when cells from both sides were plated, showing that cell-to-cell contact is essential for genetic recombination.

Question 18

What is the F factor and its role in conjugation?

Answer 18

The F factor is a fertility factor in F+ cells that allows them to donate part of their chromosomes during conjugation. It is a circular, double-stranded DNA molecule (about 100,000 nucleotides) and contains ~40 genes.

Question 19

What is the difference between an F+ cell and an Hfr cell?

Answer 19

An F+ cell contains the F factor as a plasmid, capable of donating its genes during conjugation. An Hfr cell is an F+ cell where the F factor is integrated into the chromosome, making it capable of high-frequency recombination but not converting the recipient into F+.

Question 20

What is an episome?

Answer 20

An episome is a segment of DNA that can exist as a plasmid or integrate into the bacterial chromosome. The F factor can be an episome, which is capable of integration and recombination.

Question 21

How do F+ cells and Hfr cells differ in terms of conjugation?

Answer 21

F+ cells transfer the entire F plasmid to the recipient F- cell, converting it into an F+ cell.
Hfr cells transfer chromosomal genes along with the F factor, but rarely transfer the entire F factor, so the recipient remains F- (bc the hfr one is so long, the recipient remains F- because the transfer of the F factor is rarely complete)

Question 22

Why do F- cells not become F+ after conjugation with an Hfr cell?

Answer 22

F- cells do not become F+ because the entire F factor is rarely transferred during conjugation with Hfr cells, and the F factor’s genes for forming a sex pilus are typically the last to transfer.

Question 23

What is the Origin of Transfer (OriT)?

Answer 23

The Origin of Transfer (OriT) is the specific location in the F plasmid where DNA transfer begins during conjugation, starting with the F plasmid in F+ cells and the integrated F factor in Hfr cells.

Because this integrated chromosome (in hfr) is much larger than the
F plasmid alone, conjugation is usually interrupted before transfer is
complete (so we very rarely see every gene transferred

Question 24

what is an epsiome

Answer 24

it is a segment of dna (f factor) that can either integreate into the chromsome or exist indepently like a plasmid

Question 25

what explains the wildtype presence in the lederberg and tatum experiment?

Answer 25

When the donor DNA fragment enters the recipient cell during conjugation, crossover events can occur between the donor DNA and the recipient’s chromosome, allowing the exchange of alleles. This process explains the formation of wildtype prototrophs in the Lederberg and Tatum experiment, as it restores the ability to synthesize essential compounds.