Genetics of Bacteria and Viruses

Question 1

Bacteria As Valuable Research Subjects

Answer 1

Small size
Rapid reproduction
Simple structures
Genetic variability (have only one chromosome)
Selective media (can grow on variety of different media such as antibiotics)

Question 2

Bacterial Viruses

Answer 2

Bacteriophages

Reproduce by infecting bacterial cells

Question 3

Clearances/Plaques

Answer 3

Dead colonies that were killed by viruses

Question 4

Bacteriophage T4

Answer 4

Goes through lytic phase

168 000 base paris, 150 genes

Question 5

Bacteriophage Lambda

Answer 5

48 502 base pairs, 50 genes

Lytic or lysogenic

Question 6

Lambda Life Cycle

Answer 6

Lambda attaches to bacteria, inserts DNA into bacterial cell

Then undergoes lytic or lysogenic pathways

Question 7

Lytic Pathway

Answer 7

Replication of viral chromosome, synthesis of viral proteins, lysis (viral proteins burst out and infect other cells)

Question 8

Lysogenic Pathway

Answer 8

Viral DNA fuses into bacterial chromosome (now considered a prophage)

Inactive in this state

Whenever bacteria divide, viral DNA is also replicated

If there is not a dense population of bacteria at the time of infection, virus might not want to lyse itself because there aren’t very many hosts, so it waits until there are more hosts and then lyses itself

Question 9

Genetics of Bacteria

Answer 9

Circular genomes of several million base pairs

Do not undergo meiosis, do not have chiasmata (but bacterial recombination is still possible)

Gene transfer in bacteria is unidirectional

Question 10

Episome

Answer 10

Circular DNA that can integrate into bacterial chromosome for replication or remain separate

Type of plasmid

Question 11

Plasmid

Answer 11

Small circular DNA that can replicate independently of bacterial chromosome

Question 12

Antibiotic Resistance

Answer 12

When bacterial cells are stressed/dying, proof reading for DNA loosens, allows for mutation to occur

Question 13

Auxotrophs

Answer 13

Missing gene that transcribes an essential protein

Question 14

Ways Bacteria Exchange Genetic Material

Answer 14

Transformation
Conjugation
Transduction

Question 15

Transformation

Answer 15

Uptake of free DNA

Recombination between bacterial chromosome and DNA segment (free DNA now in bacterial chromosome), can now be replicated

Sensitive to DNase

Question 16

Conjugation

Answer 16

Direct transfer of DNA from one bacterial cell to another

Donor transfers bacterial chromosome into repent

Donor replicates its chromosome as it is donating (retains chromosome), transfers a copy to recipient

Question 17

Transduction

Answer 17

Transfer of bacterial DNA by a bacteriophage (virus)

Uses a virus as a vehicle to transfer new genes into host

Head of virus contains viral and bacterial DNA (bacterial DNA accidentally got into virus head from previous host)

When virus infects new cell, it will also give segment of bacterial DNA

Question 18

U-tube Experiment

Answer 18

DNase added to medium so free flowing DNA can pass through pores are destroyed

2 strains of bacteria (a-, a+) are physically separated by a barrier, barrier has pores small enough that liquid and virus can flow through, but prevents bacteria from flowing through (prevents conjugation)

Added virus to one side, found a- becomes a+, a+ becomes a-, proves that virus can infect cell on one side, carry genes to other side, infect cells on other side

Question 19

Competent Cell

Answer 19

Cell that is able to undergo transformation

Question 20

How To Become Competent

Answer 20

If bacterial cell is in environment where other cells are dying, then it wants to find a cell with an allele that allows it to combat the environment (cell with mutant allele will die eventually)

Turns on DNA receptor, allows gene to come in, then bacterial cell can recombine with free fragment

All cells have potential to become competent, but not every cell will unless it thinks that it needs to

Question 21

Transformation and Distance Between Genes

Answer 21

If 2 genes are very close, they will be present on the same piece of transforming DNA

Question 22

Fertility/F Factor

Answer 22

Episome
Mediates conjugation
Can exists as an extra chromosomal DNA or it can insert into the bacterial chromosome and replicate as part of it

Contains genes required to build conjugation channel and pilli

Donor cell must contain F+

Question 23

Conjugation Channel

Answer 23

Connects donor and recipient cells

Question 24

F+ x F-

Answer 24

F+ replicates itself and transfers F+ into recipient cell (so both cells are F+)

Question 25

Hfr H Cell x F-

Answer 25

Hfr H (integrated F factor) integrated into bacterial chromosome

F factor allows cell to build pills, conjugation factor, wants to be transferred into F- cell, by doing so also transfers the rest of the chromosome because it is attached to it

Conjugation bridge usually breaks during transfer (very fragile)

Question 26

Generalized Transduction

Answer 26

Random fragment of bacterial DNA is packaged in phage head by mistake along with phage DNA

Question 27

Specialized Transduction

Answer 27

Prophage excises imprecisely from chromosome and produced a phage chromosome containing only adjacent bacterial genes