Lecture 3 (19) Microbial Genetics

Question 1

plasmid

Answer 1

bacterial molecule separate from chromosome that has small circular DNA that’s replicated and tx to daughter cells
can be implemented into chromosome =episome

Question 2

episome

Answer 2

plasmid into chromosome

Question 3

chromosome structure of bacteria

Answer 3

circular, large DNA

Question 4

polycistronic RNA

Answer 4

mRNA has genetic info to translate more than one protein

Question 5

negative gene regulation in bacteria

Answer 5

have a repressor binding to a promotor not allowing DNA polymerase to bind and transcribe

Question 6

positive gen regulation

Answer 6

• used when have a promotor and an RNA polymerase that don’t bind with high affinity
• use activator to bind the gene, cause the RNA polymerase to bind promotor and activate transcription

Question 7

vertical gene transfer vs horizontal gene transfer

Answer 7

vertical- genes passed via replication to progeny

horizontal- genes passed to other bacteria (not progeny) via transformation, conjugation or transduction

Question 8

why is bacterial evolution so difficult? what sort of mechanisms has it developed to foil this?

Answer 8

• no DNA is acquired at cell division, bacteria are asexual and evolution is SLOW because there are very little mutations at replication
• therefore bacteria have developed horizontal transmission

Question 9

homologous recombination

Answer 9

• exchange of DNA between two DNA molecules based on homology
• result: DNA is incorporated into chromosome and is passed to daughter cells and become permanent part of genome

Question 10

transformation

Answer 10

• horizontal gene transfer
• DNA is lysed somehow and releases DNA
• dependent on homology, new bacterial cell can implement it into its DNA and pass that new DNA onto progeny
• DNA is released into environment and NOT protected before it is implemented into second cell

Question 11

Conjugation

Answer 11

• transfer of DNA from one viable bacteria to another via a sex pilus and using plasmid
• F FACTOR (fertility) is a plasmid in the bacteria that carries genes called a TRA OPERON that encodes components of the sex pilus bridge
• ori T is the origin of transfer where the single strand break occurs for transfer
• INTERACTION IS ONLY BETWEEN A DONOR (F+) AND RECIPIANT (F-)

Question 12

f FACTOR
tra gene
ori T

Answer 12

f FACTOR- plasmid that has the ability to tx DNA
tra gene- gene in a f factor bacteria that is able to encode a sex pilus t transfer
ori T- where a single strand-break occurs for transfer on the F factor plasmid

Question 13

Hfr

Answer 13

• a different type of bacterial donor that has the F factor integrated into its chromosome versus using a PLASMID
• behaves the same as a F+ bacteria

Question 14

describe conjugation via a F+ plasmid

Answer 14

conjugation via an F+ plasmid causes gene tx at sex pilus encoded by tra gene. The DNA strand of F+ breaks at ori T and a single strand is transferred. Ori T first followed by lastly, the tra gene
F- undergoes sex change to F- and transfer is unidirectional
tra gene is the last thing to be transferred in

Question 15

describe conjugation via a HFr bacteria

Answer 15

• since the F factor is integrated into the chromosome, transfer includes part of the chromosome next to the ori T
• OFTEN, the conjugation doesn’t last long enough to transfer all of the chromosome and genes. therefore you can have homologous gene transfer of some but not all genes and since tran gene is the last to enter, it has a good likelihood that it wont be transferred
• this means that there is a chance that the bacteria getting these genes are not going to undergo a sex change but gets new genes and can interact with another HFr or a H+

Question 16

transduction

Answer 16

• transfer of bacterial DNA via bacteriophage (bacteria parasite)

Question 17

what are the two types of phages?

Answer 17

1) Lytic phage- lytic replication UPON ENTRY into bacteria- meaning that phage enters bacteria and hijacks its cellular machinery to replicate and bacteria are lysed
2) TEMPERATE/lysogenic phage- integrates itself into the chromosome of the bacteria and remains dormant until an assault occurs and the bacteria become virulent and lyses the bacteria

Question 18

describe generalized transduction

Answer 18

• a LYTIC phage injects its DNA into the bacteria
• upon replication, the phage secretes nucleases that degrade the bacteria
• phage is messy about its replication and can actually integrate bacterial chromosomal DNA into its phage head
• when phage infects another bacteria, the DNA can be incorporated into its chromosome via homologous recombination

Question 19

specialized transduction

Answer 19

• uses temperate/lysogenic phage
• phage incorporates itself into host chromosome and waits
• insult leads to conversion to a lytic lifecycle
• the phage then excises itself from the “sinking ship” of a bacteria and when it does this, it can take some of the bacterial DNA with it
• this can be implemented into other bacteria

Question 20

what type of bacterial transfer requires homologous recombination

Answer 20

transformation, transduction and conjugation with HFr. F+ and F- conjugation does not need homologous recombination

Question 21

what type of DNA is used in transformation, conjugation and transduction

Answer 21

transformation- any
conjugation- chromosomal or plasmid
transduction- Generalized is any, specialized is only genes adjacent to phage insertion

Question 22

what type of transfer process is involved in transformation, conjugation and transduction

Answer 22

transformation- uptake of free DNA
conjugation- cell to cell tx
transduction- phage tx

Question 23

what are the three types of antibiotic resistance

Answer 23

1) intrinsic
2) chromosome- mediated
3) plasmid-mediated

Question 24

intrinsic antibiotic resistance

Answer 24

• NOT horizontally transferred by bacteria
• not increasing among bacterial populations
• when a bacteria has some feature, intrinsically that makes them resistant to antibiotics

Question 25

chromosome-mediated antibiotic resistance

Answer 25

• where resistance is obtained via a RANDOM mutation in the chromosome
• this is heritable via HORIZONTAL GENE TRANSFER and incorporation into genome via homologous recombination

Question 26

plasmid mediated antibiotic resistance

Answer 26

genes that encode antibiotic resistance are incorporated into the plasmid to be transferred horizontally
these plasmids often encode proteins that degrade or modify an antibiotic or make an efflux pump to pump the antibiotic out of the cell

Question 27

resistance factor

Answer 27

has two parts:

1) resistance transfer factor- like an F factor because it encodes for all proteins needed for conjugation
2) resistance determinant- gene for drug resistance

Question 28

transposons, what they need and how they are related to antibiotic resistance

Answer 28

• Transposons are mobile repeating DNA sequences
• need a repeating sequence on each end to be recognized by transposase, need gene for transposase-an enzyme that allows the DNA to jump
• antibiotic resistance- transposons can contain DNA sequences that are resistant to antibiotics -can jump between two chromosomes, two plamids or one of each causing multidrug resistance plasmids to form and be passed on

Question 29

integrons

Answer 29

• site specific recombination system that can capture antibiotic resistance gene cassettes and express them under (move the to) the promoter and cause them to be expressed more
• associated with transposons and plasmids
• can cause increase in antibody resistance because they get these antibody resistance sequences and integrate them next to the promoter to be expressed more

Question 30

pathogenicity islands

Answer 30

• act like transposons
• region of bacterial chromosome acquired thru horizontal gen tx and often carry regulated virulence genes surrounded by insertion sequences