Bacterial Genetics

Question 1

Expression of bacterial virulence factors and surface features can be varied

Answer 1

True!

Promote bacterial colonization of the host and avoid detection

Question 2

Do bacterial genes have introns or exons?

Answer 2

EXONS! rarely have introns

Question 3

Transcriptional Regulator

Answer 3

Responds to environment stimuli.
Affects the expression of downstream genes (activate or inhibit)
Binds to promoter site

Question 4

Operon

Answer 4

multiple reading frames (genes –> proteins) linked together

Question 5

Regulon

Answer 5

multiple genes under regulation of a single regulator - not connected

Question 6

Regulation of Diptheria Toxin

Answer 6

Induced under low iron conditions.
DtxR – regulator, normally bound in high iron conditions. Prevents the expression of toxin
In human body iron is highly regulated - low iron conditions
* DtxR is released and the toxin is produced in the human body

Question 7

The ability of bacteria to change their genetic attributes is key to their success as pathogens

Answer 7

Deal with competitive challenges
Never ending game with Host
Need to rapidly respond to changing environments

Question 8

Slow Process of gene alteration

Answer 8

point mutation
gene duplication
gene deletion
chromosomal rearrangement

Bacteria short lives – meaningful mutations because of high replication rate, can affect bacteria over a short period of time

Question 9

Antibiotic resistance comes with a fitness cost

Answer 9

RNA polymerase is not as functional

Question 10

Hympermutable

Answer 10

During stressful conditions bacteria will hyper mutate.

Promotes the likelihood of developing a favorable mutaion

Question 11

Rapid process of gene alteration

Answer 11

Phase variation

Antigenic variation

Question 12

Phase variation

Answer 12

reversible switch between all or none expressing phase
change a characteristic
8 express milli don’t express pilli

Question 13

Antigenic variation

Answer 13

Change surface antigens to avoid the host immune response.

Switched on and off with varying frequencies

Environmental signals may promote the expression of specific surface antigens while down regulating others

Question 14

How long do bugs have till adaptive immunity catches up?

Answer 14

7- 10 days

Question 15

N. meningitidis

Answer 15

grow and survive in blood via capsule
turn off capsule expression to cross BBB - so that is does not interfere with biofilm formation and plus mediated attachment to host endothelial cells. Will turn on pilli

Phase variation

Question 16

Phase variation by gene conversion

Answer 16

insert a new gene to recombine forming a new expression of trait. Avoid immune detection.

non reversible

Question 17

Bordatella pertussis toxin

Answer 17

bvgS
slip strand synthesis – frameshift
Turns toxin production off
Toxin production can be restored by another frameshift

Question 18

Phase variation by promoter inversion

Answer 18

invert the direction the promoter is facing. On points towards the genes to be expressed - off points away.

E. coli type I fimbraie

• Fim B and Fim E –> off
• Fim B –> on

Question 19

Horizontal Gene Transfer

Answer 19

movement of genetic info between bacteria

• Trasnformation
• Transduction
• Conjugation

Question 20

Bacterial Transformation

Answer 20

DNA taken up directly by bacterial cells

Question 21

Competent bacteria

Answer 21

able to take up DNA in transformation
“naturally competent” – do it all the time – linear DNA
* B. subtilis
* S pneumoniae

Some bacteria require specific sequences

• H. influenzae
• N. gonorrhoeae

Question 22

Bacteriophages

Answer 22

Viruses that replicate within bacteria

Question 23

Phage Life Cycle

Answer 23

Lytic –> phage DNA replicates, assembled, lyse bacteria
Lysogenic –> phage DNA integrated into bacterial DNA (prophage), bacterium grows, phage DNA excises entering lytic phase

*Prophage carries important virulence determinants

Question 24

Generalized Transducing Phage

Answer 24

Transfer DNA from one bacterium to another during LYTIC phase. Can accidentally package bacterial genome in virus particles

Question 25

Specialized Transducing Phage

Answer 25

Undergo both LYTIC and LYSOGENIC phases.

Question 26

Conjugation

Answer 26

F - fertility plasmid
F+ if contains F plasmid – forms conjugation bridge

Replicates plasmid and transfers to new cell. May sometimes get bacterial genome in plasmid.

Question 27

High frequency of recombination cell

Answer 27

Hfr –> plasmid incorporated with chromosome. May get some bacterial chromosome replication and transfer. May not transfer all because too large

Question 28

Fertility F plasmids

Answer 28

contain tra genes – transfer

Sex pili expression

Question 29

Col plasmids

Answer 29

code for bacteriocins – proteins that kill other bacteria. Some toxic to host cells

Question 30

Virulence plasmids

Answer 30

encode virulence factors

* Salmonella

Question 31

Resistance (R) Plasmids

Answer 31

provide resistance against antibiotics and poisons

* multi drug resistance – Klebsiella pneumonia plasmid

Question 32

Some plasmids (mobilisable, mob) can only be transferred by tagging along with other plasmids containing TRA genes

Answer 32

true

Question 33

Transposons

Answer 33

Jumping genes

• DNA elements that move from one place into bacterial DNA to another
• virulence or antibiotic resistance genes