Bacterial Genetics & Macrophage Interaction

Question 1

What is the difference between bacterial chromosomes and Eukaryotic chromosome?

Answer 1

Bacteria are generally single chromosome that is circular and <5Mb

Eukaryotes have several linear chromosomes >5Mb

Question 2

Is compartmentalization of the bacterial genome similar or different to Eukaryotes? How?

Answer 2

It is different. Bacterial genomes are typically NOT compartmentalized and are simply localized in the cytoplasm

Question 3

What do bacteria frequently contain that Eukaryotes do not?

Answer 3

Plasmids

Question 4

How is bacterial DNA condensation different from Eukaryotes?

Answer 4

It is typically condensed by **supercoiling DNA itself **instead of wrapping around histones.

Question 5

Are genes encoded within operons typically a trait of bacteria or eukaryotes?

Answer 5

Bacteria

Question 6

Is the presence of introns and **exons **typical of bacteria or euks?

Answer 6

Eukaryotes

Question 7

How is the bacterial ribosome different from the eukaryotic ribosome?

Answer 7

It has 50S and 30S subunits to equal a 70S ribosome

Question 8

How is transcription/translation different in bacteria? Why?

Answer 8

It is coupled because of no compartmentalization.

Question 9

What are plasmids?

How are they transferred between bacteria?

Answer 9

They are ss- or ds- DNA the replicates independently anywhere from 1500bp to 400,000bp.

They are transferred via Transformation, Conjugation, and Transduction

Question 10

What are insertion sequences/transposons?

Can they replicate on their own?

What do they ALL possess?

How are they transferred between bacteria?

Answer 10

They are mobile, linear DNA segments that disrupt genes in the recipient.

They cannot replicate on own.

They ALL possess Inverted Terminal Repeats (ITR) on their ends.

They are transferred by **plasmids **or bacteriophages

Question 11

Describe Transformation in bacteria.

How does it happen?

Answer 11

Transformation is DNA taken up from the environment

DNA is released following lysis of bacteria. The dsDNA is then processed to ssDNA before internalization.

Question 12

Describe bacterial conjugation.

How does it happen?

Answer 12

Conjugation is the exchange of genetic material by direct cell-to-cell contact.

It requires a complex set of genes. Transfer is through a “mating bridge.” This can transfer plasmids, transposons or pathogenicity islands. The donor retains a copy of the original genetic material.

Question 13

Describe bacterial transduction.

Answer 13

Transfer of genetic material mediated by a bacteriophage.

Question 14

What type of organism is a bacteriophage?

There are 3 types, what are they?

Answer 14

They are obligate intracellular parasites.

1. Icosahedral head
2. Icosahedral head with tail
3. Filamentous

Question 15

Describe the Lytic cycle by bacteriophage.

Answer 15

New progeny phage are made and the phage genome is replicated independently of the host genome.

The numbers of phage grow, they lyse the host cell and are released into the environment.

Question 16

Describe the Lysogenic cycle by bacteriophage.

Answer 16

This is vertical transmission of phage material. The phage genome is integrated and replicated with the bacterial genome.

The host bacteria is spared.

Question 17

How is Transduction a combination of the lytic cycle and lysogenic cycle?

Answer 17

Transmission of material begins as the lytic cycle.
Bacterial genome is packaged into the phage.
Transducing phage introduces genome into new host.

Question 18

What is a transductant?

Answer 18

Transductant = stable host with transduced DNA

Question 19

How is phage introduction of toxins into a bacteria different from transduction?

Answer 19

Toxins are part of the phage genome.

Question 20

The Ace and Zot genes of Cholera toxin have what two functions?

Answer 20

1. Phage morphogenesis
2. Enterotoxic activity.

Question 21

How does Cholera toxin cause profuse watery diarrhea?

Answer 21

A-5B toxin → B subunits bind ganglioside GM₁ → A subunit is internalized → interacts with G proteins regulating adenylate cyclase → induces conversion of ATP to cAMP → BAM! Diarrhea!

Question 22

1. What type of phage carries the shiga toxin?
2. What two bacteria does the Shiga toxin phage infect?

Answer 22

1. Icosahedral head with short tail
2. Shigella dysenteriae and E. coli

Question 23

What is the mechanism of the Shiga toxin phage?

Answer 23

A-5B toxin → B subunits bind Gb3 glycolipid → A subunit translocated into cytosol → modifies ribosome acceptor site → blocks protein synthesis.

Question 24

What substances released by macrophages result in tissue damage?

Answer 24

ROI, RNI and hydrolytic enzymes

Question 25

What cytokines are released following macrophage infection with bacteria?

Answer 25

IL-1, TNF-alpha, IL-6, IL-8, IL-12

Question 26

Describe the maturation of the phagosome.

Answer 26

The pH inside the phagosome is initially 7.something and progressively decreases by way of increased # of vacuolar ATP-ase pumps. The phagosome ultimately fuses with the lysosome for the knockout punch to bacteria.

Question 27

What are three methods of killing bacteria once a phagosome has fully matured?

Answer 27

1. Oxygen independent killing - due to profoundly low pH in phagolysosome
2. Generation of nitric oxide
3. Generation of superoxide and Chlorox - via NADPH oxidase.