Bacterial Genetics: Introduction to infectious diseases

Question 1

Most bacteria are _______ which carry only one copy of each gene, as opposed to __________ organisms which have two copies of each gene.

Answer 1

haploid, diploid

Question 2

The defined site where bacterial chromose replication begins

Answer 2

origin of replication

Question 3

Describe the process of bacterial cell division including DNA replication

Answer 3

Several enzymes bind an unwind the DNA. Both strands serve as the templates. DNA is synthesized by DNA polymerase (also proofreads). After replication, chromosomes are segregated, a septum of cytoplasmic membrane and cell wall separate daughter cells. Plasmids replicate and partition independently.

Question 4

These processes occur simultaneously in bacteria since there is no nucleus present

Answer 4

transcription and translation

Question 5

What is the function of reverse transcriptase?

Answer 5

Convers ssRNA to ssDNA in retroviruses

The ssDNA is then converted to dsDNA and become part of the host chromosomal DNA

Question 6

What does quinolones inhibit?

Answer 6

DNA gyrase (or equivalent enxyme in Gram positive bacteria) – involved in unwinding DNA during chromosomal replicaion

Question 7

What does rifampicin inhibit?

Answer 7

RNA polymerase

Question 8

Groups of compounds used to inhibit protein synthesis often bind to what bacterial cell component?

Answer 8

small or large ribosomal subunits

Question 9

What is a heritable change in the nucleotide sequence of DNA and can be spontaneous or the result of exposure to chemical or physical agents?

Answer 9

mutation

Question 10

Changes in DNA that affect a single nucleotide?

How does this affect the amino acid sequences?

Answer 10

point mutation

May not affect protein’s amino acid sequence b/c genetic code is redundant

Question 11

Changes in DNA that affect several nucleotides?

If they do not occur in sets of 3s, what is the resulting problem?

Answer 11

Indels (insertions and deletions)

Frameshift

Question 12

What is a missense mutation?

Answer 12

What a point mutation results in an amino acid mutation

Question 13

non-sense mutation

Answer 13

When a point mutation results in premature termination of translation

Question 14

What is lateral movement of genes from one bacterium to another?

Answer 14

Horizontal gene transfer

Question 15

Provide an example of mutations conferring adaptive advantage to bacteria.

Answer 15

Gram-negative bacteria can accumulate mutations in porins that restrict the diffusion of antibiotics through the outer membrane, increasing the resistance to those antibiotics

Question 16

The process in which DNA from a donor cell is released into the environment and is then taken up by the recipient cell.

Answer 16

Transformation

Question 17

What does it mean for a bacterial cell to be competent?

What are the 5 common bacteria that are naturally competent?

Answer 17

bacteria that are capable of taking up naked DNA from the environment
Haemophilus influenza, Neisseria gonorrhoeae, N. meningitides, Streptococcus pneumoniae, adn Legionella pneumophilia

Question 18

Describe the process of transformation in gram positive bacteria.

Answer 18

dsDNA binds nonspecifically to the cell surface, then the DNA is cleaved, and one strand crosses to the cytosol while the other strand is degraded. The DNA crosses to the cytosol through a specific protein complex that forms a pore through the cell membrane and the cell wall. Once inside the recipient cell, the foreign DNA has to recombine with a homologous segment in the recipient’s chromosome to be stably maintained and inherited. If the DNA is a plasmid, it can replicate independently.

Question 19

Describe the process of transformation in gram negative bacteria.

Answer 19

the dsDNA first crosses a hydrophilic pore or channel located in the outer membrane. Then, the DNA crosses to the cytosol. Once inside the recipient cell, the foreign DNA has to recombine with a homologous segment in the recipient’s chromosome to be stably maintained and inherited. If the DNA is a plasmid, it can replicate independently.

Question 20

What is the transfer of DNA from a donor cell to a recipient cell through the formation of a sex pilus?

Answer 20

conjugation

Question 21

What carries the genes encoding the proteins necessary for conjugative DNA transfer?

Answer 21

conjugative plasmid

Question 22

Describe the process of conjugation

Answer 22

DNA strands separate and one strand moves to the recipient cell through the mating bridge that connects both bacterial cells. The ssDNA then serves as the template to regenerate the dsDNA again.

Question 23

How are non-conjugative plasmids transferred?

Answer 23

If a transfer system is supplied by a conjugative plasmid present in the same cell

Question 24

What is another name for a conjugative plasmid?

Answer 24

mobilizable

Question 25

What is a Hfr (high frequencyrecombination) strain?

Answer 25

When conjugative plasmids integrate into the chromosome, which can then transfer regions of adjacent chromosomal DNA into recipient strain through conjugation.

Question 26

What is the transfer of DNA through bacterial viruses?

Answer 26

Transduction

Question 27

Describe a lytic infection.

Answer 27

phage DNA and proteins are synthesized, leading to the formation of phage particles that are released upon bacterial cell lysis

Question 28

Describe a lysogenic infection.

Answer 28

the phage DNA integrates into the bacterial chromosome at specialized sites, and thus, the bacterial cell does not lyse but transmits the phage DNA to daughter cells upon cell division

Question 29

What is the name of phages that integrate into the bacterial cell DNA?

Answer 29

prophage

Question 30

What type of phage can go through either a lytic of lysogenic life cycle?

Answer 30

temperate phages

Question 31

_______ often carry on their chromosome the genomes of several prophages.

Answer 31

Pathogens

Question 32

What are three examples of prophages that carry virulence genes?

Answer 32

Vibrio cholerae, enterhemorrhagic Escherichia coli, and, Corynebacterium diptheriae

Question 33

Describe the process of generalized transduction.

Answer 33

During lytic process, bacterial DNA is erroneously packed into a phage. Upon lysis, those particles can infect new bacterial cells, thus the infected cell receives the donor DNA rather than the phage DNA. This fragment can be incorporated into the recipient's chromosome by homologous recombination.

Question 34

Describe the process of specialized transduction

Answer 34

A prophage initiating the lytic cycle may excise from the chromosome carrying a piece of bacterial DNA that is adjacent to the phage's insertion site. Both the phage DNA and bacterial DNA can be transferred to a recipient bacterium upon infection.

Question 35

What is the name of DNA elements that are able to move from one place in the bacterial DNA to another?

Answer 35

transposons

Question 36

What is replicative transposition?

Answer 36

when the transposon is duplicated as part of its movement, and one copy remains in the original site

Question 37

What is the name of the smallest mobile genetic elements? | What are its components?

Answer 37

``` insertion sequences (IS) transposase gene that is necessary for transposition and short inverted-repeat sequences at the ends ```

Question 38

What is non-replicative transposition?

Answer 38

When the DNA is not replicated and the element is just released from the flanking DNA

Question 39

What is the name for large chromosomal DNA regions characterized by distinct percent G+C content, virulence genes, and direct repeats at ends?

Answer 39

Pathogenicity Islands (PAI)

Question 40

What do the direct repeats at the ends of PAIs indicate?

Answer 40

Horizontal gene transfer took place

Question 41

Provide three examples of functions that PAIs may provide for bacteria who acquire them.

Answer 41

1. pili that allow adhesion to certain tissue 2. means for acquiring iron/other nutrients 3. complex secretion systems that allow pathogens to invade human cells or escape the immune response

Question 42

Point mutations and genomic rearrangements lead to ______ adaptive changes, whereas acquisition of a large DNA fragment, such as PAI, can convert a non-pathogenic bacterium into a pathogen in a __________. Provide an example of virulence acquired via PAI

Answer 42

slow, single step Corynebacterium diphtheriae, causing agent diphtheria. Primary virulence factor is phage-encoded diphtheria toxin. Non-virulent strains can acquire the gene to produce this toxin via transduction