Bacterial Genetics: Introduction to infectious diseases Flashcards
Most bacteria are _______ which carry only one copy of each gene, as opposed to __________ organisms which have two copies of each gene.
haploid, diploid
The defined site where bacterial chromose replication begins
origin of replication
Describe the process of bacterial cell division including DNA replication
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.
These processes occur simultaneously in bacteria since there is no nucleus present
transcription and translation
What is the function of reverse transcriptase?
Convers ssRNA to ssDNA in retroviruses
The ssDNA is then converted to dsDNA and become part of the host chromosomal DNA
What does quinolones inhibit?
DNA gyrase (or equivalent enxyme in Gram positive bacteria) – involved in unwinding DNA during chromosomal replicaion
What does rifampicin inhibit?
RNA polymerase
Groups of compounds used to inhibit protein synthesis often bind to what bacterial cell component?
small or large ribosomal subunits
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?
mutation
Changes in DNA that affect a single nucleotide?
How does this affect the amino acid sequences?
point mutation
May not affect protein’s amino acid sequence b/c genetic code is redundant
Changes in DNA that affect several nucleotides?
If they do not occur in sets of 3s, what is the resulting problem?
Indels (insertions and deletions)
Frameshift
What is a missense mutation?
What a point mutation results in an amino acid mutation
non-sense mutation
When a point mutation results in premature termination of translation
What is lateral movement of genes from one bacterium to another?
Horizontal gene transfer
Provide an example of mutations conferring adaptive advantage to bacteria.
Gram-negative bacteria can accumulate mutations in porins that restrict the diffusion of antibiotics through the outer membrane, increasing the resistance to those antibiotics
The process in which DNA from a donor cell is released into the environment and is then taken up by the recipient cell.
Transformation
What does it mean for a bacterial cell to be competent?
What are the 5 common bacteria that are naturally competent?
bacteria that are capable of taking up naked DNA from the environment
Haemophilus influenza, Neisseria gonorrhoeae, N. meningitides, Streptococcus pneumoniae, adn Legionella pneumophilia
Describe the process of transformation in gram positive bacteria.
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.
Describe the process of transformation in gram negative bacteria.
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.
What is the transfer of DNA from a donor cell to a recipient cell through the formation of a sex pilus?
conjugation
What carries the genes encoding the proteins necessary for conjugative DNA transfer?
conjugative plasmid
Describe the process of conjugation
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.
How are non-conjugative plasmids transferred?
If a transfer system is supplied by a conjugative plasmid present in the same cell
What is another name for a conjugative plasmid?
mobilizable
What is a Hfr (high frequencyrecombination) strain?
When conjugative plasmids integrate into the chromosome, which can then transfer regions of adjacent chromosomal DNA into recipient strain through conjugation.
What is the transfer of DNA through bacterial viruses?
Transduction
Describe a lytic infection.
phage DNA and proteins are synthesized, leading to the formation of phage particles that are released upon bacterial cell lysis
Describe a lysogenic infection.
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
What is the name of phages that integrate into the bacterial cell DNA?
prophage
What type of phage can go through either a lytic of lysogenic life cycle?
temperate phages
_______ often carry on their chromosome the genomes of several prophages.
Pathogens
What are three examples of prophages that carry virulence genes?
Vibrio cholerae, enterhemorrhagic Escherichia coli, and, Corynebacterium diptheriae
Describe the process of generalized transduction.
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.
Describe the process of specialized transduction
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.
What is the name of DNA elements that are able to move from one place in the bacterial DNA to another?
transposons
What is replicative transposition?
when the transposon is duplicated as part of its movement, and one copy remains in the original site
What is the name of the smallest mobile genetic elements?
What are its components?
insertion sequences (IS) transposase gene that is necessary for transposition and short inverted-repeat sequences at the ends
What is non-replicative transposition?
When the DNA is not replicated and the element is just released from the flanking DNA
What is the name for large chromosomal DNA regions characterized by distinct percent G+C content, virulence genes, and direct repeats at ends?
Pathogenicity Islands (PAI)
What do the direct repeats at the ends of PAIs indicate?
Horizontal gene transfer took place
Provide three examples of functions that PAIs may provide for bacteria who acquire them.
- pili that allow adhesion to certain tissue
- means for acquiring iron/other nutrients
- complex secretion systems that allow pathogens to invade human cells or escape the immune response
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
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
