Microbial genetics Flashcards
What is the chromosome number for bacteria?
1 (haploid)
Do bacteria have introns and exons?
no
Do bacteria have histones?
no
What are the two forms of extrachromosomal DNA that bacteria can have?
Plasmids and bacteriophages
What are episomes?
bits of DNA that can insert themselves into chromosomes
What does it mean that bacteria are polycistronic?
One gene region codes for more than one protein/gene
What are F plasmids?
plasmids in e.coli that can insert into bacterial chromosomes
What are R factors?
“Resistance factors” DNA on plasmids that confer antibiotic resistance
What are the four items that may be carried on a plasmid?
R factorsToxinsBacterocinsVirulence determinants
What are bacterocins?
a class of antibacterial agent that are active only against similar or closely related bacterial strains.
What is the lytic phase of bacteriophages?
phages take over the host replication and protein synthesizing machinery to produce new virus DNA and protein. Many new virus particles (virions) are assembled and released into the environment as the bacterial cell ruptures
What is the temperate phase of bacteriophages?
latent infection stage, where the phages enter a non-lytic prophage state in which they integrate into the bacterial chromosome and replication of their nucleic acid is linked to replication of host cell DNA
What are prophages?
The DNA of a phage that is integrated in a bacterial chromosome
What is the lysogenic cycle of phages?
When the phages integrate themselves into bacterial DNA
What is lysogenic conversion?
some lysogenized bacteria express new characteristics such as an increase in bacterial virulence (lysogenic conversion). For example, Vibrio cholerae produce the cholera toxin only when infected by CTX.
What are insertion sequences?
• Mobile genetic elements which have the ability to insert at multiple sites in a target molecule such as the chromosome or plasmids.
What are the two distinguishing characteristics of insertion sequences?
- Small size2. they only encode proteins required for insertion function such as the transposase enzyme and a regulatory protein that can either stimulate or inhibit transposition activity
What are at the ends of the insertion sequences?
Inverted repeats
What are transposons?
• Mobile genetic elements, similar to IS elements, that can transfer (transpose) DNA within a cell from one position to another in the chromosome or from an extrachromosomal genetic element to the chromosome and vice versa
What are the two major differences between transposons and insertion sequences?
- Transposons are longer2. Transposons have more DNA, including resitance genes
How can transposons be lethal for a bacteria?
• Transposons can sometimes insert into a gene thereby inactivating it. If the insertion and inactivation takes place in an essential gene, it can be lethal.
What are pathogenecity islands? What do they carry?
A special class of genomic islands acquired through horizontal gene transfer. They carry groups of coordinately regulated virulence genes surrounded by IS elements.
What are integrons?
a diverse group of genetic elements that encode a site-specific recombination system that can capture gene cassettes (most often antibiotic resistance gene cassettes).
What are the three mechansims of gene transfer in bacteria?
- Transformation2. Transduction3. Conjugation
What is transformation?
uptake of naked DNA by bacteria from the environment
Can transformation be undertaken by both gram positive and gram negative bacteria?
yes
Are most bacteria competent to take up foreign DNA through transformation?
No
What is homologous recombination?
Exchange of DNA molecules based on homology
What is the protein that mediated gene exchange at homologous regions in bacteria?
RecA
What is bacterial conjugation?
DNA transfer from one bacterial cell to another via close cell contact
What is the fertility (F) factor?
The DNA sequence that has the tra operon and other genetic material
What is the tra operon?
The genes that encode components of the sec pilus
What is the oriT?
The origin of transfer, where a single strand of DNA break occurs for transfer
What are Hfr bacteria?
If the F plasmid sequence gets integrated into the bacterial chromosome, the cell is designated an Hfr (high frequency recombination) cell.
Why does transformation rarely occur in vivo?
DNA is degraeded
What are the three steps of transformation?
1) The naked DNA must bind to the bacterial cell surface.2) The bound DNA is taken up through the cell membrane.3) All or some of the DNA is integrated into the host chromosome or replicates autonomously as a plasmid.
What determines the sex type of a bacteria capable of undergoing conjugation?
The F factor
Is conjugation a one way process, or can DNA flow freely either way through the sex pilus?
One way, from F+ to F-
What happens when a cell receives the F factor from another cell?
becomes an F+ “male” cell
What is transduction?
Genetic transfer between bacteria through bacteriophages
What is generalized transduction?
After DNase carried by bacteriophages chops up the bacterial DNA, some of those pieces can be packed with the viral DNA.
What are transducing phages?
bacteriopages that have bacterial DNA inside of them
What is specialized transduction?
When temperate phages undergo a lytic cycle, and carry a part of the bacterial DNA with them
How many strands of DNA are transferred in conjugation?
Single strand
Which type of bacterial DNA transfer uses free DNA?
Transformation
Which type of bacterial DNA transfer requires close cell-cell contact?
Conjugation
Which type of bacterial DNA transfer involves homologous recombination?
All of them, except for F+ to F- (plasmids here)
Can plasmid DNA be tranferred via the specialized transduction route?
No
Which type of bacterial DNA transfer can take place between two different bacterial species?
TransformationConjugationNOT transduction
What is site-specific recombination?
when one DNA molecule integrates into another DNA molecule with no homology other than a small site on each DNA
What is an operon?
A group of functionally related genes which are transcribed together into one mRNA and whose products are translated from the same mRNA.
What is a promoter region?
The sequence to which the RNA polymerase binds.
What is the operator region?
Sequence close to, or even overlapping the promoter, to which a repressor protein binds.
What is an activator?
A protein that positively regulates gene expression by binding upstream of the promoter, where it can help the RNA polymerase bind to the promoter
What are effectors?
Small molecules which bind to regulatory proteins and affect their activity.
What are inducers?
Effector molecules that increase transcription
What are corepressors?
Effectors that turn off gene transcription
What are the three categories of bacterial abx resistance?
IntrinsicChomosome mediatedPlasmid mediated
What is intrinsic abx resistance? Is it transferable (horizontally)? Is it currently increasing among bacterial population?
Intrinsic characteristics of bacteria that allow them to avoid being the target of an abx. These are not transferable, and this are not increasing among bacterial populations
What is chromosome-mediated abx resistance?
Chromosomal genes that encode for abx resistance. These are able to be transferred horizontally.
How do chromosomal mediated abx resistances arise?
Through random mutations
What is plasmid-mediated abx resistance?
Genes encoding abx resistance located on a plasmid
What is the resistance factor (r-factor) on plasmids?
The DNA that contains DNA that encodes for resistance.
What is the difference between the reistance transfer factor, and the reistance determinant part of the resistance factor?
Resistance transfer factor = F factorResistance determinant = actual genes that encode for resistance
Resistance transfer factor + resistance determinant = ?
Resistance factor
