BACTERIAL GENETICS Flashcards
single, long piece of circular, double-stranded DNA
Contain 2000 to 4000 genes.
Chromosome
Small DNA circles
Replicate independently
Plasmids
Call for abilities they are not born with (ability to resist antibiotics, toxins, ability to produce sex pilus) - some bacteria may acquire this from other organisms.
Genes for toxins, proteins that promote transfer
Plasmids
Genetic transfer
Vertical gene transfer
Horizontal gene transfer
Mother cell to offspring
Binary fission
Vertical Gene Transfer
From one bacterial cell to another bacterial cell
Conjugation
Transformation
Transduction
Horizontal Gene Transfer
• Bacterial mating
• Enteric, gram (-) bacteria
CONJUGATION
The F+ male has a plasmid that calls for the codes for the production of the sex pilus
It can serve as the genetic donor
Sex pilus adheres to an F- (female)
One strand of the plasmid is transferred onto the female
They are now both able to copy it - 2 copies of the strand
The female has become F+ or a male bacterium, and it is now able to code for a sex pilus.
CONJUGATION
The plasmid being shared is an R plasmid
Plasmid that can help bacteria resist some forms of antibiotic
Resistance Plasmid Conjugation
F+ r positive donor donating the R plasmid onto an F-r negative
The recipient now becomes F+ R positive bacterium.
Once it’s shared, it is automatically replicated to produce two strands, and the recipient who was previously R-(non-resistant) and F- unable to produce sex pilus can now produce six pilus.
Resistance Plasmid Conjugation
• A recombinase functioning in recombinational DNA repair in bacteria
RecA Protein
occurs after the uptake of DNA fragments from the environment
When a bacterium dies, it breaks up into pieces, and some of its genetic material may be free swimming in the environment
TRANSFORMATION
as a process of Gene transfer may occur between two different species
This process of gene transfer will occur
ONLY to a competent bacteria
Transformation
are able to accept naked DNA from the environment.
These possess the RecA protein
- which is a critical enzyme in the process of transformation
Competent bacteria
The_____ catalyzes the pairing of the single stranded
DNA with the complementary regions of the double-stranded
DNA
RecA protein
Transfer of DNA Fragments from one bacterium to another by a bacteriophage
TRANSDUCTION
are viruses that kills bacteria
Bacteriophages
“Carry-across”
Transduction
TYPES OF BACTERIOPHAGE THAT INITIATE
TRANSDUCTION
• Lytic or Virulent phage
• Temperate phage
• Involves the production of viruses using a host cell to manufacture more viruses, and then the viruses would burst out of the host bacterium -> hence the name_____
Lytic or Virulent phage
virulent
Replicate through the Lytic cycle
Lytic or Virulent phage
• T-phages
• Undergoes replication through the lysogenic cycle
Temperate phage
Involves the incorporation of the viral genome into the host cell genome creating the prophage
Temperate phage
Temperate phage
Virions will now contain the_____. It has both the genetic material of the temperate phage and the bacterial host (mixture of genes)
prophage
TWO FORMS OF TRANSDUCTION
GENERALIZED TRANSDUCTION
SPECIALIZED TRANSDUCTION
• During assembly, a genetic material is encased in a capsin.
It infects another bacteria, but the genetic material it releases is that of the first bacterial host
• The bacterium now has gained genetic material from another bacterial host.
GENERALIZED TRANSDUCTION
When the lytic phages replicate, the capsid sometimes assembles around a small fragment of the bacterial DNA that’s not viral by nature
• It appears to be a virus / bacteriophage, but it carries it a bacterial DNA so it causes the transfer of one of the genetic material of another bacteria onto another bacterium
GENERALIZED TRANSDUCTION
• Initiated by the temperate phage which undergoes the Lysogenic cycle as it replicates
• The bacterial organism that falls prey to this type of Gene transfer undergoes lysogenic conversion
SPECIALIZED TRANSDUCTION
Some bacterial DNA becomes part of the phage genome; Some phage DNA remains in the bacterial genome.
SPECIALIZED TRANSDUCTION
Examples
Corynebacterium diphtheria
Streptococcus pyogenes
Clostridium botulinum
Vibriocholerae
Specialized transduction
• Cells are immune to reinfection by the same phage
Acquired after bacterial cells under bacterial conversion
• Cells may exhibit new properties
LYSOGENIC CONVERSION
Allows phage to take a bit of the adjacent bacterial
DNA
•
There’s a prophage formation
When it transfers genetic material onto another bacterial host, it does not just carry viral DNA with it,
Carries bacterial DNA as well -› a combination
LYSOGENIC CONVERSION
The genetic material may carry a portion of the host and the temperate phage
All its offsprings, the new virions carry a combination of DNA of the bacteria and that of the virus
When it infects another bacteria, the bacteria has access to both phage DNA and bacterial DNA
LYSOGENIC CONVERSION
any change in the DNA base sequence
Example: when bacterial cells are exposed to radiation
Mutation
May cause plasmids to integrate into the chromosome
responsible for the spread of antibiotic resistance genes
Mobile Genetic Elements
: mobile DNA segments (jumping genes)
Transposons
A bacteria contains ______genes.
2000 to 4000
T or F
Plasmids
Replicate independently
True
Call for abilities they are not born with (ability to resist antibiotics, toxins, ability to produce sex pilus) – some bacteria may acquire this from other organisms
Plasmids
Genes for toxins, proteins that promote transfer
Plasmids
Types of horizontal gene transfer
Transduction
Transformation
Conjugation
Conjugation happens in…
Enteric, gram (-) bacteria
• It causes the host bacterium to die/lyse so the new variants can come out of the host cell
Create virions using the host cell
Lytic or Virulent phage
Virulent phage
■ T-phages
■ Replicate through the..
Lytic cycle
Does not kill the host cell immediately, rather slowly_> will infect it first
Release its genetic material and cause it to incorporate or mix with the host cell’s genome.
Once they mix, it is called the prophage.
Temperate phage or Phage Lambda
Temperate phage
■ Phage lambda
■ Undergoes replication through the…
lysogenic cycle
Bacteria that undergo specialized transduction
Examples
○ Corynebacterium diphtheria
○ Streptococcus pyogenes
○ Clostridium botulinum
○ Vibrio cholerae
The bacterial chromosome, also called the____, consists of a single, closed, circular piece of dsDNA that is supercoiled to fit inside the cell.
genome
It contains all the information needed for cell growth and replication
Genome
______ are specific DNA sequences that code for the amino acid sequence in one protein (e.g., one gene equals one polypeptide), but this may be sliced up or combined with other polypeptides to form more than one protein.
Genes
e genetic information encoded in the bacterial chromosome, many bacteria contain extra information on small circular pieces of extrachromosomal, dsDNA called______.
plasmids
They are not essential for bacterial growth, so they can be gained or lost.
Plasmids
Genes that code for antimicrobial resistance (and sometimes toxins or other virulence factors) are often located on plasmids.
Plasmids
Plasmids are located in the______ of the cell and are selfreplicating and passed to daughter cells, similar to chromosomal DNA
cytoplasm
Plasmids
They also may sometimes be passed (nonsexually) from one bacterial species to another through_______ (horizontal transfer of genetic material by cell-tocell contact).
This is one way drug resistance is acquired.
conjugation
Mobile Genetic Elements
Certain pieces of DNA are mobile and may jump from one place in the chromosome to another place. These are sometimes referred to as…
jumping genes
are related mobile elements that contain additional genes.
often carry drug-resistance genes and are usually located in plasmids.
Transposons
Transposons
______are changes that occur in the DNA code and often result in a change in the coded protein or in the prevention of its synthesis.
Some _____ are silent, where a change in the DNA sequence does not result in the substitution of a different amino acid in the resulting protein
Mutations
_________is a method by which genes are transferred or exchanged between homologous (similar) regions on two DNA molecules, forming new combinations of genes on a chromosome
Genetic recombination
This method provides a way for organisms to obtain new combinations of biochemical pathways and adapt to changes in their environment.
Genetic recombination
is the uptake and incorporation of free or naked DNA into a bacterial cell
Transformation
Cells that can take up naked DNA are referred to as being______.
competent
Transformation
Only a few bacterial species, such as (3), do this naturally.
Bacteria can be made competent in the laboratory, and transformation is the main method used to introduce genetically manipulated plasmids into bacteria, such as E. coli, during cloning procedures.
Streptococcus pneumoniae, Neisseria gonorrhoeae, and H. influenzae
is the transfer of bacterial genes by a bacteriophage from one cell to another
Transduction
A________ consists of a chromosome (DNA or RNA) surrounded by a protein coat.
When a phage infects a bacterial cell, it injects its genome into the bacterial cell, leaving the protein coat outside.
bacteriophage
_________, in which the bacteriophage DNA directs the bacterial cell to synthesize phage DNA and phage protein and package it into new phage particles.
The bacterial cell eventually lyses (lytic phase), releasing a new phage that can infect other bacterial cells.
lytic pathway
In some instances, the phage DNA instead becomes incorporated into the bacterial genome, where it is replicated along with the bacterial chromosomal DNA; this state is known as_______, and the phage is referred to as being_____.
lysogeny
temperate
During______, genes present in the phage DNA may be expressed by the bacterial cell
An example of this in clinical microbiology is(3) that are lysogenized with a temperate phage carrying the gene for diphtheria toxin cause disease.
Strains lacking the phage do not produce the toxin and do not cause disease. Under certain conditions, a temperate phage can be induced
Lysogeny
C. diphtheriae. Strains of C. diphtheriae
Strains lacking the phage do not produce the toxin and do not cause disease.
Under certain conditions, a _____can be induced, the phage DNA is excised from the bacterial genome, and a lytic state occurs.
temperate phage
During this process, adjacent bacterial genes may be excised with the phage DNA and packaged into the new phage. The bacterial genes may be transferred when the phage infects a new bacterium. In the field of biotechnology, phages are often used to insert cloned genes into bacteria for analysis.
Lytic stage
is the transfer of genetic material from a donor bacterial strain to a recipient strain
Conjugation
Conjugation
In the E. coli system, the donor strain (F+) possesses a fertility factor (F factor) on a plasmid that carries the genes for conjugative transfer. The donor strain produces a hollow surface appendage called a_______, which binds to the recipient F− cell and brings the two cells in close contact.
sex or conjugation pilus
When the F factor is integrated into the bacterial chromosome rather than a plasmid, there is a higher frequency of transfer of adjacent bacterial chromosomal genes. These strains are known as…
high-frequency recombination strains
