Lecture 13-15 Flashcards
What makes bacteria valuable for research
small size, rapid reproduction, simple structure, genetic variability
What are the 3 parasexual processes
conjugation, transformation and transduction
What is the term for bacterial viruses
bacteriophages
How do bacteriophages reproduce
infecting bacterial cells
What are the two media options for bacterial growth
liquid and solid
What are the circular features on a solid media if bacteria growth occurs
colonies of bacteria
If you assembled a full dish of bacterial growth and then inserted a virus, clearings would show up on the plate, what are these clearings called
plaques
Why do plaques occur
the virus kills the bacteria in the colony and forms clearings where the bacteria previously was
What is bacteriophage T4
the genome contains 168800 base pairs and 150 characterized genes
- goes through a lytic phase
What is a lytic phase
infects host, lyses host, and bursts to infect surrounding cells
What is a lysogenic phase
bacteriophage DNA is inserted onto the host genome where it is passed on to subsequent generations
Is bacteriophage T4 a lytic of lysogenic phage
lytic
What is bacteriophage lambda
genome contains 48502 base pairs and about 50 genes (smaller than T4)
- can be both lytic or lysogenic
In its integrated state, the lambda chromosome is called….
prophage
Why can bacteria not have chiasmata
they don’t have meiosis, only mitosis
Is the gene transfer of bacteria unidirectional or bidirectional
unidirectional
What are plasmids
small circular DNA sequences (episomes are a subcategory of plasmids)
What are some examples of phenotypes in bacteria
colony colour, nutritional mutants, phototrophs (wild type) and auxotrophs (cannot synthesize certain AAs), and antibiotic resistance
What are prototrophs
wild type bacterial chromosomes
What are auxotrophs
cannot synthesize certain AAs
What is conjugation
a cytoplasmic bridge is formed between two bacterial cells and DNA replicates and transfers from donor to recipient
- crossover then occurs to implement new DNA onto original plasmid and a recombinant chromosome appears
What is transformation
DNA fragments from a dead cell in the colony (naked DNA) is taken up by a host
- a crossover then occurs to implement new DNA onto original plasmid and a recombinant chromosome appears
What is transduction
a virus attaches itself to a host bacterial cell and injects its DNA, which splits up the original chromosome of the host cell
- the bacterial cell lyses, however, some of the bacterial DNA is taken up by the viral head and transferred to the next host cell
- a crossover the occurs to implement new DNA onto original plasmid and a recombinant chromosome appears
What parasexual process requires physical contact
conjugation
What parasexual process requires a virus
transduction
What parasexual process is sensitive to DNase
transformation
Why is transformation sensitive to DNase
because the function of DNase is to chop up free floating DNA and make it useless to the cell - in this case transformation would not occur because the free DNA outside the cell would no longer be viable
What experiment determined the need for contact in bacterial DNA conjugation
the U-tube experiment
In what parasexual process does a bacterial cell take up DNA from its outer environment
transformation
What does it mean for a bacterium to be competent
can bind exogenous DNA and transport it into the cell (therefore bacterium must be competent to undergo transformation)
What can transformation be used to determine
distance between bacterial genes
How is transformation measured
as a change in phenotype (which occurs at a certain frequency)
How does transformation determine the distance between genes on the original chromosome
because when looking at the uptake of varying DNA fragments, different results are seen in the transformants
ie. if a+ b+ and c+ are all fragments of donor DNA, and uptake of a+ alone, b+ alone, c+ alone, and a+b+ together are seen, that would mean a and b were close together on the original plasmid, while c was further away (don’t see a+c+ together or b+c+ together)
Is conjugation sexual or asexual
sexual reproduction mediated by the F factor (fertility factor)
What physical formation is F factor
it is an episome
In conjugation, what is ALWAYS a recipient cell and cannot act as a donor
F- cells (don’t have fertility factor to donate)
What is a cell with F factor NOT incorporated into the chromosome called
F+ cell (has autonomous F factor)
What is a cell with F factor incorporated into the chromosome called
Hfr cell (has integrated F factor)
What are the two cell types that can act as donors in conjugation
F+ cells and Hfr cells
What is the product of conjugation between an F+ cell and an F- cell
2 F+ cells
What is the product of conjugation between an Hfr cell and an F- cell
an F- cell and an Hfr cell
What occurs in the conjugation of an Hfr and an F- cell
the Hfr acts as the donor and the F- cell acts as the recipient, Hfr synthesizes its DNA and inserts it onto the recipient for genetic recombination, but the F factor is not passed on to the recipient (no change in cell type, only see recombination of DNA)
What occurs in the conjugation of an F- cell and an F+ cell
the F+ cell acts as the donor, and the F- cell acts as the recipient, the F factor in the F+ cell synthesizes its DNA and it crosses over the bridge into the recipient cell to form autonomous F factor in the recipient, therefore the recipient becomes F+ and two F+ cells are seen as the final product
What is the term for an extra-chromosomal circular piece of DNA that can replicate independently of the chromosome
a plasmid
What are plasmids/episomes found in E.coli
F factor and R plasmids
Is an episome/plasmid essential to the host cell
no, it can either replication autonomously (F+ cell) or integrate into the chromosome (Hfr)
What occurs in transaction
bacteriophages attack the host bacterial cell, take up DNA of the host, and donate it to other host cells during infection efforts
What is a cotransuctant
when two genes are close on the original chromosome and both are taken up by the virus and inputted into a new host (2 genes transducted)
