Weeks 4-5 Flashcards
What is a bacteriophage and how do they reproduce?
= a bacterial virus, most abundant of any biological agent
- by infecting bacterial cells by injecting genetic material into bacterium
- can be lytic (T4) or lysogenic and lytic (lambda)
What are prototrophs?
wild type bacteria that can grow on minimal media plate, i.e. can synthesize everything they need
themselves
(is a phenotype)
What are auxotrophs?
mutant bacteria strains that lack certain enzymes which they cannot synthesize, so they need to be grown in complete media
What is a prophage?
= inserted viral DNA in bacterial cell
Lysogenic cycle
- phage DNA integrates into bacterial chromosome and becomes a prophage
- prophage is replicated as part of bacterial chromosome
- prophage may separate from chromosome and cell enters lytic cycle
Gene transfer in Bacteria
- always unidirectional from donor cells to recipient cells
Viral Genome
- very small and mostly linear but can be circular
- only about 300 genes
- the smaller the faster to replicate
- some viruses have RNA genome
Bacterial Genome
- several million base pairs but smaller than eukaryotes
- circular
- additional genetic material in plasmids and episomes
Plasmid
- small circular DNA, can replicate independently of bacterial chromosomes
- usually non-essential genes since plasmids can be lost but they are very mobile, often responsible for antibiotic resistance genes
Episomes
- large circular DNA that can integrate into bacterial chromosome for replication or remain separate
- can consist of fertility factor, viral genomes, transposons, etc.
Conjugation
- requires direct physical contact between two cells, form cytoplasmic bridge
- some DNA is transferred and replicates
- crossover in recipient cell leads to recombinant chromosome
Transformation
- DNA fragments are taken up by a recipient cell
- crossover in bacterium leads to creation of recombinant chromosome
Transduction
- virus attaches to bacterial cell and injects its DNA
- DNA is replicated, then bacterial cell lyses
- virus takes up some bacterial DNA with its own and carries it to next cell where it injects
- bacterial cell creates a recombinant chromosome from crossing over
- bacteriophage acts as a vector
Which parasexual process in bacteria requires cell contact?
Conjugation
Which parasexual process in bacteria is sensitive to DNase?
Transformation (b/c neither a bridge nor protected by bacteriophage)
What is a competent bacterial cell?
- one that can take up free DNA (even from other species)
- essentially refers to permeability of the cell
What is cotransformation?
- when multiple genes on same DNA fragment are taken up by recipient cell
- the closer together two genes are, the more likely that they will be taken up and transformed together
- therefore, can be used to map distance
What is the fertility factor?
- an episome or plasmid
- it mediates conjugation
- F- is always recipient cell
- F+ can be a donor cell with F factor but not on bacterial chromosome (rather plasmid or episome)
- Hfr cell: when the F factor has been integrated into bacterial chromosome and this can also be a donor
Generalized Transduction
= when a random fragment of bacterial DNA is packaged in the phage head by mistake
Specialized Transduction
= when the prophage excises imprecisely from the chromosome and produces a phage chromosome that only contains the adjacent bacterial genes not entire bacterial genome
3 Basic Components of nucleotides
1) Nitrogen containing bases (ATGCU)
2) Sugar (pentose - either deoxyribose or ribose)
3) Phosphate-diester bond (joins nucleotides)
Which bases are purines?
Adenine and Guanine
Which bases are pyrimidines?
Cytosine, Thymine, Uracil
What forms the backbone of the helix?
sugar and phosphate
the bases face inward and base pair
