bacterial growth and microbial genetics Flashcards
what is a pure culture
population of organisms descended from a single cell and is therefore separated from all other species
what did Robert Koch develop?
solid media (agar-agar derived from seaweed) Contained in dishes invented by Kochs lab assistant Julius Richard Petri
What is Binary fission?
after a bacterial cell has increased in size and doubled all of its parts, it divides
Define microbial growth
an increase in the number of cells in a population
Define generation time
time it takes for a population to double in number
Bacterial growth in a lab (a closed system) follows a pattern of stages called _______
Growth curve
What are the 4 stages of the growth curve?
Lag phase (latent)
Exponential phase (log)
Stationary phase
Death phase
Describe the lag phase (latent)
Cells “ramp up” by synthesizing macromolecules required for division & ATP
Describe the exponential phase (log)
cells dividing at a constant rate, growth is balanced with available nutrients
Describe the stationary phase
cells have exhausted supply of energy and nutrients, number of cells remains relatively constant
Describe the death phase
population decreases as cells die off at a constant rate
What are the 2 methods to measure growth?
- direct count method using microscope and hemacytometer
- indirect cell counting using serial dilution
Adenine pairs with?
Thymine
Guanine pairs with?
Cytosine
A set of 3 nucleotides on a single strand =
a codon - this encodes a specific AA
Where does DNA replication begin?
replication origin (ori)
Is DNA replication semi-conservative?
Yes
What direction does DNA replication proceed in?
5’ to 3’
Whats the difference between the leading strand & the lagging strand?
Leading strand= continuously synthesized
Lagging strand= discontinous, synthesized in pieces
What are the pieces of the lagging strand called?
Okazaki fragments
Describe the central dogma
DNA –> (transcription) –> RNA –> (translation) –> protein
Describe transcription
mRNA is synthesized from DNA via RNA polymerase
RNA nucleotides are adenine, uracil, guanine, cytosine
new mRNA is moved to ribosomes for translation
Describe translation
process of synthesizing proteins
occurs on ribosome
AAs are assembled into growing polypeptide chain (when folded= protein)
During transcription what acts as an on/off switch?
A regulatory region near the promotor which a regulatory protein can bind to
What is an operon?
a set of adjacent genes coordinately controlled by a regulatory protein and transcribed as a single RNA message
Is an operon inducible, repressible or both?
Both
Genes that are not always being transcribe must be ______ to function
Induced
Genes that are always being transcribed must be ______ to prevent proteins from being made
Repressed
An inducible operon requires what?
an inducer to prevent a repressor protein from binding to the operator
Where does spontaneous mutation occur?
natural environment
What is a base substitution?
an incorrect base is incorporated into the DNA during replication
Point mutation?
only 1 base is changed
Missense mutation?
substitution of different AA in protein
Nonsense mutation?
change creates stop codon instead of normal AA coding codon
Frameshift?
removal or addition of nucleotides that leads to change in way the DNA sequence is read- changes the codon frame or reading frame
Transposones?
segments of DNA that can move spontaneously from one site or another in the same or different DNA molecules
aka Jumping genes
What is an induced mutation?
a change in DNA sequence that is the result of a mutagen such as radiation or chemical agents
What are chemical mutagens?
- they alter the binding of DNA molecule
Alkalyting agents
base analogs
intercalating agents
What are the 2 types of radiation?
UV- causes thymine dimers
X-ray- causes single and double stranded breaks in DNA
How do we repair mutations?
Bacteria employ mismatch (or excision repair) as well as a mechanism called SOS repair
What is a prototroph?
Cells that grow without added growth factors (natural)
What is a auxotroph?
Cells that grow only with growth factors added in lab
What is a conditional lethal mutant?
Mutants defective for the synthesis of an essential macromolecule under specific conditions
What does the term “competent” refer to?
recipient cells that are able to take up DNA
- many populations are naturally competent during log phase of growth
How can competence be induced?
CaCl2 or an electrical current = electroporation
What are the steps of genetic recombination?
Transformation
Conjugation
Transduction
What are the 2 ways two bacterial cells can contact one antoher?
Plasmid DNA transfer
Chromosomal DNA transfer
Describe Plasmid DNA transfer
Plasmid transferred = F plasmid (fertility plasmid)
Donor cell containing F is called F+ or male
Recipient cell= F- or female
F plasmid has series of genes that code for formation of a sex pilus
Describe Chromosomal DNA transfer
F plasmid can transfer chromosomal DNA if it integrates into the chromosome and then excises, bringing a portion of chromosome (F’ cell)
A cell with a F plasmid that has integrated into the chromosome = Hfr cell
In order to transfer DNA, a Hfr cell must excise the F plasmid
The excised plasmid= F’
What is transduction?
Transfer of DNA from cell to cell via a bacteriophage
What are the two ways a bacteriophage can interact with cells?
Lytic
Lysogenic
Describe Lytic interaction
Phage (virus) overtakes cell
Assembly of new phages occur while bacterial chromosmomal DNA may be incorporated
Cell lyses to expel new phages containing bacterial DNA
phage is capable of transduction
Describe Lysogenic interaction
phage (virus) DNA integrates into host DNA (temperate phase)
Phage DNA remains in cell for few to many generations
Eventually becomes lytic
If a viral gene is permanently incorporated into bacterial DNA = lysogenic conversion
What is lysogenic conversion
When a viral gene (phage DNA) is permanently incorporated into bacterial DNA. This results in new bacterial strain
What are the two types of transduction?
Generalized
Specialized
Describe generalized transduction
During production some phages accidentally package only bacterial chromosomal DNA, not viral DNA
This phage can still infect cells, but injects bacterial chromosomal DNA into host
Describe specialized transduction
The phage packages both viral DNA and bacterial chromosomal DNA
It packages specific chromosomal DNA found near where viral DNA integrated during lysogenic phage
