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Tidewater Community College
Ch. 8 lecture
Ch. 8 lecture
Tidewater Community College
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cell has one copy of every chromosome
cell has two copies of every chromosome
-change in the DNA sequence
- this is a random/chance event, bacteria have no control over it
organism that has a mutation
mutant that is no longer able to synthesize a nutrient for itself, it must now acquire it from the environment
organism that doesn't have a mutation
the genes itself
expression of that gene
the 3 ways bacteria can adapt to their environment?
2) gene transfer
3) regulating gene expression
gives different bacteria different properties. some may be able to survive in certain environments then others
bacteria can transfer copies of their DNA to other bacteria-essentially sharing it
regulating gene expression
turning gene on & off as necessary
type of mutation in which one or more then one incorrect base is added during DNA synthesis
type of base substitution in which only one base is incorrect
type of base substitution in which a different amino acid is inserted in the protein. protein has some functionality but doesn't work as well as a wild type protein
inactivates the entire gene, it is not transcribed or translated, no protein is made at all
-one, or more then one base is removed
-can cause a frameshift mutation-ribosome reads the transcript in the wrong frame
-one or more bases is added
-could also cause a frameshift mutation
ribosome reads the the transcript in the wrong frame
-large segment of DNA that removes itself from its original position & inserts itself somewhere else in the chromosome
-causes a large insertion mutation-functional protein is not made
why do scientists use bacteria to study mutations?
1) they are haploid-any mutation will be expressed b/c they have only one chromosome
2) they are easy to grow
3) they are cheap to purchase & maintain
4)they grow to large numbers in a short amount of time
5) no ethical issues with mutating bacteria
agents of mutation (things that can cause mutation to occur)
causes cytosine to be converted to Uracil
add short chains of carbon to bases which changes how they hydrogen bond
insert themselves at the replication fork during DNA synthesis & cause insertion mutations
UV light causes thymine dimer formation-causes the DNA to bend -no transcription or DNA replication can occur past the thymine dimer
-covalent bond between two adjacent thymines
-causes the DNA to bend-no transcription or DNA replication can occur past the thymine dimer
causes single & double stranded breaks in the DNA
is only in one sugar phosphate backbone
through both sugar phosphate backbones. these are usually lethal to the cell
how can DNA polymerase fix incorrect base pairing during DNA replication?
while it is making a new piece of DNA it can correct its own mistakes. if it misses mistake it can not go backwards to fix it
enzyme that goes behind DNA polymerase to check its work; if it finds a mismatch it cuts out the wrong base & calls another DNA polymerase molecule in to add the correct one
in the presence of sunlight an enzyme is activated that can break the covalent bond between adjacent thymines
does not use sunlight, but it can occur in daylight hours. a different enzyme cuts out the section of DNA that contains the thymine dimer & calls DNA polymerase in to add new bases
only used by bacteria that have suffered heavy UV light damage. They are in danger of dying.
use a media (agar or broth) that only the mutated bacteria will grow on
used for identifying auxotrophic bacteria; there is no media that only the mutant will grow on
mutant that can no longer make a particular nutrient for itself. The nutrient must be present in the media in order for the bacteria to grow
test that uses auxotrophic bacteria to determine if a chemical might cause cancer
what are the 3 principles the ames test is based on?
1) reversion to wild type can be measured
2) mutagens will increase the rate of reversion
3) carcinogens are mutagens
vertical gene transfer
from parent bacteria to offspring bacteria through binary fission
lateral gene transfer
from one "adult" bacteria to another "adult" bacteria
what are the 3 methods of lateral gene transfer?
1) DNA mediated transformation
what 2 things do all the methods of lateral gene transfer have in common?
1) they only transfer a piece of the chromosome, not the entire chromosome
2) they all use a process called homologous recombination
- a single stranded piece of DNA from the donor bacteria, replaces the homologous genes in the recipient cell
-homologous means the genes are the instructions for how to make the same proteins, but they are not identical instructions
DNA mediated transformation
-Donor DNA is naked-it is free floating in the environment & is not surrounded by a cell
-recipient cell must be competent-capable of taking in naked DNA
what are two ways we can force bacteria to become competent?
2) calcium chloride
mild electric shock causes the cell to become leaky, it will now take in naked DNa
weak solutions of this also cause the cell to become leaky & take in naked DNA
Donor DNA is brought into the recipient cell by a virus
virus that only infects bacteria
involves plasmids and requires two bacteria to physically touch
small extrachromosomal piece of DNA that does not carry any genes that are necessary to life; only has genes that may be helpful; they are self-replicating
narrow host range plasmid
can only be transferred between specific types of bacteria
wide host range plasmid
can be transferred between many types of bacteria
resistance plasmids- have genes for antibiotic resistance (surviving in the presence of antibiotics)
cell in conjugation that has an F plasmid
cell in conjugation that has no plasmid
has the instructions for making the sex pills-structure used to temporarily attach the F+ and F- cells together
transfer of the bacterial chromosome in conjugation occurs in what type of cells?
Hfr= high frequency of transfer; F plasmid is not free floating, it is integrated into the bacterial chromosome
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