Mutations, Ames test, Genetic recombination Flashcards
Mutation
a change in phenotype due to change in genotype (nitrogen base sequence of DNA)
wild type
A natural, nonmutated characteristic is known as a wild type (wild strain)
Define mutant strain
An organism that has a mutation is a mutant strain, showing variance in morphology, nutritional characteristics, genetic control mechanisms, resistance to chemicals, etc.
Isolating Mutants Replica
- plating technique allows identification of mutants:
describe process (a-d)
a) Culture is exposed to mutagen
(b) Isolated colonies are transferred on a master plate
(c) tiny clump of cells are picked up and transferred to a plate with complete medium and another with incomplete medium
(d) Colonies in the complete medium plate missing from the incomplete one are mutant colonies that can be subcultured for further use
Define spontaneous mutations
random change in the DNA due to errors in replication that occur without known cause
Define induced mutations
result from exposure to known mutagens, physical (primarily radiation) or chemical agents that interact with DNA in a disruptive manner
Any chemical capable of mutating bacterial DNA can similarly mutate what?
mammalian DNA
What 3 things can the Ames Test screen for?
Agricultural, industrial, and medicinal compounds are screened using
What is the indicator organism, that is a mutant strain, that has lost the ability to synthesize histidine
Salmonella typhimurium is HIS (-)
If the his (-) culture of salmonella becomes his (+) it means
it is highly, increasingly, mutagenic then bacteria will become HIS (+)
Describe control setup of Ames test
bacteria plated on a histidine-free medium containing liver enzymes but NO test agent
EXPECT NO GROWTH
What would you expect of control plate if his(+) arises? after 12 h incubation
his(+) colonies arising from spontaneous back-mutation
little growth
describe the test plate conditions of Ames test
plated on a histidine-free medium containing liver enzymes AND test chemical
Describe expected results of test plate his (+) colonies after 12 h incubation
his(+) colonies in presence of the chemical
causes mutations mutant
ames fluctuation test using multiple wells
what does blue well indicate?
no back-mutation
ames fluctuation test using multiple wells
what does yellow well indicate?
indicates back-mutation
Define Genetic recombination
occurs when an organism acquires and expresses genes that originated in another organism
3 means for genetic recombination in bacteria:
- Conjugation
- Transformation
- Transduction
Conjugation
Transfer of a plasmid or chromosomal fragment from a donor cell to a recipient cell via direct contact
for conjugation, what allows the synthesis of a conjugative pilus of a gram-negative cell donor
Gram-negative cell donor has a fertility plasmid (F factor) that allows the synthesis of a conjugative pilus
How does Donor (F+ cell) transfers fertility plasmid through? what is the recipient cell?
Donor (F+ cell) transfers fertility plasmid through pilus to recipient (F- cell), which becomes F+ cell
Some F+ cells become what
Hfr cells (high frequency of recombination)
High-frequency recombination – donor’s fertility plasmid is integrated into the bacterial chromosome
Transformation
Chromosome fragments from a lysed cell are accepted by a recipient cell; the genetic code of the DNA fragment is acquired by the recipient
for transformation, Donor and recipient cells can be unrelated – T or F?
T
what is a useful tool in recombinant DNA technology?
transformation
do the donor and recipient cell have to be related to exchange genes?
no
Streptococcus pneumoniae describe G (+) or (-) and shape
Gram+ cocci that occur in pairs or chains.
Encapsulated strains: Cells of virulent stains of S. pneumoniae are surrounded by a polysaccharide capsule which protects them from being digested by
phagocytic white blood cells.
Unencapsulated strains: Those with no capsule/glycocalyx are normal microbiota of lungs, sinuses and middle ear of 75% of people. does it cause disease?
no
Transduction
Bacteriophage serves as a carrier of DNA from a donor cell to a recipient cell
what are the two types of transduction?
generalized and specialized
Generalized transduction
random fragments of disintegrating host DNA are picked up by the phage during assembly; any gene can be transmitted this way
Specialized transduction
a highly specific part of the host genome is regularly incorporated into the virus
Transposons
Special DNA segments that have the capability of moving from one location in the genome to another – “jumping genes”
Transposons function
- Cause rearrangement of the genetic material
- Can move from one chromosome site to another, from a chromosome to a plasmid, or from a plasmid to a chromosome
- May be beneficial or harmf
is conjugation direct or indirect?
direct
is transformation direct or indirect?
indirect
is transduction direct or indirect?
indirect
