CH16 Flashcards
total genetic potential of MO, code in its DNA
gene
the DNA that is expressed by the MO under a given set of conditions
phenotype
change in nucleotide sequence, may result in change of protein
mutation
types of mutations
mutant/wild type
spontaneous
induced
product of the standard “normal” allele at a locus, in contrast to that produced by a non-standard, “mutant” allele
wild type mutation
errors that lead to changes in DNA
spontaneous mutation
exposed to chemical or physical agent
induced mutation
- damage DNA
- alter DNA chemistry
- interfere with repair mechanism
mutagen
point mutations can be
silent
missense
nonsense
- AAU–>AAC
- both code for same AA
- protein unaltered
- no consequence for organism
silent point mutation
- GAG–>GUG
- AA is different
- significant but not always deadly
- sickle cell anemia
missense point mutation
- UAU–>UAA
- stops instead of AA
- non functional product protein fragment
nonsense pont mutation
insertion or deletion of nucleotide
frameshift mutations
describe the Ames Test
- The Ames test is based on the observation that many carcinogens also are mutagens.
- The test determines if a substance increases the rate of mutation; that is, if it is a mutagen. If the substance is a mutagen, then it is also likely to be carcinogenic if an animal is exposed to it at sufficient levels
what was Bruce Ames procedure for his experiment with histidine + Salmonella
- had culture of Salmonella histidine auxotroph and added it to a plate with complete medium and small amount of histidine (control) and to a plate that had medium with test mutagen and small amount of histidine
- incubated at 37 degrees C for a day or two
- the control plate had spontaneous revertants and the other had revertants induced by the mutagen
- if numbers are larger on mutant plate than control, then the revertants are induced by mutagen
why add liver enzymes to the Ames test?
alfotoxins (produced by fungus) are mutagenic when broken down and makes results more accurate
exchange/combining of genetic material from two organisms
recombination
recombination in eukaryotes and prokaryotes
-eukaryotes
diploid; crossing over b/t chromosome pairs (meiosis)
-prokaryotic
transfer of pieces of DNA from a donor bacterium to recipient (another bacteria)
incorporate into recipient DNA
mechanisms of DNA transfer
conjugation
transformation
transduction
cell to cell contact, depends on presence of plasmids
conjugation
recipient bacterium takes up “free-floating” DNA
transformation
bacterial virus (phage) transfers DNA from donor to recipient
transduction
small pieces of extra DNA
plasmids
how are plasmids independent of host chromosome
- can be eliminated (hi temp, starvation)
- multiple copies
- some can integrate with chromosome (episome)
genes for pili sex (conjugation)
fertility F plasmids
antibiotic resistance genes
R plasmids
toxin genes
virulence plasmids
- genes to degrade pesticides (Sutamonas sp)
- N2 fixation (Ribosium bacteria)
metabolic plasmids
Lederburg and Tatum experiment
- used triple mutants
- positive, mixture and negative strains in tubes
- positive and negative tubes had no spontaneous generation on plates
- mixture plate had bacteria that synthesized all 6
- conclusion: must be genetic change in bacteria
Davis experiment
- “U tube” experiment
- positive and negative strains were separated by a fritted glass filter
- filter does not allow bacteria to move, avoids cross feeding, no cells pass but media and nutrients,
- mixes back and forth from pressure/suction
- conclusion: cells need to interact to be phototrophs
describe F+ by F+ mating
- transfer of plasmid and gene
- F+ pillus connects to F- cell
- conjugation bridge forms, origin of transfer pulls of a strand of DNA and nuclease binds to origin of transfer
- F- cell translates new strand (plasmid from F+) and becomes F+, which means it can conjugate with other cells
describe Hfr by F- mating
- most DNA transferred
- plasmid incorporated into host chromosome (Hfr)
- pillus connects Hfr to F- by forming conjugation bridge
- little bit of plasmid and chromosome gene transferred into cell recipient(F-)
- donor DNA replicated by rolling circle method and transferred
- donor remains unchanged and recipient loses plasmid; donor DNA incorporated into recipient chromosome(F-)
- F- cell is genetically distinct from original
Griffith’s transformation experiment
- heat-killed smooth pneumococci with capsule
- > mouse lives
- live, virulent, smooth pneumococci, with capsule
- > mouse dies
- live, nonvirulent, rough, pneumococci, no capsule
- > mouse lives
heat-killed smooth pneumococci with capsule
+
live, nonvirulent, rough, pneumococci, no capsule
=
Live, smooth, pneumococci, with capsule PLUS
live, rough, pneumococci, no capsule isolated from dead mouse
conclusion: must have picked up trait (floating DNA) to form capsule (transformation)
one complex mRNA with numerous ribosomes attached to produce lots of proteins in short amount of time
polyribosome
describe transformation with DNA (chromosome) fragments
-bacterial chromosome uptakes SS of DNA and either integrates by nonreciprocal recombination (stable transformation) or degradation (unsuccessful transformation)
describe transformation with a plasmid
-bacterial chromosome uptakes the plasmid and doesn’t incorporate it into its DNA (stable transformation)
describe transduction
-phage attaches and causes destruction of host DNA
-synthesis of viral DNA and coat proteins
-virus capsid protein synthesis and virus assembly
-lysis of cell with release of phage particles and subsequent infection of another cell
-phage recognizes and binds to new cell
causes either:
-integration of donor DNA into recipient chromosome (stable gene transfer)
-degradation (unsuccessful gene transfer)
-survival of donor DNA (abortive transduction)
ability to pick up DNA fragments
competent cells
