Mutations, Transformations, and Plasmids

Question 1

what is a mutation / what classification are most mutations

Answer 1

change in genetic code inherited vertically through division / detrimental or neutral

Question 2

what is a silent mutation

Answer 2

nothing happens to the amino acid - the genotype changes but the same amino acid is coded for

Question 3

what is a missense mutation

Answer 3

a change in the encoded amino acid

Question 4

what is a nonsense mutation

Answer 4

the creation of a premature stop codon - as well as a truncated protein produced

Question 5

what is a frame shift (Indels)

Answer 5

Insertions or deletions that are not multiples of 3 that change the reading frame of the DNA

Question 6

is predicting or measuring phenotypic changes from genotypic changes difficult

Answer 6

yes it is often difficult - the organism must be in the right environment for us to see the effects

Question 7

how many rounds of replication does it take a spontaneous mutation to fix / why

Answer 7

takes two round / because a spontaneous mutation will only change one nucleic acid so only one daughter cell gets it - when that mutated daughter cell replicates again then the mutation will become fixed

Question 8

how do cells know which amino acid to correct with a spontaneous mutation

Answer 8

cells methylate their DNA so if there is a mutation then the nucleic acid with the least methylation is the mutation and will get repaired

Question 9

why is water a source of spontaneous mutation / why is oxygen a source of spontaneous mutation

Answer 9

deamination of a cytosine to a uracil / the intermediates of breaking oxygen down are very reactive and can modify residues which can interfere with polymerases to stop replication or transcription

Question 10

what are transposable elements / what are they called / what do they lead to

Answer 10

they are “jumping genes” that can cut themselves out and reinsert in a different location / called a transposon / lead to large DNA insertions

Question 11

what binds to the inverted repeats of the insertion sequence and makes a staggered cut in the target DNA / what usually happens to a gene that receives an insertion

Answer 11

transposase / often get disrupted

Question 12

how does a lab use transposons in bacteria to identify which genes are esential for infection

Answer 12

a transposon is introduced into bacteria - every gene that is non essential becomes mutated because of the transposon - lets you find which genes are used to cause infection

Question 13

what are induced mutations

Answer 13

occur as a result of environmental mutagens (things like UV light, ionizing radiation, reactive oxygen species)

Question 14

what is deinococcus radiodurans / what can we learn from it

Answer 14

one of the most radioresistant organisms known / the mechanisms it uses to repair its DNA (homologous recombination)

Question 15

what is homologous recombination / why is it important

Answer 15

introduction of DNA with two regions of homology into an organism - resulting in a double cross-over / important for genetic evolution

Question 16

what is the process for the repair of a double stranded break

Answer 16

1. nuclease digests 5’ ends of broken strands 2. RecA binds 3’ ssDNA overhangs - mediating strand invasions by complementary base pairing 3. repair polymerase synthesizes DNA 4. invading strand is released - reanealment of the complementary strand of broken DNA occurs 5. DNA synthesis fills in remaining strands 6. DNA ligase restores chromosome

Question 17

what is horizontal gene transfer / what are the three forms of horizontal gene transfer

Answer 17

the transfer of DNA between organisms / transduction, transformation, and conjugation

Question 18

what is transduction / what is transformation / what is conjugation

Answer 18

phage transfers DNA from one bacteria to another (phage mediated transfer) / uptake of naked DNA / transfer of DNA by the F-pilus

Question 19

what are some bacteria that can perform transformation / what is an example of a transformation

Answer 19

Streptococcus pyogenes (strep throat), Streptococcus pneumoniae (pneumonia), Yersinia pestis (plague), Bacillus anthracis (anthrax), and Neisseria meningitidis (meningitis) / putting living non-encapsulated cells into a mouse with dead encapsulated cells and getting a dead mouse

Question 20

what does transformation require, why? / what pulls the single stranded DNA through the pilus / what recruits the ssDNA to homologous sites for integration

Answer 20

requires pillus because it binds to floating ssDNA and pulls it in / ComEA / RecA

Question 21

what are plasmids / what must they have / what do they carry

Answer 21

extrachromosomal heritable DNA / must have an origin or replication and terminator / no essential genes but important genes responsible for survival in specific environments (toxins, antibiotic resistance genes, etc) - some encode for transfer between bacteria

Question 22

what is conjugation / what two origins of replication does a pladmis encode / what cells can conjugation occur in

Answer 22

plasmid mediated vertical transmission by the fertility factor (F-factor) / oriV (vertical inheritance of plasmid) and oriT (trasmission between bacteria) / any species even between species or different domains

Question 23

what does the plasmid encode for to do conjugation / what does it do

Answer 23

a type IV secretion system pilus / transfers DNA between donor (F+) and recipient (F-) - long rod that mediates attachment

Question 24

what happens if the F-factor has homology to a region of the F+ cell

Answer 24

homologous recombination between the F- and F+ cell could occur as however the F- would not become F+ because it would not get the entire plasmid