Question

Please answer 54, 55, 61,62,64,66,70,72,82,83

on the facs that newly replicated DNA strands are ethylated relative to older DNA 54, Ir used u ished to study the SOS response in Escherichi col, which of the following esperimental procodures could b A.All ofthe choices are correct Expoe cells to nonionising radiation for 20 es C. Espose cells to soniring radiation for 10 minutes Transfer log phase cells frees complete medium to thymine minimal medium What wouild be the hypothetical outcome if the action of RecA were inhibited during the SOS response? LeNA would autolyse, and therefore the transcription of DNA repair genes would occur Inactivate genes that encode DNA polymerases not autolyse, and therefore the transcription of DNA repair genes would not occur A would autolyse, and therefore the transcription of repair genes would not eceur not autolyse, and therefore the transcription of repair genes would occur D. LexA would sh. Repair of an spurinic or apyrimidinic site in DNA by AlP endonuclease mmast be completed by the action of A. UTABC endonuclease RecA protein. NA polymerase I None of the choices are correct 7. Which of the following is the most eror-prone of the repair mechanisms? A. Postreplication repair Recombination repair C) SOS repair Photoreactivation S8. Repair of dhymine dimers using light to split the dimers apart into separate monomers is called A. photodedimerication C photoreparation. D. None of the choices are correct. 59. SOS repair A. requires RecA protein B. is inducible by DNA damage. is error prone, i.e., produces mutations All of the choices are correct. 60. Microbial strains that can grow on minimal medium are called A. autotrophs B. auxotrophs prototrophs minitrophs 61. A public health microbiologist plans to screen a particular bacterial species that was isolated from several patients i intensive care unit to detect if any of the cells are penicillin-resistant mutants. What is the first step in conducting this experiment? Determine whether or not wild type cells of the same bacterial species are susceptible to penicillin B, Test the cells to see if they can grow on media to which penicillin has been added. Perform an antibiotic susceptibility test on the cells using antibiotics other than penicillin that are known to be e D. Set up an Ames test to see if any of the isolates are mutagenic. 62. Which type of medium support growth of mutant bacteria that are threonine auxotrophs? A. Threonine auxotrophs only grow on media that is supplemented with threonine. B. Threonine auxotrophs only grow on media that lacks threonine. C. Since threonine is essential for growth, threonine auxotrophs do not grow on any type of media. of media. 63. What type of procedure is appropriate to isolate revertants from a population of thrconine auxotrophic cells nlate without threonine; any colonies that form are presumed revertar

Answer 1

ANS 54) To study the SOS response in Escherichia coli, which of the following experimental procedure could be used:

The correct answer is : A) All of the choices are correct.

---------------------------------------------------------------------------------------------------------------------------------------------------------

ANS 55) What is the hypothetical outcome if the cation of RecA were inhibited during the SOS response:

The correct answer is :A) LexA would not autolyse, and therefore the transcription of DNA repair genes would not occur

--------------------------------------------------------------------------------------------------------------------------------------------------------

ANS 61) Microbial strais that can grow on minimal medium are called________

The correct answer is C) Prototrophs

------------------------------------------------------------------------------------------------------------------------------------------------------

ANS 62) Type of medium support growth of utant bacteria that are threonine auxotrophs:

The correct answer is: A) Threonine auxotrophs only grow on media that is supplemented with threonine

---------------------------------------------------------------------------------------------------------------------------------------------------------

ANS 64) The type of mutation might lead to a theronine auxotrophic revertant:

The correct answer is: A) All the choices are correct

---------------------------------------------------------------------------------------------------------------------------------------------------------

ANS 66) The one that contributes to the utility of the strains of Salmonella typhimurium used in the Ames reversion assay:

The correct answer is: A) They are highly permeable to test substances.

---------------------------------------------------------------------------------------------------------------------------------------------------------

ANS 70) The region of DNA contained numerous mismatches due to a modifying agent that caused methylation of guanine, which of the following mutagens is most likely the cause:

The correct answer is : C) A DNA modifier such as an alkylating agent

-----------------------------------------------------------------------------------------------------------------------------------------------------

ANS 72) A microbial geneticist observes that a significant number of pyrimidine dimers are present in bacterial DNA following exposure to a particular mutagen. To which mutagen were the bacterial cells likely exposed:

The correct answer is : A) UV Light

----------------------------------------------------------------------------------------------------------------------------------------------------

ANS 82) As the result of exposure to a mutagen, cytosine is substituted for thymine in one strand of DNA. Upon subsequent DNA replication, one of the daughter cells will have a GC pair in this position instead of an AT pair. This is called a(n) __________ mutation

The correct answer is : B) Transition

--------------------------------------------------------------------------------------------------------------------------------------------------------

ANS 83) Transition mutations can result from :

The correct answer is: C) incorporation of a base analog that exhibits different base-pairing properties from the base it replaces and chemical modification of an existing base in the DNA so that in the next round of replication it will pair differently from the unmodified base.