1 ) A temperature-sensitive mutation in the lacI gene of E. coli creates a repressor protein that has wild-type function at 30°, but is a superrepressor protein at 42° (unable to bind allolactose). You test this strain with and without lactose, at two temperatures, for expression of beta-galactosidase. Which answer below shows the way you fill out the data table in your lab notebook to indicate expression of beta-galactosidase?
plus lactose 30° ?
plus lactose 42° ?
no lactose 30° ?
no lactose 42° ?
a. yes, yes, yes, yes
b. no, no, no, no
c. yes, no, no, no
d. yes, yes, no, no
e. yes, no, yes, no
(Transcription is not inducible due to lac/s mutation so the answer would be "B")
2) If the two Trp codons in the leader of the trp operon were changed to codons for His, what would be the consequence for regulation of the trp operon? ( don't know this one)
a. expression of the trp operon would show attenuation based on the levels of histidine in the cell
b. expression of the trp operon would now be under transcriptional control by the His Repressor protein
c. the trp operon would now be constitutively expressed
d. two of the above
e. all of the above
3 ) Which statement is true about DNA methylation in eukaryotes?
a. it is used to regulate DNA replication
b. it is used to regulate mutation repair
c. it is used to regulate transcription
d. it is used to regulate protein translation
e. it is used to regulate heterochromatin spreading
4 ) Which of these enzymes must be expressed for a retrotransposon to transpose within a cell?
a. transposase
b. beta-galactosidase
c. reverse transcriptase ( my answer)
d. telomerase
e. DNA methyltransferase
5 ) Transposable elements are found in
a. prokaryotes only
b. eukaryotes only
c. both prokaryotes and eukaryotes ( my answer)
d. bacteria and yeast only
e. bacteria, yeast and corn, but not mammals
6) What is the normal human female karyotype?
a. 46, XY
b. 46, XX ( my answer )
c. 23, XY
d. 23, XX
e. 48, XX
7 ) What do regulation of the bacterial lac and trp operons have in common? ( don't know this one)
a. the presence of a small molecule in the environment leads to expression oft he operon
b. the presence of a small molecule in the environment leads to repression of the operon
c. a small molecule inside the cell binds to a repressor protein and causes the repressor to change its conformation
d. ribosome pausing at the start of the transcript can lead to transcription
termination
e. two of the above
8) If a cell has the partial diploid genotype lacI+ lacOc lacZ+ lacY+ /
lacI- lacOc lacZ+ lacY. how will the operon genes be regulated by lactose in the environment?
a. wild-type induction pattern
b. constitutive expression ( my answer )
c. uninducible expression
d. expression at 50% of wild type levels in the presence of lactose
e. none of the above
8 ) Although the genes of the trp operon can be expressed in mammalian cells if placed downstream of a proper eukaryotic promoter, the mechanism of attenuation does not work. Which of these is the best explanation for this observation? ( don't know this one)
a. mammalian cells do not have free tryptophan inside the cell
b. bacterial codons are not recognized by eukaryotic tRNA anticodons
c. transcription and translation are not coupled in mammalian cells
d. the RNA hairpins do not form in mammalian cells
e. bacterial RNA is not stable in eukaryotic cells
9 ) Which of the following pairs of sequences would you expect to find in the E. coli chromosome on either side of an insertion sequence? The sequences shown are on the same strand of the DNA.
a. 5’ GAGACTCTAC 3’ and 5’ CATCTCAGAG 3’
b. 5’ GAGACTCTAC 3’ and 5’ GTAGAGTCTC 3’
c. 5’ GAGACTCTAC 3’ and 5’ GAGACTCTAC 3’ ( my answer)
d. 5’ GAGACTCTAC 3’ and 5’ CTCTGAGATG 3’
1) The correct answer is c. yes, no, no, no.
To determine the expression of beta-galactosidase in the given scenario, the data table should be filled out as follows:
plus lactose 30° - yes (wild-type function at 30°)
plus lactose 42° - no (superrepressor protein at 42°)
no lactose 30° - no (repressor protein present, no inducer)
no lactose 42° - no (superrepressor protein at 42°)
2) The consequence for the regulation of the trp operon if the two Trp codons are changed to codons for His would be constitutive expression of the trp operon.
3) The correct answer is c. DNA methylation in eukaryotes is used to regulate transcription. It involves the addition of a methyl group to DNA, which can affect the binding of transcription factors and other regulatory proteins, thereby controlling gene expression.
4) The correct answer is c. Reverse transcriptase must be expressed for a retrotransposon to transpose within a cell. Reverse transcriptase is an enzyme that synthesizes a complementary DNA strand using an RNA template, allowing retrotransposons (which are RNA-based transposable elements) to insert themselves into new genomic locations.
5) The correct answer is c. Transposable elements are found in both prokaryotes and eukaryotes. These genetic elements can move within a genome and can have significant impacts on genome structure and function.
6) The normal human female karyotype is 46, XX. This means that females have 46 chromosomes, including two X chromosomes.
7) The common feature of regulation in the bacterial lac and trp operons is that the presence of a small molecule in the environment leads to repression of the operon. In the lac operon, the small molecule is allolactose, which binds to the lac repressor protein and prevents it from binding to the operator, allowing transcription. In the trp operon, the small molecule is tryptophan, which binds to the trp repressor protein and enables it to bind to the operator, blocking transcription.
8) The operon genes in the given partial diploid genotype (lacI+ lacOc lacZ+ lacY+ / lacI- lacOc lacZ+ lacY) will be constitutively expressed. The presence of lacI- eliminates the ability of the repressor protein to bind to the operator, resulting in constitutive expression of the operon genes.
9) The correct answer is b. The expected sequences on either side of an insertion sequence in the E. coli chromosome would be 5’ GAGACTCTAC 3’ and 5’ GTAGAGTCTC 3’. The insertion sequence acts as a mobile genetic element that can move to different locations within the genome, leaving these specific sequences on either side of its insertion point.