Chapter 15; Hello. Hope you are doing well, you have reached ch15 so you are almost done. I
wrote a detailed answer key for every single question so that if I didn’t finish them during the
lecture you will hopefully understand why this answer is correct from the answerkey.
Good luck :D
1. Which of the following statements about regulation of eukaryotic gene expression is
INCORRECT?
A) The presence of a nuclear membrane separating transcription and translation in
eukaryotes led to the evolution of additional mechanisms of gene regulation.
B) In eukaryotes, most structural genes are found within operons.
C) Eukaryotic mRNAs are generally more stable than prokaryotic mRNAs.
D) The rate of degradation of mRNAs is important in regulation in eukaryotes.
E) Posttranslational regulation of histones is unique to eukaryotes.
Answer: B operons is famously known to be found in prokaryotes
2. Which of the following molecules is capable of targeting chromatin-remodeling
complexes to specific DNA sequences to modify chromatin structure and activate gene
expression?
A) transcriptional repressor
B) enhancer
C) DNAse I
D) transcriptional activator
E) histone deacetylase
Answer: D, an activator leads to ‘activation of gene expression’ by multiple diff ways
Increasing or activating gene expression can come from histone acetylation, DNA
demethylation, binding to an enhancer (transcription factors)
3. What is the consequence of methylation of DNA sequences called CpG islands?
A) active transcription
B) transcription repression
C) recruitment of chromosome-remodeling complex
D) transcriptional stalling
E) insulator sequence formation
Answer: B , methylation will repress transcription since it will favor DNA coiling which is
known to be transcriptionally inactive. Note that this is different than methylated cap in mRNA,
different functions.
4. Which of the following CANNOT be determined by chromatin immunoprecipitation
(ChIP)?
A) the types of modification present on the DNA-binding proteins
B) the location of modified histones that activate or repress transcription
C) the position of transcription factors and associated regulators on the chromosome
D) identification of active promoters on a genome-wide level
E) the exact amount of protein expressed from a gene
Answer: E, ChIP detects DNA-binding protein, this is the main concept here. Histones,
Transcription factors, and RNA polymerases (which will be acting on active promoters) will be
determined by ChIP, however the protein expressed by a gene is now in the cytosol and not part
of the DNA-binding protein family. (in general, theorizing the exact amount of protein
expression is hard, we need to do a protein isolation to determine that, analyzing DNA is not
enough). To be a DNA binding protein you must have a DNA binding domain such as the helixturn-helix and the zinc finger.
5. Which of the following statements about CpG islands is CORRECT?
A) CpG islands are commonly found at the 3 UTR regions.
B) The CpG island methylation is universal across both prokaryotes and eukaryotes.
C) Methylated CpG islands are associated with long-term gene repression.
D) Transcriptionally active DNA has a higher frequency of methylated CpG.
E) There is an association between DNA methylation at the CpG island and
acetylation of histone via recruitment of acetylases.
Answer: C, on the majority of cases (not all) , the CG repeat expansion occurs within the 5’UTR, CpG is a eukaryotic regulation, remember, dna methylation represses transcription. DNA
methylation represses gene expression whereas histone acetylation activates it.
6. If a DNA methylase inhibitor were injected into a mouse brain, which of the following
would you expect to occur?
A) A general increase in gene expression would occur.
B) A general decrease in gene expression would occur.
C) A general increase or decrease in gene expression, depending on the gene, would
occur.
D) Acetyl groups would be removed from histones.
Answer: A, inhibiting the inhibitor, DNA methylation inhibits gene expression. INHIBITING
DNA methylation will lead to an increase in gene expression
7. A scientist has discovered a new gene that she believes encodes a transcriptional
activator protein. She is trying to determine where this protein binds. Which of the
following describes a technique she could use to answer her question?
A) Chromatin immunoprecipitation to determine the DNA sequences to which the
putative transcriptional activator protein binds
B) RNA interference to determine the RNA sequences to which the putative
transcriptional activator protein binds
C) Crosslinking to determine the interactions the putative transcriptional activator
protein has with other proteins
D) Chromative immunoprecipitation to determine the proteins to which the putative
transcriptional activator protein binds
E) RNA interference combined with crosslinking to determine all DNA and RNA
sequences to which the putative transcriptional activator protein binds
Answer: A, tip of the day… sometimes its just much easier than it looks. She wants to see where
this protein binds in the DNA. This is the specialty of ChIP. We don’t care about any other
protein or RNA .
8. Which of the following facts about eukaryotic gene regulation is TRUE?
A) Transcriptional activator proteins bind to the DNA in a nonspecific manner.
B) Eukaryotic enhancers are a part of the basal transcription apparatus.
C) The eukaryotic regulatory promoters are highly conserved with the same consensus
sequences throughout the genome.
D) Mediators are protein complexes involved in regulating transcription rates.
E) The transcriptional repressors always bind to the insulator elements.
Answer: D, Activators are proteins… All proteins act in a specific manner acc to their domains
and what they have affinity to. Enhancers are not part of basal transcription. Basal means ‘basic’
hence transcription without any activators, ONLY promoter and general transcription factors, no
enhancer. Promoters have TATA box, but it can be TATATTT or TATAAAA it isn’t conserved.
Mediators are involved in part of the enhancer-transcription factors- promoter complex.
9. Which of the following sequences or molecules is LEAST relevant to the assembly of
the basal transcription apparatus for transcription?
A) core promoter
B) general transcription factors
C) TATA box
D) RNA polymerase
E) enhancer
Answer: E, I am getting the same concept twice just to make sure if you solved question 8 you
actually understood it. So again, enhancers aren’t related to the basal transcription apparatus.
Everything else is, please memorize the 4 elements here that are part of the basal transcription.
10.Given the following figure, what would be the effect of a mutation that occurred in the
insulator that prevented the binding of the insulator-binding protein?
A) Both Enhancer 1 and Enhancer II would be able to stimulate the transcription of
Genes A and B.
B) Enhancer I would no longer be able to stimulate the transcription of Gene B.
C) Enhancer I will be able to hypermethylate Gene B.
D) As long as the insulator sequence is not deleted, there will be no change in the
transcription regulation of Gene A or B.
E) Enhancer II will no longer be able to stimulate the transcription of Gene A.
Answer: A, insulator dictates the enhancer which promoter it can act on, if the insulator is
mutated, enhancer I and II can stimulate genes A and B
(since there is no more an insulator blocking enhancer I from activating gene B )
11. mRNAs are degraded by enzymes called:
A) DNAse I.
B) ribozymes.
C) heat-shock proteins.
D) silencers.
E) ribonucleases.
Answer: E, ribonuclease also known as RNase, just a sneak peak of the questions coming at the
end of this chapter
.
12. A fly (Drosophila) with an XY genotype has a mutation in its sex-lethal (Sxl) gene that
renders its protein product nonfunctional. Which of the following describes the sex of
this fly?
A) male
B) female
C) intersex
D) male, but it will be sterile
E) female, but it will be sterile
Answer: A please follow this pathway and see what happens when you mutate a gene or turn it
off (sxl, tra, dbl). When no protein is formed it is said to be a male. This is a classic example of
alternative splicing.
13. A
genetics student identified a male fly (Drosophila) that had an XX genotype. Which
of the following is the MOST accurate plausible explanation?
A) The fly could only have a mutation in its sex-lethal (Sxl) gene.
B) The fly could only have a mutation in its transformer (tra) gene.
C) The fly could only have a mutation in its double-sex (dsx) gene.
D) Impossible to be male with an XX genotype
Answer: B, sxl from its name is lethal if an XX had a mutation in it. As mentioned earlier if tra
was mutated, no protein will be produced. Leading to a male like phenotype. (acts like what
happens when the drosophila is a male)
14. When siRNAs are present, the rate of mRNA degradation _____ and the rate of protein
production _____.
A) increases; increases
B) increases; decreases
C) decreases; decreases
D) decreases; increases
E) stays constant; decreases
Answer: B, all these siRNA, miRNA degrade mRNA. But each has a different way of doing so.
What happens? They bind to a specific mRNA complimentary sequence, the cell will degrade
these mRNA (dsRNA is abnormal) leading to degradation of an mRNA that codes a protein.
Less mRNA, less protein
15. Which of the following mechanisms does NOT involve siRNA- and miRNA-based gene
regulation?
A) cleavage of mRNA
B) inhibition of translation
C) posttranslational modification
D) degradation of mRNA
Answer: C, mi and siRNAs act on mRNA, whether during post-transcription or translation.
However they cannot ‘bind to proteins’. Post-translational modifications take place after the
protein is made,
16. A scientist created transgenic C. elegans worms that expressed a gene that made the
worms glow green under fluorescent light. Then she injected miRNA
complementary to the mRNA of this gene. Which of the following results was MOST likely to
be seen?
A) The worms glowed green under fluorescent light.
B) The worms were not able to glow green under fluorescent light.
C) The injection of double-stranded RNA was lethal and the worms died.
D) The worms had an increased life span.
E) The CpG islands near the promoter of the gene became demethylated
Answer: B, love this question, so this is a method used in the lab to ‘silence a gene’. After adding
miRNA, it will bind to the mRNA of this gene, leading to inhibition of the translation to protein.
Hence, no protein will be formed. So the worm will no fluoresce. This is used in a lab to silence
its gene and observe what happens after.
17. FOLLOW UP: Suppose a scientist discovered a mutant strain of C. elegans worms that had
lost the ability to regulate gene expression via RNA interference mechanisms. Which of the
following might she predict is a possible source of this defect?
A) There is a mutation in the gene that encodes the Dicer enzyme that makes it
nonfunctional.
B) There is a mutation that results in an overexpression of siRNAs.
C) There is a mutation in a gene that encodes an acetylase enzyme that prevents
histone acetylation.
D) There is a mutation in a gene that encodes an enzyme that selects the correct splice
site for alternative splicing
Answer: A, RNA interference mechanism/gene silencing/miRNA, you should think the same
when reading those 3 phrases. miRNA and siRNA would be decreased and not increased. Dicer
enzyme forms these RNA and will be expected to be nonfunctional. C and D do affect the
protein produced but not via RNA interference.
18. A heterozygous father has a paternally imprinted mutation leading to a specific disease. If he
married a normal homozygous wife. All of their grandchildren (kids of their daughter) will not
have the disease.
True or False?
False, paternally imprinted means the gene is methylated paternally, hence only mothers can give
the mutation to their children. So the father will give the mutation to the daughter, however it
will be methylated (hidden). HOWEVER, the daughter can give the mutation to their children
now. If it was methylated in the daughter, doesn’t have to be methylated in the children, It is
paternally imprinted, so the daughter can give either allele and each will be expressed. If the
couple had a son, the statement would have been true
Chapter 16:
Hardy-Weinberg Equilibrium, also referred to as the Hardy-Weinberg principle, is used to
compare allele frequencies in a given population over a period of time.
A population of alleles must meet five rules in order to be considered “in equilibrium”:
1) No gene mutations may occur and therefore allele changes do not occur.
2) There must be no migration of individuals either into or out of the population.
3) Random mating must occur, meaning individuals mate by chance.
4) No genetic drift, a chance change in allele frequency, may occur
. 5) No natural selection, a change in allele frequency due to environment, may occur.
Hardy-Weinberg Equilibrium never occurs in nature because there is always at least one rule
being violated. Hardy-Weinberg Equilibrium is an ideal state that provides a baseline against
which scientists measure gene evolution in a given population. The Hardy-Weinberg equations
can be used for any population; the population does not need to be in equilibrium.