exam 4 genetics

1. E. coli lac operon control by CAP is:

positive inducible

2. A partial diploid E. coli cell of lacI+ lacP– lacOc lacI+ lacY+ / lacIs lacP+ lacO+ lacZ+ lacY– will synthesize:

neither lacZ nor lacY functional gene products in the presence of lactose.

3. RITS consists of

siRNAs and proteins.

4. Assume that you have discovered a new chemical mutagen that modifies guanine so that it mispairs with adenine when adenine is in the template DNA strand during DNA replication. However, this mispairing is limited to when the modified guanine is being added to the newly replicating DNA strand. When the modified guanine is in the template DNA strand, it always pairs normally with cytosine being added to the growing newly synthesized strand. What type of mutation would you predict would be caused by the new chemical mutagen?

b. A‐to‐C base substitutions

5. Practically all transposable elements that have been studied are associated with which of the following?

flanking direct repeats

In base excision repair, which enzyme is needed to add nucleotides to the exposed 3′–OH group?

DNA polymerase

During T cell proliferation, which molecules are translated into proteins as initiation factors increase?

 mRNAs

8. When a structural gene is under negative inducible control, what would be the result of a mutation that eliminated the repressor protein?

 The structural gene would be constitutively expressed due to the lack of negative inducible control

9. A polypeptide has the following amino acid sequence: Met‐Ala‐Gln‐Arg‐Glu‐Leu. This polypeptide was mutated to produce the following mutant sequence: Met‐Ala. Which describes the MOST likely type of mutation that occurred?

 nonsense mutation

10. Which of the following statements about chromatin‐remodeling complexes is INCORRECT?

They can alter the chemical structure of histones.

11. Which of the following DNA repair systems does NOT involve the activity of a DNA polymerase?

 photoreactivation in E. coli

12. Which of the following proteins does NOT play a role in nucleotide‐excision repair?

DNA glycosylase

13. In the absence of tryptophan, what happens to the genes within the trp operon?

The regulator dissociates from the operator, and structural genes get transcribed.

14. What type of cellular activity is known to occur within P bodies?

RNA degradation

15. An example of a genetic disorder in humans that results from a loss‐of‐function mutation is:

cystic fibrosis.

16. What is the function of cAMP in regulation of the lac operon?

It activates an activator protein.

17. siRNAs and miRNAs are produced by the:

cutting and processing of double‐stranded RNA by Dicer enzymes

18. Which of the following statements about DNA‐binding proteins is NOT true?

 Once bound, most of DNA‐binding proteins remain on DNA permanently

19. Which of the following is generally constitutively transcribed?

 regulatory genes

20. Which of the following statements about eukaryotic gene regulation is TRUE?

Mediators are protein complexes involved in regulating transcription rates

21. In Arabidopsis, FLD (a deacetylase enzyme) stimulates flowering. Which of the following statements is TRUE?

 FLD deacetylates histones that bind to the FLC gene, causing repression of FLC transcription.

22. Ultraviolet light causes what type of DNA lesion?

 pyrimidine dimers

23. Which of the following processes is also known as RNA silencing or posttranscriptional gene silencing?

RNA interference

24. A promoter that affects only genes that are on the same piece of DNA is referred to as a(n) _____‐acting promoter.

 cis

25. Alternative splicing is known to be important in the regulation of the:

sexual development in Drosophila melanogaster.

26. What is responsible for induction of the lac operon?

 allolactose

27. Which of the following statements about an animal bearing a somatic mutation is TRUE?

The animal but not its offspring can be affected by the mutation.

28. Which of the following statements about gene regulation concerning operons is INCORRECT?

For a gene under negative repressible control, a small molecule is required to prevent the gene's repressor from binding to DNA.

29. A lac operon of genotype lacI– lacP+ lacO+ lacZ+ lacY+ will produce β‐galactosidase and permease when:

lactose is present or not.

30. What type of transcriptional control occurs when an active repressor protein binds to the operator?

negative

31. Flowering in Arabidopsis thaliania is suppressed by the FLC gene to prevent flowering at the wrong time of the year. At the right time of the year, the gene FLD stimulates flowering by repressing the activity of FLC. What type of genetic pathway is demonstrated in this scenario?

negative regulatory pathway

32. Insertion or removal of one or more nucleotide base pairs in DNA within a gene often results in a _____ mutation.

frameshift

33. What would happen to the lac operon in the absence of allolactose?

The repressor regulator protein binds to the operator and prevents the transcription of the structural gene.

34. Which of the following types of mutations does NOT lead to a change in the amino acid sequence of the gene product?

silent mutation

35. How do germ‐line mutations differ from somatic mutations?

Germ‐line mutations can be passed on to offspring, while somatic mutations cannot.

What statement describes the central dogma of molecular genetics?

Genetic information flows from DNA to RNA to proteins.

The regulator protein binds the _____ of the operon.

operator

The first structural gene of the trp operon, trpE, contains a 5' UTR which is also known as a(n) _____ that has four regions.

leader

At what level of gene regulation do antisense RNAs act?

They prevent the initiation of translation.

What is the difference between positive control and negative control of gene expression?

Positive control stimulates expression; negative control inhibits expression.

A mutation that prevents the catabolite activator protein (CAP) from binding to the lac operon promoter will result in

a decrease in the ability of RNA polymerase to initiate transcription.

When tryptophan levels are _____, regions _____ of the 5' UTR pair, followed by a string of uracil nucleotides.

high; 3 and 4

In E. coli, under conditions of high extracellular osmolarity, which of these occur?

The micF gene produces an antisense RNA that binds to the mRNA of the ompF gene and blocks its translation.

Which of these statements identifies a reason why gene regulation is more challenging for eukaryotic cells than prokaryotic cells?

Eukaryotic cells only express subsets of gene types.

Which genes would likely be part of the same operon?
Gene

A = defense against other bacteria

Gene B = defense against bacteriophages

Gene C = carbohydrate metabolism

Gene D = cell motility protein

Gene E = toxin production

genes B, E, A

A mutation in the 5' UTR of the trp operon reduces the ability for region 2 to pair with region 3. What would be the effect of this mutation on the trp operon when tryptophan levels are high?

The mutation would have no effect on the trp operon.

What is the benefit of requiring a regulatory molecule to activate various types of gene regulation?

Expression can be adjusted rapidly.

Seth is conducting genetic imaging for a project. He draws up a sample and feeds it to a processor. He finds that the shape resembles two alpha helices bound to the major groove of DNA. What type of motif is Seth evaluating?

helix-turn-helix

A mutant strain of E. coli produces β-galactosidase in the presence and in the absence of lactose. The mutation in this operon lies in the lacZ gene.

operator

If regions 2 and 3 of the 5' UTR trp operon base pair to form a hairpin, will the structural genes be transcribed?

Yes, this hairpin does not prevent transcription.

The shift in transcription rate due to bacterial enhancers is prompted by what mechanism?

interaction between the enhancer and RNA polymerase

In regard to the ompF mRNA, which of these steps is considered true?

The production of micF RNA is due in part to gene activation in the extracellular space when osmolarity is high.

How do posttranslational modifications that change the structure of a chromosome, such as DNA methylation and changes to chromatin structure, regulate gene expression?

Modified genes are accessible for transcription.

Which of these is NOT recognized as an important level of gene regulation?

recombination after DNA synthesis

The DNA that follows the DNA corresponding to region 4 in the mRNA 5′ UTR in the trp operon is AT-rich. What is the role of this AT-rich region in the functioning of the trp operon?

It facilitates the termination of transcription when region 3 pairs with region 4 in the mRNA 5′ UTR.

Assume that a deletion mutation occurs in the trp operon so that the DNA corresponding to the last (distal) part of region 1 and the first (proximal) part of region 2 of the mRNA 5′ UTR is removed. What will be the effect of this deletion on the expression of the trp structural genes?

In the absence of tryptophan, transcription of the structural genes will be reduced compared to a wild-type operon.

A bacterial cell is grown in the presence of both glucose and lactose. Over time, a researcher measures the amount of glucose and lactose that have been used by the cells. She finds that glucose levels are reduced, but lactose levels have remained constant. She proposes that these bacterial cells are exhibiting

catabolite repression.

Which of these E. coli strains with the lac genotypes will synthesize β-galactosidase in the absence of both lactose and glucose?

lacI^– lacP⁺ lacO⁺ lacZ^- lacY^–/lacI⁺ lacP⁺ lacO^c lacZ⁺ lacY^-

Mutations in which of these lac operon genes or regions are cis in their effect on the regulation of the operon?

the lacO operator

Mutations in which of these lac operon genes or regions are trans in their effect on the regulation of the operon?

the lacI gene

Several examples of antisense RNA regulating translation in bacterial cells have been discovered. If you wanted to design a construct to artificially control the expression of a bacterial gene with antisense RNA, what sequences might the antisense RNA contain?

sequence complementary to a 5' UTR of mRNA target

Which characteristic of gene regulation is shared between prokaryotes and eukaryotes?

DNA binding proteins influence the ability of RNA polymerase to initiate transcription.

CpG islands are regions of DNA with heavy cytosine

methylation.

_____ regulate transcription by recruiting other proteins called cofactors.

Transcription factors

The most common method of mRNA degradation begins with the

shortening of the 3' poly(A)tail.

RNA interference is activated by which of the following pairs of RNA molecules?

miRNAs and siRNAs

Which of these is NOT required for the translation of mRNAs?

P bodies

Which of the following organisms has transcription and translation occurring separately within their cell(s)?

melanogaster

_____ has been used to determine the locations of histones that have undergone modifications.

ChIP

At some genes, RNA polymerase _____ transcription and transcribes 24 to 50 nucleotides of RNA, but then _____.

initiates; pauses

Which of the following statements best describes the function of a nuclease enzyme?

an enzyme that cleaves the bonds between nucleotides

How does the addition of methyl groups to histones affect the structure of chromatin?

It causes histones to bind DNA more tightly.

What influences gene expression by affecting the rate of translation?

the availability of ribosomes, charged tRNAs, initiation factors, and elongation factors

Which of these is NOT a reason why eukaryotic gene regulation is less well understood than bacterial gene regulation?

Scientists have not spent the same amount of time studying eukaryotes compared to prokaryotes.

All are processes that affect gene regulation by altering chromatin structure, EXCEPT

transcription factors.

The basal transcription apparatus—consisting of RNA polymerase, general transcription factors, and other proteins—assembles at the

core promoter.

One SR protein, called splicing factor 2 (SF2), stimulates the binding of snRNPs to the 5' splice site. What effect would this likely have on RNA splicing?

It would enhance the use of that splice site.

A genetic form of hearing loss has been associated with a mutation in the gene that encodes for which type of RNA molecule?

miRNA

A scientist places a female adult fruit fly in an incubator that is roughly 50 ℃. Based on these conditions, the scientist can expect the fly to have high expression levels of

heat-shock genes

Many archaeal genes are regulated within operons. Which organism type would most likely have a gene regulation mechanism similar to that of archaea?

a unicellular organism

How does the binding of transcription factors to enhancers affect transcription at genes that are thousands of base pairs away?

the DNA between the enhancer and the promoter looping out

A patient exhibits a disease resulting from a lack of a protein that is transcribed by gene X. The protein encoded by gene X cannot be detected in the patient's cells. Furthermore, the mRNA of gene X is absent as well. After genetic testing, it has been determined that gene X in this patient contains an abnormally large amount of cytosine- and guanine-rich repeats near the transcription start site of the DNA. Which of the hypotheses could be generated from this finding?

The chromatin of gene X is more heavily deacetylated compared to that from normal healthy individuals.

Some siRNAs alter chromatin structure. What is the likely end result of such a modification?

transcriptional silencing

Which of the following is not involved in gene regulation in a human cheek cell?

operons

The expression of the _______ gene in Drosophila directly leads to the ______ development.

sex-lethal; female

In yeast cells, the absence of galactose causes GAL80 to bind to GAL4 and prevents transcription activation of galactose metabolizing genes. When galactose is present, it binds to GAL3, causing it to interact with GAL80 and release GAL4 to activate transcription of genes necessary for galactose metabolism. Which of these hypotheses explains the cause of a yeast cell that is unable to properly metabolize galactose?

A mutation in the GAL80 protein results in an inability to undergo conformational changes resulting in constitutive interaction with GAL4.

What would be the result if a cell contained poly (A)-binding proteins (PABPs) that are defective in being able to bind to the poly (A) tail of mRNA?

The 5' cap of the mRNA would have decreased stability.

What is the purpose of the antibody in a crosslinked ChIP (xChIP) assay?

to separate the DNA fragments bound to the protein of interest from the DNA fragments that are not bound

You are investigating a potential translational control mechanism for your favorite mRNA. You determine that protein X is binding to the 5' UTR region of your mRNA and initiating translation. However, when you mutate the possible binding site in the 5' UTR sequence, you still see protein X binding. How do you explain this result?

Protein X binds to the secondary structure of the DNA.

Which protein(s) would be found in the RITS complex (RNA transcriptional silencing)?

methyltransferases

You have isolated a protein that you hypothesize to be a transcriptional activator. What is one characteristic of the protein that would support your hypothesis?

The protein contains helix-turn-helix and zinc-finger motifs.

Malaria is one of the most pervasive and destructive of all infectious diseases transmitted by mosquitoes. About 300 million people worldwide are infected by malaria, which results in upward of a million deaths every year. The causative agents of malaria are protozoan parasites of the genus Plasmodium. The surface antigen is encoded by the var gene family, which consists of about 60 genes whose DNA sequences vary slightly. Expression of the type of var protein is known to change continuously, which allows parasites to evade the immune system. The var genes are located near the telomeres that are typically in heterochromatin state. The studies from 2006 revealed that the var genes are expressed when chromatin structure is disrupted via chemical changes in the histone proteins. Which of these may serve as a plausible explanation that links var gene expression to chromatin changes?

the H3K4me3 type modification on histone H3

Proteins that may get held up on certain genes in the absence of stress, but are then quickly released when stress is encountered, are called _____. They allow for rapid transcription of genes that facilitate adaptation to a stressful environment.

stalled RNA polymerases

Somatic mutations

only affect nonreproductive tissues.

Which of these processes is most likely to create deletions and insertions?

unequal crossing over

Substances capable of causing cancer are known as

carcinogens

During transposition, a retrotransposon may be transcribed into RNA to produce double-stranded DNA by which process?

reverse transcription

In base-excision repair, ________ is needed to add nucleotides to the exposed 3'-OH group.

DNA polymerase

One of the codons that specify the amino acid Gly (GGU, GGC, GGA, and GGG) undergoes a single-base substitution to become a nonsense mutation (UAA, UAG, and UGA). This mutation is a

transversion at the first position of the GGA codon.

A nonsense mutation cannot be reversed by hydroxylamine exposure. This is because

hydroxylamine can only induce a CG-to-TA transition.