MCB Exam 2 Form A (3/7/24)

In central dogma of molecular biology, what is the direction of flow of genetic

information?

a) RNA→ DNA→Protein

b) DNA→RNA→ Protein

c) Protein→DNA→RNA

d) DNA→Protein→RNA

e) RNA→Protein→DNA

DNA→RNA→ Protein

Which of the following forms the backbone of a DNA?

a) Sugars and bases.

b) Bases and phosphates

c) Phosphates and sugars

d) Nucleotides and sugars

e) Phosphates and nucleotides

Phosphates and sugars

Which of the following interactions contributes to the stabilization of the DNA

double helix?

a) disulfide bonds

b) peptide bonds

c) phosphodiester bonds

d) glycosidic bonds

e) hydrogen bonds

hydrogen bonds

Which of the following statement is NOT true of an intercalating agent?

a) They do not covalently bond with the DNA molecule.

b) They interact electrostatically by wedging in between bases of a DNA molecule.

c) They block DNA replication and transcription.

d) Ethidium bromide is considered an intercalating agent.

e) They induce DNA damage.

They interact electrostatically by wedging in between bases of a DNA molecule.

Ciprofloxacin is used as antimicrobial agent because

a) it binds to the minor groove of DNA and prevents DNA replication.

b) it binds to the DNA polymerase beta subunits and inhibits DNA replication.

c) it inhibits bacterial synthesis of folic acid.

d) it inhibits the activity of bacterial topoisomerase II (DNA gyrase).

e) It binds to RNA polymerase and inhibits the initiation of transcription.

it inhibits the activity of bacterial topoisomerase II (DNA gyrase).

Which of the following statements is FALSE for both DNA polymerase I and RNA polymerase?

a) Both enzymes require a primer.

b) Both enzymes require all four dNTP or NTP.

c) Both enzymes mediate the formation of phosphodiester bonds.

d) Both extend the nucleotide chain in the direction of 5' ⇒ 3'.

e) Both use a DNA template.

Both enzymes require a primer.

Which of the following is NOT a characteristic of telomerase?

a) For the extension of 3' overhang of the end of DNA.

b) A reverse transcriptase.

c) Contains an RNA molecule.

d) Highly active in cancer cells.

e) Splices introns from primary transcript.

Splices introns from primary transcript.

Which of the following is TRUE about the proofreading activity of DNA

polymerase to maintain the fidelity of DNA synthesis?

a) Proofreading occurs after the DNA synthesis has been completed.

b) It is a function of the 3'-5' exonuclease activity of the DNA polymerases.

c) Proof reading requires the presence of an enzyme separate from the DNA

polymerases.

d) Proofreading occurs in prokaryotes but not eukaryotes.

e) Proofreading is a type of DNA repair.

It is a function of the 3'-5' exonuclease activity of the DNA polymerases.

When ACG is mutated to ACT, what type of point mutation is this?

a) Translocation mutation

b) Deletion mutation

c) Transversion mutation

d) Insertion mutation

e) Transition mutation

Transversion mutation

In which type of DNA repair, is an apyrimidinic or apurinic (AP) site formed?

a) Base excision repair

b) Direct repair

c) Mismatch repair

d) Nucleotide excision repair

e) Photoreactivation

Base excision repair

Which of the following types of mutations most likely occur in a patient with a diagnosis of Xeroderma pigmentosum (XP), a rare autosomal recessive disease?

a) A mutation causing defects in the mismatch repair system.

b) A point mutation in the gene coding region for an excision endonuclease.

c) A reciprocal translocation between chromosomes 8 and 14, associated with the Epstein-Barr virus.

d) Loss of the retinoblastoma (RB) tumor suppressor gene.

e) A mutation causing defects in the removal of thymine dimer.

A point mutation in the gene coding region for an excision endonuclease.

DNA methylation contributes to more than 50% of all the tumor suppressor p53 mutation in sporadic colorectal cancer. Which of the following functions are directly affected by mutation of p53 protein?

a) Maturation of mRNA.

b) Peptidyl transferase activity in stalled ribosomes.

c) DNA polymerase activity.

d) Cell cycle arrest in response to DNA damage.

e) Direct DNA repair.

Cell cycle arrest in response to DNA damage.

Ames test is used to assess the potential carcinogenic effect of chemicals by using the bacterial strain Salmonella typhimurium. What does it mean if a plate has very few colonies on it after the Ames test?

a) The chemical did not cause mutations in Salmonella, and likely not a

carcinogen.

b) The chemical was a mutagen.

c) The chemical was a carcinogen.

d) The chemical is a tumor suppressor.

e) The chemical is an oncogene.

Vinyl chloride, the chemical in several of the train cars that derailed and burned in East Palestine, Ohio, in February 2023, is a potent carcinogen and can cause liver cancer. Exposure to Vinyl chloride can lead to

a) the expansion of repeats of three nucleotides.

b) the defective repair of DNA.

c) the recombination of DNA.

d) formation of thymine dimer.

e) DNA damage by alkylation.

DNA damage by alkylation.

Apurinic/apyrimidinic (AP) endonuclease is an enzyme that is involved in which of the following DNA repair?

a) Mismatch repair.

b) Nucleotide excision repair.

c) Direct reversal repair.

d) Base excision repair.

e) Double-strand DAN break repair.

Base excision repair.

The tumor suppressor proteins can function as inhibitors of the cell cycle in the cell signaling pathway. Retinoblastoma (Rb) protein is a tumor suppressor, and it inhibits cell cycle by its ability to

a) phosphorylate and activate the p53 tumor suppressor function.

b) form complex with and inactivate the cyclin dependent kinase inhibitor p21

protein.

c) form complex with and inactivate the E2F transcription factor.

d) form complex with and inactivate Proliferation Specific Cell Nuclear Antigen

(PCNA).

e) form complex with and inactivate oncogene Ras.

form complex with and inactivate the E2F transcription factor.

Which of the following statement is TRUE regarding the difference between the nucleotide of DNA and RNA?

a) DNA nucleotide might have uracil whereas RNA nucleotide cannot.

b) DNA nucleotide doesn't have a phosphate group whereas RNA nucleotide does.

c) DNA nucleotide has a pentose sugar whereas RNA nucleotide has a hexose

sugar.

d) DNA nucleotide can form hydrogen bonds during base pairing while RNA

nucleotide cannot.

e) The sugar in DNA nucleotide is deoxyribose whereas the sugar in RNA

nucleotide is ribose.

The sugar in DNA nucleotide is deoxyribose whereas the sugar in RNA

nucleotide is ribose.

Which of the following proteins directs the RNA polymerase to the promoter

during the initiation of transcription in prokaryotic cells?

a) Alpha factor

b) Beta subunit

c) Sigma factor

d) Helicase

e) Beta factor

Sigma factor

The TATA box is bound by which of the following proteins?

a) Sigma factor

b) RNA polymerase

c) DNA polymerase I

d) Transcription factors

e) DNA polymerase III

Transcription factors

A fragment of DNA has the following sequence:

5' CATGCCGATC 3'

3' GTACGGCTAG 5'

What is the sequence of the transcribed mRNA if the above DNA fragment serves as template for mRNA synthesis?

a) 5' CUAGCCGUAC 3'

b) 5' GAUCGGCAUG 3'

c) 5' GUACGGCUAG 3'

d) 5' CAUGCCGAUC 3'

e) 3' CAUGCCGAUC 5'

5' CAUGCCGAUC 3'

A strong hairpin followed by a stretch of U nucleotides in the 3' untranslated

region of a prokaryotic RNA results in

a) the addition of a polyA tail

b) Rho independent termination of transcription

c) Rho dependent termination of transcription

d) the termination of translation of the RNA

e) Sigma dependent termination of transcription

Rho independent termination of transcription

Which of the following biological events is NOT carried out by a ribozyme?

a) Removal of internal transcribed spacers in rRNA.

b) Formation of peptide bonds during protein synthesis.

c) Cleavage of a 16-nucleotide sequence at the 5'-end of tRNA.

d) Removal of introns by spliceosome.

e) Formation of phosphodiester bonds during DNA synthesis.

Formation of phosphodiester bonds during DNA synthesis.

Why is the 3' addition of a poly-A tail an important post-transcriptional

modification to eukaryotic mRNA molecules?

a) The 3' poly-A tail addition adds stability to mRNA and facilitates the exit of mRNA from nucleus.

b) The 3' poly-A tail addition signals the initiation of transcription by the RNA

polymerase.

c) The 3' poly-A tail addition signals the end of transcription by the RNA

polymerase.

d) The 3' poly-A tail addition is a part of the protein translated from the mRNA.

e) The 3' poly-A tail addition facilitates the splicing of introns.

The 3' poly-A tail addition adds stability to mRNA and facilitates the exit of mRNA from nucleus.

Antimicrobial drug Rifampicin is sometimes used to treat tuberculosis. What is the mechanism of action of this antibiotic to clear infection?

a) It inhibits the transcription of pre-mRNA in bacteria.

b) It prevents the access of the aminoacyl-tRNA to the mRNA-ribosome

complex.

c) It inhibits the initiation and elongation of transcription.

d) It prevents ribosomal translocation.

e) It causes the early termination of transcription.

It inhibits the initiation and elongation of transcription.

Which statement best describes the distinction between the two RNAi pathways within the eukaryotic cells?

a) miRNA-mediated gene silencing represents a back-up pathway should siRNA-mediated gene silencing be unsuccessful at silencing the target dsRNA.

b) siRNA-mediated gene silencing represents a cell defense mechanism against exogenous dsRNA; miRNA-mediated gene silencing is an integral gene expression regulation process.

c) siRNA and miRNA-mediated gene silencing pathways must both be active to successfully silence the target dsRNA.

d) miRNA and siRNA-mediated gene silencing represent evolutionary-

independent pathways which confer identical silencing mechanisms on the target dsRNA.

e) None of the above are correct.

siRNA-mediated gene silencing represents a cell defense mechanism against exogenous dsRNA; miRNA-mediated gene silencing is an integral gene expression regulation process.

In a genetic disease, one normal RNA codon UUU is mutated to UUC. What kind of mutation is this codon alteration based on the genetic code provided above?

a) Nonsense mutation

b) Silent mutation

c) Missense mutation

d) Deletion mutation

e) Insertion mutation

Silent mutation

Which of the following options best describes the wobble hypothesis?

a) Abnormal base paring can occur between a codon and anticodon.

b) A codon is composed of three amino acids.

c) Only certain amino acid sequences can act as start codons.

d) Direction of the flow of genetic information: DNA → RNA → Proteins.

e) Ribosomes move in an unstable fashion during translation.

Abnormal base paring can occur between a codon and anticodon.

Which of the following enzymes maintains the fidelity of protein translation?

a) Primase

b) RNA polymerase

c) DNA polymerase

d) Aminoacyl-tRNA synthetase

e) Helicase

Aminoacyl-tRNA synthetase

Which of the following will most likely be found in the P (peptidyl) site of the large ribosomal unit?

a) The amino-acid free tRNA.

b) tRNA molecule with the growing polypeptide chain.

c) Initiation factors.

d) The charged tRNA molecule with the next amino acid to be added to the

polypeptide chain.

e) rRNA.

tRNA molecule with the growing polypeptide chain.

Which of the following RNAs facilitates the positioning of mRNA on small

ribosome subunit by pairing with the Shine-Dalgarno sequence of mRNA in prokaryotic protein synthesis?

a) tRNA

b) siRNA

c) microRNA

d) 16s rRNA

e) 23s rRNA

16s rRNA

Chloramphenicol is an antibiotic which is effective against many microorganisms by inhibiting bacterial protein translation. It interferes with translation by:

a) Releasing the partially-formed peptide before translation is complete.

b) Hydrolyzing peptides prematurely.

c) Interfering with fMet-tRNA binding to ribosome for protein initiation.

d) Preventing the peptidyl-tRNA from moving from the amino acid site to the

peptide site of the ribosome.

e) Inhibiting prokaryotic peptidyltransferase activity for protein elongation.

Inhibiting prokaryotic peptidyltransferase activity for protein elongation.

Toxin ricin fatally modifies 28S ribosomal RNA to inhibit protein synthesis. What is the role of 28S ribosomal RNA in protein synthesis?

a) It facilitates the positioning of mRNA to ribosome.

b) It carries amino acids to ribosome for protein synthesis.

c) It creates peptide bonds between two amino acids on ribosome.

d) It facilitates the translocation of ribosome during protein synthesis.

e) It dictates the termination of protein synthesis.

It creates peptide bonds between two amino acids on ribosome.

Which of the following proteins is synthesized in RER-bound ribosome?

a) Histone proteins

b) Insulin

c) Tumor suppressor p53

d) Mitochondria proteins

e) Proteins in peroxisomes

Insulin

In the lac operon, the repressor protein exerts a negative effect on the expression of the structural genes in the absence of the inducer molecule. In the case of the lac operon, what is the inducer molecule?

a) Lactose

b) Allolactose.

c) Glucose.

d) RNA polymerase.

e) CAP (catabolite activator protein).

Allolactose

The function of enhancers is an example of

a) the stimulation of translation by initiation factors.

b) a post-transcriptional mechanism for editing RNA.

c) post-translational control that activates certain genes

d) transcriptional control of gene expression

e) a eukaryotic equivalent of prokaryotic promoter functioning.

transcriptional control of gene expression

The major difference between hormones that have cell membrane receptors and those that have intracellular receptors is that the former tend to be

a) larger

b) non-polar

c) hydrophobic

d) lipid soluble

e) water soluble

water soluble

Which of the following is an example of post-transcriptional control of gene

expression?

a) The removal of introns and splicing together of exons.

b) Gene amplification during a stage in development.

c) The folding of DNA to form heterochromatin.

d) the binding of transcription factors to a promoter.

e) The addition of methyl group to cytosine bases of DNA.

The removal of introns and splicing together of exons.

Which of the following statements regarding regulation of transferrin-receptor protein

(TfR) synthesis is CORRECT?

a) The iron-responsive element is an iron-binding sequence in the mRNA that

encodes transferrin-receptor protein.

b) The iron-responsive element is in the 5' untranslated region of the mRNA that

encodes transferrin-receptor protein.

c) When iron is abundant, the IRE-binding protein binds to and stabilizes the mRNA that encodes transferrin-receptor protein.

d) When iron is abundant, irons bind to the IRE-binding protein and remove them from the 3'-UTR of TfR mRNA, destabilizing the mRNA that encodes transferrin-receptor protein.

e) The iron-responsive element serves as an enhancer to facilitate the transcription of transferrin-receptor.

When iron is abundant, irons bind to the IRE-binding protein and remove them from the 3'-UTR of TfR mRNA, destabilizing the mRNA that encodes transferrin-receptor protein.

Histones are proteins that bind to and order the DNA into tight clusters, making it inaccessible to transcription machinery. How do cells loosen the interaction of the histone and DNA?

a) By adding methyl groups to the histones.

b) By methylating the DNA

c) By adding acetyl groups to the DNA

d) By removing acyl groups from the histone

e) By adding acetyl groups to the histone.

By adding acetyl groups to the histone.

Cytidine analog 5'-azacytidine has been used as a therapeutic drug in the treatment of leukemia and myelodysplastic syndrome. What is the target of this drug in cells?

a) DNA topoisomerase II.

b) Dihydrofolate reductase

c) Histone deacetylases.

d) DNA methyltransferases.

e) Thymidylate synthase.

DNA methyltransferases.

Fragile X syndrome is due to the insertion of trinucleotide repeats (CGG) into the 5' untranslated region of FMRI gene. This insertion results in epigenetic changes of FMRI gene expression. What is this type of epigenetic change called?

a) ApT methylation.

b) CpG methylation.

c) Histone modification.

d) Deamination modification.

e) Lysine acetylation.

CpG methylation.

Which of the following best describes the basic components of a nucleosome?

a) DNA+H2A+H2B+H3+H4

b) DNA+H1+H2+H3+H4

c) DNA+2H2A+2H2B+2H3+2H4

d) DNA+2H1+2H2+2H3+2H4

e) DNA+linker DNA+ H1+H2+H3+H4

DNA+2H2A+2H2B+2H3+2H4

Which of the following sequences in double-stranded DNA is most likely to be recognized as a cutting site for a restriction enzyme?

a)

5'-TATACC-3'

3'-ATATGG-5'

b)

5'-GGATTA-3'

3'-CCTAAT-5'

c)

5'-GGAACC-3'

3'-CCTTGG-5'

d)

5'-GAATTC-3'

3'-CTTAAG-5'

e)

5'-CGATTA-3'

3'-GCTAAT-5'

5'-GAATTC-3'

3'-CTTAAG-5'

In a polymerase chain reaction (PCR), the first step is to heat the reaction mixture to 95 °C. What is the purpose of this high temperature?

a) It ensures that the primers bind correctly.

b) It allows DNA polymerase to bind properly.

c) It separates the two strands of DNA by breaking the hydrogen bonds.

d) It denatures any potential contaminated proteins in the reaction.

e) It increases the copy number of the reaction.

It separates the two strands of DNA by breaking the hydrogen bonds.

Which of the following tools of recombinant DNA technology is INCORRECTLY paired with its use?

a) Reverse transcriptase-production of cDNA from mRNA.

b) Restriction endonucleases-enzymes that cut DNA, creating the sticky ends of restriction fragments.

c) Electrophoresis-separation of DNA fragments.

d) Southern blot-detection of mRNA.

e) DNA polymerase-use in a polymerase chain reaction to amplify sections of DNA.

Southern blot-detection of mRNA.

In the process of cloning eukaryotic DNA into prokaryotic cells, the role of reverse transcriptase is to make

a) Double-stranded eukaryotic cDNA from mature mRNA.

b) Mature mRNA from precursor mRNA.

c) Bacterial DNA from eukaryotic DNA.

d) Double-stranded DNA with introns added back.

e) mRNA from DNA.

Double-stranded eukaryotic cDNA from mature mRNA.

In SDS-PAGE, a protein sample is first treated with sodium dodecyl sulfate (SDS). What is the purpose of this step?

a) To make all the proteins positively charged.

b) To make all the proteins negatively charged.

c) To adjust the pH of proteins.

d) To introduce proper folding of the proteins.

e) To allow the visualization of the proteins.

To make all the proteins negatively charged.

Which statement is most accurate regarding mRNA vaccines?

a) mRNA vaccines are produced in vitro from a DNA template.

b) mRNA vaccines are translated into DNA in the body, changing DNA

composition.

c) mRNA vaccines are delivered into body via viral vectors.

d) mRNA vaccines use mRNA to translate viral proteins in vitro for immunization.

e) mRNA vaccines typically take longer to produce than conventional vaccines.

mRNA vaccines are produced in vitro from a DNA template.

What kind of assay is the antigen rapid test for SARS-CoV-2 infection?

a) A PCR-based assay that detects the presence of specific viral RNA.

b) An assay that separates the viral proteins by their sizes.

c) An assay that detects a small amount of viral DNA.

d) An immunoassay that detects a specific cytokine to monitor inflammatory response.

e) An immunoassay that detects the presence of specific viral antigens, which indicates current viral infection.

An immunoassay that detects the presence of specific viral antigens, which indicates current viral infection.

Remdesivir is an antiviral medication that has been used as a treatment for patients with COVID-19. What is the mechanism of action of this drug?

a) It blocks the viral entry.

b) It blocks viral replication by targeting viral RNA polymerase.

c) It blocks the reassembly of viral particles by inhibiting proteases.

d) It inhibits the reverse transcription using viral RNA as template.

e) It targets the immune cells to suppress the production of pro-inflammatory cytokines.

It blocks viral replication by targeting viral RNA polymerase.