MCB450 Exam 2 (3/9/23)

Which of the following is an exception to the central dogma of molecular biology?

a) Genetic information is transferred from DNA to DNA through DNA replication.

b) Genetic information is transferred from DNA to RNA through transcription.

c) Genetic information is transferred from RNA to protein through translation.

d) Genetic information of RNA viruses is transferred from RNA to RNA via RNA dependent RNA synthesis.

e) One mRNA precursor could be spliced to various mature RNAs via alternative splicing.

Genetic information of RNA viruses is transferred from RNA to RNA via RNA dependent RNA synthesis.

If a region of one strand of a Watson-Crick DNA double helix has the sequence ATCGGTGACTATCG, what is the sequence of the complementary region of the other strand? (All sequences are written 5'-3' according to standard convention.)

a) GCTATCAGTGGCTA

b) CGATAGTCACCGAT

c) TAGCCACTGATAGC

d) UAGCCACUGAUAGC

e) CGAUAGUCACCGAU

CGATAGTCACCGAT

Which of the following bonds holds the two strands of the DNA double helix together?

a) Hydrogen bonds

b) Phosphodiester bonds

c) Covalent bonds

d) Ionic bonds

e) Peptide bonds

Hydrogen bonds

Proteins that DNA wraps around to form tightly packaged and organized structural units are referred to as __________.

a) nucleosome

b)chromatin

c) chromosomes

d) histones

e) Nucleosome filaments

histones

During DNA replication, single-stranded DNA is kept from reannealing due to the function of __________.

a) Histones

b)Helicase

c) Single-strand binding proteins (SSB)

d)DNA topoisomerase

e) Telomerase

Single-strand binding proteins (SSB)

Which prokaryotic polymerase is primarily responsible for filling in DNA nucleotides into the gap created by the removal of RNA primers?

a) Reverse transcriptase

b) DNA polymerase III

c) RNA polymerase

d) DNA polymerase II

e) DNA polymerase I

DNA polymerase I

Which of the following does not characterize a 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 transcripts

Splices introns from primary transcripts

Remdesivir has been used in the treatment of some COVID-19 patients infected with SARS-CoV-2, which of the following best describes its mechanism of action?

a) It blocks the entry of SARS-CoV-2 into host cells.

b) It suppresses the cytokine storm.

c) It is a nucleoside analogue which inhibits viral RNA replication.

d) It activates the innate immune response.

e) It enhances antiviral adaptive immune response.

It is a nucleoside analogue which inhibits viral RNA replication.

Imagine the DNA sequence ATTTCTGCCTAG. The answer choices show possible mutations for this DNA sequence. Which choice gives the correct name for that mutation type?

a) ATTTCTGCCTGG is a transition.

b) ATTCTGCCTAG is a transversion.

c) ACTTTCTGCCTAG is a transition.

d) ATTTCTGTCTAG is a transversion.

e) ATTTCTGCCTTG is a transition.

ATTTCTGCCTGG is a transition.

When p53 increases in response to DNA damage. Which of the following events occurs?

a) p53 induces transcription of Rb for G1 cell cycle arrest.

b) p53 induces transcription of cyclin D for G2 cell cycle arrest.

c) p53 bind E2F to activate transcription for S phase.

d) p53 induces transcription of p2l for G1 cell cycle arrest.

e) p53 directly phosphorylate the transcription factor E2F.

p53 induces transcription of p2l for G1 cell cycle arrest.

Inherited mutations that affect DNA repair genes are strongly associated with high cancer risks in humans. Which DNA repair system is defective in Hereditary non polyposis colon cancer (HNPCC)?

a) Direct reversal repair

b) Mismatch repair

c) Base excision repair

d) Nucleotide excision repair

e) Double-strand break repair

Mismatch repair

Which of the following repair pathways is capable of repairing the damage resulting from UV-induced Thymine?

a) Direct repair

b) Nucleotide excision repair

c) Mismatch repair

d) Proofreading

e) dsDNA break repair

Nucleotide excision repair

Which of the following best describes an oncogene?

a) A gene that causes uncontrollable grow.

b) A gene that no longer makes a viable protein.

c) A gene that restricts cell growth.

d) A gene that stimulates apoptosis in cells.

e) A gene that induces cell cycle arrest.

A gene that causes uncontrollable grow.

The Ames test is based on the relationship between ______.

a) Transcription and translation.

b) Mutagenicity and carcinogenicity.

c) Liver and Cytochrome P450.

d) Histidine and tetrahydrofolate.

e) none of the above is correct.

Mutagenicity and carcinogenicity.

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) DNA damage by alkylation.

c) the defective repair of DNA.

d) the recombination of DNA.

e) Formation of thymine dimer.

DNA damage by alkylation.

What is the function of glycosylase involved in base excision repair?

a) Addition of correct base

b) Addition of correct nucleotide

c) Removal of incorrect base

d) Removal of phosphodiester

e) Removal of incorrect nucleotide

Removal of incorrect base

Which of the following nitrogenous bases is NOT found in RNA?

a) Cytosine

b) Uracil

c) Thymine

d) Adenine

e) None of the above.

Thymine

RNA synthesis in prokaryotes is catalyzed by the large enzyme RNA polymerase, the holoenzyme of which consists of four subunits. Which of the four subunits is responsible for the recognition of promoters?

a) alpha

b) beta

c) beta-prime

d) delta

e) sigma

sigma

The TATA box is a _____.

a) sequence upstream of the transcription starting site of many eukaryotic genes.

b) sequence in mRNAs that marks translation start sites.

c) enhancer consensus sequence.

d) sequence in chromosomes that marks replication origins.

e) sequence in primary transcripts that marks splice sites.

sequence upstream of the transcription starting site of many eukaryotic genes.

Rifampin is one of the first-line drugs used in treating TB. What's the most likely mechanism of action for this anti-bacterial drug?

a) Interferes with initiation of translation in bacteria

b) Interferes with elongation of translation in bacteria

c) Interferes with initiation of transcription in bacteria

d) Interferes with elongation of transcription in bacteria

e) Interferes with termination of transcription in bacteria

Interferes with elongation of transcription in bacteria

Which of the following biological events does not involve a ribozyme?

a) Removal of internal transcribed spacers of rRNA.

b) Removal of a 16-nucleotide sequence at the 5'-end of tRNA.

c) Removal of introns during RNA splicing.

d) Formation of peptide bonds during protein translation.

e) Formation of phosphodiester bonds during DNA replication.

Formation of phosphodiester bonds during DNA replication.

Which of the following statements is TRUE regarding replication, transcription or translation?

a) Okazaki fragments are the short fragments of DNA that are produced on the leading strand at the DNA replication fork.

b) The 5' to 3' direction of DNA synthesis implies that deoxyribonucleotides are added to the 5' OH group on the growing strand.

c) Transcription is initiated at promoter sequences in the DNA.

d) RNA polymerase requires primers to initiate RNA synthesis.

e) Transcription is terminated at stop codons in the mRNA.

Transcription is initiated at promoter sequences in the DNA.

The 3' end of an intron is marked by a__________.

a) Splice donor site

b) Splice acceptor site

c) AT rich site

d) Branch point site

e) Poly-A tails

Splice acceptor site

Which of the following statements about RNA interference is false?

a) RNA interference is triggered by double-stranded molecules.

b) Double stranded RNA is cleaved by Dicer into smaller RNAs.

c) Smaller RNAs associate with an RNA-induced silencing complex, a complex that binds to and stabilizes the target message resulting in an increase in translation.

d) Smaller RNAs associate with an RNA-induced silencing complex, a complex that binds to and silences the target message.

e) It is a host immune response to restrict viral amplification in some plants.

Smaller RNAs associate with an RNA-induced silencing complex, a complex that binds to and stabilizes the target message resulting in an increase in translation.

Which type of mutation creates a premature stop codon in the mRNA?

a) Silent mutation

b) Missense mutation

c) Frameshift mutation

d) Nonsense mutation

e) Insertion mutation

Nonsense mutation

Using the codon chart provided above, what is the sequence of amino acids that is produced when this gene is translated?

a) Gly-Ser-Arg

b) Gly-Leu-Ser

c) Ser-Arg-Gly

d) Thr-Arg-Gly

e) Ser-Arg-Thr

Gly-Ser-Arg

Which of the following enzymes charges tRNA molecules?

a) Primase

b) RNA polymerase

c) DNA polymerase

d) Kinase

e) Aminoacyl-tRNA synthetase

Aminoacyl-tRNA synthetase

Which of the following choices will most likely be found in the aminoacyl site of the large ribosomal unit?

a) The amino-acid free tRNA

b) 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

The charged tRNA molecule with the next amino acid to be added to the polypeptide chain

Which statement is true regarding the 16s rRNA in prokaryotes?

a) It is a component of the 50S (large subunit) prokaryotic ribosomes.

b) It binds to the Shine-Delgarno sequence of mRNA to initiate protein synthesis.

c) It pairs with initiator tRNA to initiate translation.

d) It carries amino acid to the P site of ribosome.

e) It catalyzes peptide formation in ribosome.

It binds to the Shine-Delgarno sequence of mRNA to initiate protein synthesis.

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

a) Releasing the partially-formed peptide before translation is complete. b) Hydrolyzing peptides prematurely.

c) Preventing the peptidyl-tRNA from moving from the amino acid site to the peptide site of the ribsome.

d) inhibiting prokaryotic peptidyltransferase activity for protein elongation.

e) Interfering with fMet-tRNA binding to ribosome.

inhibiting prokaryotic peptidyltransferase activity for protein elongation

Toxin ricin fatally modifies 28S ribosomal RNA to inhibit protein synthesis. What is the mechanism of action of this inhibition by ricin?

a) Ricin serves as an alkylating agent to bind to 28S rRNA.

b) Ricin serves as an intercalating agent to bind to 28S rRNA.

c) Ricin serves as a glycosidase for the depurination of 28S rRNA.

d) Ricin serves as a protease to degrade ribosome.

e) Ricin serves as an antibiotic to inhibit the initiation of protein synthesis.

Ricin serves as a glycosidase for the depurination of 28S rRNA.

For protein synthesis in the rough endoplasmic reticulum (RER)-bound ribosomes, the function of signal recognition particle (SRP) is___

a) to associate with signaling hormones

b) to enhance G-protein-couple receptor signaling

c) to distinguish phosphorylated proteins from dephosphorylated proteins

d) to recognize a signal peptide and deliver ribosomes to endoplasmic reticulum

e) to recognize the amino acid sequence for N-linked glycosylation

to recognize a signal peptide and deliver ribosomes to endoplasmic reticulum

Which of the following amino acids can be post-translationally modified by ubiquitination for protein degradation?

a) Lysine

b) Arginine

c) Glutamine

d) Serine

e) Proline

Lysine

In the lac operon, the repressor protein exerts a negative effect on the expression of the structural genes. Binding of an inducer molecule to a repressor would change its conformation and prevent its binding to operator. In the case of the lac operon, what is the direct inducer molecule?

a) Glucose

b) Lactose

c) cAMP

d) RNA polymerase

e) Allolactose

Allolactose

The functioning of enhancers is an example of

a) a eukaryotic equivalent of prokaryotic promoter functioning.

b) transcriptional control of gene expression.

c) a post-transcriptional mechanism for editing mRNA.

d) post-translational control that activates certain proteins.

e) the stimulation of translation by initiation factors.

transcriptional control of gene expression.

The major difference between hormones that have intracellular receptors and those that have cell membrane receptors is that the latter tend to be_____.

a) larger

b) charged

c) lipid soluble

d) hydrophobic

e) water soluble

water soluble

Which of the following statements regarding regulation of transferrin-receptor protein 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 scarce, the IRE-binding protein binds to and stabilizes 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 scarce, the IRE-binding protein binds to and stabilizes the mRNA that encodes transferrin-receptor protein.

Which of the following is an example of post-transcriptional regulation 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 groups to cytosine bases of DNA.

The removal of introns and splicing together of exons.

DNA is methylated on which nucleotide?

a) Adenine

b) Cytosine

c) Guanine

d) Thymine

e) Uridine

Cytosine

DNA methylation and post-translational modifications of histone proteins are two major components in epigenetics. Which of the following statements does NOT correctly describe the mechanism of epigenetic regulation of gene expression?

a) Addition of DNA and histone modifications in the cell is performed by protein based enzymes.

b) Lysine acetylation leads to a tighter association of histone proteins with DNA in the promoter regions.

c) DNA methylation patterns can be propagated to daughter strands after DNA replication.

d) The covalent addition of methyl groups to DNA is reversible in the cells.

e) The covalent addition of acetyl groups to lysine is reversible in the cells.

Lysine acetylation leads to a tighter association of histone proteins with DNA in the promoter regions.

Fragile X syndrome is due to the insertion of trinucleotide repeats (CGG) into the 5' untranslated region of FMR1 gene. This insertion results in:

a) aggregation of the unstable FMR1 proteins.

b) prevention of DNA unwinding for the transcription initiation.

c) prevention of initiation of protein translation.

d) a decrease in mRNA synthesis due to DNA methylation.

e) a nonsense mutation which causes the termination of translation.

a decrease in mRNA synthesis due to DNA methylation.

Which of the following DNA sequences could most likely be cleaved by a restriction enzyme?

a)

5'-TATACC-3'

3'-ATATGG-5'

b)

5'-GAATTC-3'

3'-CTTAAG-5'

c)

5'-GGAACC-3'

3'-CCTTGG-5'

d)

5'-CGATTA-3'

3'-GCTAAT-5'

e)

5'-GGATTA-3'

3'-CCTAAT-5'

5'-GAATTC-3'

3'-CTTAAG-5'

A doctor has recovered a bit of saliva from a covid-19 patient. The doctor would like to compare a specific region of viral nucleic acid from the sample with previous viral isolates to see whether there is any mutation in the virus. Which of the following would be the most useful for increasing the amount of nucleic acid in the sample available for testing.

a) Gel electrophoresis

b) Restriction enzyme digestion

c) Southern blot

d) Northern blot

e) Polymerase chain reaction (PCR)

Polymerase chain reaction (PCR)

Why are protein samples boiled with SDS (sodium dodecyl sulfate) and 2- mecaptoethanol before separating them by SDS-PAGE (SDS polyacrylamide gel electrophoresis)?

a) To add positive charges to the proteins to make them migrate easier.

b) To preserve the protein's native shape.

c) To increase resistance during migration through the gel.

d) To denature protein so they run according to their size.

e) To remove any contamination in the samples.

To denature protein so they run according to their size.

cDNA synthesis from mRNA is catalyzed by which of the following enzymes?

a) DNA polymerase I

b) Reverse transcriptase

c) Taq DNA polymerase

d) RNA polymerase

e) DNA polymerase III

Reverse transcriptase

SYBR® Green is commonly used as a non-radioactive marker to stain DNA during the real-time PCR. Which term best describes the mechanism of action for SYBR® Green?

a) Alkylating agent

b) Antisense agent

c) Chain cutter

d) Intercalating agent

e) Topoisomerase poison

Intercalating agent

Which of the following statement is TRUE regarding the Johnson & Johnson's Janssen viral vector vaccine against SARS-CoV-2?

a) Viral vector vaccine works by injecting a small piece of mRNA from the coronavirus that codes for the virus' spike protein.

b) Viral vector vaccine works by injecting viral vectors carrying a small piece of mRNA from the coronavirus that codes for the virus' spike protein. c) Viral vector vaccine works by injecting a small piece of mRNA from the coronavirus that neutralizes viral RNA.

d) Viral vector vaccine works by injecting plasmid DNAs that carry a small piece of DNA that codes for the virus' spike protein.

e) Viral vector vaccine works by injecting viral vectors carrying a small piece of DNA that codes for the virus' spike protein.

Viral vector vaccine works by injecting viral vectors carrying a small piece of DNA that codes for the virus' spike protein.

Monoclonal antibodies against SARS-CoV-2 spike protein have been approved by the FDA as an option for the treatment of COVID-19. What is the mechanism of action for this type of drug?

a) It blocks the integration of virus RNA into the genome.

b) It blocks the entry of the viruses.

c) It inhibits the reverse transcriptase.

d) It serves as an anti-inflammatory drug.

e) It inhibits the RNA polymerase of SARS-CoV-2.

It blocks the entry of the viruses.

Paxlovid is a combination therapy that includes two drugs (nirmatrelvir and ritonavir) for the treatment of COVID-19 patients. What is the mechanism of action of Paxlovid?

a) It blocks the binding of SPIKE protein to ACE2 receptor.

b) It blocks the viral entry by binding to the SPIKE protein.

c) It suppresses host immune response to prevent cytokine storm.

d) It targets viral RNA polymerase to inhibit RNA replication.

e) It blocks the proteolysis of viral proteins to small functional proteins.

It blocks the proteolysis of viral proteins to small functional proteins.

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

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

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

c) An assay that detects the small amount viral DNA.

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

e) An immunoassay that detects the specific cytokine to monitor inflammatory response.

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