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OS 201 [2019 exams] > Exam 3 > Flashcards

Exam 3 Flashcards

1
Q

Which of the following statements is/are incorrect?

a) The phosphate component of nucleic acids is negatively charged at physiologic pH.
b) The phosphate component of nucleic acids is positively charged at basic pH.
c) The sugar component of nucleic acids is uncharged at neutral pH.
d) A & B

A

b) The phosphate component of nucleic acids is positively charged at basic pH.

At physiologic pH, the phosphate component of nucleic acid is negatively charged while its sugar component is neutral.

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2
Q

. Which of the following statements is/are incorrect?

a) Uracil resembles cytosine more than thymine in base pairing.
b) Adenine typically forms two hydrogen bonds in a base pair.
c) Both adenine and guanine are pyrimidine bases.
d) A & C

A

a) A & C

Thymine differs from uracil by only a methyl group while cytosine has to have its carbonyl group replaced with an amine. Adenine and Thymine form two hydrogen bonds while Cytosine and Guanine form three. Adenine and Guanine are purines while Cytosine, Uracil, and Thymine are pyrimidines.

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3
Q

Which of the following is incorrect?

a) Every DNA has deoxyribose while RNA has ribose
b) Every DNA has thymine while RNA has uracil
c) In RNA, the nitrogenous base participates in glycosidic bond
d) Both B & C

A

b) Every DNA has thymine while RNA has uracil

DNA and RNA are defined based on the sugars in their sugar backbone (deoxyribose for DNA and ribose for RNA). Moreover, there exists DNA with uracil (e.g. dUMP in thymidine synthesis). In DNA and RNA, nitrogenous bases participate in hydrogen bonds with each other and glycosidic bonds with their sugar backbone. The phosphate groups and sugar molecules in the backbone participate in a phosphodiester bond.

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4
Q

Which of the following statements is incorrect?

a) A-DNA is the biologically predominant form of DNA.
b) B-DNA is a right-handed double helix.
c) Z-DNA is a left-handed double helix.
d) A & B

A

a) A-DNA is the biologically predominant form of DNA.

A and B-DNA are right handed while Z-DNA is left handed. B-DNA is the biologically dominant form of DNA.

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5
Q

Which is/are incorrect of the following?

a) RNA contains base pairs
b) tRNA exhibits completely unfolded conformations
c) tRNA contains more than 4 nucleotide bases
d) A & C are incorrect

A

b) tRNA exhibits completely unfolded conformations

tRNA exhibits a folded form.

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6
Q

Which of the following statements is/are incorrect?

a) Nucleases typically catalyze hydrolysis of phosphodiester bonds.
b) An endonuclease attacks sequences from either or both the 5’ and 3’ ends
c) A restriction enzyme is a type of endonuclease.
d) B & C

A

b) An endonuclease attacks sequences from either or both the 5’ and 3’ ends

An endonuclease cleaves sites within the sequence.

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7
Q

Which of the following statements is incorrect?

a) Ligases catalyze recombination of nucleic acid
b) Ligases covalently join the ends of nucleic acid strands
c) Ligases hydrolyze high energy phosphoanhydride bonds
d) Ligases initiate DNA synthesis by extending RNA primers

A

a) Ligases catalyze recombination of nucleic acid

Ligases covalently join the ends of nucleic acid strands (including RNA primers) by hydrolyzing the high energy phosphoanhydride bonds in ATP.

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8
Q

Which of the following is/are wrong?

a) DNA Polymerase works in a 3’  5’ direction
b) 3’ -> 5’ exonuclease activity is for proofreading
c) Error rates are lower in unprimed synthesis
d) A & C

A

d) A & C

DNA Polymerase works in a 5’-> 3’ direction. Error rates are higher in unprimed synthesis.

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9
Q

Which of the following statements is/are incorrect?

a) Replication of double-stranded DNA typically incorporates new nucleotides into both parent and daughter strands.
b) DNA synthesis is typically discontinuous on the lagging strand.
c) DNA synthesis is typically continuous on the leading strand.
d) B & C

A

a) Replication of double-stranded DNA typically incorporates new nucleotides into both parent and daughter strands.

Incorporation of new nucleotides only occurs in one of the two strands, the daughter strand (i.e., the non-template strand). The parent strand remains intact, however, the resulting double strand is now a hybrid of the parent and the daughter strand—semi-conservative replication.

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10
Q

Which of the following statements is/are incorrect?

a) In the human genetic code, every amino acid is coded for by exactly one codon sequence.
b) In the human genetic code, every stop codon sequence codes for exactly one amino acid.
c) In the human genetic code, every codon is a sequence of exactly three nucleotides.
d) A & B

A

d) A & B

The degenerate nature of the genetic code and the wobble effect allows for some amino acids corresponding to multiple codons. However, each codon is only comprised of three nucleotides. Stop codons do not code for amino acids. Instead they recruit release factors.

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11
Q

Which of the following statements is/are incorrect?

a) DNA can serve as a template for synthesizing both RNA and protein.
b) RNA can serve as a template for synthesizing both RNA and protein.
c) Protein can serve as a template for synthesizing both DNA and RNA.
d) A & C

A

d) A & C

DNA serves as a template for RNA, but not proteins. Proteins cannot serve as templates for DNA nor RNA.

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12
Q

Which of the following is/are incorrect?

a) All introns function as noncoding sequences
b) All untranslated regions (UTRs) function as noncoding sequences
c) All UTRs form introns or parts of it
d) Both B & C

A

c) All UTRs form introns or parts of it

Introns are excised during post-transcriptional modification and are not translated. Untranslated regions are not coded. However, untranslated regions need not be excised as introns. Promoter reqions for example are untranslated but need to remain in the RNA transcript.

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13
Q

Which of the following statements is/are incorrect?

a) A single insertion or deletion mutation can itself always produce a change in genomic nucleic-acid sequence length
b) A single insertion or deletion mutation by itself can produce a change in translated amino-acid sequence.
c) A single point mutation by itself can produce a shift in translational reading frame
d) A & B

A

c) A single point mutation by itself can produce a shift in translational reading frame

Insertions and deletions are able to produce shifts in the reading frame as well as changes in the translated amino-acid sequence. Point mutations are only able to change the translated amino-acid sequence.

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14
Q

Which of the following statements is/are incorrect?

a) AP site formation is characteristic of damage induced by ultraviolet radiation.
b) AP site formation results from the removal of a pyrimidine base or purine base.
c) Pyrimidine cyclobutane dimers typically form as a result of thermal collisions.
d) A & C

A

d) A & C

AP (apurinic) site formation is caused by thermal collisions or alkylation of purines.

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15
Q

Which of the following is/are true of purine and pyrimidine nucleotides?

a) They are degraded to free bases, sugars, and phosphate in the gastrointestinal tract.
b) They are synthesized de novo from simple precursors
c) They are salvaged from preformed bases and nucleosides
d) AOTA
e) B & C

A

d) AOTA

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16
Q

Which of the following will differentiate de novo purine biosynthesis from de novo pyrimidine biosynthesis?

a) PRPP is the donor of ribose group.
b) ATP is required in some steps of the pathway.
c) The amino acid glycine is a precursor of the ring structure.
d) One carbon group carried by tetrahydrofolate participates in the biosynthesis.

A

c) The amino acid glycine is a precursor of the ring structure.

Above is the structure of a pyrimidine; below is a purine. A tetrahydrofolate transfers a methyl group to purines during thymidine synthesis.

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17
Q

Which of the following ensures appropriate balance between AMP and GMP levels during purine biosynthesis?

a) AMP, GMP, and IMP inhibit the rate limiting step of de novo synthesis
b) The reactions after the branch part in AMP and GMP are not subject to allosteric inhibition
c) ATP provides energy for GMP production and GTP provides energy for AMP production
d) AOTA

A

c) ATP provides energy for GMP production and GTP provides energy for AMP production

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18
Q

Which should not be considered in distinguishing carbamoyl phosphate I and CPS II?

a) Cellular location
b) Type of reaction
c) Source of nitrogenous substrate
d) Metabolic pathway which utilizes carbamoyl phosphate

A

b) Type of reaction

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19
Q

Which of the following is not a salvage reaction for purine and pyrimidine nucleotides?

a) Phosphoribosylation of hypoxanthine and guanine
b) Phosphorylation of thymidine
c) Phosphoribosylation of adenine
d) Phosphorylation of uracil

A

d) Phosphorylation of uracil

The following are the salvage pathways for purines:

  • hypoxanthine –(hypoxanthine-guanine phosphoribosyltransferase)–> IMP
  • guanine –(hypoxanthine-guanine phosphoribosyltransferase)–> GMP
  • Adenine –(adenine phosphoribosyltransferase)–> AMP

The following are the salvage pathways for pyrimidines:
Phosphoribosylation
*uracil +PRPP -> UMP
Phosphorylation of free pyrimidine nucleosides
*uses nucleoside kinases that utilize ATP in the phosphorylation of nucleosides to nucleotides
*thymidine + ATP -> TMP + ADP
*uracil + ribose -> uridine + Pi
*uridine + ATP -> UMP + ADP
*cytidine + ATP -> CMP + ADP

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20
Q

A deficiency in hypoxanthine guanine-phosphoribosyltransferase affecs what pathway?

a) De novo biosynthesis of purine nucleotides
b) Catabolism of pyrimidine nucleotides
c) Salvage of purine bases
d) Salvage of pyrimidine bases

A

c) Salvage of purine bases

The following are the salvage pathways for purines:

  • hypoxanthine –(hypoxanthine-guanine phosphoribosyltransferase)–> IMP
  • guanine –(hypoxanthine-guanine phosphoribosyltransferase)–> GMP
  • Adenine –(adenine phosphoribosyltransferase)–> AMP
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21
Q

Which of the following is a common negative effector in the conversion of the four different ribonucleoside diphosphates to their corresponding deoxyribonucleotides?

a) ATP
b) dGTP
c) dCTP
d) dATP

A

d) dATP

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22
Q

Which of the following is the site of action of 5-fluorouracil?

a) Hypoxamine -> Xanthine -> Uric Acid
b) Folate -> DHF -> THF
c) Uracil + PRPP -> UMP
d) dUMP -> TMP

A

d) dUMP -> TMP

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23
Q

Which of the following genetic abnormalities is NOT associated with gout?

a) PRPP synthetase with high Vmax.
b) Defective xanthine oxidase.
c) Lack of hypoxanthine-guanine phosphoribosyl transferase
d) Gln phosphoribosyl amino transferase that is resistant to feedback inhibition

A

b) Defective xanthine oxidase.

Xanthine oxidase is responsible for converting xanthine to uric acid. A defective enzyme would therefore not lead to the accumulation of uric acid, and therefore would not lead to gout.

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24
Q

Patients with gout arising from biochemical causes are sometimes treated with allopurinol. Which of the following reactions is the site of action of allopurinol?

a) Reduction of ribonucleosides to deoxyribonucleotides
b) Degradation of hypoxanthine to xanthine and uric acid
c) Formation of TMP
d) Conversion of Adenosine to Adenine

A

b) Degradation of hypoxanthine to xanthine and uric acid

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25
Q

Which pathway is affected in adenosine deaminase deficiency that results in Severe Combined immune Deficiency disorder?

a) Salvage of purine bases
b) Formation of deoxyribonucleotides
c) De novo biosynthesis of pyrimidines
d) Catabolism of purines

A

d) Catabolism of purines

Adenosine deaminase is involved in catabolizing adenosine, a purine.

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26
Q

Which of the following is unique to catabolic pathway of pyrimidine nucleotide?

a) Deamination reactions
b) Removal of ribose/deoxyribose
c) Opening of ring structure of the base
d) Oxidative reactions

A

c) Opening of ring structure of the base

In purines, the ring structure is left unopened. Instead, it is excreted as uric acid.

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27
Q

Which of the following conditions will be observed when a healthy adult is placed on a diet deficient in lysine?

a) Gradual shift to positive nitrogen balance
b) No change in nitrogen balance
c) Decreased urea excretion
d) Shift to negative nitrogen balance

A

d) Shift to negative nitrogen balance

A positive nitrogen balance is when N input> N output. A negative nitrogen balance is when N input

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28
Q

Which of the following nitrogenous compounds constitute… Output in nitrogen balance studies?

a) Ammonia
b) Urea
c) Carbamoyl phosphate
d) AOTA
e) A & B

A

e) A & B

Ammonia, urea, and uric acid are nitrogenous waste products. Carbamoyl phosphate is merely an intermediate (in the urea cycle).

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29
Q

Which of the following statements is true for the genome?

a) More coding than non-coding segments
b) More exon associated bases than intron associated bases
c) More nonrepetitive than repetitive segments
d) A & B

A

c) More nonrepetitive than repetitive segments

There are more non-coding segments and intron associated bases in the eukaryotic genome. Their purpose

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30
Q

Which of the following statements about mitochondrial DNA is/are true?

a) A disease due to a mutation in the mitochondrial DNA is transmitted to daughters but not sons.
b) It contains the genes that encode all the proteins needed in the mitochondria.
c) It is inherited primarily through the mother.
d) A & C

A

c) It is inherited primarily through the mother.

Mitochondrial DNA is always passed on from mother to ALL offspring. While it codes for necessary mitochondrial proteins, nuclear DNA also codes for mitochondrial proteins.

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31
Q

Which of the following is not a component of nucleosome?

a) 30 bp linker
b) 146 bp DNA wrapped around histone core
c) H3 & H4 tetramer
d) Histone octamer

A

a) 30 bp linker

The 30bp linker is unbound to histones. It links nucleosomes but is not a part of it.

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32
Q

Which of the following is the correct sequence of DNA packaging?

a) DNA, 10 nm fibril, 30 nm fibril, looped domains, condensed domains, metaphase chromosome
b) DNA, nucleosome, 30 nm fibril, looped domains, condensed domains, metaphase chromosome
c) DNA, 10 nm fibril, 30 nm fibril, condensed domains, looped domains, metaphase chromosome
d) DNA, nucleosome, 30 nm fibril, condensed domains, looped domains, metaphase chromosome

A

a) DNA, 10 nm fibril, 30 nm fibril, looped domains, condensed domains, metaphase chromosome

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33
Q

What is the region composed of TG rich repeats located at the tip of all eukaryotic chromosomes?

a) Centromere
b) Chromomere
c) Kinetochore
d) Telomere

A

d) Telomere

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34
Q

At the DNA level, which of the following is not part of a gene?

a) 3’ Poly A tail
b) Exon
c) Intron
d) Promotor

A

a) 3’ Poly A tail

The poly-A tail is a post-transcriptional modification to the mRNA transcript.

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35
Q

Which of the following statements about replication is true?

a) An RNA primer is needed to begin daughter strand synthesis in prokaryotes.
b) It begins in more than one replication of origin in eukaryotes.
c) It is semi-conservative only in prokaryotes.
d) Okazaki fragments form in the leading strand but not in the lagging strand in eukaryotes.

A

a) An RNA primer is needed to begin daughter strand synthesis in prokaryotes.
b) It begins in more than one replication of origin in eukaryotes.

In replication in prokaryotes, there is only one replication site for their circular DNA, in contrast to many in the linear DNA of eukaryotes. Replication in prokaryotes and eukaryotes requires a primer, is always semi-conservative, just as Okazaki fragments always form on the lagging strand.

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36
Q

Which of the following statements about RNA polymerase is not true?
a) Uses single stranded DNA is a template

A

(lack choices)

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37
Q

Replication in humans occurs in which phase of cell cycle?

a) G1
b) S
c) G2
d) M

A

b) S

S stands for synthesis phase, where DNA replication takes place.

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38
Q

A scientist isolated a mutant DNA polymerase that assists phosphodiester bond formation through glutamic acid residue (GAG) instead of an aspartic acid residue (GAC) in wild type DNA polymerase. The scientist observed that the mutant protein is as efficient in phosphodiester bond formation as the wild type and has no apparent changes. What is the type of mutation?

a) Same sense
b) Missense
c) Nonsense
d) Frame shift

A

b) Missense

While there is no apparent change in protein function, its sequence did change. This is called a conservative missense mutation.

Double stranded DNA breaks are the most dangerous form of DNA damage as it could cause cell death or cancer.

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39
Q

Which of the following would most likely cause double stranded DNA breaks?

a) Alkylating agents
b) Replication (something)
c) UV light
d) X-ray

A

c) UV light

d) X-ray

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40
Q

What is the repair mechanism for double stranded breaks?

a) Homologous recombination and non-homologous end joining
b) Nucleotide excision repair and non-homologous end joining
c) Base excision repair and non-homologous end joining
d) Nucleotide and base excision repair

A

a) Homologous recombination and non-homologous end joining

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41
Q

Which of the following statements about mismatch repair is true?

a) It can occur all throughout the cell cycle.
b) It can repair both subtle (alkylation) and bulky (pyrimidine dimer) DNA lesions.
c) The main enzyme (MutS) involved in repair directly binds and removes the incorrect nitrogenous base.
d) The parental strand is differentiated from the daughter stranded through the presence of methylated sites.

A

d) The parental strand is differentiated from the daughter stranded through the presence of methylated sites.

Mismatch repair only occurs during replication. It can repair only lesions brought about by mismatched base pairs. It is MutH that exhibits endonuclease activity, with MutL and MutH along with ATP form the complex where MutH can attach.

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42
Q

Which of the following is an example of comparative genomics?

a) Comparing the genomes of human and rat
b) Comparing male and female human genomes
c) Comparing nuclear and mitochondrial genomes
d) Comparing genomes of 2 humans

A

a) Comparing the genomes of human and rat

Comparative genomics involves comparing the genomes of two different species.

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43
Q

Limb buds form in the developing embryo during the 1st trimester of pregnancy. Which of the following statements describes how these cells develop?

a) They alter the sequence of their DNA to develop into different cell lines.
b) Large blocks of DNA are lost during vertebrate development.
c) They synthesize and accumulate different sets of RNA and protein molecules
d) NOTA

A

c) They synthesize and accumulate different sets of RNA and protein molecules

Cells do not alter their sequences nor lose blocks of DNA during development. They merely undergo differential gene expression (the synthesis and accumulation of different sets of RNA and protein due to different patterns of epigenetic control).

44
Q

Which of the following about DNA Methylation is false?

a) Loss of CpG dinucleotides increases control by DNA methylation
b) Methylation patterns can be inherited
c) Unmethylated regions are transcriptionally active
d) Methylation patterns change through development

A

a) Loss of CpG dinucleotides increases control by DNA methylation

CpG islands are sites for DNA methylation. Loss of CpG dinucleotides will lead to a decrease in control by DNA methylation. All others are true.

45
Q

Which of the following is/are characteristic of transcriptionally active chromatin?

a) Tightly packed chromatin
b) Methylated histones
c) A & B
d) Neither A nor B

A

b) Methylated histones

Transcriptionally active chromatin

chromatin conformation: open, extended conformation
DNA methylation: relatively unmethylated, especially at promoter regions
histone acetylation: acetylated histones

histone methylation

  • methylation (up to 3 methyl groups) at lysine and arginine of histones
  • may activate or inactivate, depending on the kind of gene
  • histone H3 lysine 4, 27, 36 -activate
  • histone H3 lysine 9, 27; H4 lysine 2 -inactive
    note: methylation is not 1:1 in histones
46
Q

As a mesenchymal stem cell undergoes differentiation to a terminally differentiated cell, which of the following processes is not likely to happen?

a) Increase in methylation of CpG islands
b) Acetylation of histones
c) Same level of de novo methylation as a blastocyst
d) Methylation of histones

A

c) Same level of de novo methylation as a blastocyst

Anytime that a cell differentiates there is an increase in de novo methylation because differential gene expression is needed. However, in early embryo, when a fertilized egg becomes a blastocyst, there is a decrease in methylation because there is no differentiation yet, only replication.

47
Q

Glucocorticoids are used to treat a variety of medical conditions from hypersensitivity to autoimmune diseases. The mechanism of action of this class of drugs involves influencing gene expression. Which of the following is involved in the action of glucocorticoids?

a) Glucocorticoids bind to sequences of RNA to block RNA modification.
b) Glucocorticoids and their receptors act on response elements on DNA.
c) Glucocorticoids bind to membrane receptors that send out secondary messengers to activate transcription factors.
d) Glucocorticoids modify protein structure by phosphorylation.

A

b) Glucocorticoids and their receptors act on response elements on DNA.

48
Q

A certain protein X regulates its own production by exerting influence on its own pre-mRNA. By binding to its own pre-mRNA, it allows cleavage but not polyadenylation of the pre-mRNA. Which is a consequence?

a) Transport to cytoplasm, but no translation
b) Errors in RNA splicing
c) Formation of alternative isoforms of the protein
d) Degradation of pre-mRNA of exonucleases

A

d) Degradation of pre-mRNA of exonucleases

Polyadenylation protects the mRNA strand from exonucleases.

49
Q

The fibronectin gene is expressed in hepatocytes and fibrblasts. The pre-mRNAs produced in the two cell types both contain the exons EIIIA and EIIIB. In the fibroblast, these two exons are present in the mRNA and allow the protein to adhere to cell surfaces. In the hepatocyte, the mRNA does not contain these 2 exons, allowing the protein product to circulate in the serum. Which type of control of gene expression is this?

a) Epigenetic control
b) Transcriptional control
c) RNA transport control
d) Post-transcriptional control
e) Translational control

A

d) Post-transcriptional control

This is an example of RNA editing.

50
Q

Peptide hormones exert their influence on gene expression by initially binding to cell surface receptors. Secondary messengers like cAMP can cause a series of events resulting in the binding of CREB to cAMP response elements in the DNA. Which type of control of gene expression is this?

a) Epigenetic control
b) Transcriptional control
c) RNA transport control
d) Post-transcriptional control
e) Translational control

A

a) Transcriptional control

CREB falls under cis-acting response elements responsible for transcriptional control.

51
Q

Each individual has an immune system that is unique from those of his parents and siblings. Which type of gene regulation is mainly responsible for this?

a) DNA Rearrangement
b) Gene amplification
c) RNA editing
d) Alternative splicing

A

a) DNA Rearrangement

DNA rearrangement is particularly important in increasing possible combinations for immune reactions.

52
Q

Proteins of the hsp family (heat-shock protein) have been found to facilitate accurate folding of polypeptides they are being synthesized. If these molecular chaperones were to cease functioning, which of the following would likely occur?

a) Correct folding of polypeptides would continue at the same rate
b) Increase in activity of proteasome
c) Decrease in protein aggregates
d) AOTA

A

b) Increase in activity of proteasome

HSPs are chaperone proteins which aid in proper protein folding. Unfolded proteins with hydrophobic areas exposed are sent to proteasomes for destruction, otherwise they will form clumps that will precipitate and damage cells.

53
Q

What best describes trans-acting factors?

a) TF are base sequences that are in the same strand of DNA as the gene they control
b) TF need to be near gene of interest to exert action
c) TF suppreses/activates gene expression
d) TF are transcribed in the opposite strand of DNA

A

c) TF suppreses/activates gene expression

Trans-acting factors are protein products from distally located genes on the same strand. They interact with cis-acting elements to promote or silence pertinent genes.

54
Q

Which of the following are ways by which histones are modified to regulate gene expression?

a) Acetylation
b) Ubiquitination
c) Methylation
d) AOTA
e) All except B

A

d) AOTA

55
Q

the CpG segment just proximal to a promotor of a tumor suppressor gene is amplified 100-fold, which of the following is most likely to happen?

a) Increase in the acetylation of the segment
b) Increase in protection against tumorigenesis
c) Deactivation of the MecP2 protein
d) Increase in the likelihood of developing a tumor

A

d) Increase in the likelihood of developing a tumor

CpG islands are sites of methylation. Their amplification will lead to inactivation of the gene, resulting in d.

56
Q

A gene contains 6 exons (1, 2, 3, 4, 5a, 5 b). In the thyroid, mRNA has exons 1-4. In neural tissues, mRNA has exons 1, 2, 3, 5a, and 5b. What causes this?

a) Alternative splicing
b) Alternative Polydenylation
c) A & B
d) Neither A & B

A

a) Alternative splicing
b) Alternative Polydenylation
c) A & B

While the calcitonin gene in the thyroid is the prime example of alternative polyadenylation, the example given clearly shows that alternative splicing also occurred.

57
Q

Which of the following condition:platform is not a match?

a) Monogenic disease : Genotyping
b) Polygenic Disease: Genotyping
c) Epigenetic Disease: Sequencing
d) Presence of pathogen : Antibody-based detection

A

c) Epigenetic Disease: Sequencing

Sequencing cannot reveal epigenetic diseases since patterns of epigenetic control merely alter gene expression. They do not alter the gene sequence.

58
Q

Which of the following procedures is useful for both determining genomic variants and gene expression?

a) Genomic sequencing
b) Quantitative PCR
c) ELISA
d) Immunohistochemistry

A

b) Quantitative PCR

Quantitative PCR can identify and quantify gene sequences. The quantity of the gene can reveal clues about its expression (e.g. a sequence that is plentiful is actively transcribed and actively expressed).

59
Q

Which of the following diagnostics is most compliant with the World Health Organization’s criteria for diagnostics for pathogenic diseases, such as Ebola virus?

a) Quantiative PCR
b) Isothermal/LAMP
c) ELISA
d) Lateral flow assay

A

d) Lateral flow assay

The WHO criteria for diagnostics for pathogenic diseases address the following: being affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free and deliverable to end-users (ASSURED criteria). Quantitative PCR requires DNA extraction and equipment. While B is designed to be portable, LAMP requires the DNA/RNA to be exposed. DNA-based methods (A and B) would require extraction. C and D could employ the viral surface antigens, which could be detected by antigen-specific antibodies. The lateral flow assay however is more sensitive and specific because the sample is passed through pores where a control is included, and a specific capture molecule is included.

60
Q

What is the main advantage of sequencing over probe-based assays?

a) It is cheaper
b) It can detect previously unknown variants
c) It doesn’t require complex technical expertise
d) IT is more sensitive

A

b) It can detect previously unknown variants

Probe-based assays require the use of site-specific probes which are engineered based on known sites of attachment. These assays will therefore fail in determining previously unknown variants.

61
Q

A doctor referred you to a patient he suspects to have colon cancer. He is interested to know if the patient’s colon cancer cells are responsive to a type of chemotherapy that is dependent on the expression of specific cell membrane transporters. Which method is the most appropriate to use to rapidly answer his query?

a) Genomic Sequencing
b) Quantitative PCR
c) ELISA
d) Immunohistochemistry

A

d) Immunohistochemistry

Immunohistochemistry makes use of antibodies that may target these cell surface proteins.

62
Q

What is the true genomic/genetic sequencing?

a) Derived variants are typically not causative of disease they are associated with
b) It is more applicable to complex and quantitative traits than monogenic traits
c) It detects changes that mainly result to change in protein structure
d) It is getting more expensive as technology advances

A

a) Derived variants are typically not causative of disease they are associated with

Genetic variations may not guarantee the development of disease. Associations are not necessarily causations.

63
Q

You suspected that a blood-borne mutated protein is potentially useful in patients because it is associated with development of early heart attack. If you were to develop a test to identify susceptible individuals, which of the following platforms is most considered?

a) Genomic sequencing
b) Exomic sequencing
c) Targeted sequencing
d) Promotor region sequencing

A

c) Targeted sequencing

Targeted sequencing makes use of primers that are specific to the gene of interest (i.e. the protein of interest, the mutated protein). With this method, sequencing of the fragment flanked by designed primers will confirm whether the protein flanked by the primers is mutated or not.

64
Q

Which of the following is not true of quantitative PCR?

a) It can detect nucleic acids qualitatively and quantitatively.
b) It can differentiate gene variations, including deletions and insertions.
c) It can differentiate genotypes.
d) It can differentiate the relative quantity of translated proteins.

A

d) It can differentiate the relative quantity of translated proteins.

Quantitative PCR can detect the relative quantity of transcripts (i.e. RNA), however, this does not necessarily translate into proteins; the amount of RNA may not be reflective of the amount of proteins.

65
Q

Which of the following is typically true of probe-based tests?

a) In ELISA assays, antibodies can detect proteins, but not other antibodies.
b) In lateral flow assays, nucleic acids can be detected with nucleic acid probes.
c) In dipsticks, antibodies typically detect nucleic acids.
d) In immunohistochemistry, nucleic acids are used to detect antibodies.

A

a) In lateral flow assays, nucleic acids can be detected with nucleic acid probes.

In ELISA assays, secondary antibodies are not unusual. The primary antibody detects the protein of interest, while the secondary antibody detects the primary antibody. In dipsticks, the analytes usually detected by antibodies are protein, sugars, ketones, etc., not nucleic acids. In immunohistochemistry, antibodies are used to detect antigens, or vice versa.

66
Q

Which strategy is used to detect DNA methylation?

a) Treatment with bisulfite and subsequent probing
b) Generation and diagnosis using specific DNA primers
c) Generation and probing with specific antibodies
d) Sequencing of exons of genes of interest

A

a) Treatment with bisulfite and subsequent probing

Bisulfite treatment converts the unmethylated cytosine residues into uracil, but it does not affect the 5-methylcytosine of CpG islands. Comparison of sequencing before and after the conversion of unmethylated cytosines into uracil gives a clue as to the DNA methylation pattern.

67
Q

Which of the following is not useful in the determination of a genotype of an individual?

a) Quantitative PCR
b) Microarray
c) Genomic sequencing
d) Western blot

A

d) Western blot

Western blot visualizes proteins that have been separated by gel electrophoresis on a membrane blotted atop the gel. Antibodies are involved to capture the specific proteins of interest. This cannot be used to determine the genotype of an individual.

68
Q

As a biomedical scientist, you wanted to discover genetic and molecular changes associated with certain medical conditions. Which of the following is not true of the following approaches?

a) Next-generation sequencing offers the investigation of whole genomes and the discovery of novel genomic variants.
b) Microarray offers glimpses into gene expression changes and the discovery of potential molecular networks/pathways.
c) Immunochemistry offers the investigation of different cell types and the inference of protein pathways involved in a disease.
d) Mass spectrometer offers the investigation of protein sets and the discovery of protein signatures.

A

a) Immunochemistry offers the investigation of different cell types and the inference of protein pathways involved in a disease.
While immunochemistry can investigate different cell types, protein pathways involved in a disease may not be inferred from immunochemistry. Immunochemistry involves the application of the attractive binding of antibodies and their corresponding antigens (epitopes). Cell types may be differentiated where antibodies are specific to epitopes (cell surface receptors, e.g.) unique to a cell type. Protein pathways involved in a disease, on the other hand, may not be inferred from the application of antibody-antigen bindings.

69
Q

True of immunohistochemistry but not ELISA

a) Requires specific antibodies of detection of biomolecule
b) Requires detection method, usually (something that starts with C), fluorouracil, or electrochemical
c) Can localize signal to specific cell types
d) Usually quantitative for protein of interest

A

a) Can localize signal to specific cell types

ELISA cannot localize proteins to specific cell types since its sample preparation necessitates homogenization.

70
Q

Which is true of western blot?

a) It quantifies the expression of mRNA
b) It can localize the presence of a protein to a specific cell type
c) It does not require the use of probes
d) It requires the use of internal controls

A

d) It requires the use of internal controls

The western blot quantifies proteins, but cannot localize its presence (Immunohistochemistry does that). It requires antibody probes as well as internal controls of constitutively active genes.

71
Q

Which among the following is not involved in eukaryotic transcription?

a) TAFs
b) TATA-binding protein
c) RNA polymerase
d) RNA primer

A

d) RNA primer

RNA primers are involved in DNA replication.

72
Q

Which among the following RNAs is not involved in eukaryotic translation?

a) mRNA
b) rRNA
c) snRNA
d) tRNA

A

a) snRNA

snRNA is instead involved in splicing.

73
Q

Which of the following is unique to prokaryotic gene expression?

a) Polyribosomes can form during transcription
b) Splicing together exons in the polycistronic gene during transcription
c) Binding of a release factor to the ribosome when UAG codon enters the A site
d) Fmet-tRNA attaches to the large subunit of the ribosome prior to binding to small unit.

A

a) Polyribosomes can form during transcription

All others are characteristics of eukaryotic gene expression.

74
Q

What could be the anticodon segment for the tRNA from the first amino acid translation?

a) 5’ UAC 3’
b) 3’ UAC 5’
c) 5’ AUG 3’
d) 3’ AUG 3’

A

a) 3’ UAC 5’

The start codon reads 5’ AUG 3’ in the mRNA strand. This corresponds to b in the tRNA strand.

75
Q

Which is not true of RNA processing modification?

a) Excision of intron
b) Polyadenylation at 5’
c) Capping of 7-methylguanin
d) Branch site of intron at adenine

A

b) Polyadenylation at 5’

Polyadenylation occurs at the 3’ end.

76
Q

Which is not needed for eukaryotic basal transcription?

a) TATA box
b) RNA Polymerase
c) GC/CAAT box
d) Enhancer

A

d) Enhancer

The TATA box and GC/CAAT box are promoter regions that are needed to initiate transcription. RNA polymerase is needed to synthesize the mRNA transcript. Enhancers stimulate increased transcription, but are not required.

77
Q

Which of the following transcription factors is responsible for proper recognition of the promotor by the RNA Polymerase?

a) TFIID
b) SP1
c) TFIIA
d) TAF

A

a) TFIID

Transcription Factor (TF)
TFIID - recognizes TATA box
TFIIF - brings the polymerase to the promoter
TFIIH - meets DNA through its helicase activity and phosphorylates polymerase through its kinase activity to clear the promoter
Sp1 - recognizes GC box
CTF - recognizes CAAT box

78
Q

Where are amino acids attacked to in the tRNA

a) 5’ end
b) 3’ end

A

b) 3’ end

79
Q

How much energy is needed for attachment of one amino acid to the polypeptide during translation? (Assuming 1 ATP = 1 GTP)

a) 1 GTP
b) 2 GTP
c) 3 GTP
d) 4 GTP

A

c) 3 GTP

**Each cycle of elongation uses 1 GTP (incoming tRNA) + 1 ATP (pept. transf.) + 1 GTP (translocation), which are 4 high energy bonds.

80
Q

What is in the proteins synthesized in the rough endoplasmic reticulum that is not present in the proteins synthesized in the cytosol?

A

no choices

81
Q

What does mRNA 5’ AAUAA 3’ signal?

a) Polyadenylation
b) 5’ Exon-intron boundary
c) 3’ intron-exon boundary
d) 3’ cleavage site

A

d) 3’ cleavage site

The 5’ AAUAA 3’ site signals the terminal end of the mRNA strand post-transcriptionally.

82
Q

Not true of miRNA and siRINA

a) Involved in RNA degradation
b) Broken into segments by dicer
c) 5’ capping and 3’ polyadenylation
d) Associated with RISC

A

a) 5’ capping and 3’ polyadenylation

5’capping and 3’polyadenylation apply to mRNA.

83
Q

Which of the following describes the genetic code?

A

no choices

84
Q

Which of the following antibiotic prevents the attachment of the aminoacyl-tRNA to the mRNA-ribosome complex?

a) Tetracycline
b) Erythryomycin
c) Streptomycin
d) Chloramphericol

A

a) Tetracycline

Streptomycin changes the shape of the 30s ribosomal subunit causing mRNA to be read incorrectly. Tetracyclines interfere with tRNA attachment to the ribosome complex. Erythromycin binds to the 50s ribosomal subunit preventing translocation movement of ribosome along mRNA. Chloramphenicol binds to the 50s ribosomal subunit inhibiting peptide bond formation.

85
Q

Which of the following characteristics of autosomal dominant inheritance?

a) Male to female transmission occurs
b) Male to male transmission occurs
c) Males can have unaffected daughters.
d) AOTA
e) NOTA

A

a) Males can have unaffected daughters.
b) AOTA

Sex is irrelevant in autosomal mode of inheritance.

86
Q

Which of the following statements is true regarding the use of pedigree as a diagnostic tool?

a) It can establish the pattern of inheritance in a family.
b) It can explore the patient’s level of understanding of his/her disease
c) It helps in identifying at-risk family members
d) All are correct
e) All are incorrect

A

a) All are correct

Pedigree analysis can identify risk of heritable disorders.

87
Q

Which of the following does not show non-Mendelian pattern of inheritance?

a) Genomic Imprinting
b) Mitochondrial Disorders
c) Triplet repeat expansion disorders
d) All show
e) All do not show

A

a) All show

Be careful of semantics.

88
Q

Which of the following are not factors that increase risk for multifactorial diseases in relatives?

a) Low heritability of disorder
b) Proband of more rarely affected sex
c) Severe or early onset of disease in proband
d) AOTA
e) NOTA

A

a) Low heritability of disorder

Factors increasing risk to relatives:

  • close relationship to the proband
  • high heritability of the disorder
  • proband of more rarely affected sex. If rarely affected sex is affected, there is greater risk for the more affected sex.
  • severe of early onset of disease in proband (e.g. Hirschprung’s disease: long segment affected; higher risk for other family members)
  • multiple family members affected
89
Q

Which of the following does not confound recognition of patterns of inheritance?

a) Non-paternity
b) Sex-influenced/sex-linked gene expression
c) Small family size
d) AOTA
e) NOTA

A

e) NOTA

Confounding factors in recognizing patters of inheritance:

  • variable expressivity
  • clinical or genetic heterogeneity
  • sex-influenced/ limited gene expression
  • assortative mating (people tend to marry individuals who are physically similar to them)
  • small paternity size
  • information on unaffected relative is just as important as information on affected ones
  • non-paternity is probably the primary explanation for confusion in pedigree interpretation (assume there are no paternity issues but add a disclaimer)
90
Q

Which of the following is/are true of mitochondrial disorders?

a) Males and females are equally affected often in multiple generations
b) The father does not transmit the condition to his children
c) There is high variability in clinical expressivity
d) AOTA
e) NOTA

A

d) AOTA

Mitochondrial disorders follow maternal inheritance. The sex of offspring is irrelevant; what is relevant is if the mother possesses the abnormal mitochondrial genes. These disorders manifest in any symptom, any organ and any age.

91
Q

Which of the following is/are true regarding a multifactorial inheritance pattern?

A

no choices

92
Q

Which of the following is/are true in an x-linked recessive inheritance?

a) Carrier females have a 50% chance of having unaffected carrier daughters.
b) Heterozygous females can manifest the disorder.
c) The gene is never transmitted directly from father to son.
d) AOTA
e) NOTA

A

a) AOTA

Carrier females have a 50% chance of having unaffected daughters if the father is unaffected. Inactivation of an X chromosome in females is practically random, hence heterozygous females can manifest the disorder if it is the normal X chromosome that is inactivated. Fathers are only able to pass on their Y chromosome to their sons.

93
Q

Which of the following are characteristics of triplet repeat expansion disorders?

a) All affected members of a family share the same number of triplet repeat numbers.
b) An expansion of the triplet repeats can happen from one generation to the next.
c) Segments of DNA that contains a repeat of three nucleotides
d) AOTA
e) NOTA

A

a) An expansion of the triplet repeats can happen from one generation to the next.
b) Segments of DNA that contains a repeat of three nucleotides
c) AOTA

Triplet repeat disorders exhibit the phenomenon of anticipation since expansion of triplet repeats may occur from one generation to the next. By definition, triplet repeats are segments of DNA that contain repeats of three nucleotides. A is typically false but not always, so D is considered to recognize that B and C are true.

94
Q

Which of the following is/are true regarding x-linked dominant disorders?

a) Females usually express the condition
b) It is often lethal in males
c) There is male to male transmission
d) AOTA
e) A & C

A

a) It is often lethal in males
b) AOTA
c) A & C

X-linked dominant disorders are almost always expressed. It is often lethal in males since males do not have a back up of the genes responsible for the disorder. There is no male to male transmission since males pass on their Y chromosome to their male children.

95
Q

Angel, the obese 25 year old call center agent, went on the website ww.fathistory.com. On the website, it was claimed that she can have injections of a miracle drug which will make her thin in no time at all. You learn that this supposed miracle drug is recombinant human leptin. Which of the following is most likely to occur with exogenous administration of leptin?

a) Angel will continue to have the same amount of food but will start losing weight.
b) Angel will develop a strong drive to start an exercise regimen.
c) Angel will have no desire to eat her favorite foods.
d) Angel will start to have a higher basal metabolic rate.

A

c) Angel will have no desire to eat her favorite foods.

Ghrelin stimulates appetite while leptin decreases it.

96
Q

Which of the following does imprinting refer to?

a) A parent of origin effect in which modification of a gene allows it to be expressed differently.
b) Conditions such as Prader Willi Syndrome and Angelman Syndrome
c) Inactivation of the imprinted copy of the gene which prevents gene expression
d) AOTA
e) NOTA

A

a) AOTA

All of the above are true. Remember that Prader Willi syndrome arises when the q11 to q13 region of the paternal chromosome 15 is imprinted. Angelman syndrome arises when the maternal counterpart is imprinted.

97
Q

Which of the following statements is true about the “thrifty genotype” hypothesis?

a) The “thrifty genes” have been removed from the human genome by evolution because of the availability of food in modern times.
b) A century ago, according to this hypothesis, individuals with the “thrifty genes” had a better chance of surviving famines.
c) The “thrifty genes” are detrimental in modern times when an individual goes on a diet.
d) NOTA

A

b) A century ago, according to this hypothesis, individuals with the “thrifty genes” had a better chance of surviving famines.

98
Q

Which of the following statements about genograms is/are true?

a) Relationship line is horizontal
b) Sibship line is horizontal
c) Line of descent is vertical
d) AOTA
e) NOTA

A

d) AOTA

99
Q

Which is true?

a) Get 2 alleles of HGPRT2 from mother
b) Get 2 alleles of HGPRT2 from father
c) 2 alleles, one from each parent
d) Not all individuals have HPRT1 gene

A

c) 2 alleles, one from each parent

HGPRT gene is X-linked. You will receive one X from the mother, and another from the father (if you are female).

100
Q

Which of the following statements about autosomal recessive inheritance is correct?

a) Each offspring has a 50/50 chance of developing the disease if both parents have an abnormal allele.
b) Each offspring has a 1/4th chance of developing the disease of both parents have an abnormal allele.
c) Each offspring has a 50/50 chance of developing the disease if only the father is the carrier of the abnormal allele.
d) Each offspring has a 1/4th chance of developing the disease if only the mother is the carrier of the abnormal allele.

A

b) Each offspring has a 1/4th chance of developing the disease of both parents have an abnormal allele.
c) Each offspring has a 50/50 chance of developing the disease if only the father is the carrier of the abnormal allele.

Between a and b, b is true. Between c and d, c is true (the sex of the parent is irrelevant in autosomal mode of inheritance).

101
Q

Which of the following statements is incorrect?

a) Some mutations can lead to diseases.
b) Some mutations can lead to advantageous traits.
c) Some mutations have an effect on the ability to survive or adapt.
d) NOTA

A

d) NOTA

Mutations are often deleterious but are sometimes beneficial.

102
Q

Which of the following statements is not true regarding Lesch-Nyhan Syndrome?

a) Excess uric acid is detected in the blood and urine
b) The building blocks for purine and pyrimidine biosynthesis are affected
c) Females are affected more frequently than males
d) B and C

A

c) Females are affected more frequently than males

Lesch–Nyhan syndrome is associated with excess uric acid due to a mutation in the gene coding for hypoxanthine-guanine phosphoribosyltransferase, the enzyme responsible for purine salvage reactions. It is X-linked and therefore manifests more frequently in males.

103
Q

Which of the following is true?

a) Galactose rich diet can help prevent clinical manifestations of galactosemia.
b) Parents of an individual with galactosemia each carry one copy of a mutated GALT allele.
c) All children of a woman who is a carrier of a defective GALT allele will have galactosemia.
d) A & C

A

b) Parents of an individual with galactosemia each carry one copy of a mutated GALT allele.

Galactosemia is an autosomal recessive condition where galactose digestion is defective. Galactose rich diets will aggravate the condition. For the condition to manifest, an individual must have the allele from both parents.

104
Q

Which of the following statements about colorectal cancer is not true?

a) It is a single gene trait.
b) It is due to a defect in the proofreading ability of DNA polymerase.
c) It is both sporadic and inherited.
d) A & C

A

a) It is a single gene trait.

There are three types of colon cancer: sporadic, familial, and hereditary. Hereditary Non-Polyposis Colon Cancer is a type of colorectal cancer which involves a defective DNA polymerase proofreading ability (defective mismatch repair mechanism).

105
Q

Which of the following can be used for genetic screening?

a) Genes
b) Chromosomes
c) Proteins
d) AOTA
e) A & C

A

d) AOTA

Despite the name, genetic screening can make use of genes, chromosomes, as well as proteins.

106
Q

What is true of newborn screening?

a) NBS serves as treatment for infants with metabolic disorders
b) NBS allows for early detection of metabolic disorders
c) NBS allows for early intervention of affected infants
d) AOTA
e) B & C

A

b) NBS allows for early detection of metabolic disorders
c) NBS allows for early intervention of affected infants
e) B & C

While newborn screening serves to detect metabolic disorders and not treat them, early detection allows for early intervention (semantics).

107
Q

Which is not a component of NBS in the Philippines?

a) Galactosemia
b) Phenylketonuria
c) Alkaptonuria
d) G6PD Deficiency

A

c) Alkaptonuria

The following are the conditions tested in NBS in the Philippines:
Congenital Hypothyroidism (CH)
Congenital Adrenal Hyperplasia (CAH)
Galactosemia (GAL)
Phenylketonuria (PKU)
Glucose-6-Phosphate Dehydrogenase Deficiency (G6PD def)

OS 201 [2019 exams] (5 decks)

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