Nucleic Acids
What describes the complementary base pairing arrangement of a double-stranded helical polymer? A. 2 hydrogen bonds between 1 purine and 1 pyrimidine B. 2 hydrogen bonds between 2 purines C. 3 hydrogen bonds between 2 purines D. 3 hydrogen bonds between 2 pyrimidines
A. 2 hydrogen bonds between 1 purine and 1 pyrimidine Complementary base pairing describes the bonding between adenine and thymine or between cytosine and guanine. Adenine and thymine: a purine pairs with a pyrimidine with two hydrogen bonds. Cytosine and guanine: a pyrimidine pairs with a purine with three hydrogen bonds.
Two strands of DNA are arranged in an antiparallel fashion. What is positioned across from the 5' end of one strand? A. 3' end of the opposite strand B. 5' end of the opposite strand C. Major groove of the double helix D. Minor groove of the double helix
A. 3' end of the opposite strand The antiparallel arrangement of B-DNA dictates that the 5' end of one strand is positioned across from the 3' end of the opposite strand. The major and minor grooves of the double helix are the spaces between the two antiparallel strands. The major grove is where the spaces are furthest apart, and the minor groove is where the spaces are closer together. The antiparallel arrangement of DNA strands creates these grooves rather than occupying a position relative to the grooves.
What sequence of units marks the most common beginning of a protein sequence? A. AUG B. UAA C. UAG D. UGA
A. AUG AUG is the codon specifying for the amino acid methionine and for the start of a protein sequence. UAA, UAG, and UGA are stop codons. They specify the end of a protein sequence.
What process protects the 5' end of a newly formed mRNA molecule from degradation? A. Addition of 7-methylguanosine B. Addition of the poly-A-tail C. Splicing D. Ubiquitination
A. Addition of 7-methylguanosine The addition of 7-methylguanosine to the 5' end of a newly formed mRNA molecule protects it from exonuclease degradation as it travels from the nucleus to ribosomes. The addition of the poly-A-tail is also a protective modification, but it occurs at the 3' end of the molecule. Splicing is the process that removes introns, leaving exons. Ubiquitination is a modification process of proteins.
Which part of RNA polymerase contains N-terminal and C-terminal domains that recognize the UP-element on the DNA molecule? A. Alpha two B. Beta C. Omega D. Sigma factor
A. Alpha two Alpha one and alpha two are subunits of RNA polymerase. Both contain N-terminal and C-terminal domains. These domains recognize the UP-element on the DNA molecule. Beta prime and beta are subunits of RNA polymerase. Together they form the active site. Omega is the smallest subunit and acts as a chaperone for beta prime. Sigma factor is a specificity factor of bacterial RNA polymerase. The regions of this molecule interact with DNA and protein and enable the core to recognize the promoter.
Tumor suppressor genes utilize which of the following mechanisms to slow or prevent the development of cancer? A. Apoptosis B. Cell division C. Gene activation D. Mutation
A. Apoptosis Apoptosis (cell death) is necessary to keep cancer cells from dividing. Tumor suppressor genes limit cell division. They are involved in DNA repair from mutations. Most tumor suppressor genes are involved in gene inactivation, not gene activation.
Mutation of a regulatory sequence has occurred. Which type of sequence is most likely to be mutated if a failure to mobilize and modify nucleosomes occurs? A. Chromatin regulator B. Elongation factor C. microRNA D. Transfer RNA
A. Chromatin regulator During transcription, chromatin regulators mobilize and modify nucleosomes. Elongation factors are also involved in transcriptional regulation. They are recruited by transcription factors and they enable elongation to proceed. MicroRNA and transfer RNA are also regulatory sequences, but they function at the level of translation.
What type of event activates a protooncogene? A. Chromosomal rearrangement B. Epigenetic modification C. Gene deletion D. Translation
A. Chromosomal rearrangement Oncogenes can become activated by a mutation, chromosomal rearrangement, or gene duplication. A mutation can change the function of a gene. Chromosomal rearrangements can put one gene near another for activation. Gene duplication makes more copies of a gene and then a protein. Gene deletions typically decrease protein output. Translation is a natural part of converting mRNA to protein. Epigenetic modifications are usually involved in altering protein levels but not in activating oncogenes.
What binds to a double-stranded helical polymer and is crucial for its formation of higher-order structures, such as the solenoid and zigzag model? A. H1 B. H2 C. H3 D. H4
A. H1 DNA associates with proteins known as histones. H1 is the histone protein that binds to DNA adjacent to a nucleosome. H1 is necessary for formation of complicated structures, and it facilitates additional compaction. Nucleosomes are formed by an octamer of eight histones wrapped by DNA. H2A, H2B, H3, and H4 are the histone subunits that function to compose this octamer. Two of each are included in the octamer. H2A, H2B, H3, and H4 are the constituents of the octamer, but H1 is the histone essential for formation of the solenoid and zigzag model due to its ability to bind linker DNA.
The RAS genes are the most frequently mutated oncogenes observed in human cancer. RAS is part of the mitogen-activated protein kinase (MAPK) signaling pathway, and the downstream effects of MAPK signaling are cell cycle progression. RAS exists in a non-active form bound to GDP and an active form bound to GTP. The transition between RAS-GDP and RAS-GTP is regulated by guanine exchange factors and GTPase-activating proteins. A mutant RAS protein is identified as insensitive to cytosolic GAP. What effects will this mutant RAS protein have if left unchecked? A. Activate MAPK signaling and arrest the cell cycle B. Activate MAPK signaling and cause cell proliferation C. Inhibit MAPK signaling and cause apoptosis D. Inhibit MAPK signaling and inhibit angiogenesis
B. Activate MAPK signaling and cause cell proliferation Because it is insensitive to cytosolic GAP, this mutant RAS will activate MAPK signaling, not inhibit MAPK signaling. Because MAPK signaling encourages progression through the cell cycle, the downstream effect of this will be cell proliferation, not cell cycle arrest. Oncogenes frequently inhibit apoptosis rather than cause it, and they encourage angiogenesis rather than inhibiting it.
What does the transcription process produce? A. Antiparallel complementary DNA strand B. Antiparallel complementary RNA strand C. Parallel complementary DNA strand D. Parallel complementary RNA strand
B. Antiparallel complementary RNA strand The transcription process takes DNA and creates an antiparallel complementary RNA strand. The process always works in an antiparallel process where it reads in a 5' to 3' direction of the DNA. Transcription produces RNA strands, and translation produces protein from RNA.
Which subunit of this RNA polymerase has demonstrated mutations that account for rifamycin-resistant tuberculosis strains? A. Alpha B. Beta C. Omega D. Sigma
B. Beta Resistant tuberculosis strains are associated with mutations of the beta subunit of RNA polymerase, so research initiatives exist to develop new antibacterial therapeutics that bind to different sites. An antibacterial with an alpha, omega, or sigma binding site may prevent cross-resistance to rifamycins.
A molecule is composed of a five-carbon sugar, a phosphate group, and four different nitrogenous bases. How can the structure of a molecule composed through polymerization of these units be described for eukaryotes? A. Circular B. Condensed C. Fixed D. Relaxed
B. Condensed The structure of eukaryotic B-DNA becomes condensed and associated with various proteins as it organizes into chromosomes. Coiling and supercoiling allow an enormous amount of material to be packed into a nucleus—something that would be impossible if DNA were relaxed. Prokaryotes have circular chromosomes, while eukaryotes have linear chromosomes (though mtDNA is circular). The structure of DNA cannot be described as fixed because coiling, positive supercoiling, negative supercoiling, and separation are all events that routinely occur throughout the cell cycle to accommodate transcription and DNA replication.
What genome is organized in the nucleus? A. Chloroplast genome B. Eukaryotic genome C. Mitochondrial genome D. Prokaryotic genome
B. Eukaryotic genome The eukaryotic genome is organized in the nucleus. The chloroplast genome is organized in the chloroplast. The mitochondrial genome is organized in the mitochondria. Prokaryotes do not have nuclei. Their genome is found inside the nucleoid.
During what phase is a double-stranded helical polymer compacted with scaffolding proteins? A. Anaphase B. Interphase C. Metaphase D. Prophase
B. Interphase During interphase, organization and compaction of DNA are facilitated by scaffolding proteins. During phases of cell division such as anaphase, metaphase, and prophase, the organization of DNA is not facilitated by these proteins. DNA is condensed into chromosomes during cell division.
A cancer-associated variant has been discovered in a sequence of regulatory DNA. Which type of sequence is most likely to be mutated if abnormal silencing of tumor suppressors has occurred? A. Chromatin regulator B. Long non-coding RNA C. Mediator coactivator D. Transcription factor
B. Long non-coding RNA Mutations of long non-coding RNAs affect cancer progression through the abnormal silencing of tumor suppressors. Mutations of chromatin regulators are implicated in cancer through aberrant histone modification, defective nucleosome mobilization, defective gene silencing, aberrant gene activation, deregulation of HOX genes, and altered transcription elongation. Mutations of mediator coactivators are also implicated in cancer development through gene activation and repression, involving both transcription initiation and elongation. The majority of tumor cells utilize c-Myc (a transcription factor) for growth and proliferation. Overexpression of oncogenic transcription factors can result in tumor growth and proliferation.
Which type of mutation causes sickle cell disease? A. Frameshift B. Missense C. Nonsense D. Synonymous
B. Missense Missense mutations result in a substitution of one amino acid for another. Sickle cell anemia is caused by substitution of a single amino acid (out of 600 total). Valine is substituted for glutamic acid. This single substitution causes drastic consequences. Frameshift mutations result in a shift in the reading frame of a coding sequence. They can arise from insertion or deletion mutations. Ultimately, the code no longer specifies the correct amino acid sequence. Nonsense mutations result in a stop codon arising prematurely. Synonymous mutations (silent mutations) result in a change to the sequence of a nucleotide that may not produce a change to amino acids.
Which transcription factor has a TATA-binding protein? A. TFIIB B. TFIID C. TFIIE D. TFIIH
B. TFIID Transcription factors are required by RNA polymerase during eukaryotic transcription. They facilitate binding of RNAP to the promoter region. TFIID is the transcription factor with the TATA-binding protein. TFIIB determines the position of the start of transcription. TFIIE recruits TF-II H, which unwinds DNA at the transcription starting position.
How many units compose the groups that specify amino acids during the central dogma process? A. 1 B. 2 C. 3 D. 4
C. 3 The code of a gene is a combination based upon four nucleotides - adenine, guanine, cytosine, and thymine. These four units combine to form 64 sequence permutations, known as codons. Codons are composed of a three nucleotide combination. These 64 codons specify 20 amino acids.
How many hydrogen bonds are formed between guanine and another of the four bases in a polynucleotide molecule? A. 1 B. 2 C. 3 D. 4
C. 3 When cytosine and guanine pair, three hydrogen bonds are formed. When adenine and thymine pair, two hydrogen bonds are formed. Bonding between purines and pyrimidines does not typically occur via one or four hydrogen bonds.
Which part of RNA polymerase pairs with the beta subunit to form the active site? A. Alpha one B. Alpha two C. Beta prime D. Omega
C. Beta prime Beta prime and beta are subunits of RNA polymerase. Together they form the active site. Alpha one and alpha two are also subunits. Both contain N-terminal and C-terminal domains. Omega is the smallest subunit and acts as a chaperone for beta prime.
What is composed of two polynucleotide molecules intertwining? A. Amino acid B. Carbohydrate C. DNA D. Protein
C. DNA DNA is a double helix composed of two polynucleotide molecules. The polynucleotide molecules are composed of deoxyribose (a five-carbon sugar), a phosphate group, and four different nitrogenous bases. Amino acids are composed of an alpha carbon, a hydrogen, an amino group, a carboxyl group, and a specific side chain. Carbohydrates can be monosaccharides, disaccharides, oligosaccharides, or polysaccharides and are composed of carbon, hydrogen, and oxygen. Proteins are composed of amino acids and can have primary, secondary, tertiary, and quaternary structures.
HER2 is a well-known proto-oncogene. The HER2 gene encodes a tyrosine kinase receptor called human epidermal growth factor receptor 2 (HER2). HER2 has roles in cell growth and cell division, and HER2 overexpression has been reported in many types of human cancers. HER2 dimerization leads to autophosphorylation, which leads to the activation of HER2. Given this information, how might a laboratory target HER2 to develop a novel treatment for cancer? A. HER2 dimerization factor B. HER2 inducer C. HER2 inhibitor D. HER2 kinase
C. HER2 inhibitor HER2 inhibitors have been developed as effective cancer treatments, and new inhibitors continue to be developed. Because HER2 overexpression is involved in many types of human cancer, a HER2 inducer would not be an effective treatment. HER2 dimerization results in its autophosphorylation, so dimerization factors and a HER2 kinase would not be effective treatments.
What associates with a double-stranded helical polymer to facilitate compaction? A. Chromosome B. Gene C. Histome D. Nucleosome
C. Histome The human genome organization is facilitated by DNA associating with histones. DNA is compacted and coiled into chromosomes, of which there are 23 pairs. Genes are the units of DNA used to produce single proteins. An octamer of eight histone proteins is wrapped by DNA to form a nucleosome.
A cancer-associated variant has been discovered in a sequence of regulatory DNA. Which type of sequence is most likely to be mutated if activation and repression functions of a multi-subunit assembly operate during both initiation and elongation? A. Chromatin regulator B. Long non-coding RNA C. Mediator coactivator D. Transcription factor
C. Mediator coactivator Mutations of mediator coactivators are implicated in cancer development through gene activation and repression, involving both transcription initiation and elongation. The mediator complex is a multi-subunit assembly. Mutations of chromatin regulators are implicated in cancer through aberrant histone modification, defective nucleosome mobilization, defective gene silencing, aberrant gene activation, deregulation of HOX genes, and altered transcription elongation. Mutations of long non-coding RNAs affect cancer progression through the abnormal silencing of tumor suppressors. The majority of tumor cells utilize c-Myc (a transcription factor) for growth and proliferation. Overexpression of oncogenic transcription factors can result in tumor growth and proliferation.
Mutation of a regulatory sequence has occurred. Which type of sequence is most likely to be mutated if DNA methylation targeting has become aberrant? A. Cofactor B. Enhancer C. Non-coding RNA D. RNA polymerase
C. Non-coding RNA Non-coding RNAs interact with regulatory sequence regions, and their misregulation is implicated in disease. This group of molecules is large and heterogeneous. Some types of this group have demonstrated key roles in DNA methylation patterns. During formation of the pre-initiation complex, transcription factors bind to enhancers. They also bind to coactivators and RNA polymerase. Upon binding of general transcription factors, a DNA loop is formed between the start site and enhancer. Cofactors stabilize this loop. Mutations to any of these sequences may also result in disease.
What enzyme facilitates the three-step process that generates mRNA? A. DNA polymerase B. RNA polymerase I C. RNA polymerase II D. RNA polymerase III
C. RNA polymerase II RNA polymerase II is the enzyme that transcribes mRNA. DNA polymerase is the enzyme that carries out DNA replication. RNA polymerase I is the enzyme that transcribes rRNA. RNA polymerase III is the enzyme that transcribes tRNA.
What target might a researcher explore if they want to prevent release of RNA polymerase from a transcript? A. Alpha one B. Beta prime C. Rho D. Sigma
C. Rho Rho is a transcription protein that aids in transcription termination. During rho-dependent termination, the mRNA/RNA polymerase/template interaction is disrupted by rho. During rho-independent termination, a loop is formed on the mRNA, allowing RNA polymerase to dissociate. Alpha one and beta prime are subunits of RNA polymerase. They are not responsible for release during termination. Sigma factor is a specificity factor of bacterial RNA polymerase. The regions of this molecule interact with DNA and protein and enable the core to recognize the promoter.
Which of DNA bases can pair with adenine? A. Cytosine B. Guanine C. Thymine D. Uracil
C. Thymine DNA contains four nitrogenous bases: adenine, cytosine, thymine, and guanine. Adenine pairs with thymine. Cytosine pairs with guanine. Uracil is present in RNA, rather than DNA.
What replaces thymine when DNA is translated into RNA? A. Tryptophan B. Tyrosine C. Uracil D. Valine
C. Uracil Uracil replaces thymine when DNA is translated to RNA. Tryptophan, tyrosine, and valine are amino acids. They are not substituted for bases.
How many different base pairs have the potential to form a codon during the central dogma process? A. 1 B. 2 C. 3 D. 4
D. 4 The code of a gene is a combination based on four nucleotides: adenine, guanine, cytosine, and thymine. These four units combine to form 64 sequence permutations (three nucleotide combination). These 64 codons specify 20 amino acids.
How many sequence permutations are formed due to the degeneracy of the central dogma process? A. 3 B. 4 C. 20 D. 64
D. 64 The code of a gene is a combination based on four nucleotides: adenine, guanine, cytosine, and thymine. These four units combine to form 64 sequence permutations, known as codons. Codons are composed of a three nucleotide combination. These 64 codons specify 20 amino acids.
What codon is responsible for starting the process of translation? A. AAG B. ACG C. AGG D. AUG
D. AUG The start codon in translation is AUG. It encodes for the amino acid methionine. AAG encodes for the amino acid lysine. ACG encodes for the amino acid threonine. AGG encodes for the amino acid arginine.
What basic unit, composed by a double-stranded helical polymer and its associated proteins, forms chromatin? A. Chromosome B. Gene C. Histone D. Nucleosome
D. Nucleosome Genes are the units of DNA used to produce single proteins. DNA contains more information than just genes. All of this information is compacted and coiled into a chromosome. This organization is facilitated by DNA associating with histones. An octamer of eight histone proteins is wrapped by DNA to form a nucleosome, the single unit of chromatin.
Which structure of RNA polymerase is prevented from forming when fidaxomicin is administered for a Clostridium difficile infection? A. Closed complex B. Holoenzyme C. Initiating abortive D. Open complex
D. Open complex Fidaxomicin is an antibiotic that binds to the closed complex of RNA polymerase, which prevents formation of the open complex. The holoenzyme is formed by a combination of RNA polymerase and the sigma factor. Initiating abortives are very short RNA products that are produced and released as non-functional.
What enzyme facilitates the three-step process that generates tRNA? A. DNA polymerase B. RNA polymerase I C. RNA polymerase II D. RNA polymerase III
D. RNA polymerase III RNA polymerase III is the enzyme that transcribes tRNA. DNA polymerase is the enzyme that carries out DNA replication. RNA polymerase I is the enzyme that transcribes rRNA. RNA polymerase II is the enzyme that transcribes mRNA.
How do tumor suppressor genes contribute to a reduction in cancer? A. Create more healthy cells B. Increase cell cycle progression C. Modify cell structure D. Stop cell cycle progression
D. Stop cell cycle progression Tumor suppressor genes are responsible for stopping cell cycle progression in cancerous cells. Mutated tumor suppressor genes may increase cell cycle progression. Tumor suppressor genes are not responsible for creating more healthy cells necessarily, but they can use DNA repair mechanisms to repair a cancerous cell. Modifications of cell structure are not due to tumor suppressor genes.
A molecule enables RNA polymerase to bind to eukaryotic DNA. Where does this binding occur? A. 5' cap B. Polyadenylation signal C. Ribosome D. TATA box
D. TATA box Eukaryotic mRNA precursors are produced during transcription. The TATA box is a promoter sequence that specifies the location of the beginning of transcription. After being transcribed, mRNA must undergo processing before translation. During this process, transcription machinery encounters a polyadenylation signal that indicates termination. A 5' cap is added as a protective modification to newly formed mRNA. The addition of 7-methylguanosine to the 5' end protects it from exonuclease degradation as it travels from the nucleus to ribosomes, where translation occurs.
What must regulatory elements bind to for transcription to occur in eukaryotic cells? A. Homeobox genes B. Homeodomains C. Promoter D. TATA box
D. TATA box The TATA box is where regulatory elements must bind to start the transcription process. Homeobox genes are important for regulating development. Homeobox genes create homeodomains, which are transcription factors responsible for the activities of other genes. Regulatory elements bind to the TATA box, then RNA polymerase can bind to the promoter region and start transcription.
A cancer-associated variant has been discovered in a sequence of regulatory DNA. Which type of sequence is most likely to be mutated if it recruits RNA polymerase? A. Chromatin regulator B. Cofactor C. microRNA D. Transcription factor
D. Transcription factor Certain transcription factors affect gene expression by recruiting RNA polymerase. Mutation to these transcription factors can lead to disease. Mutations of chromatin regulators are also implicated in cancer through aberrant histone modification, defective nucleosome mobilization, defective gene silencing, aberrant gene activation, deregulation of HOX genes, and altered transcription elongation. During formation of the pre-initiation complex, transcription factors bind to enhancers. They also bind to coactivators and RNA polymerase. Upon binding of general transcription factors, a DNA loop is formed between the start site and enhancer. Cofactors stabilize this loop. Cohesin cofactors are an example; there are phenotypic consequences of cohesin complex mutations. When a microRNA is altered, it can also be implicated in disease, but this occurs at the level of translation.
What process involves the entire protooncogene jumping from one position to another in the genome under the control of promoter? A. Transfection B. Transformation C. Translation D. Translocation
D. Translocation Genetic translocation is the process of exchange of genetic material between chromosomes in the genome. Transfection is the process of deliberately introducing naked or purified nucleic acids into eukaryotic cells. Transformation is one of three processes for horizontal gene transfer, in which exogenous genetic material passes from one bacterium to another. Translation refers to the process of creating proteins from an mRNA template. The sequence of nucleotides on the RNA is translated into the amino acid sequence of proteins; this reaction is carried out by ribosomes.
