Midterm 2 Chee 370

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Midterm Biology Quizzes & Trivia

Questions and Answers
  • 1. 

    What term would be applied to a regulatory condition that occurs when protein is associated with a particular section of DNA and greatly reduces transcription?

    • A.

      Induction

    • B.

      Activation

    • C.

      Negative control

    • D.

      Positive control

    • E.

      Stimulation

    Correct Answer
    C. Negative control
    Explanation
    A regulatory condition that occurs when protein is associated with a particular section of DNA and greatly reduces transcription is known as negative control. In this scenario, the protein acts as a repressor, inhibiting the transcription process and reducing the expression of the associated gene. This negative control mechanism helps regulate gene expression and can be crucial for maintaining proper cellular function and homeostasis.

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  • 2. 

    Secondary metabolites appear during which of the following stages?

    • A.

      At, near, or in the lag phase

    • B.

      At, near, or in the stationary phase

    • C.

      At, near, or in the exponential phase

    • D.

      At, near, or in the death phase

    Correct Answer
    B. At, near, or in the stationary phase
    Explanation
    Secondary metabolites are chemical compounds produced by organisms that are not directly involved in growth or reproduction. These metabolites often have important ecological functions, such as defense against predators or competition for resources. The stationary phase of microbial growth occurs when the rate of cell division equals the rate of cell death, resulting in a stable population size. It is during this phase that secondary metabolites are typically produced. Therefore, secondary metabolites appear at, near, or in the stationary phase.

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  • 3. 

    DNA moves within an electric field because it

    • A.

      Is positively charged

    • B.

      Is negatively charged

    • C.

      Makes up chromosomes, which are slightly electromagnetic

    • D.

      Can possess different charges (positive or negative) depending on its base sequence

    Correct Answer
    B. Is negatively charged
    Explanation
    DNA moves within an electric field because it is negatively charged. DNA is composed of phosphate groups, which have a negative charge. When placed in an electric field, the negatively charged DNA molecules are attracted towards the positive electrode and move towards it. This phenomenon is known as electrophoresis and is commonly used in laboratories to separate and analyze DNA fragments based on their size and charge.

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  • 4. 

    Which of the following is NOT a means of regulating gene expression?

    • A.

      Modifying proteins after they are synthesized

    • B.

      Varying the rate at which messenger RNAs are transcribed

    • C.

      Varying the rate at which messenger RNAs are translated

    • D.

      Deleting genes from cells in which they are not needed

    • E.

      Regulating the life span of a protein

    Correct Answer
    D. Deleting genes from cells in which they are not needed
    Explanation
    Deleting genes from cells in which they are not needed is not a means of regulating gene expression because once a gene is deleted, it is permanently removed from the genome and cannot be expressed or regulated further. Gene regulation typically involves controlling the activity or expression of existing genes rather than removing them entirely. This can be done through various mechanisms such as modifying proteins after synthesis, regulating transcription and translation rates, and controlling the lifespan of proteins.

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  • 5. 

    Dideoxyribonucleotides (ddNTPs) used for DNA sequencing lack oxygen atoms at

    • A.

      The 1' carbon of the pentose sugar

    • B.

      The 3' and 5' carbons of the pentose sugar

    • C.

      The 2' and 3' carbons of the pentose sugar

    • D.

      The 1' and 2' carbons of the pentose sugar

    • E.

      The 5' carbon of the pentose sugar

    Correct Answer
    C. The 2' and 3' carbons of the pentose sugar
    Explanation
    Dideoxyribonucleotides (ddNTPs) used for DNA sequencing lack oxygen atoms at the 2' and 3' carbons of the pentose sugar. This is important because the presence of oxygen at these positions is necessary for the formation of a phosphodiester bond, which links nucleotides together in a DNA strand. By removing the oxygen atoms at the 2' and 3' carbons, ddNTPs prevent further nucleotide addition during DNA synthesis, allowing for the identification of the specific nucleotide at that position in the DNA sequence.

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  • 6. 

    Which of the following best describes siRNA?

    • A.

      A double-stranded RNA that is formed by cleavage of hairpin loops in a larger precursor

    • B.

      A molecule, known as Dicer, that can degrade other mRNA sequences

    • C.

      A portion of rRNA that allows it to bind to several ribosomal proteins in forming large or small subunits

    • D.

      A short double-stranded RNA, one of whose strands can complement and inactivate a sequence of mRNA

    • E.

      A single-stranded RNA that can, where it has internal complementary base pairs, fold into cloverleaf patterns

    Correct Answer
    D. A short double-stranded RNA, one of whose strands can complement and inactivate a sequence of mRNA
    Explanation
    siRNA is a short double-stranded RNA that can complement and inactivate a sequence of mRNA. It is formed by cleavage of hairpin loops in a larger precursor. This double-stranded RNA can bind to mRNA and prevent its translation into protein, leading to gene silencing. siRNA is an important tool used in gene regulation and has applications in research and therapeutics.

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  • 7. 

    The reason for using Taq polymerase for PCR is that

    • A.

      Only minute amounts are needed for each cycle of PCR

    • B.

      It has regions that are complementary to primers

    • C.

      It is heat stable and can withstand the temperature changes of the cycler

    • D.

      It binds more readily than other polymerases to primer

    • E.

      All of these are correct

    Correct Answer
    C. It is heat stable and can withstand the temperature changes of the cycler
    Explanation
    Taq polymerase is commonly used in PCR because it is heat stable and can withstand the temperature changes during the PCR cycles. PCR involves repeated cycles of heating and cooling, and the high temperatures required to denature the DNA would normally inactivate most enzymes. However, Taq polymerase, derived from Thermus aquaticus bacteria, is able to withstand these temperature changes and remain active throughout the PCR process. This makes it an ideal choice for PCR, as it allows for efficient amplification of DNA without the need to add fresh enzyme after each cycle.

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  • 8. 

    Yeast artificial chromosomes contain which of the following elements?

    • A.

      Origin of replication only

    • B.

      Centromeres and telomeres only

    • C.

      Centromeres, telomeres, and an origin of replication

    • D.

      Telomeres only

    Correct Answer
    C. Centromeres, telomeres, and an origin of replication
    Explanation
    Yeast artificial chromosomes (YACs) are used to clone large fragments of DNA in yeast cells. They are designed to mimic the structure and behavior of natural chromosomes. In order to function properly, YACs must contain certain elements. Centromeres are necessary for proper segregation of the chromosome during cell division. Telomeres are required to protect the ends of the chromosome from degradation. An origin of replication is essential for DNA replication to occur. Therefore, the correct answer is centromeres, telomeres, and an origin of replication.

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  • 9. 

    Some vectors such as pUC18 and others of the pUC series contain a large number of restriction enzyme sites clustered in one region. What term is given to this advantageous arrangement of restriction sites?

    • A.

      Palindrome

    • B.

      Complementation

    • C.

      Consensus sequence

    • D.

      Polylinker

    • E.

      B-galatosidase

    Correct Answer
    D. Polylinker
    Explanation
    A polylinker, also known as a multiple cloning site (MCS), is a DNA sequence that contains multiple unique restriction enzyme recognition sites. These sites allow for the insertion of DNA fragments into the vector at different locations, providing flexibility in the cloning process. In the case of vectors like pUC18, the advantageous arrangement of restriction enzyme sites in a polylinker region simplifies the cloning process by providing a variety of options for inserting DNA fragments.

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  • 10. 

    A metabolite excreted by a microorganism during exponential growth is called 

    • A.

      Primary metabolite

    • B.

      Immobilized enzyme

    • C.

      Secondary metabolite

    • D.

      Exoenzyme

    Correct Answer
    A. Primary metabolite
    Explanation
    During exponential growth, microorganisms produce primary metabolites. These are essential compounds involved in basic cellular functions such as growth, reproduction, and energy production. Primary metabolites are synthesized in large quantities and are necessary for the survival of the microorganism. In contrast, secondary metabolites are produced during the stationary phase and are not essential for growth but often have important ecological roles, such as antibiotic production. Immobilized enzyme refers to the technique of immobilizing enzymes for industrial applications, while exoenzyme refers to an enzyme that is secreted by a microorganism to break down external substances.

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  • 11. 

    Which pair of enzymes is necessary to make recombinant DNA?

    • A.

      Ligase and restriction enzyme

    • B.

      DNA polymerase and RNA polymerase

    • C.

      DNA polymerase and ligase

    • D.

      Restriction enzyme and DNA polymerase

    Correct Answer
    A. Ligase and restriction enzyme
    Explanation
    Ligase and restriction enzyme are necessary to make recombinant DNA. Ligase is responsible for joining DNA fragments together, while restriction enzymes cut DNA at specific sequences. By using these two enzymes together, DNA fragments can be cut and then recombined to create recombinant DNA molecules. DNA polymerase and RNA polymerase are not directly involved in the process of making recombinant DNA.

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  • 12. 

    Type II restriction endonucleases

    • A.

      Natively function to methylate specific nucleotides and prevent foreign DNA from being incorporated into the genome

    • B.

      Recognize nucleotide sequences that are palindromic

    • C.

      Are heterodimers

    • D.

      Require ATP energy to cleave dsDNA

    Correct Answer
    B. Recognize nucleotide sequences that are palindromic
    Explanation
    Type II restriction endonucleases recognize nucleotide sequences that are palindromic. Palindromic sequences are DNA sequences that read the same on both strands when the orientation is reversed. These enzymes bind to these palindromic sequences and cleave the DNA at specific sites, leading to the formation of double-stranded breaks. This recognition of palindromic sequences allows Type II restriction endonucleases to accurately target and cleave specific DNA sequences, making them important tools in molecular biology for DNA manipulation and genetic engineering.

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  • 13. 

    The promoters of positively controlled operons require activator proteins, because

    • A.

      RNA polymerase easily recognizes the consensus sequence

    • B.

      They are needed to bind to the allosteric site of RNA polymerase

    • C.

      They are required to inactivate the repressor proteins

    • D.

      The promoters have nucleotide sequences that bind RNA polymerase weakly, which are not close matches to the consensus sequence

    Correct Answer
    D. The promoters have nucleotide sequences that bind RNA polymerase weakly, which are not close matches to the consensus sequence
    Explanation
    The promoters of positively controlled operons require activator proteins because the promoters have nucleotide sequences that bind RNA polymerase weakly, which are not close matches to the consensus sequence. Activator proteins help enhance the binding of RNA polymerase to the promoter region by interacting with both the weak binding site on the promoter and the RNA polymerase itself. This interaction facilitates the recruitment and positioning of RNA polymerase at the promoter, leading to efficient transcription initiation. Without the activator proteins, the weak binding of RNA polymerase to the promoter would result in low transcription levels.

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  • 14. 

    Suppose ENZ-1 and ENZ-2 are two different restriction enzymes. If various pieces of DNA from different species are cut with these enzymes (as follows), which would most easily form recombinant molecules?

    • A.

      Human DNA cut with ENZ-1 and gorilla DNA cut with ENZ-2

    • B.

      Human DNA cut with ENZ-1 and human DNA cut with ENZ-2

    • C.

      Bacterial DNA cut with ENZ-1 and gorilla DNA cut with ENZ-2

    • D.

      Human DNA cut with ENZ-2 and bacterial DNA cut with ENZ-2

    Correct Answer
    D. Human DNA cut with ENZ-2 and bacterial DNA cut with ENZ-2
    Explanation
    u gotta use the same enzymes

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  • 15. 

    In biotechnology research, DNA fragments created by restriction enzyme action are separated from one another via

    • A.

      Centrifugation

    • B.

      Crossing over

    • C.

      The polymerase chain reaction

    • D.

      Gel electrophoresis

    • E.

      Filtering

    Correct Answer
    D. Gel electrophoresis
    Explanation
    Gel electrophoresis is a technique commonly used in biotechnology research to separate DNA fragments based on their size and charge. It involves placing the DNA fragments in a gel matrix and applying an electric field. Since DNA is negatively charged, it moves towards the positive electrode. Smaller fragments move faster and travel further through the gel, while larger fragments move slower and remain closer to the starting point. This separation allows researchers to analyze and study the DNA fragments further. Therefore, gel electrophoresis is the most appropriate method for separating DNA fragments created by restriction enzyme action.

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  • 16. 

    Genomic imprinting, DNA methylation, and histone acetylation are all examples of

    • A.

      Karyotypes

    • B.

      Chromosomal rearrangements

    • C.

      Epigenetic phenomena

    • D.

      Genetic mutation

    • E.

      Translocation

    Correct Answer
    C. Epigenetic phenomena
    Explanation
    epigenetics is the study of heritable changes in gene activity which are not caused by changes in the DNA sequence

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  • 17. 

    Which of the following is the correct sequence of the polymerase chain reaction?

    • A.

      Heat to 90 celsius (to bind primers and enzymes), then cool to 50 celsius (to separate DNA), then reheat to 70 celsius (to synthesize DNA)

    • B.

      Heat to 70 celsius (to bind primers and enzymes), then cool to 50 celsius (to synthesize DNA), then reheat to 90 celsius (to separate DNA)

    • C.

      Heat to 90 celsius (to separate DNA), then cool to 50 celsius (to bind primers and enzymes), then reheat to 70 celsius (to synthesize DNA)

    • D.

      Heat to 70 celsius (to separate DNA), then cool to 50 celsius (to bind primers and enzymes), then reheat to 90 celsius (to synthesize DNA)

    Correct Answer
    C. Heat to 90 celsius (to separate DNA), then cool to 50 celsius (to bind primers and enzymes), then reheat to 70 celsius (to synthesize DNA)
    Explanation
    denaturing ~94 celsius
    annealing ~30-65 celsius
    polymerization/elongation ~ 65-75 celsius

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  • 18. 

    A ______ consists of cloned DNA fragments for all expressed genes in a particular tissue. 

    • A.

      PCR library

    • B.

      Shotgun library

    • C.

      Guggenheim library

    • D.

      Genomic DNA library

    • E.

      CDNA library

    Correct Answer
    E. CDNA library
    Explanation
    A cDNA library is a collection of cloned DNA fragments that represent all the expressed genes in a specific tissue. This library is created by converting the messenger RNA (mRNA) molecules into complementary DNA (cDNA) molecules using the enzyme reverse transcriptase. The cDNA library provides a snapshot of the genes that are actively being transcribed and expressed in the tissue, allowing researchers to study gene expression patterns and identify specific genes of interest.

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  • 19. 

    A _______ is a single-stranded DNA molecule attached to a radioactive or fluorescent compound that is complementary to a specific sequence of DNA. Such pieces of DNA are used to identify and study cloned genes in hybridization experiments. 

    • A.

      Probe

    • B.

      Vector

    • C.

      Promoter

    • D.

      Polypeptide

    • E.

      Plasmid

    Correct Answer
    A. Probe
    Explanation
    A probe is a single-stranded DNA molecule attached to a radioactive or fluorescent compound that is complementary to a specific sequence of DNA. Probes are used in hybridization experiments to identify and study cloned genes. They bind to the target DNA sequence and allow researchers to visualize and locate specific genes or sequences of interest.

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  • 20. 

    Which of the following does not apply to eukaryotic gene regulation?

    • A.

      Regulation as a result of compartmentalization

    • B.

      Protein degradation (turnover)

    • C.

      Gene regulation by attenuation

    • D.

      Protein folding

    • E.

      MRNA degradation (turnover)

    Correct Answer
    C. Gene regulation by attenuation
    Explanation
    Attenuation (in genetics) is a proposed mechanism of control in some bacterial operons which results in premature termination of transcription and which is based on the fact that, in bacteria, transcription and translation proceed simultaneously

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  • 21. 

    A student wishes to clone a sequence of DNA of ~200 kb. Which vector would be appropriate?

    • A.

      A large polypeptide

    • B.

      A plant virus

    • C.

      A plasmid

    • D.

      A typical bacteriophage

    • E.

      A BAC

    Correct Answer
    E. A BAC
    Explanation
    BAC can carry up to 500 kb

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  • 22. 

    When making a complementary DNA (cDNA) library, which enzyme is used to copy mRNA into DNA?

    • A.

      RNA polymerase

    • B.

      Primase

    • C.

      Reverse transcriptase

    • D.

      DNA polymerase

    • E.

      DNA ligase

    Correct Answer
    C. Reverse transcriptase
    Explanation
    Reverse transcriptase is the enzyme used to copy mRNA into DNA when making a complementary DNA (cDNA) library. This enzyme is capable of synthesizing a complementary DNA strand from an RNA template, allowing for the conversion of mRNA into DNA. It is commonly used in molecular biology techniques such as cDNA synthesis and gene expression analysis. RNA polymerase, primase, DNA polymerase, and DNA ligase are not involved in the process of copying mRNA into DNA.

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  • 23. 

    A mutation that inactivates the regulatory gene of a repressible operon in an E. coli cell would result in

    • A.

      Continuous translation of the mRNA because of alteration of its structure

    • B.

      Irreversible binding of the repressor to the operator

    • C.

      Continuous transcription of the structural gene controlled by that regulator

    • D.

      Complete inhibition of transcription of the structural gene controlled by that regulator

    • E.

      Inactivation of RNA polymerase by alteration of its active site

    Correct Answer
    C. Continuous transcription of the structural gene controlled by that regulator
    Explanation
    A mutation that inactivates the regulatory gene of a repressible operon in an E. coli cell would result in continuous transcription of the structural gene controlled by that regulator. This is because the regulatory gene produces a repressor protein that normally binds to the operator region of the operon, preventing transcription of the structural gene. If the regulatory gene is inactivated, the repressor protein cannot be produced, leading to the continuous transcription of the structural gene.

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  • 24. 

    During DNA replication,

    • A.

      Methylated DNA is copied in the cytoplasm, and unmethylated DNA is copied in the nucleus

    • B.

      Methylation of the DNA is maintained because DNA polymerase directly incorporates methylated nucleotides into the new strand opposite any methylated nucleotides in the template

    • C.

      DNA polymerase is blocked by methyl groups, and methylated regions of the genome are therefore left uncopied

    • D.

      All methylation of the DNA is lost at the first round of replication

    • E.

      Methylation of the DNA is maintained because methylation enzymes act at DNA sites where one strand is already methylated and thus correctly methylates daughter strands after replication

    Correct Answer
    E. Methylation of the DNA is maintained because methylation enzymes act at DNA sites where one strand is already methylated and thus correctly methylates daughter strands after replication
    Explanation
    Methylation of the DNA is maintained because methylation enzymes act at DNA sites where one strand is already methylated and thus correctly methylates daughter strands after replication. This means that during DNA replication, the methylation pattern is faithfully copied onto the newly synthesized DNA strands. Methylation enzymes recognize and methylate DNA sites that are already methylated on one strand, ensuring that the daughter strands are also methylated in the same pattern. This process helps to maintain the epigenetic information encoded in DNA methylation, which is important for gene regulation and cellular identity.

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  • 25. 

    Attenuation occurs in the biosynthetic pathway for phenylalanine in E. coli. Therefore, the leader sequence for this pathway will be rich in which of the following?

    • A.

      Threonine

    • B.

      Phenylalanine

    • C.

      Histidine

    • D.

      Isoleucine

    Correct Answer
    B. Phenylalanine
    Explanation
    The leader sequence for the biosynthetic pathway for phenylalanine in E. coli will be rich in phenylalanine because attenuation occurs in this pathway. Attenuation is a regulatory mechanism that occurs in bacterial operons, where the synthesis of a protein is controlled by the presence or absence of a specific metabolite. In the case of the phenylalanine biosynthetic pathway, the leader sequence will have a high concentration of phenylalanine to regulate the expression of the genes involved in the pathway.

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  • 26. 

    You are studying a biochemical pathway. Preliminary results suggest that this pathway is subject to end-product repression. This pathway is therefore most likely to be a(n) _____ pathway

    • A.

      Constitutive

    • B.

      Anabolic

    • C.

      Induced

    • D.

      Catabolic

    • E.

      Unregulated

    Correct Answer
    B. Anabolic
    Explanation
    Based on the preliminary results suggesting end-product repression, it can be inferred that this pathway is regulated in response to the presence of its end product. Anabolic pathways involve the synthesis of complex molecules from simpler ones, and the regulation of such pathways is important to prevent the overproduction of end products. Therefore, the most likely explanation is that this pathway is an anabolic pathway, which is subject to end-product repression to maintain homeostasis.

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  • 27. 

    In positive control of several sugar-metabolism-related operons, the catabolite activator protein (CAP) binds to DNA to stimulate transcription. What causes an increase in CAP?

    • A.

      Decrease in glucose and increase in cAMP

    • B.

      Increase in glucose and increase in cAMP

    • C.

      Increase in glucose and decrease in cAMP

    • D.

      Decrease in glucose and increase in repressor

    • E.

      Decrease in glucose and decrease in repressor

    Correct Answer
    A. Decrease in glucose and increase in cAMP
    Explanation
    An increase in cAMP and a decrease in glucose levels cause an increase in the catabolite activator protein (CAP). CAP binds to DNA and stimulates transcription of sugar-metabolism-related operons. When glucose levels are low, cAMP levels increase, which leads to the binding of CAP to DNA and the activation of transcription. This mechanism allows the cell to respond to low glucose levels and activate the expression of genes involved in sugar metabolism. The decrease in glucose and increase in cAMP work together to regulate the activity of CAP.

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  • 28. 

    DNA methylation may be a significant mode of genetic regulation in eukaryotes. Methylation refers to:

    • A.

      Altering RNA polymerase activity by methylation

    • B.

      Changes in DNA-DNA hydrogen binding

    • C.

      Addition of methyl groups to the cytosine of CG doublets

    • D.

      Altering translational activity, especially of highly methylated tRNAs

    • E.

      Alteration of DNA polymerase activity by addition of methyl groups to glycine residues

    Correct Answer
    C. Addition of methyl groups to the cytosine of CG doublets
    Explanation
    DNA methylation refers to the addition of methyl groups to the cytosine of CG doublets. Methylation of DNA plays a significant role in genetic regulation in eukaryotes. It can affect gene expression by influencing the binding of transcription factors and other regulatory proteins to DNA. Methylation patterns can be heritable and can impact various cellular processes such as development, differentiation, and disease. Therefore, the addition of methyl groups to the cytosine of CG doublets is a crucial mechanism for genetic regulation in eukaryotes.

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  • 29. 

    When arginine is added to a culture growing exponentially in a medium without arginine, what occurs?

    • A.

      All cellular growth ceases

    • B.

      Growth continues, but the production of enzymes required for the synthesis of arginine increases

    • C.

      Growth continues, but the production of enzymes required for the synthesis of arginine ceases

    • D.

      The cell returns to the lag stage of growth to synthesize the proteins necessary for the metabolism of arginine.

    Correct Answer
    C. Growth continues, but the production of enzymes required for the synthesis of arginine ceases
    Explanation
    When arginine is added to a culture growing exponentially in a medium without arginine, the growth of the cells continues. However, the production of enzymes required for the synthesis of arginine ceases. This means that the cells are no longer able to produce arginine on their own and rely on the externally added arginine for their growth.

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  • 30. 

    Assume that a circular plasmid is 3200 base pairs in length and has restriction sites at the following locations: 400, 700, 1400, 2600. Give the expected sizes of the restriction fragments following complete digestion.

    • A.

      300, 700, 2200

    • B.

      400, 1200, 1600

    • C.

      700, 400, 1400, 2600

    • D.

      400, 800, 1000 (two of these)

    • E.

      300, 700, 1000, 1200

    Correct Answer
    E. 300, 700, 1000, 1200
    Explanation
    The given answer is the expected sizes of the restriction fragments following complete digestion of the circular plasmid. The restriction sites indicate where the plasmid will be cut by restriction enzymes. The expected sizes of the fragments are determined by the distance between adjacent restriction sites. In this case, the plasmid will be cut at the following locations: 400, 700, 1400, and 2600. The expected sizes of the fragments are then calculated as the distance between these sites: 400-0=400, 700-400=300, 1400-700=700, and 3200-2600=600. Therefore, the expected sizes of the restriction fragments are 300, 700, 1000, and 1200.

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  • 31. 

    Specific fragments of DNA on a gel can be visualized using

    • A.

      Electrophoresis

    • B.

      A polymerase chain reaction (PCR)

    • C.

      Single tandem repeats

    • D.

      DNA probes

    • E.

      Restriction enzymes

    Correct Answer
    D. DNA probes
    Explanation
    DNA probes are small fragments of DNA that are labeled with a fluorescent or radioactive tag. These probes are complementary to specific DNA sequences and can bind to these sequences on the gel. When the gel is exposed to a UV light or X-ray film, the labeled probes emit a signal, allowing the visualization of the specific DNA fragments on the gel. Therefore, DNA probes can be used to identify and locate specific fragments of DNA on a gel.

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  • 32. 

    What occurs when an inducer is added to an environment containing an organism with a metabolic pathway controlled by a repressor?

    • A.

      The inducer combines with the substrate and blocs induction

    • B.

      The inducer does not combine with, but functions as a chaperone molecule for, the enzyme-substrate complex

    • C.

      The inducer combines with the repressor and activates the pathway

    • D.

      The inducer combines with the repressor and inactivates the pathway

    Correct Answer
    C. The inducer combines with the repressor and activates the pathway
    Explanation
    When an inducer is added to an environment containing an organism with a metabolic pathway controlled by a repressor, the inducer combines with the repressor and activates the pathway. This means that the inducer molecule binds to the repressor protein, causing a conformational change that prevents the repressor from binding to the operator region of the DNA. As a result, the pathway is no longer repressed and can proceed, leading to the activation of the metabolic pathway.

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  • 33. 

    In negative control of transcription, how does the presence of an inducer affect transcription?

    • A.

      The inducer causes the repressor to bind to the operator

    • B.

      The inducer binds to the operator

    • C.

      The inducer prevents the repressor from binding to the operator

    • D.

      The inducer does not bind to the operator

    Correct Answer
    C. The inducer prevents the repressor from binding to the operator
    Explanation
    The correct answer is that the inducer prevents the repressor from binding to the operator. In negative control of transcription, the repressor protein normally binds to the operator region of the DNA, blocking the RNA polymerase from binding and initiating transcription. However, when an inducer molecule is present, it binds to the repressor protein and causes a conformational change, preventing the repressor from binding to the operator. This allows the RNA polymerase to bind and transcribe the gene.

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  • 34. 

    DNA fragments from a gel are transferred to a nitrocellulose paper during the procedure called Southern blotting. What is the purpose of transferring the DNA from a gel to a nitrocellulose paper?

    • A.

      To separate out the PCRs

    • B.

      To transfer only the DNA that is of interest

    • C.

      To attach the DNA fragments to a permanent substrate

    • D.

      To separate the two complementary DNA strands

    • E.

      To prepare the DNA for digestion with restriction enzymes

    Correct Answer
    C. To attach the DNA fragments to a permanent substrate
    Explanation
    The purpose of transferring the DNA from a gel to a nitrocellulose paper is to attach the DNA fragments to a permanent substrate. This allows for further analysis and manipulation of the DNA fragments, such as hybridization with specific probes or sequencing. By transferring the DNA to a nitrocellulose paper, the DNA fragments become immobilized and can be easily handled and studied.

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  • 35. 

    How can a single gene code for more than one protein?

    • A.

      Different RNA polymerases transcribe it and produce different proteins

    • B.

      Different types of ribosome translate the resulting mRNA, producing different proteins

    • C.

      The exons within a mRNA can be spliced together in different ways

    • D.

      Different introns can be removed to produce different proteins

    Correct Answer
    C. The exons within a mRNA can be spliced together in different ways
    Explanation
    The correct answer is that the exons within a mRNA can be spliced together in different ways. This is possible because genes contain both exons (coding regions) and introns (non-coding regions). During the process of mRNA processing, introns are removed and exons are joined together in different combinations, resulting in different mRNA molecules. These different mRNA molecules can then be translated by ribosomes to produce different proteins. This process is known as alternative splicing and allows a single gene to code for multiple proteins with different functions.

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