Molecular Biology MCQ Quiz With Answers

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Stephen Reinbold has a Ph.D. in Biological Sciences with a particular interest in teaching. He taught General Biology, Environmental Science, Zoology, Genetics, and Anatomy & Physiology for almost thirty years at Metropolitan Community College in Kansas City, Missouri. He particularly enjoyed emphasizing scientific methodology and student research projects. Now, enjoying retirement, he works part-time as an editor while also engaging in online activities.
, PhD, Biological Sciences
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Molecular Biology MCQ Quiz With Answers - Quiz

Do you know all about DNA and RNA? Check out this molecular Biology MCQ quiz with answers and review your knowledge of DNA and RNA structure, replication, transcription & translation. Molecular biology is a branch of Biology that is concerned with studying chemical structures and biological phenomenon processes. It is mostly focused on nucleic acids (DNA and RNA) and proteins. This is an advanced-level test, so questions might be hard for you. Answer the questions carefully. Play the quiz now.


Molecular Biology Questions and Answers

  • 1. 

    DNA nucleotides have three components. Which one of these is NOT part of a DNA nucleotide?

    • A.

      Phosphate

    • B.

      Deoxyribose sugar

    • C.

      Ribose sugar

    • D.

      A nitrogenous base

    Correct Answer
    C. Ribose sugar
    Explanation
    Ribose sugar is not part of a DNA nucleotide. DNA nucleotides consist of a phosphate group, a deoxyribose sugar, and a nitrogenous base. Ribose sugar is found in RNA nucleotides, not DNA nucleotides. RNA nucleotides contain a ribose sugar instead of a deoxyribose sugar.

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  • 2. 

    When considering DNA replication, the best way to describe it is:

    • A.

      Semiconservative (half old, half new)

    • B.

      Conservative (original remains, a new one is formed)

    • C.

      Semipermeable (letting some molecules through)

    • D.

      All of these

    Correct Answer
    A. Semiconservative (half old, half new)
    Explanation
    DNA replication is described as semiconservative because during the process, each strand of the original DNA molecule serves as a template for the synthesis of a new complementary strand. As a result, the newly formed DNA molecule contains one strand from the original molecule and one newly synthesized strand. Therefore, the term "semiconservative" accurately describes the process as half of the DNA is conserved from the original molecule and half is newly synthesized.

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  • 3. 

    In DNA replication, the enzyme responsible for untwisting & 'unzipping' the DNA strands is....

    • A.

      Helicase & gyrase

    • B.

      Ligase

    • C.

      DNA Polymerase III

    • D.

      Primase

    • E.

      RNAse H (DNA Polymerase I)

    Correct Answer
    A. Helicase & gyrase
    Explanation
    Helicase is the enzyme responsible for untwisting the DNA strands during replication. It breaks the hydrogen bonds between the base pairs, separating the double-stranded DNA into two single strands. Gyrase, also known as topoisomerase II, helps to relieve the tension that builds up ahead of the replication fork by introducing negative supercoils into the DNA. This allows the DNA strands to unwind more easily. Together, helicase and gyrase play crucial roles in the initial step of DNA replication by unwinding and separating the DNA strands.

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  • 4. 

    During DNA Replication, a short segment of RNA must form before DNA synthesis can begin. This is done by which enzyme?

    • A.

      Helicase & gyrase

    • B.

      DNA Polymerase III

    • C.

      Ligase

    • D.

      RNAse H (DNA Polymerase I)

    • E.

      Primase

    Correct Answer
    E. Primase
    Explanation
    During DNA replication, a short segment of RNA called a primer is required to initiate DNA synthesis. This primer is synthesized by an enzyme called primase. Primase synthesizes a short RNA sequence that serves as a starting point for DNA polymerase to add nucleotides and extend the DNA strand. Therefore, the correct answer is Primase.

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  • 5. 

    Small discontinuous fragments of DNA, called Okazaki Fragments, need to be joined together to form a complete strand. Which enzyme carries out this reaction?

    • A.

      Helicase & gyrase

    • B.

      DNA Polymerase III

    • C.

      Ligase

    • D.

      RNAse H (DNA Polymerase I)

    • E.

      Primase

    Correct Answer
    C. Ligase
    Explanation
    Ligase is the enzyme that carries out the reaction of joining small discontinuous fragments of DNA, called Okazaki Fragments, to form a complete strand. It catalyzes the formation of phosphodiester bonds between the adjacent nucleotides, sealing the gaps in the DNA strand. This process is crucial during DNA replication, where the lagging strand is synthesized in short fragments. Ligase plays a vital role in ensuring the integrity and continuity of the newly synthesized DNA strand.

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  • 6. 

    A new strand of DNA forms when nucleotides are linked together by phosphodiester bonds. The enzyme that enables this is...

    • A.

      Helicase & gyrase

    • B.

      DNA Polymerase III

    • C.

      Ligase

    • D.

      RNAse H (DNA Polymerase I)

    • E.

      Primase

    Correct Answer
    B. DNA Polymerase III
    Explanation
    DNA Polymerase III is the correct answer because it is the enzyme responsible for catalyzing the formation of new strands of DNA during DNA replication. It adds nucleotides to the growing DNA strand and forms phosphodiester bonds between them. Helicase and gyrase are involved in unwinding and stabilizing the DNA, respectively. Ligase is responsible for joining Okazaki fragments on the lagging strand. RNAse H (DNA Polymerase I) is involved in removing RNA primers during DNA replication. Primase is responsible for synthesizing RNA primers that are necessary for DNA replication to begin.

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  • 7. 

    During DNA replication, there are two other proteins involved that aren't enzymes. These are the SSB's and the "sliding clamp" protein. What are their jobs?

    • A.

      To speed up the copying of DNA & make sure it happens correctly

    • B.

      To prevent annealing (closing) of 'unzipped' DNA + increase processivity

    • C.

      To ensure that any errors in copying are excised before they become permanent

    • D.

      To bring the correct nucleotides to their correct complementary partners

    Correct Answer
    B. To prevent annealing (closing) of 'unzipped' DNA + increase processivity
    Explanation
    The SSB proteins and the "sliding clamp" protein have the job of preventing the annealing or closing of the "unzipped" DNA strands and increasing the processivity of DNA replication. This means that they help to keep the DNA strands separated and stable during replication, allowing for the accurate copying of DNA to occur at a faster rate.

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  • 8. 

    During DNA Transcription, only one strand is copied. This strand is the 3' -- 5' strand, and is called the _______________ strand.

    • A.

      Leading

    • B.

      Lagging

    • C.

      Template

    • D.

      Adenine

    Correct Answer
    C. Template
    Explanation
    During DNA transcription, only one strand is copied, which is the 3' -- 5' strand. This strand serves as a template for the synthesis of a complementary RNA molecule. Therefore, it is called the template strand. The other strand, known as the non-template or coding strand, is not directly involved in the transcription process.

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  • 9. 

    During DNA replication, one strand is copied in a nice, smooth, continuous manner. This strand is called the ______________ strand.

    • A.

      Leading

    • B.

      Lagging

    • C.

      Template

    • D.

      Adenine

    Correct Answer
    A. Leading
    Explanation
    During DNA replication, one strand is copied in a nice, smooth, continuous manner. This strand is called the leading strand. The leading strand is synthesized continuously by DNA polymerase in the 5' to 3' direction, as the replication fork opens up. In contrast, the lagging strand is synthesized discontinuously in short fragments called Okazaki fragments, which are later joined together by DNA ligase. The template strand is the original strand of DNA that is used as a guide for the synthesis of the new complementary strand. Adenine is one of the four nucleotide bases that make up DNA but is not directly related to the process of DNA replication.

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  • 10. 

    During DNA replication, one strand is made discontinuously, in short fragments, little by little. This is called the ____________________ strand.

    • A.

      Leading

    • B.

      Lagging

    • C.

      Template

    • D.

      Adenine

    Correct Answer
    B. Lagging
    Explanation
    During DNA replication, one strand is made continuously in the 5' to 3' direction, while the other strand is synthesized in short fragments called Okazaki fragments. These fragments are later joined together by DNA ligase. The strand that is synthesized in the form of these fragments is known as the lagging strand.

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  • 11. 

    During transcription, a segment of DNA coding  AACGGATTATAT  would be transcribed to....

    • A.

      TTGCCTAATATA

    • B.

      AACGGATTATAT

    • C.

      AACGGAUUAUAU

    • D.

      UUGCCUAAUAUA

    Correct Answer
    D. UUGCCUAAUAUA
    Explanation
    During transcription, the DNA sequence is transcribed into RNA. The RNA sequence is complementary to the DNA sequence, with the exception that RNA contains uracil (U) instead of thymine (T). Therefore, the correct answer is UUGCCUAAUAUA, which is the RNA sequence transcribed from the given DNA sequence AACGGATTATAT.

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  • 12. 

    Although there are only 20 amino acids, there are 64 possible codons in the Genetic Code.  This is because of a property of the code called....

    • A.

      Redundancy

    • B.

      Repetitiveness

    • C.

      Recombination

    • D.

      Frequency

    Correct Answer
    A. Redundancy
    Explanation
    The correct answer is redundancy. The genetic code is redundant because multiple codons can code for the same amino acid. This redundancy allows for flexibility and error tolerance in the translation process. For example, the amino acid leucine can be coded by six different codons (CUU, CUC, CUA, CUG, UUA, and UUG). This redundancy ensures that even if there are errors or mutations in the DNA sequence, the correct amino acid can still be synthesized.

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  • 13. 

    Because the mRNA codon, AUG, stands for an amino acid, it means that technically, every protein begins with which amino acid?

    • A.

      Isoleucine

    • B.

      Proline

    • C.

      Methionine

    • D.

      Tryptophan

    Correct Answer
    C. Methionine
    Explanation
    The mRNA codon AUG is known as the start codon, which signals the beginning of protein synthesis. Methionine is the amino acid that is coded by the start codon, and therefore, every protein technically begins with methionine.

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  • 14. 

    A sequence of DNA codes: AAAAAAAAAAAAAAAAAAAAA After transcription and translation, it would yield which of the following?

    • A.

      Nothing.... that's ridiculous!

    • B.

      A polypeptide composed of 7 Lysines

    • C.

      A polypeptide composed of 7 Phenylalanines

    • D.

      A polypeptide composed of 6 Lysines

    Correct Answer
    C. A polypeptide composed of 7 Phenylalanines
    Explanation
    The given sequence of DNA codes, AAAAAAAAAAAAAAAAAAAAA, would transcribe into a sequence of mRNA codes, UUUUUUUUUUUUUUUUUUUU. This mRNA sequence would then be translated into a polypeptide composed of amino acids. Each codon in the mRNA sequence codes for an amino acid, and in this case, the codon UUU codes for Phenylalanine. Since there are 7 UUU codons in the mRNA sequence, it would yield a polypeptide composed of 7 Phenylalanines.

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  • 15. 

    Where in the cell does transcription of DNA occur?

    • A.

      The nucleus

    • B.

      The cytoplasm

    • C.

      Anywhere there is a ribosome

    • D.

      All of these

    Correct Answer
    A. The nucleus
    Explanation
    Transcription of DNA occurs in the nucleus. This is because the nucleus is where the DNA is located in a eukaryotic cell. Transcription is the process by which the DNA sequence is copied into a messenger RNA (mRNA) molecule, which can then be used to produce proteins. Since the DNA is present in the nucleus, it is here that the transcription machinery, including RNA polymerase, binds to the DNA and carries out the process of transcription. Therefore, the correct answer is the nucleus.

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  • 16. 

    Where in the cell does translation of mRNA happen?

    • A.

      The nucleus

    • B.

      The cytoplasm

    • C.

      Anywhere there is a ribosome

    • D.

      All of these

    Correct Answer
    C. Anywhere there is a ribosome
    Explanation
    You need a ribosome for translation. They can be free ribosomes in the cytoplasm, but the RER, Golgi and nucleolus are all possible sites for translation.

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  • 17. 

    If an mRNA has a codon which is CGC, then the tRNA anticodon will be...

    • A.

      CGC

    • B.

      GCG

    • C.

      UAU

    • D.

      ATA

    Correct Answer
    B. GCG
    Explanation
    The tRNA anticodon will be GCG because it is complementary to the mRNA codon CGC. In the process of protein synthesis, tRNA molecules carry specific amino acids to the ribosomes, where they bind to the mRNA codons through complementary base pairing. The complementary anticodon on the tRNA molecule ensures that the correct amino acid is added to the growing polypeptide chain according to the genetic code. Therefore, in this case, the tRNA anticodon must be GCG to pair with the mRNA codon CGC.

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  • 18. 

    Which of the following is NOT true about the Ribosome?

    • A.

      It is composed of two subunits, large & small

    • B.

      It is a vital participant in both transcription & translation

    • C.

      It has three sites (E, P, A) that accomodate tRNA's

    • D.

      It is the cell's protein maker

    Correct Answer
    B. It is a vital participant in both transcription & translation
    Explanation
    The given correct answer is that the Ribosome is NOT a vital participant in both transcription and translation. Ribosomes are responsible for protein synthesis during translation, but they are not directly involved in transcription, which is the process of synthesizing RNA from DNA. Transcription occurs in the nucleus, while translation takes place in the cytoplasm. Therefore, the statement that the Ribosome is a vital participant in both transcription and translation is not true.

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  • 19. 

    A tRNA molecule picks up a Cysteine amino acid. The anticodon loop of this tRNA might have which of the following sequences?

    • A.

      UGU, UGC

    • B.

      ACA, ACG

    • C.

      TGT, TGC

    • D.

      All of these

    Correct Answer
    B. ACA, ACG
    Explanation
    The mRNA codons UGU and UGC code for Cysteine. The anticodons would be either ACA or ACG.

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  • 20. 

    The 'rough draft' version of an mRNA, the Primary Transcript, needs to be 'cleaned up' or edited before translation can occur. This editing involves....

    • A.

      Removal of exons

    • B.

      Removal of introns

    • C.

      Complementary pairing

    • D.

      Secondary pairing

    Correct Answer
    B. Removal of introns
    Explanation
    The primary transcript of mRNA contains both exons and introns. Exons are the coding regions that will be translated into proteins, while introns are non-coding regions. Before translation can occur, the introns need to be removed through a process called splicing. This editing step ensures that only the necessary coding regions are present in the mature mRNA molecule, allowing for accurate translation and protein synthesis. Therefore, the correct answer is the removal of introns.

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  • 21. 

    If the DNA sequence of a gene is  TACCCATGTAAGGGC, then the final amino acid sequence produced from it, after transcription and translation, will be  

    • A.

      TRP - PHE - LYS - ILE - LEU

    • B.

      MET - GLY - SER - PHE - SER

    • C.

      GLY - ASP - GLU - MET - MET

    • D.

      None of the above

    Correct Answer
    B. MET - GLY - SER - PHE - SER
    Explanation
    The DNA sequence TACCCATGTAAGGGC will be transcribed into the RNA sequence AUGGGUACAUUCCCG, which will then be translated into the amino acid sequenceMET-GLY-THR-PHE-ALA. This is because the DNA sequence is transcribed into RNA using the complementary base pairs (A-U, T-A, G-C, C-G), and the RNA sequence is translated into amino acids using the genetic code.

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  • 22. 

    When cells transcribe & translate their DNA, the term we use for this is...

    • A.

      Gene expression

    • B.

      Genetic mutation

    • C.

      General mayhem

    • D.

      Genetic coding

    Correct Answer
    A. Gene expression
    Explanation
    Gene expression refers to the process by which information encoded in a gene is used to create a functional product, such as a protein. It involves two steps: transcription, where the DNA sequence is transcribed into RNA, and translation, where the RNA is translated into a protein. This term accurately describes the process of cells transcribing and translating their DNA to produce proteins and carry out their functions.

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Stephen Reinbold |PhD, Biological Sciences |
Biology Expert
Stephen Reinbold has a Ph.D. in Biological Sciences with a particular interest in teaching. He taught General Biology, Environmental Science, Zoology, Genetics, and Anatomy & Physiology for almost thirty years at Metropolitan Community College in Kansas City, Missouri. He particularly enjoyed emphasizing scientific methodology and student research projects. Now, enjoying retirement, he works part-time as an editor while also engaging in online activities.

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