ASBiologyOCRExam Questions2. Foundations in Biology2.3 Nucleotides & Nucleic Acids

Nucleotides & Nucleic Acids (OCR AS Biology)

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2.3 Nucleotides & Nucleic Acids

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1
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In DNA, which of the following nitrogenous bases is the correct pair for cytosine?

  • Adenine

  • Guanine

  • Thymine

  • Uracil

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2
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Which statement regarding the nucleotide monomer is correct?

1 They comprise three parts: a 5-carbon sugar, two phosphate groups and a nitrogenous base
2 The organic bases adenine and guanine are called purines due to having two joined rings in their structure
3 The sugar and phosphate group form a 3’-5’ phosphodiester bond

  • 1, 2 and 3

  • Only 1 and 2

  • Only 2 and 3

  • Only 1

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3
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Where does mRNA carry information from and to?

  • From cytoplasm to mitochondria

  • From cytoplasm to nucleus

  • From nucleus to cytoplasm

  • From nucleus to mitochondria

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4
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During the transcription of DNA, the DNA double helix unwinds and the strands separate to allow for the RNA nucleotides to attach.

What type of chemical bond do RNA nucleotides use to attach to the exposed bases on the DNA strand?

  • Covalent bond

  • Ester bond

  • Hydrogen bond

  • Peptide bond

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5
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What is the name of the RNA that binds amino acids and matches them to codons?

  • mRNA

  • rRNA

  • siRNA

  • tRNA

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1
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Which of the following statements is/are evidence that DNA replication is semiconservative?

1  After one replication, the number of adenine nucleotides is equal to the number of guanine nucleotides.
2 After two replications, two DNA molecules have one original and one new strand, and two DNA molecules have two new strands.
3 After three replications, there are eight DNA molecules, only two of which have strands from the original DNA.

  • 1, 2 and 3

  • only 1 and 2

  • only 2 and 3

  • only 1

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2
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Hox genes contain a homeobox sequence of 180 base pairs.

Two species have a homeobox sequence of 180 base pairs where 1.7% of the base pairs are different.

Which of the following shows the number of amino acids coded for that would be different in the two species?

  • minimum 0 and maximum 1

  • minimum 0 and maximum 3

  • minimum 1 and maximum 2

  • minimum 1 and maximum 3

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3
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Which of the following nucleotides contains uracil?

q12-paper-2-june-2019-ocr-a-level-biology

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    4
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    Which of the following statements, A to D, about DNA replication is correct?

    • RNA will bind to DNA through complementary base-pairing.

    • The distance between the strands in the double helix will always be the same.

    • The proportion of adenine in a nucleic acid will always equal the proportion of guanine.

    • The formation of phosphodiester bonds will occur in the same direction on each strand during DNA replication.

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    5
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    Which of the following processes occur during DNA replication?

    1 breakage and (re)formation of phosphodiester bonds
    2 breakage and (re)formation of hydrogen bonds
    3 alignment of free nucleotides with their complementary bases

    • 1, 2 and 3

    • Only 1 and 2

    • Only 2 and 3

    • Only 1

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    6
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    An anticodon sequence of five successive tRNA molecules involved in protein synthesis was analysed and found to have the following percentage base composition.

    Adenine 40; Cytosine 27; Guanine 13; Thymine 0; Uracil 20 %

    Which row shows the percentage base composition of the template strand of the original DNA molecule?

      Adenine Cytosine Guanine Thymine Uracil
    A 40 27 13 20 0
    B 20 13 27 40 0
    C 20 13 27 0 40
    D 40 27 13 0 20

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      7
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      The following statements are about the structure of DNA.

      Which of the following statement(s) is/are true?

      Statement 1:   Purine bases pair with pyrimidine bases.
      Statement 2:   Phosphodiester bonds link adjacent nucleotides.
      Statement 3:   There are always equal amounts of adenine and guanine.

      • 1, 2 and 3

      • Only 1 and 2

      • Only 2 and 3

      • Only 1

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      8
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      A standard method can be used to extract DNA from the nuclei of cells in kiwi fruit.

      The statements below list some of the steps involved in this method, in no particular order. 

      Which statement is not correct?

      • Filter to remove cell debris such as cell membranes

      • Add detergent to dissolve nuclear membranes

      • Add protease to digest histone proteins

      • Pour ice cold ethanol onto filtrate to stop enzyme activity

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      9
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      The approximate angle of orientation ('twist') of one nucleotide in respect to its neighbouring nucleotide in a given strand of DNA is between 35 and 40 degrees.

      How many base pairs are required for the double-helix to twist by one whole turn?

      • 5

      • 8

      • 10

      • 12

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      10
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      In 1958, Meselson and Stahl carried out an experiment that provided evidence to support the hypothesis of semi-conservative replication of DNA.

      They grew E. coli bacteria in a growth medium that contained only the heavy isotope of nitrogen 15N. They transferred the bacteria to a growth medium that had the light 14N isotope and allowed the bacteria to undergo cell division.

      After each division, the DNA from some of the bacteria was extracted from the culture and centrifuged to separate it. The image below shows results of this experiment after one generation of divisions. 

      wkN7bqBi_meselson-stahl-mcq

      The tube labelled Generation 0 shows a single band of DNA containing bases that contain only the heavy isotope of nitrogen 15N.

      Which of the options below shows the correct appearance of the third tube after two generations of divisions? 

      FOGYIkeF_m-s-experiment-mcq-answer-options

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        1
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        Ricin is a poison that affects cells by removing an adenine from the 60S ribosomal subunit. Which of the following statements explains why ricin leads to cell death?

        • Anticodons on tRNA molecules cannot pair with codons on mRNA molecules.

        • RNA polymerase cannot move along the template strand in a 3’ to 5’ direction.

        • Ester bonds cannot form between amino acids to form proteins.

        • Adenine cannot pair with uracil in the formation of mRNA in the nucleus.

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        2
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        When extracting and purifying DNA from a strawberry, various substances have to be added to successfully isolate the DNA by precipitation.

        Which of the rows in the table below correctly explains the reasons for adding each of the stated substances?

          Substance added
        Detergent Protease Ice-cold ethanol
        A Disrupts phospholipid bilayer Breaks down histones Allows precipitate formation
        B Breaks down cell walls Disrupts phospholipid bilayer Denatures proteins
        C Disrupts phospholipid bilayer Breaks down cell walls Allows precipitate formation
        D Allows precipitate formation Breaks down histones Disrupts phospholipid bilayer

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          3
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          DNA polymerase and RNA polymerase are both enzymes. Which of the following statements correctly describe the functions of these two enzymes?

          1 DNA polymerase and RNA polymerase catalyse condensation reactions.
          2 RNA polymerase uses a short section of DNA.
          3 DNA polymerase produces a double stranded molecule.
          4 RNA polymerase moves in a 5’ to 3’ direction.

          • All four statements.

          • 2, 3 and 4.

          • 1, 3 and 4.

          • 1, 2 and 3.

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          4
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          The table below shows the amino acids coded for by mRNA codons.

          ocra-2-3h-mcq-amino-acid-table

          An insertion mutation occurs at point 3 of the following DNA sequence, introducing a guanine base:

          CAGGGGATA

          Which of the following sequences of amino acids are coded for by the newly formed DNA sequence? 

          • Glu, Gly, Iso

          • Val, Pro, Leu

          • Val, Pro, Tyr

          • Thr, His, Ser

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