0%

DP IB Biology: HL

Topic Questions

Home / IB / Biology: HL / DP / Topic Questions / 2. Molecular Biology / 2.5 Nucleic Acids: Structure & DNA Replication / Structured Questions: Paper 2


2.5 Nucleic Acids: Structure & DNA Replication

Question 1a

Marks: 3
a)

The ends of a DNA strand are referred to as the 3’ end and the 5’ end.

Describe the aspects of DNA structure that give rise to this naming system.

[3 marks]

    Assess your score
      
    Key Concepts
    Double Helix Structure

    Question 1b

    Marks: 2
    b)

    Adenine/thymine and guanine/cytosine form hydrogen-bonds with each other in complementary base-pairing within the DNA double helix. These bases can also form bonds with other molecules in order to carry out their function.

    i)

    Suggest one other molecule that might form bonds with the bases in a DNA molecule.

    [1 mark]

    ii)

    State the role of the molecule identified in part i).

    [1 mark]

      Assess your score
        
      Key Concepts
      Double Helix Structure

      Question 1c

      Marks: 4
      c)

      The structure of DNA has many characteristics that enable it to carry out its function.  

      i)

      Identify two structural features that help DNA to carry out its function.

      [2 marks]

      ii)

      For each feature identified at part i), explain how it assists with DNA function.

      [2 marks]

        Assess your score
          
        Key Concepts
        Double Helix Structure

        Question 2a

        Marks: 2
        a)
        Explain why only bases that are complementary to the bases on the template strand can be added to the new DNA strand during DNA replication. 
        [2 marks]
          Assess your score
            
          Key Concepts
          DNA Replication

          Question 2b

          Marks: 3
          b)
          Ultraviolet exposure can cause guanine to be oxidised to 8-oxyguanine, which is no longer complementary to cytosine. Instead, during replication, 8-oxyguanine can form bonds with adenine, resulting in a base pair.

          Outline the possible consequences of this change.  


          [3 marks]

            Assess your score
              
            Key Concepts
            DNA Replication

            Question 2c

            Marks: 1
            c)

            In the absence of mutagens, the rate of mutations during DNA replication is very low, approximately 160 bases per cell cycle.

            Given that the human genome contains 3.2 billion base pairs, calculate the percentage copying error rate of each cell cycle. 

            [1 mark]

              Assess your score
                

              Question 3a

              Marks: 2
              a)
              Even the smallest DNA molecules are very long.
                • A kilobase (Kb) is a unit equivalent to 1000 base pairs of a DNA molecule.
                • One Kb of double stranded DNA has a length of 0.34 μm.

              The DNA in the nucleus of a cell from a fruit fly (Drosophila) is 5.6 cm long.

              Calculate the number of Kb in the DNA of the fruit fly. Give your answer to the nearest whole number.

              [2 marks]

                Assess your score
                  

                Question 3b

                Marks: 1
                b)

                The amount of DNA found in the nucleus of cells can vary amongst people, with each human chromosome containing between 5 x 104 and 26 x 104 Kb of DNA.

                Suggest one reason why people might have different quantities of DNA to each other.

                [1 mark]
                  Assess your score
                    
                  Key Concepts
                  Use of Karyograms

                  Question 3c

                  Marks: 1
                  c)
                  Other than for use in replication, explain one advantage of DNA molecules having two strands.

                  [1 mark]

                    Assess your score
                      
                    Key Concepts
                    Double Helix Structure

                    Question 4a

                    Marks: 4
                    a)
                    A section of DNA contains 1,200 base pairs.
                    • The number of guanine molecules on strand one was counted as 156.
                    • The number of cytosine molecules on strand one was counted as 209.
                    • The number of adenine molecules on strand two was counted as 264.

                    Complete the table below to include the total number of each base present in the section, and the % composition of each base. 

                      Number of molecules present % composition
                    Adenine    
                    Cytosine    
                    Guanine    
                    Thymine    

                    [4 marks]

                      Assess your score
                        
                      Key Concepts
                      Double Helix Structure

                      Question 4b

                      Marks: 2
                      b)
                      The image below shows a section of the skeletal formula of a DNA molecule.

                      Number the carbon atoms of all the pentose sugars shown in the image using the standard numbering format.

                      h-4b

                      [2 marks]
                        Assess your score
                          
                        Key Concepts
                        Double Helix Structure

                        Question 4c

                        Marks: 2
                        c)
                        The DNA nucleotides are covalently bonded together in the sugar-phosphate backbone between the pentose sugar and the phosphate group, however, they are hydrogen bonded together between the bases. 
                        Explain why both types of bonds are important for the functioning of DNA. 
                        [2 marks]
                          Assess your score
                            
                          Key Concepts
                          Double Helix Structure

                          Question 4d

                          Marks: 1
                          d)
                          During DNA replication both DNA strands act as a template, whereas in transcription only one strand acts as a template. 
                          Outline what is meant by the word 'template' in this context. 
                          [1 mark]
                            Assess your score
                              

                            Question 5a

                            Marks: 4

                            One mark is available for clarity of communication throughout this question. 

                            a)
                            ATP is a source of energy used in cells and is produced from processes such as respiration. 

                            The structure of ATP is shown in the diagram below.T7rO3wHK_h-5a

                            Use the information in the diagram, as well as your own knowledge, to compare and contrast the structure of ATP with an adenine DNA nucleotide.
                            [4 marks]
                              Assess your score
                                

                              Question 5b

                              Marks: 4
                              b)
                              Explain how the structure of DNA allows replication.
                              [4 marks]
                                Assess your score
                                  
                                Key Concepts
                                DNA Replication

                                Question 5c

                                Marks: 7
                                c)
                                Outline the steps in the experiment that Meselson and Stahl carried out to determine the semi-conservative nature of DNA replication. 
                                [7 marks]
                                  Assess your score