| Date | November 2020 | Marks available | 1 | Reference code | 20N.1.HL.TZ0.27 |
| Level | Higher level | Paper | Paper 1 | Time zone | TZ0 / no time zone |
| Command term | Question number | 27 | Adapted from | N/A |
Question
Which are two proteins that assist in the unwinding and separation of DNA strands during replication?
A. Helicase and DNA polymerase III
B. DNA gyrase and DNA polymerase I
C. Helicase and DNA primase
D. Single-strand binding protein and DNA gyrase
Markscheme
D
Examiners report
For reasons that are hard to explain, this question had one of the highest ever discrimination indices at 0.72, with about half of candidates answering correctly.
Syllabus sections
- 22M.1.HL.TZ1.26: The image shows a replication fork. Which row identifies X, Y and Z in the diagram?
- 18M.2.HL.TZ2.2b.ii: Outline how Hershey and Chase’s experiment provided evidence for DNA as the genetic material.
- 22M.2.HL.TZ2.5a.i: Describe the structure of nucleosomes.
- 18N.1.HL.TZ0.26: Current understanding of DNA is an example of the accumulated discoveries of many scientists....
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17N.1.HL.TZ0.27:
Which letter (A–D) indicates where a new nucleotide would attach?
- 17M.2.HL.TZ1.2a.i: Nucleosomes help to regulate transcription in eukaryotes. State the components of a nucleosome.
- 19M.1.HL.TZ2.13: A nucleotide containing dideoxyribose is shown. What is the reason for the use of...
- 19M.1.HL.TZ2.14: What applies to DNA base sequences? I. Some genes do not code for proteins. II. Promoters...
- 18M.1.HL.TZ1.27: What does eukaryotic DNA have that is missing from prokaryotic DNA? A. Uracil B. Promoter...
- 18N.2.HL.TZ0.3b: Outline the role of short tandem repeats in DNA profiling.
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21N.1.HL.TZ1.27:
What is the difference between the DNA of adult identical (monozygotic) twins?
A. Order of genes
B. Sequence of nucleotides
C. Methylation pattern
D. Ratio of complementary base pairs
- 18N.2.HL.TZ0.3a: State one similarity and one difference between the structure of genes and short tandem...
- 18M.2.HL.TZ2.2b.iii: State one function for a region of DNA that does not code for proteins.
- 18M.2.HL.TZ2.2b.i: State one role of nucleosomes in eukaryotic cells.
- 19M.1.HL.TZ1.26: What contribution did the X-ray diffraction conducted by Rosalind Franklin make to our...
- 19M.1.HL.TZ2.12: What are the functions of DNA primase and DNA polymerase I in DNA replication?
- 17M.1.SL.TZ1.1: Which structure found in eukaryotes has a single membrane? A. Nucleus B. Lysosome C....
- 17M.1.HL.TZ1.27: The diagram shows how pre-mRNA is processed into mature mRNA. Which structures are indicated...
- 21M.1.HL.TZ1.26: Which regions of DNA code for the production of specific proteins? A. Telomeres B. Genes...
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19M.1.HL.TZ2.11:
Hershey and Chase used a bacteriophage (a virus that infects bacteria) to investigate the chemical nature of genes. The diagram shows a bacteriophage.
[Source: Graham Knott and Christel Genoud, ‘Commentary: is EM dead?’, Journal of Cell Science (2013),
126: 4545–4552, reproduced with permission. http://jcs.biologists.org/content/126/20/4545.figures-only
doi: 10.1242/jcs.124123 http://www.biologists.com/journal-of-cell-science]The sulphur in the protein and the phosphorus in the DNA of the bacteriophage were radioactively labelled. The data obtained after bacterial infection and centrifugation are shown in the table.
What did Hershey and Chase conclude from their experiment?
A. DNA was mainly outside the bacterial cells.
B. Viruses infect bacterial cells with proteins.
C. Viral DNA was found within the bacterial cells.
D. Neither protein nor DNA were chemicals making up genes in viruses.
- 21M.1.HL.TZ1.27: Which statement applies to tRNA? A. There is at least one type of tRNA that combines with...
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22M.1.HL.TZ2.26:
The diagram shows the structure of a nucleosome.
[Source: Zephyris. Nucleosome 1KX5 colour coded. Available at https://en.wikipedia.org/wiki/Nucleosome#/media/File:Nucleosome_1KX5_colour_coded.png
This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license (https://creativecommons.org/licenses/by-sa/3.0/deed.en).]What is the structure labelled T?
A. 5' end of RNA
B. 5' end of uncoiled DNA
C. N-terminal tail of one DNA strand
D. N-terminal tail of one histone
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22M.2.HL.TZ2.5a.iii:
There are multiple tandem repeats of nucleotide segments of DNA found in the non-coding DNA between genes. Outline how tandem repeats are used for DNA profiling.
- 16N.1.SL.TZ0.15: Which is a valid comparison between prokaryotic and eukaryotic DNA?
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16N.2.HL.TZ0.7c:
Growth in living organisms includes replication of DNA. Explain DNA replication.
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17N.3.HL.TZ0.03a:
The Hershey and Chase experiment supported DNA as the hereditary material. Describe the experiment.
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21M.1.HL.TZ2.26:
The graph shows results of an experiment by Hershey and Chase in 1952 in which bacteria were infected with a mixture of virus particles labelled with either 32P or 35S. A suspension of the infected bacteria was agitated with a blender, and samples collected from the suspension were centrifuged to record the percentage of isotope remaining on the outside of the cells.
[Source: Republished with permission of ROCKEFELLER UNIVERSITY PRESS, from Independent functions of protein and nucleic acid in growth of bacteriophage. Hershey, A.D. and Chase, M., 1952. (Journal of General Physiology, 36(1), p.47). Society of General Physiologists, Rockefeller Institute for Medical Research, Rockefeller Institute; permission conveyed through Copyright Clearance Center, Inc.]
What do curves X and Y represent?
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19M.1.HL.TZ1.27:
The diagram shows the arrangement of introns and exons in a segment of pre-mRNA. Pre-mRNA is immature mRNA containing introns and exons.
Which is a mature mRNA molecule derived from the pre-mRNA by splicing?
[Source: © International Baccalaureate Organization 2019]
- 19M.2.HL.TZ1.7a: Outline the roles of helicase and ligase in DNA replication.
- 19N.1.HL.TZ0.26: What is a function of DNA polymerase I? A. Adds nucleotides in a 5’ to 3’ direction to...
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19M.2.HL.TZ2.2a.iii:
DNA has regions that do not code for proteins. State two functions of these regions.
1.
2.
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21N.1.HL.TZ1.26:
Rosalind Franklin produced X-ray diffraction images of DNA.
[Source: © King’s College, London. KCL Department of Biophysics KDBP/1/1.]
Which previously unknown aspect of DNA was deduced from these images?
A. Chromosomes are made of DNA.
B. Deoxyribose sugar is attached to a phosphate group.
C. The base A pairs with T and C with G.
D. The DNA molecule is a double helix.
