Syllabus Edition

First teaching 2023

First exams 2025

|

DNA Replication (HL IB Biology)

Exam Questions

3 hours42 questions
1a1 mark

State the purpose of DNA replication. 

1b2 marks

The diagrams below show two models of DNA replication.

dna-replication-sq

State, with a reason, which diagram, A or B, is correct.

1c2 marks

Identify two enzymes that are involved with the process of DNA replication.

1d
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2 marks

Calculate the fraction of a cell’s original DNA that will be present after 3 full cycles of DNA replication.

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2a1 mark

Both DNA and RNA contain pentose sugars in their sugar-phosphate backbones. 

Define the term pentose in reference to sugar molecules. 

2b2 marks

During DNA replication the new bases are added to the new strand by the enzyme DNA polymerase in the 5' to 3' direction. 

Use your knowledge of enzymes to explain why it would not be possible for DNA polymerase to add the new bases in the 3' to 5' direction. 

2c2 marks

When bases are bonded to the new DNA strands during replication they undergo a condensation reaction. 

Describe the events that occur during a condensation reaction.

2d2 marks

In a length of DNA 1 000 nucleotides long there are 382 guanine nucleotides in one of the strands.

Explain why it is not possible to calculate the number of guanine nucleotides in the opposite strand from the information provided.  

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3a
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3 marks

Describe how the structure of a tRNA molecule contributes to the accuracy of the translation.

3b
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5 marks

Draw a labelled diagram of two nucleotides bonded together within the same DNA strand.

3c
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7 marks

Outline the three stages of polymerase chain reaction (PCR).

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4a
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2 marks

The diagram below shows the process of DNA replication.

dna-replication-sq

Identify which strand of X and Y is the leading and lagging strand of the original DNA molecule.

4b
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1 mark

DNA replicates in a semi-conservative way.

Define the term 'semi-conservative' with regards to DNA replication.

4c
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2 marks

One of the enzymes involved with DNA replication is DNA primase.

Describe the role of DNA primase during DNA replication.

4d
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1 mark

DNA replication can only occur in the 5' to 3' direction in the new strand.

State the reason for this.

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5a
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1 mark

A crime was committed and the DNA profiles of the victim and a drop of blood found at the crime scene were constructed. These were compared to the DNA profiles of three possible suspects, as seen in the diagram below.

moMzkGAz_hl-ib-7-1-e-q3a

Identify the suspect that most likely committed the crime.

5b
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2 marks

Variable number tandem repeats (VNTRs) are short, non-coding regions of DNA that can be used in DNA profiling.

Explain the use of VNTRs in DNA profiling.

5c
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2 marks

The diagram below represents the structure of a chromosome.

dv29FFmY_hl-ib-7-1-e-q3c

Label parts R and S of the chromosome.

5d
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2 marks

R and S from the chromosome at part c) represents non-coding regions of DNA.

State the function of R and S in a chromosome.

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6a1 mark

In the electrophoretogram, the DNA has moved from the negative cathode to the positive anode.

unnamed-27

State the property of DNA which results in movement from cathode to anode.

6b2 marks

State two uses of gel electrophoresis.

6c1 mark

In some situations, gel electrophoresis cannot be carried out as the DNA samples are not collected in a large enough quantity.

Identify the process used to amplify the DNA in order to supply enough DNA for electrophoresis to be successful.

6d2 marks

The stages of electrophoresis can be seen below.

Complete the table below by adding a number to the column to show the correct sequence of events in the process. The first one has been done for you.

A sample of DNA is collected from an individual 1
Samples of DNA fragments are loaded into wells in the agarose gel using a micropipette  
An enzyme is used to create fragments of the DNA in the sample  
An electrical current is applied to the tank  

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7a3 marks

The molecules named below are all required during the process of PCR.

Draw a line between the boxes to show the function for each of the molecules named.

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7b1 mark

State the property of Taq polymerase that makes it suitable for use in PCR.

7c1 mark

The graph shows how the quantity of DNA increases over several cycles of PCR

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Identify the stage of the graph where replication is exponential.

7d1 mark

The electrophoretogram shows a pattern produced from the DNA of two people.

IZ6xi5CK_e-2d

State how the electrophoretogram shows that the two people are identical twins.

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8a
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2 marks

During electrophoresis, molecules travel through an agarose gel.

State two properties of the molecules that determine how far through the gel they can travel. 

8b3 marks

Outline the process used to determine paternity using electrophoretograms produced in gel electrophoresis. 

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1a4 marks

Describe the structural features of a DNA molecule.

1b8 marks

Describe the process of semi-conservative replication of DNA in eukaryotes. In your answer, include details of any molecules, bonds or enzymes involved.

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2a3 marks

The diagram below shows one cycle of the polymerase chain reaction (PCR). 


biology-2-6-sq-ib-hl

Outline the events that are taking place during stage 1 in the diagram.

2b1 mark

Molecule X in the diagram shown in part (a) is a DNA primer.

State the role of a DNA primer in PCR.

2c2 marks

Stage 3 in PCR involves an enzyme.

Explain how the enzyme is suitable for its role in PCR.

2d2 marks

State two applications of PCR.

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3a2 marks

The diagram below illustrates a small section of a DNA molecule from the nucleus of a eukaryotic cell.

   q2a_7-1_dna_structure_replication_medium_ib_hl_biology_sqState the structures labelled X and Y.

3b2 marks

A repetitive sequence of DNA occurs at the ends of eukaryotic chromosomes, called a telomere.

Explain the role of a telomere. 

3c3 marks

Most of the DNA in an organism is contained within the nucleus. Some of this DNA is unique, whilst some is made up of highly repetitive sequences.

Contrast unique and highly repetitive sequences of DNA

3d3 marks

DNA was originally thought of as a protein. In the 1950s, Alfred Hershey and Martha Chase showed that DNA is a factor of heredity responsible for carrying genetic information from one generation to another.

Describe their experiment.

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4a1 mark

The chain termination process can be used to identify the sequence of base pairs.

q3b_7-1_dna_structure_replication_medium_ib_hl_biology_sq
   

Use the image above to identify the order of bases, starting with the smallest, in the block of DNA labelled X, on the right.

4b1 mark

Results from a paternity test using gel electrophoresis are shown in the image below. DNA was isolated from a mother, her child and two potential fathers. Primers designed to amplify different satellite DNA regions were used and amplified alleles are shown in the results below.

q3c_7-1-dna-structure--replication_ib_hl_biology

Use the gel electrophoresis DNA profiles in the image above to determine which male is the child's father.

4c2 marks

The DNA fragments separated in the gel electrophoresis in part (c) vary in size from 100 bp (base pairs) up to 5 000 bp. DNA fragments of known size were used to create the plot shown in the graph below.

q3d_7-1-dna-structure--replication_ib_hl_biology_sq

Use the line of best fit on the graph to determine the base pair length for DNA fragments that travelled 5 cm on the gel electrophoresis plate. Give answers to the nearest whole number.

4d6 marks

Outline the steps of DNA replication at a replication fork, describing the role of each of the enzymes involved.

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5a2 marks

State two features that allow nucleic acids or proteins to be separated by gel electrophoresis.

5b3 marks

During gel electrophoresis of a sample of DNA fragments,

(i)
Identify which electrode the DNA would move towards. Justify your answer.

(ii)
State which component of DNA gives it its charge.
5c1 mark

State which class of enzymes can be used to cleave DNA into fragments prior to gel electrophoresis.

5d3 marks

Restriction enzymes and gel electrophoresis can be used in genetic screening, to identify genes associated with a disease. The mutation of the Beta-globin gene which gives rise to sickle-cell anaemia removes a recognition site of the restriction enzyme DdeI as shown in the diagram below. The lengths of some fragments are shown in base pairs (bp).

biology-q1d-3-4-sq-ib-hl

(i)

Deduce the size of fragment X. 

(ii)
DdeI digested DNA from an individual who was a carrier for the sickle-cell beta-globin gene was analysed with gel electrophoresis as shown below. Draw and label the DNA fragments that would result from a normal individual.
biology-q1d2-3-4-ib-hl-sq

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6a5 marks

Archaeologists in Pompeii recently discovered the remains of seven human skeletons within a house that was buried under volcanic ash when Mount Vesuvius erupted during ancient Roman times in 79 AD. Researchers were interested to know if the skeletons were from related individuals, they isolated DNA from the skeletons and used it in the Polymerase Chain Reaction (PCR).

PCR utilises multiple cycles of three simple steps, describe these steps and suggest why the researchers used PCR in their investigation.

6b3 marks

DNA profiling was carried out on the PCR products to identify if the skeletons came from related individuals. The results are seen in the image below.

biology-q5b-3-4-ib-hl-sq

It was determined that the three children were siblings and shared the same biological parents. Their mother is Adult B.

(i)

Predict which adult is the children’s father. Justify your answer.

(ii)

Suggest why the profiles for Child 1 and Child 2 are the same.

6c7 marks

Outline the method by which DNA profiling is undertaken and describe why it is a useful technique.

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1a2 marks

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. 

1b3 marks

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.  

1c
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1 mark

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. 

1d
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5 marks

Discuss the formation of Okazaki fragments during the process of replication on the lagging strand of a DNA molecule.

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2a
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2 marks

A group of scientists studied the replication of DNA in Escherichia coli bacteria.

During their investigation, radioactive nucleotides were added to DNA that was actively replicating in a short pulse of about 5 seconds. This allowed the radioactive nucleotides to be incorporated into the new DNA strands. 

This was followed by a "chase" period, during which an abundance of unlabelled nucleotides was added to the DNA for different amounts of time, between 7 and 120 seconds. After the isolation and centrifugation of the DNA molecules, the results were obtained.

The graph below shows the results of their investigation.

size-of-dna-fragments-during-replication-graph-sq

Contrast the results obtained at a "chase" period of 7 seconds with those obtained at 120 seconds.

2b
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2 marks

Explain the results obtained at a "chase" period of 60 seconds.

2c
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1 mark

Suggest a possible explanation for the low number of small fragments present at 120 seconds.

2d
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2 marks

Sketch a line on the graph of the predicted results that could be obtained at a "chase" period of 150 seconds.

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3
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3 marks

One round of PCR takes approximately 75 seconds.

Calculate how many copies of DNA would be produced after a single fragment of DNA has been in the thermal cycler for 1.5 hours. Give your answer in standard form.

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4a6 marks

The diagram below shows the processes involved in the amplification of a sample of viral RNA.

Qdc4LjMO_h-2a

Compare and contrast the process in the image with the process used in the amplification of a fragment of DNA.

4b2 marks

The addition of RNAase enzyme occurs between stages 3 and 4 shown in the diagram from part a).

Suggest why this is a necessary part of the process.

4c2 marks

Seven skeletons were discovered in a house in Pompeii, three of which were children. It is believed they were inhabitants and workers within the house when Mount Vesuvius erupted in 79 AD.

Researchers were able to isolate very small amounts of DNA from these skeletons. The DNA obtained was used in the polymerase chain reaction (PCR). Genetic fingerprinting was then carried out on this DNA to identify the skeletons.

The image below shows some of the results of the genetic fingerprinting of the three children and four adults.

unnamed-25

Explain why the researchers used PCR in their investigation.

4d2 marks

It was determined that the three children were siblings and shared the same biological parents. Their mother is Adult B.

Identify, with a reason, which of the other adults was the children’s father.

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54 marks

During PCR DNA is heated to 94 °C and DNA primers, nucleotides and thermostable enzymes are added to the mixture.

Explain the purpose of these steps.

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