State the purpose of DNA replication.
The diagrams below show two models of DNA replication.
State, with a reason, which diagram, A or B, is correct.
Calculate the amount of the total DNA that consists of the original DNA strands after 3 full cycles
Was this exam question helpful?
Both DNA and RNA contain pentose sugars in their sugar-phosphate backbones.
Define the term pentose in reference to sugar molecules.
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.
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.
Was this exam question helpful?
Describe how the structure of a tRNA molecule contributes to the accuracy of the translation.
Draw a labelled diagram of two nucleotides bonded together within the same DNA strand.
Outline the three stages of polymerase chain reaction (PCR).
Was this exam question helpful?
DNA replicates in a semi-conservative way.
Define the term 'semi-conservative' with regards to DNA replication.
Was this exam question helpful?
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.
Identify the suspect that most likely committed the crime.
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.
Was this exam question helpful?
In the electrophoretogram, the DNA has moved from the negative cathode to the positive anode.
State the property of DNA which results in movement from cathode to anode.
State two uses of gel electrophoresis.
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.
The stages of electrophoresis are shown below.
Construct a logical sequence of events in gel electrophoresis by numbering the steps 1–4. 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 |
A sample of DNA is collected from an individual 1. 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
Was this exam question helpful?
The molecules named below are all required during the process of PCR.
Identify the function for each of the molecules named by drawing a line between the boxes to show
State the property of Taq polymerase that makes it suitable for use in PCR.
The graph shows how the quantity of DNA increases over several cycles of PCR
Identify the stage of the graph where replication is exponential.
The electrophoretogram shows a pattern produced from the DNA of two people.
State how the electrophoretogram shows that the two people are identical twins.
Was this exam question helpful?
During electrophoresis, molecules travel through an agarose gel.
State two properties of the molecules that determine how far through the gel they can travel.
Outline the process used to determine paternity using electrophoretograms produced in gel electrophoresis.
Was this exam question helpful?
Describe the structural features of a DNA molecule.
Was this exam question helpful?
The diagram below shows one cycle of the polymerase chain reaction (PCR).
Outline the events that are taking place during stage 1 in the diagram.
Molecule X in the diagram shown in part (a) is a DNA primer.
State the role of a DNA primer in PCR.
Stage 3 in PCR involves an enzyme.
Explain how the enzyme is suitable for its role in PCR.
State two applications of PCR.
Was this exam question helpful?
State two features that allow nucleic acids or proteins to be separated by gel electrophoresis.
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.
State which class of enzymes can be used to cleave DNA into fragments prior to gel electrophoresis.
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).
(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.
Was this exam question helpful?
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
(i) Name and describe these steps
[3]
(ii) Suggest why the researchers used PCR in their investigation.
[2]
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.
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.
[2]
(ii) Suggest why the profiles for Child 1 and Child 2 are the same.
[1]
Describe the method by which DNA profiling is undertaken and explain why it is a useful technique.
Was this exam question helpful?
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.
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.
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.
Was this exam question helpful?
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.
Was this exam question helpful?
The diagram below shows the processes involved in the amplification of a sample of viral RNA.
Compare and contrast the process in the image with the process used in the amplification of a fragment of DNA.
RNAase is an enzyme that digests RNA. 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.
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.
Explain why the researchers used PCR in their investigation.
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.
Was this exam question helpful?
During PCR DNA is heated to 94 °C and DNA primers, nucleotides and thermostable enzymes are added to the mixture.
Explain why:
(i) DNA is heated to 94 °C.
[1]
(ii) DNA primers are used.
[1]
(iii) Nucleotides are used.
[1]
(iv) Thermostable enzymes are used.
[1]
Was this exam question helpful?