chapter 21 exam questions Flashcards
BRCA1 and BRCA2 are human genes that code for tumour suppressor proteins. Mutations
in BRCA1 and BRCA2 can cause cancer (lines 1–2). Explain how (3)
-change to DNA base sequence
-change to amino acid sequence
-results in uncontrollable cell division
Genetic testing, using DNA from saliva, can screen for all known harmful mutations in both
genes (lines 5–6). Describe how this DNA could be screened for all known harmful
mutations in both genes (4)
-amplify using PCR
-cut using restriction endonuclease
-separate using gel electropherisis
-add dna probe nad binding by DNA hybridisation.
Effective treatment of ER-positive breast cancers often involves the use of drugs which
have a similar structure to oestrogen (lines 9–10).
Suggest and explain how these drugs are an effective treatment of ER-positive breast
cancers. (3)
-drug binds to receptor
-prevents oestrogen binding
-transcription factor cannot bind to promoter.
Describe and explain how the polymerase chain reaction (PCR) is used to amplify a DNA
4.
fragment. (4)
-requires DNA nucleotides, primer, DNA polymerase
-heat to 95 degrees to break hydrogen bonds
-cool to 40 degrees to allow primer to bind to DNA
-heat to 70 degrees so DNA polymerase can join adjacent nucleotides by forming phosphodiester bonds.
A scientist produced transgenic zebrafish.
5.
She obtained a gene from silverside fish. The gene codes for a growth hormone (GH).
She inserted copies of this GH gene into plasmids. She then microinjected these recombinant
plasmids into fertilised egg cells of zebrafish.
(a)
Describe how enzymes could be used to insert the GH gene into a plasmid. (2)
restriction endonuclease cuts plasmid
-DNA ligase joins DNA and plasmid.
Microinjection of DNA into fertilised egg cells is a frequent method of producing transgenic
fish. However, the insertion of the transferred gene into nuclear DNA may be delayed.
Consequently, the offspring of transgenic fish may not possess the desired characteristic.
Suggest and explain how delayed insertion of the GH gene could produce offspring of
transgenic fish without the desired characteristic (2)
-cell division has already occured
-gametes do not receive the gene.
Haematopoietic stem cell transplantation (HSCT) is a long-term treatment for SCD. In HSCT, the
patient receives stem cells from the bone marrow of a person who does not have SCD. The
donor is often the patient’s brother or sister. Before the treatment starts, the patient’s faulty bone
marrow cells have to be destroyed.
(b)
Use this information to explain how HSCT is an effective long-term treatment for SCD (3)
-stem cells divide/replicate
-healthy cells produced
-no faulty cells
Some scientists have concluded that this method of gene therapy will be a more effective
long-term treatment for SCD than HSCT. Use all the information provided to evaluate this
conclusion (3)
-donors not required
-long term effects not known
-less chance of rejection.
what is a DNA probe? (2)
-short single strand of DNA
-bases complimentary to mutation/allele/gene
Lane 1 of Figure 2 enabled the size of the different viral fragments to be determined.
Suggest and explain how. (2)
-known sizes/lengths
-compare
Another group of scientists thought that pesticide resistance in some flies was related
toincreased activity of an enzyme called P450 monooxygenase (PM). This enzyme breaks
down insecticides.
The scientists obtained large numbers of resistant and non-resistant flies. They then set up
the following experiments.
* Non-resistant flies exposed to insecticide.
(3)
(2)
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* Resistant flies exposed to insecticide.
* Resistant flies treated with an inhibitor of PM and then exposed to insecticide.
They then determined the percentage of flies that were dead at different times after being
exposed to insecticide.
Figure 2 shows their results.
Figure 2
(i)
(ii)
Explain why the scientists carried out the control experiment with the non
resistantflies. (2)
______________________________________________________________
to see effect of enzyme
to compare with other two experiments.
The scientists used the polymerase chain reaction (PCR) to produce copies of the cDNA.
They added a DNA probe for allele A to the cDNA copies. This DNA probe had a dye attached
to it. This dye glows with a green light only when the DNA probe is attached to its target
cDNA. (b) Explain why this DNA probe will only detect allele A. (2)
DNA probe is complimentary and will bind by forming hydrogen bonds/complimentary bases.
-so only this DNA will give out green light.
The scientists used this method with cells from two people, H and G.
One person was homozygous, AA, and the other was heterozygous, Aa.
The scientists used the PCR and the DNA probe specific for allele A on the cDNA from
both people.
The figure shows the scientists’ results.
(i)
(ii)
Explain the curve for person H. (3)
-more DNA probe binds
-DNA doubles with each PCR cycle
-so double the amount of light.
Which person, H or G, was heterozygous, Aa? Explain your answer. (2)
G as half the amount of DNA probe attaching
so half the intensity of green light.
The jellyfish gene attached to the human Factor IX gene (Stage 2) codes for a
protein that glows green under fluorescent light. Explain the purpose of attaching this
gene. __ (2)
-acts as market gene to show that gene has been take up
-only insert gene that shows flurescence.
