chapter 21 exam questions

Question 1

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)

Answer 1

-change to DNA base sequence
-change to amino acid sequence
-results in uncontrollable cell division

Question 2

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)

Answer 2

-amplify using PCR
-cut using restriction endonuclease
-separate using gel electropherisis
-add dna probe nad binding by DNA hybridisation.

Question 3

 
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)

Answer 3

-drug binds to receptor
-prevents oestrogen binding
-transcription factor cannot bind to promoter.

Question 4

Describe and explain how the polymerase chain reaction (PCR) is used to amplify a DNA
4.
fragment. (4)

Answer 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.

Question 5

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)

Answer 5

restriction endonuclease cuts plasmid
-DNA ligase joins DNA and plasmid.

Question 6

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)

Answer 6

-cell division has already occured
-gametes do not receive the gene.

Question 7

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)

Answer 7

-stem cells divide/replicate
-healthy cells produced
-no faulty cells

Question 8

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)

Answer 8

-donors not required
-long term effects not known
-less chance of rejection.

Question 9

what is a DNA probe? (2)

Answer 9

-short single strand of DNA
-bases complimentary to mutation/allele/gene

Question 10

Lane 1 of Figure 2 enabled the size of the different viral fragments to be determined.
Suggest and explain how. (2)

Answer 10

-known sizes/lengths
-compare

Question 11

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)
______________________________________________________________

Answer 11

to see effect of enzyme
to compare with other two experiments.

Question 12

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)

Answer 12

DNA probe is complimentary and will bind by forming hydrogen bonds/complimentary bases.
-so only this DNA will give out green light.

Question 13

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)

Answer 13

-more DNA probe binds
-DNA doubles with each PCR cycle
-so double the amount of light.

Question 14

Which person, H or G, was heterozygous, Aa? Explain your answer. (2)

Answer 14

G as half the amount of DNA probe attaching
so half the intensity of green light.

Question 15

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)

Answer 15

-acts as market gene to show that gene has been take up
-only insert gene that shows flurescence.

Question 16

The promoter DNA from sheep (Stage 3) causes transcription of genes coding for
proteins found in sheep milk.
Suggest the advantage of using this promoter DNA

Answer 16

gene only expressed in mammary glands
do not need to kill sheep

Question 17

Many attempts to produce transgenic animals have failed. Very few live births result
fromthe many embryos that are implanted.
(i)
(ii)
Suggest one reason why very few live births result from the many embryos that are
implanted.

Answer 17

antigens of embryo are foreign
triggers immune response.

Question 18

It is important that scientists still report the results from failed attempts to
producetransgenic animals. Explain why (2)

Answer 18

saves time
method can be improved

Question 19

Comparing the base sequence of genes provides more evolutionary information than
comparing the structure of proteins. Explain why. (2)

Answer 19

-more bases than amino acids
-introns

Question 20

Scientists have used the RT-PCR method to detect the presence of
different RNA viruses in patients suffering from respiratory diseases.
The scientists produced a variety of primers for this procedure.
Explain why.

Answer 20

base sequences differ
complimentary primers needed

Question 21

(c)
(d)
The geneticist concluded it would be faster to create the HGH gene using a
gene machine than by using reverse transcriptase to convert mRNA for
HGH into cDNA.
Suggest why the geneticist reached this conclusion.

Answer 21

-faster to use gene machine than all enzyme catalysed reactions/extra step.

Question 22

The geneticist plans to use the plasmids containing the HGH gene to try to
transform cells of E. coli. She knows that some E. coli might not take up
the plasmid.
To enable her to identify which bacteria have taken up the plasmid with the
HGH gene, the plasmids she intends to use contain a gene that codes for a
green fluorescent protein (GFP). Bacteria that contain this plasmid glow
green under UV light.
(2)
(1)
(3)
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Suggest one advantage of using this gene for GFP to identify bacteria that
have taken up plasmids. (1)

Answer 22

can quickly identify transformed bacteria using UV light.

Question 23

After obtaining copies of the HGH gene, the geneticist will attempt to insert
them into plasmid vectors.
Describe how the geneticist would attempt to insert copies of the HGH
gene into these plasmids (3)

Answer 23

-use restriction endonuclease to cut plasmid
-creates sticky ends
-use DNA ligase to join complimentary sticky ends.

Question 24

SUT1 is a sucrose co-transporter protein.
Scientists investigated whether the cells of tobacco plant leaves used SUT1 to
transport sucrose to other tissues.
(a)
(b)
The scientists used a radioactively labelled DNA probe to show that the
cells of tobacco plant leaves contained the SUT1 gene.
Describe how they would do this.
Do not include PCR in your answer.
________________________________

Answer 24

-extract DNA and add restriction enzyme
-separate using gel electropherisi
treat to make sample single stranded
the DNA probe will hydrbridise with the gene
-use autoradiography

Question 25

xplain how the use of DNA probes produced the results in the diagram. (3)

Answer 25

DNA probe has specific base sequence
complimentary to base sequence on spacer
binds and produces light/fluroescene