Control of Gene Expression

Question 1

Explain how a single base substitution causes a change in the structure of this polypeptide

Answer 1

Change in primary structure
Means different hydrogen/ionic/disulphide bonds
Which causes a change in tertiary structure

Question 2

Increased methylation of the promoter region of a tumour suppressor gene
causes one type of human throat cancer.
In this type of throat cancer, cancer cells are able to pass on the increased
methylation to daughter cells. The methylation is caused by an enzyme called
DNMT.
Scientists have found that a chemical in green tea, called EGCG, is a
competitive inhibitor of DNMT. EGCG enables daughter cells to produce
messenger RNA (mRNA) from the tumour suppressor gene.
(b) Suggest how EGCG allows the production of mRNA in daughter cells.

Answer 2

ECCG binds to the active site of DNMT
This prevents it from methylating the promoter region of the tumour suppressor gene
This means that transcription factors can bind to promoter region
So RNA polymerase can also bind

Question 3

Describe how alterations to tumour suppressor genes can lead to the
development of tumours

Answer 3

Increased methylation of tumour suppressor gene means it is no longer transcribed
A DNA mutation can mean that primary structure and tertiary structure is changed so it is no longer complementary to the active site
Results in uncontrolled cell division

Question 4

Sometimes, a mutagenic agent causes DNA to break. A different enzyme called ATM binds to the broken DNA. This leads to the activation of a protein coded for by a tumour suppressor gene. The effect of ATM binding is to stop cell division until DNA is repaired. A mutation could result in a person having non-functional forms of the gene that produces ATM.
What can you predict about the possible effects of having a non-functional
form of ATM?

Answer 4

ATM is no longer complementary to the broken DNA so it will not bind.
This leads to cell division replicating the broken DNA
Tumour suppressor gene is not activated
May have no effect on heterozygous organism that still has a copy of the functional ATM gene

Question 5

Define what is meant by epigenetics.

Answer 5

A heritable change in an organisms gene function
Without a change in DNA base sequence

Question 6

Explain how increased methylation could lead to cancer

Answer 6

Increased methylation of a tumour suppressor gene
Transcription of tumour suppressor gene is inhibited
Which leads to uncontrolled cell division

Question 7

Give one way in which benign tumours differ from malignant tumours

Answer 7

They cannot invade into neighbouring tissues
They cannot metastasize and spread to other parts of the body

Question 8

MM is caused by a faulty receptor protein in cell-surface membranes. Cells in MM tumours can be destroyed by the immune system.
Suggest why they can be destroyed by the immune system

Answer 8

Receptor proteins are recognised by the immune system as foreign
T cells bind to faulty protein
Stimulate B cells to divide by clonal selection
B cells release antibodies against faulty protein

Question 9

One method of transferring RNAi molecules into cells involves combining
these molecules with a lipid. Suggest why this increases uptake of RNAi
molecules into cells

Answer 9

Lipids can diffuse across the phospholipid bilayer so no need for channel protein

Question 10

Steroid hormones are hydrophobic.
Explain why steroid hormones can rapidly enter a cell by passing through
its cell-surface membrane.

Answer 10

They are lipid soluble
They can diffuse through the phospholipid bilayer

Question 11

In the cytoplasm, testosterone binds to a specific androgen receptor (AR).
An AR is a protein.
Suggest and explain why testosterone binds to a specific AR

Answer 11

Testosterone has a specific tertiary structure that makes is complementary to the structure of a specific AR

Question 12

The binding of testosterone to an AR changes the shape of the AR. This
AR molecule now enters the nucleus and stimulates gene expression.
Suggest how the AR could stimulate gene expression.

Answer 12

It is a transcription factor
By binding to the promoter region of a gene it stimulates RNA transcriptase to bind and transcribe the gene

Question 13

Suggest how the production of ‘antisense’ SUT1 mRNA in type A plants
would reduce the expression of the SUT1 gene

Answer 13

Antisense is complementary to sense mRNA
Antisense mRNA binds to sense mRNA
This prevents the mRNA from binding to a ribosome
This means the mRNA will not be translated into a protein

Question 14

The first successful drug trial to reduce concentrations of huntingtin in the
brain used single-stranded DNA molecules (lines 13–14).
Suggest and explain how this drug could cause a reduction in the
concentration of the protein huntingtin.

Answer 14

DNA is complementary to mRNA
Binds to mRNA and becomes double stranded
Prevents mRNA from being translated

Question 15

Suggest how the siRNA produced a reduction in protein production.

Answer 15

siRNA is complementary to mRNA for producing proteins
It binds to mRNA and makes it double stranded
This means it can no longer be translated as it will not bind to ribosomes
siRNA also allows enzymes to bind and hydrolyse mRNA to prevent translation
This decreases the levels of proteins produced by this gene

Question 16

Myelodysplastic syndromes (MDS) are a group of malignant cancers. In MDS,
the bone marrow does not produce healthy blood cells.
Haematopoietic stem cell transplantation (HSCT) is one treatment for MDS. In
HSCT, the patient receives stem cells from the bone marrow of a person who
does not have MDS. Before the treatment starts, the patient’s faulty bone
marrow is destroyed.
(a) For some patients, HSCT is an effective treatment for MDS.
Explain how

Answer 16

The transplanted bone marrow can produce healthy blood cells to replace those effected by MDS
As the old bone marrow is removed there is no more MDS blood cells produced
Stem cells divide and replicate to replace old bone marrow

Question 17

Current research into the treatment of red-green colour blindness involves
the use of induced pluripotent stem cells (iPS cells) (lines 17–19).
Suggest how iPS cells could correct red-green colour blindness.

Answer 17

iPS cells divide
and differentiate into green sensitive cone cells

Question 18

The use of iPS cells could have advantages over the use of gene therapy to
correct red-green colour blindness (lines 19–20).
Using the information from the passage, suggest and explain reasons why

Answer 18

iPS are long term
They only require one surgery
There is a smaller chance of them being rejected by the body
Gene therapy has risks due to using viruses to transmit DNA

Question 19

Suggest how transcription factors can reprogramme cells to form iPS
cells

Answer 19

Bind to promoter region
Stimulate RNA polymerase

Question 20

Suggest how the growth of new blood vessels into damaged heart tissues
could increase the rate of repair of tissues

Answer 20

Increased blood flow means more oxygen and glucose
This means more respiration which produces ATP needed for protein synthesis and DNA replication to produce new cells to replace damaged ones
Also provides more amino acids for protein synthesis

Question 21

Name two techniques the scientists may have used when analysing viral
DNA to determine that the viruses were closely related.

Answer 21

PCR
Genetic fingerprinting
Gel Electrophoresis
Genome sequencing

Question 22

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 22

Extract DNA and add restriction endonucleases
Separate fragments using gel electrophoresis
Treat DNA to form single strands
The probe will hybridise to the SUT1 gene
Use autoradiography to show bound probe

Question 23

What is a DNA probe?

Answer 23

Short single strand of DNA
With bases complementary to a gene/allele

Question 24

Describe how the DNA is broken down into smaller fragments.

Answer 24

Add restriction endonucleases to the DNA
They cut at specific recognition sequences

Question 25

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

Answer 25

Lane 1 contains DNA fragments of known lengths
To compare the viral DNA fragments to

Question 26

Suggest and explain why it is important to be able to identify the specific
strain of M. tuberculosis infecting a patient.

Answer 26

To see if it is resistant to any antibiotics
So effective ones are prescribed
To produce a specific vaccine
As vaccination will stop the spread
Can test to see if other people have the same strain
Allowing controlling spread of disease by treating contacts before they get TB

Question 27

Describe how enzymes could be used to insert the GH gene into a
plasmid.

Answer 27

Restriction endonucleases cut at specific recognition sequences leaving sticky ends
DNA ligase joins DNA and plasmid

Question 28

Suggest and explain how delayed insertion of the GH gene could produce
offspring of transgenic fish without the desired characteristic

Answer 28

Mitosis has occurred before the gene is added
So the gametes of the fish may not contain the gene

Question 29

Suggest two features of the structure of different proteins that enable them
to be separated by gel electrophoresis.

Answer 29

Different mass of polypeptides
They have different charges
R groups differ

Question 30

Any DNA in the sample is hydrolysed by enzymes before the sample is
added to the reaction mixture.
Explain why

Answer 30

To remove any other DNA present
As this DNA would also be amplified

Question 31

Suggest one reason why DNA replication stops in the polymerase chain
reaction.

Answer 31

Limited number of nucleotides/primers

Question 32

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 32

Base sequences differ
So a number of different complementary primers are required

Question 33

Explain why only reverse transcriptase and a gene machine would produce DNA that E. coli could
use to make HGH.

Answer 33

DNA from restriction endonucleases contains introns
E.coli cannot remove introns

Question 34

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.

Answer 34

Use restriction endonucleases on the plasmids to cut at specific recognition sequences
So that both have complementary sticky ends
Use DNA ligase to join the complementary sticky ends

Question 35

Suggest why the plasmids were injected into the eggs of silkworms, rather
than into the silkworms.

Answer 35

As it will then be present in all of the silkworms cells
So it will be present in cells that produce silk

Question 36

Suggest why the scientists used a marker gene and why they used the
EGFP gene.

Answer 36

Not all silkworms will take up plasmid
Those that have will glow under UV

Question 37

What would the scientists have inserted into the plasmid along with the
spider gene to ensure that the spider gene was only expressed in the silk
glands of the silkworms?

Answer 37

Promoter region

Question 38

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

Answer 38

Add DNA fragment, primers, Taq polymerase and DNA nucleotides
DNA fragment is heated up to 95C so that hydrogen bonds are broken and strands separate
Reaction mixture cooled to 50C to allow DNA primers to anneal
Reaction mixture heated to 72C, Taq polymerase joins nucleotides

Question 39

The figure below shows the number of DNA molecules produced using a PCR.
(b) Explain the shape of the curve in the figure above

Answer 39

Initial growth is slow and then grows exponentially as number of DNA molecules doubles with each cycle
It then levels off as it runs out of primers/nucleotides