epigenetics questions

Question 1

use info from the diagram to suggest how the binding of interferon gamma to its receptor protein leads to the production of phosphorylated STAT 1 (2)

Answer 1

interferon gama alters tertiary structure of receptor protein
-activates enzyme
-use of ATP to phosphorylate STAT1

Question 2

oestrogen is a hormone that affects transcription. It forms a complex with a receptor in the cytoplasm of target cells.
Explain how an activated oestrogen receptor affects the target cell (2)

Answer 2

transcription factor binds to promoter and stimulates RNA polymerase
initiates transcription.

Question 3

oestrogen only affects target cells. Explain why oestrogen does not affect other cells in the body (1)

Answer 3

other cells do not have an oestrogen receptor site

Question 4

Scientists investigated the effectiveness of two types of RNA interference (RNAi)
molecules on reducing HBV replication. These molecules were:
* short hairpin RNA (shRNA)
* long hairpin RNA (IhRNA).
The scientists infected mouse liver cells with HBV and transferred either shRNA
or lhRNA into these cells. Then they determined the concentration of the
attachment proteins, HBsAg, in these cells.
The concentration of HBsAg is a measure of HBV replication.
Figure2 shows the scientists’ results.
The error bars represent ±2 standard deviations from the mean, which includes
over 95% of the data.
Figure 2

Using all the information provided, evaluate the use of the two types of
RNAi in treating hepatitis B in humans.
Do not refer in your answer to how RNAi reduces HBV replication. (5)

Answer 4

-both more effective than the control
shRNA more effective than iHRNA
significant difference
as standard deviations do not overlap
-only tested in mice/not tested in humans
do not know long term effects
in vitro not in vivo

Question 5

Testosterone is a steroid hormone that belongs to a group of male sex hormones
called androgens.
(a)
(b)
Steroid hormones are hydrophobic.
Explain why steroid hormones can rapidly enter a cell by passing through
its cell-surface membrane. (2)

Answer 5

lipid soluble
so can diffuse through the phospholipid bilayer

Question 6

Plants transport sucrose from leaves to other tissues for growth and storage.
SUT1 is a sucrose co-transporter protein.
Scientists investigated whether the cells of tobacco plant leaves used SUT1 to
transport sucrose to other tissues.
(b)
To study the role of SUT1 in tobacco plants, scientists reduced the
expression of the SUT1 gene.
When the SUT1 gene is transcribed, the SUT1 mRNA produced is called
‘sense’ SUT1 mRNA. The scientists genetically modified plants by inserting
an extra gene so that this also allowed the production of ‘antisense’ SUT1
mRNA.
The scientists had two types of tobacco plants:
* type A – plants that were genetically modified
* type B – plants that were not genetically modified.
Suggest how the production of ‘antisense’ SUT1 mRNA in type A plants
would reduce the expression of the SUT1 gene.

Answer 6

-antisense mRNA complimentary to sense mRNA
-binds to sense mRNA
ribosomes wil not be able to bind
-prevents mRNA being translated.

Question 7

Guillain–Barré syndrome is a rare disease in which the immune system
damages the myelin sheath of neurones. Myelin sheath damage can cause a
range of symptoms, for example numbness, muscular weakness and muscular
paralysis. Sometimes, neurones of the autonomic nervous system are
affected, causing heart rate irregularities.
Huntington’s disease is a disorder caused when a protein called huntingtin
damages the brain. Huntingtin is produced because of a dominant, mutant
allele.
The first successful drug trial to reduce concentrations of huntingtin in the
human brain involved 46 patients. The patients received the drug for 4
5
10
months. The concentration of huntingtin was reduced in all the patients.
The drug was injected at the base of the spine into the cerebrospinal fluid
bathing the brain and spinal cord. The drug contains single-stranded DNA
molecules. These single-stranded molecules inhibit the mRNA needed to
produce huntingtin.
Symptoms of Huntington’s disease can start at any time, but usually develop
between 30 and 50 years of age. The likelihood and age when symptoms start
are linked to the number of CAG base sequence repeats in the gene for
Huntington’s disease. However, recent studies have suggested that
epigenetics may also affect the age when symptoms first start.
(c)
15
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. (3)

Answer 7

DNA is complementary to (m)RNA;
Binds to mRNA (for huntingtin);
Prevents translation;

Question 8

Suggest two reasons why people had the drug injected into the
cerebrospinal fluid (lines 12–13) rather than taking a pill containing the
drug (2)

Answer 8

drug will quickly reach brain.
drug not destroyed by acid.

Question 9

Suggest and explain one way epigenetics may affect the age when
symptoms of Huntington’s disease start. (2)

Answer 9

decreased acetylation of histone proteins
inhibits transcription.

Question 10

Scientists investigated the role of a protein called CENP-W in mitosis. Their
method involved cell and ultracentrifugation.
(a)
(b)
(c)
The scientists began by lysing (breaking open) cells and organelles using a
detergent that dissolves lipids in water.
Suggest how the detergent releases CENP-W from cells. (2)

Answer 10

-cell membrane has phospholipid bilayer structure
-detergent dissolves phospholipids

Question 12

Explain how ultracentrifugation separates CENP-W from other molecules (2)

Answer 12

-spin at high increasing speed
-separates organelles according to density.