gene technology

Question 1

There are different types of gene mutation.
Put a tick (✓) in the box next to the statement which describes incorrectly the effect of the mutation in an exon of a gene.

A substitution may not result in a change to the encoded amino acid.

An inversion will result in a change in the number of DNA bases.

A deletion will result in a frame shift.

An addition will result in a frame shift.

Answer 1

Box 2

Question 2

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

Answer 2

1. (Increased) methylation (of tumour suppressor genes);
   Accept abnormal methylation or hypermethylation
   Ignore decreased acetylation of histones
2. Mutation (in tumour suppressor genes);
3. Tumour suppressor genes are not transcribed/expressed
   OR
   Amino acid sequence/primary structure altered;
   Accept mRNA for transcription/transcribed
   Accept tertiary structure altered
   Accept different amino acid
   Ignore reference to protein not being formed
4. (Results in) rapid/uncontrollable cell division;

Question 3

What is meant by a genome?

Answer 3

(All) the DNA in a cell/organism;

Question 4

Describe the roles of two named types of enzymes used to insert DNA fragments into plasmids.

Answer 4

1. Restriction (endonuclease/enzyme) to cut plasmid/vector;

2. Ligase joins gene/DNA to plasmid/vector;

Question 5

The soybean cells were screened for the presence of the P34 protein. This process involved the use of gel electrophoresis to separate proteins extracted from soybean cells.
Suggest two features of the structure of different proteins that enable them to be separated by gel electrophoresis.

Answer 5

1. Mass/number of amino acids/polypeptides;
2. Charge;
3. R groups (differ);

Question 6

Scientists investigated the role of a protein called CENP-W in mitosis. Their method involved cell fractionation and ultracentrifugation.
(a) 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.

Answer 6

1. Cell membranes made from phospholipid;
   Note: candidates may make both mark points in once statement
2. (Detergent) dissolves membranes / phospholipid (bilayer);

Question 7

Explain how ultracentrifugation separates CENP-W from other molecules.

Answer 7

1. Spin (liquid / supernatant) at (very) high speed / high g;
2. Molecules / CENP-W separates depending on (molecular) mass / size / density

Question 8

Dengue is a serious disease that is caused by a virus. The virus is carried from one person to another by a mosquito, Aedes aegypti. One method used to try to reduce transmission of this disease is the Sterile Insect Technique (SIT). This involves releasing large numbers of sterile (infertile) male A. aegypti into the habitat. These males have been made infertile by using radiation.
(a) Explain how using the SIT could reduce transmission of dengue.

Answer 8

1.      Compete (with fertile males) to mate / for food / resources
OR
intraspecific competition;
2.      Do not reproduce / breed
OR
Reduces population (of mosquitoes);

Question 9

Describe how the mark-release-recapture method could be used to determine the population of A. aegypti at the start of the investigation.

Answer 9

1. Capture / collect / sample, mark and release;
2. Leave time for mosquitoes / Aedes to disperse before second sampling / collection;
3. (Population =) number in first sample × number in second sample divided by number of marked in second sample / number recaptured;

Question 10

Each year, a few people with type I diabetes are given a pancreas transplant. Pancreas transplants are not used to treat people with type II diabetes.
Give two reasons why pancreas transplants are not used for the treatment of type II diabetes.

Answer 10

1. (Usually)Type II produce insulin;
2. Cells / receptors less sensitive / responsive (to insulin)
   OR
   Faulty (insulin) receptors;
3. (Treated / controlled by) diet / exercise;

Question 11

The pancreas produces the hormone insulin.
Put a tick (✔) in the box next to the statement which describes incorrectly the action of insulin.

Activates enzymes involved in the conversion of glucose to glycogen.

Controls the uptake of glucose by regulating the inclusion of channel proteins in the surface membranes of target cells.

Attaches to receptors on the surfaces of target cells.

Activates enzymes involved in the conversion of glycerol to glucose.

Answer 11

Tick in box 4

Question 12

Explain the role of reverse transcriptase in RT-PCR.

Answer 12

Produces (c)DNA using (m)RNA

Question 13

Explain the role of DNA polymerase in RT-PCR

Answer 13

Joins nucleotides to produce (complementary strand/s of) DNA;

Question 14

Any DNA in the sample is hydrolysed by enzymes before the sample is added to the reaction mixture.
Explain why. (RT-PCR)

Answer 14

1. To remove any DNA present;

2. As this DNA would be amplified / replicated

Question 15

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

Answer 15

Limited number of primers / nucleotides;

Question 16

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 16

1. Base sequences differ;

2. (Different) complementary primers required;

Question 17

Explain the role of reverse transcriptase

Answer 17

Produces (c)DNA using (m)RNA;

Question 18

Explain the role of DNA polymerase in RT-PCR.

Answer 18

Joins nucleotides to produce (complementary strand/s of) DNA;

Question 19

Name two enzymes involved in the semi-conservative replication of DNA.

Answer 19

(DNA) helicase;

2. (DNA) polymerase;

Question 20

The enzyme-catalysed reactions activated by ATR only occur if the substrates have been phosphorylated.
Use your knowledge of energy changes in enzyme-catalysed reactions to suggest why.

Answer 20

(Phosphorylation / phosphate) makes substrates more reactive / raises their energy level(s) / lowers activation energy for the reaction;

Question 21

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 21

1. ATM will not bind to (broken) DNA;
2. DNA not repaired / cell still has broken DNA;
3. Cell division continues / tumour forms;
4. Tumour suppressor (gene) not effective / not activated;
5. May have no effect in diploid / heterozygous (organism);
6. (Which) still has a functional ATM / ATM gene;

Question 22

Define what is meant by epigenetics.

Answer 22

1. Heritable changes in gene function;

2. Without changes to the base sequence of DNA;

Question 23

Explain how increased methylation could lead to cancer.

Answer 23

1. Methyl groups (could be) added to (both copies of) a tumour suppressor gene;
2. The transcription of tumour suppressor genes is inhibited;
3. Leading to uncontrolled cell division.

Question 24

Give one way in which benign tumours differ from malignant tumours.

Answer 24

Cells of benign tumours cannot spread to other parts of the body / metastasise;
OR
Cells of benign tumours cannot invade neighbouring tissues.

Question 25

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 25

Faster to use gene machine than all the enzyme-catalysed reactions (involving reverse transcriptase);

Question 26

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 26

1. Cut the plasmid with a restriction endonuclease;
   Allow ‘add base sequences to blunt ends of plasmid and HGH gene’
2. (So that) both have complementary / sticky ends;
3. (Mix together) and add ligase to join the complementary / sticky ends;