8- Gene Technologies =)

Question 1

Explain the role of reverse transcriptase in RT-PCR (reverse transcriptase-polymerase chain reaction). (1)

Answer 1

produces cDNA using mRNA

Question 2

Explain the role of DNA polymerase in RT-PCR (reverse transcriptase-polymerase chain reaction). (1)

Answer 2

joins nucleotides to produce complementary strand of DNA

Question 3

Any DNA in the sample is hydrolysed by enzymes before the sample is added to
the reaction mixture, in RT-PCR (reverse transcriptase-polymerase chain reaction).
Explain why. (2)

Answer 3

• remove any DNA present
• ∵ this DNA would be amplified

Question 4

Suggest one reason why DNA replication stops in the polymerase chain reaction. (1)

Answer 4

limited no. of primers

Question 5

Name two techniques the scientists may have used when analysing viral DNA to determine that the viruses were closely related. (1)

Answer 5

1. DNA sequencing
2. Polymerase Chain Reaction
3. genetic fingerprinting
4. gel electrophoresis

Question 6

Determining the genome of the viruses could allow scientists to develop a vaccine.
Explain how. (2)

Answer 6

1. identify proteome
2. identify potential antigens

Question 7

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. (4)

Answer 7

1. extract DNA + add restriction endonucleases
2. electrophoresis to separate fragments
3. treat DNA –> single strands
4. probe w/ hybridise w/ SUT1 gene
5. autoradiography to show bound probe

Question 8

What is a DNA probe? (2)

Answer 8

• short single stranded DNA
• bases complimentary to gene/ known base seq

Question 9

Describe how DNA is broken down into smaller fragments. (2)

Answer 9

• restriction endonucleases
• cut DNA at specific base seq.

Question 10

What is meant by a non-coding base sequence? (1)

Answer 10

x code for a.a.

Question 11

Doctors can use the method with DNA probes to identify the specific strain of M. tuberculosis infecting a patient. This is very important when there is an outbreak of a number of cases of tuberculosis in a city.
Suggest and explain why it is important to be able to identify the specific strain of M. tuberculosis infecting a patient. (2)

Answer 11

1. 👑 see if strain resistant to any antibiotics –> prescribe right one//
2. see if any vaccine works against this strain –> vaccinate potential contacts
3. test other ppl to see if they have the same strain –> control spread

Question 12

Suggest one reason why DNA replication stops in the polymerase chain reaction. (1)

Answer 12

limited no. of primers

Question 13

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. (2)

Answer 13

• base seq. differ
• diff. complimentary primers required

Question 14

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. (1)

Answer 14

faster to use gene machine than all the enzyme-catalysed reactions (/ ↓ steps)

Question 15

Short tandem repeats (STRs) are short sequences of DNA, usually 2 to 7 base pairs, which are repeated a number of times.
STRs are found throughout the whole genome.
The repeated dequences in STRs are common to all humans. Due to variation in the number of repeats, STRs can be used in gentic fingerprinting.
Describe how STRs could be removed from a sample of DNA. (2)

Answer 15

• restriction endonucleases
• cut DNA at specific base seq

Question 16

Short tandem repeats (STRs) are short sequences of DNA, usually 2 to 7 base pairs, which are repeated a number of times.
STRs are found throughout the whole genome.
The repeated dequences in STRs are common to all humans. Due to variation in the number of repeats, STRs can be used in gentic fingerprinting.
Genetic fingerprinting using STRs requires amplification of the STRs using PCR. The short base sequences either side of a specific STR are known.
Explain the importance of knowing these base sequences in PCR. (2)

Answer 16

• for primers
• to produce complementary base seq

Question 17

Short tandem repeats (STRs) are short sequences of DNA, usually 2 to 7 base pairs, which are repeated a number of times.
During geneic fingerprinting, the different STRsare separated by gel electrophoresis.
Give two features of STRs which enable them to be separated by gel electrophoresis. (2)

Answer 17

1. -ve chrage
2. no. of nucleotides/ length

Question 18

3 uses of labelled DNA probes

Answer 18

screening patients for:
1. heritable conditions
2. drug responses
3. health risks

Question 19

The scientists wanted to know on which chromosome the gene with alleles R and r was located.
From the flies with genotype RR, they obtained cells that were in mitosis and added a labelled DNA probe specific for allele R.
They then looked at the cells under an optical microscope.
Explain why they used cells that were in mitosis. (2)

Answer 19

• chromosomes visible in cells in mitosis
• ✔ see which chromosome DNA probe attached to

Question 20

What is the role of a primer in PCR? (1)

Answer 20

enable replication to start

Question 21

Suggest one use of the polymerase chain reaction. (1)

Answer 21

replication of DNA in crime scene/ tissue sample/ for DNA sequencing/ gene cloning

Question 22

Give a reason why the reaction mixture is cooled to 40oC in PCR. (1)

Answer 22

binding of primers to DNA strands

primers/ nuleotides

Question 23

Explain one way in which the polymerase chain reaction differs from DNA replication in a cell. (2)

Answer 23

1. H bonds broken + separate strands formed by heat
2. PCR replicates pieces of DNA- ∵ DNA has been cut
3. primers added in PCR- to initiate replication

Question 24

Explain how electrophoresis separates the fragments of DNA cut by restriction endonuclease. (2)

Answer 24

• move towards +ve electrode ∵ DNA -ve charged
• diff rates of movement related to size/ charge

Question 25

Explain why base pairing are a suitable way of measuring the length of a piece of DNA. (2)

Answer 25

• DNA made of base pairs
• each base pair is the same length

Question 26

In 1991, 9 skeletons were found on an island. Very small amounts of DNA were isolated from these skeletons.
This DNA was used in the polymerase chain reaction (PCR). Genetic fingerprinting was then carried out on this DNA to identify the skeletons.
Explain why PCR was used in this investigation. (2)

Answer 26

• only small amounts –> PCR ↑ amount
• so enough DNA available for genetic fingerprinting

Question 27

  Scientists made an artificial gene which codes for insulin. They put the gene into a virus which was then injected into rats with type I diabetes. The virus was harmless to the rats but carried the gene into the cells of the rats.

The treated rats produced insulin for up to 8 months and showed no side-effects. The scientists measured the blood glucose concentrations of the rats at regular intervals. While the rats were producing the insulin, their blood glucose concentrations were normal.
Research workers have suggested that treating diabetes in humans by this method of gene therapy would be better than injecting insulin.
Evaluate this suggestion. (4)

Answer 27

➕ avoids injections (pain/ discomfort)
➕ longer lasting- new cells will have gene for insulin
➕ ↓ need to measure blood glucose conc (regulate)
➕ ↓ restriction on diet
➖ rats are diff to humans
➖ may have side effects
➖ long term effects x known
➖ substitute insulin may be rejected by body

Question 28

Explain the purpose of a marker gene when genetically modifying cells. (1)

Answer 28

• shows gene has been taken up//
• ✔ detection of genetically modified cells

Question 29

A husband and wife wanted to know whether they were carriers of the mutated form of a gene. This mutation is a deletion that causes a serious inherited genetic disorder in people who are homozygous.
A geneticist took samples of DNA from the husband and the wife. He used a DNA probe to look for the deletion mutation. The DNA probe was specific to a particular base
sequence in an exon in the gene. Exons are the coding sequences in a gene.
The DNA probe the geneticist used was for an exon in the DNA, not an intron.
Explain why. (3)

Answer 29

1. introns x translated
2. mutations of exons affect a.a. seq. –> Δ 3’ struc of protein
3. important to know if parents’ exons affected instead of introns (/ other parts of DNA)

Question 30

To make the DNA probe, the geneticist had to find the base sequence of the normal
gene. Once he had copies of the gene, what methods would he use to find the base
sequence of the gene? (2)

Answer 30

1. restriction mapping
2. DNA sequencing

Question 31

The scientists analysed the DNA on the Y chromosome and the DNA in the mitochondria of the Swedish wolves. They concluded that the Swedish wolf population descended from one male wolf from Finland and one female wolf from Russia.
Suggest why DNA in the mitochondria helped them to reach this conclusion. (1)

Answer 31

mitochondria in egg x sperm!

Question 32

Explain how genetic fingerprinting allows scientists to identify the father of a particular panda cub. (2)

Answer 32

• all bands in cub that x come from mother
• must be in father’s DNA fingerprint

Question 33

When pandas are bred in zoos, it is important to ensure only unrelated pandas breed.
Suggest how gentic fingerprints might be used to sdo this. (1)

Answer 33

select pairs w/ dissimilar DN fingerprints