16 DNA technology

Question 1

Name the enzyme used to produce cDNA. (1)

Answer 1

Reverse transcriptase

Question 2

One of the viral enzymes makes a DNA copy of the virus RNA. Name this enzyme. (1)

Answer 2

Reverse transcriptase

Question 3

What is restriction endonuclease used to do? (1)

Answer 3

To cut the DNA;

Question 4

mRNA can be converted to cDNA. Name the enzyme used in this process. (1)

Answer 4

Reverse transcriptase;

Question 5

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.

Explain why this DNA probe will only detect allele A. (2)

Answer 5

1. Probe (base sequence) complementary (to
   DNA of allele A/where A is);
2. (Probe) binds by forming base pairs/hydrogen
   bonds;
3. So (only) this DNA labelled/has green dye/gives
   out (green) light;

Question 6

How can you tell an individual is heterozygous by using gene probe? (2)

Answer 6

(G because)
1. (Heterozygous) only has half the amount of
probe for A attaching / only half the amount of
DNA/allele A (to bind to);
2. (So,) only produced (about) half the
light/glow/intensity (of H) (per cycle of PCR);

Question 7

For what purpose did the scientists use electrophoresis?

Answer 7

To separate the (pieces of) DNA;

Question 8

Explain why the labelled DNA probe could be used to find out whether the haplotypes
were the same. (2)

Answer 8

Complimentary base sequence/complementary DNA;
Binds to both (haplotypes);
Label would show up in both;

Question 9

5 (a) When the scientists digested one of the recombinant plasmids with Kpn1, they
obtained two fragments. One fragment was measured as 1 000 bp.
The other fragment was described as “very large”.
5 (a) (i) What does this show about the base sequence of the unknown piece of DNA? (2)

Answer 9

1. Has the restriction site (cut by Kpn1);
2. Once;
3. 1000bp from Kpn1 on site of plasmid / ⅓ way along;

Question 10

One of the fragments that the scientists obtained was described as “very large”.
What is represented by this very large fragment? (1)

Answer 10

(Most of) plasmid and rest of unknown DNA / rest of

recombinant plasmid / rest of plasmid but not 1000 bp part;

Question 11

Scientists can separate fragments of DNA using electrophoresis. Suggest how they
can use electrophoresis to estimate the number of base pairs in the separated
fragments. (2)

Answer 11

Give one mark for answer confined to smaller fragments
move further/faster;
Give two marks for comparing with distance/speed moved by
fragments of known size/markers / DNA ladder;;

Question 12

Scientists need to take precautions when they carry out restriction mapping. They
need to make sure that the enzyme they have used has completely digested the DNA.
One check they may carry out is to add the sizes of the fragments together.
How could scientists use this information to show that the DNA has not been
completely digested? Explain your answer (2)

Answer 12

1. Large pieces of DNA present;
2. Add up to more than total length of original DNA / plasmid
   plus inserted DNA;
3. Because this would add undigested to total (original)
   length;

Question 13

Name the type of enzyme that is used to cut the gene for Factor IX from human DNA
(Stage 1) . (1)

Answer 13

Restriction / endonuclease;

Question 14

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 14

1. (Acts as a) marker gene;
2. Shows that the (human)
   gene has been taken
   up/expressed;
3. (Only) implant cells/embryos
   that show fluorescence /
   contain the jellyfish gene;

Question 15

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. (2)

Answer 15

1. Factor IX present in /
extracted from milk;
2. Gene only expressed in
mammary glands/udder /
gene not expressed
elsewhere;
3. Do not need to kill sheep
(to obtain Factor IX);

Question 16

Many attempts to produce transgenic animals have failed. Very few live births result
from the many embryos that are implanted.
5 (c) (i) Suggest one reason why very few live births result from the many embryos that are
implanted. (2)

Answer 16

1. Mutation / nucleus/
chromosomes/DNA may be
damaged / disrupts genes;
2. May interfere with proteins
(produced)/gene expression/
translation;
OR
3. Embryo/antigens foreign;
4. Embryo is rejected/attacked
 by immune system;

Question 17

Only one of these people tested positive for Huntington’s disease. Which person was
this? Explain your answer.
Person ……………………………………………………………………………………………………………….
Explanation ………………………………………………………………………………………………………. (2)

jun12

Answer 17

1. Person K;
2. (As has) high(est) band/band
   that travelled a short(est)
   distance/slow(er) so has
   large(st) fragment/number of
   CAG repeats;

Question 18

) The diagram only shows part of the gel. Suggest how the scientists found the number
of CAG repeats in the bands shown on the gel. (1)

Answer 18

Run fragments of known length /
CAG repeats (at the same time);

Question 19

) Two bands are usually seen for each person tested. Suggest why only one band was
seen for Person L. (1)

Answer 19

Homozygous / (CAG) fragments

are the same length/size/mass;

Question 20

The geneticist told the couple they were both carriers of the mutated gene.
Explain how he reached this conclusion. (3)

jun13

Answer 20

1. Carriers are heterozygous/have
one normal copy and one mutant
copy of gene/have one recessive
allele/don’t have the condition;
2. Both have DNA that binds (about)
half/50% amount of probe (that
non-carrier does);
3. Probe binds to dominant/healthy
allele;
4. So only one copy of exon in their
DNA/ have one copy of gene
without exon/base sequence for
probe to bind to;

Question 21

The DNA probe the geneticist used was for an exon in the DNA, not an intron. Explain why (3)

Answer 21

1. Introns not translated/not in
mRNA;
2. (Exons) code for amino
acids/introns do not code for
amino acids;
3. Mutations of these (exons) affect
amino acid sequences;
4. (That produce) faulty
protein/change tertiary structure
of protein;
5. So important to know if parents’
exons affected, rather than any
other part of DNA/introns;

Question 22

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 22

1. Restriction mapping/described;
2. DNA/base sequencing (of
   fragments)/ description/name of
   method;

Question 23

What is the role of DNA polymerase?

Answer 23

Joins nucleotides together

Question 24

What is the role of DNA ligase?

Answer 24

Permanently joins complementary bases of sticky ends

Question 25

Why must the same restriction endonuclease be used to cut plasmid/fragment being inserted? (3)

Answer 25

sticky ends
complementary bases
DNA ligase

Question 26

Advantages of in vivo? (3)

in vitro?

Answer 26

Recombinant DNA, accurate, low contamination

Rapid, non-living cells

Question 27

Describle PCR (3)

Answer 27

95 degrees - DNA fragments, DNA polymerase and primers in thermocycler. DNA strands separate.
55 degrees - Primers attach to end of DNA fragment - DNA polymerase activated.
72 degrees - optimum temperature for DNA polymerase - joins nucleotides together.

Question 28

What causes CF? (5)

How is treated?

By?

Answer 28

Mutation of recessive allele, nonfunctional CFTR gene, no Cl ions transported, no osmosis, dry epithelial membranes.

Gene supplementation/replacement

Somatic-cell gene therapy

Question 29

DNA probes:

Function?

How do they work? (3)

Answer 29

Identify particular genes

1. Base sequence complementary particular gene
2. Binds by forming base pairs/hydrogen bonds;
3. Gene labelled by fluorescent/radioactive

Question 30

Function of:

Base sequencing?
Method?

Restriction mapping?
Method?

Electrophoresis?
Method?

Answer 30

Identifies base sequence of gene trying to locate
Sanger method (uses terminator molecules to produce different length fragments)

Identifies base sequence of gene trying to locate
Restriction endonucleases - specific recognition sites.

Used to separate DNA fragments.
Smaller fragments move faster/further.

Question 31

Uses?

Genetic screening? (2)

Genetic fingerprinting? (2)

Answer 31

Determines probability of couple having offspring with genetic disorder.
Heterozygous = carriers.

Crime scene
Parental DNA testing