16 DNA technology Flashcards
Name the enzyme used to produce cDNA. (1)
Reverse transcriptase
One of the viral enzymes makes a DNA copy of the virus RNA. Name this enzyme. (1)
Reverse transcriptase
What is restriction endonuclease used to do? (1)
To cut the DNA;
mRNA can be converted to cDNA. Name the enzyme used in this process. (1)
Reverse transcriptase;
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)
- Probe (base sequence) complementary (to
DNA of allele A/where A is); - (Probe) binds by forming base pairs/hydrogen
bonds; - So (only) this DNA labelled/has green dye/gives
out (green) light;
How can you tell an individual is heterozygous by using gene probe? (2)
(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);
For what purpose did the scientists use electrophoresis?
To separate the (pieces of) DNA;
Explain why the labelled DNA probe could be used to find out whether the haplotypes
were the same. (2)
Complimentary base sequence/complementary DNA;
Binds to both (haplotypes);
Label would show up in both;
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)
- Has the restriction site (cut by Kpn1);
- Once;
- 1000bp from Kpn1 on site of plasmid / ⅓ way along;
One of the fragments that the scientists obtained was described as “very large”.
What is represented by this very large fragment? (1)
(Most of) plasmid and rest of unknown DNA / rest of
recombinant plasmid / rest of plasmid but not 1000 bp part;
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)
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;;
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)
- Large pieces of DNA present;
- Add up to more than total length of original DNA / plasmid
plus inserted DNA; - Because this would add undigested to total (original)
length;
Name the type of enzyme that is used to cut the gene for Factor IX from human DNA
(Stage 1) . (1)
Restriction / endonuclease;
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)
- (Acts as a) marker gene;
- Shows that the (human)
gene has been taken
up/expressed; - (Only) implant cells/embryos
that show fluorescence /
contain the jellyfish gene;
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)
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);
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)
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;
Only one of these people tested positive for Huntington’s disease. Which person was
this? Explain your answer.
Person ……………………………………………………………………………………………………………….
Explanation ………………………………………………………………………………………………………. (2)
jun12
- Person K;
- (As has) high(est) band/band
that travelled a short(est)
distance/slow(er) so has
large(st) fragment/number of
CAG repeats;
) 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)
Run fragments of known length / CAG repeats (at the same time);
) Two bands are usually seen for each person tested. Suggest why only one band was
seen for Person L. (1)
Homozygous / (CAG) fragments
are the same length/size/mass;
The geneticist told the couple they were both carriers of the mutated gene.
Explain how he reached this conclusion. (3)
jun13
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;
The DNA probe the geneticist used was for an exon in the DNA, not an intron. Explain why (3)
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;
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)
- Restriction mapping/described;
- DNA/base sequencing (of
fragments)/ description/name of
method;
What is the role of DNA polymerase?
Joins nucleotides together
What is the role of DNA ligase?
Permanently joins complementary bases of sticky ends
Why must the same restriction endonuclease be used to cut plasmid/fragment being inserted? (3)
sticky ends
complementary bases
DNA ligase
Advantages of in vivo? (3)
in vitro?
Recombinant DNA, accurate, low contamination
Rapid, non-living cells
Describle PCR (3)
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.
What causes CF? (5)
How is treated?
By?
Mutation of recessive allele, nonfunctional CFTR gene, no Cl ions transported, no osmosis, dry epithelial membranes.
Gene supplementation/replacement
Somatic-cell gene therapy
DNA probes:
Function?
How do they work? (3)
Identify particular genes
- Base sequence complementary particular gene
- Binds by forming base pairs/hydrogen bonds;
- Gene labelled by fluorescent/radioactive
Function of:
Base sequencing?
Method?
Restriction mapping?
Method?
Electrophoresis?
Method?
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.
Uses?
Genetic screening? (2)
Genetic fingerprinting? (2)
Determines probability of couple having offspring with genetic disorder.
Heterozygous = carriers.
Crime scene
Parental DNA testing
