Edexcel International A-Level Biology I
Unit 8 Coordination, Response and Gene
Technology Exam Questions with
Correct Answers
POLYMERASE CHAIN REACTION [PCR] - Answer-An automated process that
amplifies selected regions of DNA using alternate stages of polynucleotide separation
[denaturation of DNA] and the replication of new DNA strands catalyzed by DNA
polymerase.
PRIMERS - Answer-Short sequences of nucleotides used in the polymerase chain
reaction. Primers have a set of bases complementary to those at one end of each of the
two DNA fragments. Primers provide the starting sequences for DNA polymerase to
begin DNA copying because DNA polymerase can only attach DNA nucleotides to the
end of an existing chain.
DNA POLYMERASE - Answer-An enzyme which joins DNA nucleotides together during
DNA replication and the polymerase chain reaction. Taq polymerase is an example of
such an enzyme. This was originally obtained from bacteria in hot springs and is
thermostable.
THERMOCYCLER - Answer-A computer controlled machine used in the polymerase
chain reaction that varies temperatures precisely over a period of time.
ANNEALING - Answer-The process where primers join to their complementary bases at
the end of the DNA fragment. This occurs during the PCR when the mixture is cooled to
55oC.
DNA PROBE - Answer-A short, single stranded length of DNA that either has
nucleotides labelled with a radioactive isotope e.g. 32P or fluorescently labelled to emit
light under certain conditions. DNA probes are used to locate a particular gene or DNA
sequence.
DNA HYBRIDISATION - Answer-When separated DNA strands carrying the
gene/nucleotide sequence to be identified, is mixed with a DNA probe, the probe binds
to the complementary base sequence on one of the DNA strands. The site where the
probe binds can be identified by the radioactivity or fluorescence emitted.
"VARIABLE NUMBER TANDEM - Answer-
REPEATS [VNTRs]" - Answer-DNA bases which are non coding. In every individual
[except identical twins] the number and length of VNTR's is unique. The probability of
, two individuals having identical VNTR sequences is very very small. However the more
closely related two individuals are, the more similar the VNTR sequences will be. This
forms the basis of genetic fingerprinting , a diagnostic tool used in paternity cases,
forensic science, plant and animal breeding and medical diagnosis e.g. Huntington's
disease.
GENETIC FINGERPRINTING - Answer-A diagnostic tool used in paternity cases,
forensic science, plant and animal breeding and medical diagnosis e.g. Huntington's
disease. The technique is based on the unique pattern of variable number tandem
repeats. The number and length of VNTR's is different in all individuals except identical
twins. The making of a genetic fingerprint consists of five stages: extraction of DNA and
its quantity increased by PCR; digestion of DNA into fragments, separation of DNA
fragments by gel electrophoresis; hybridisation where DNA probes bind to the VNTR's
and then development to reveal the position of the DNA probes using southern blotting
techniques.
DNA GEL ELECTROPHORESIS - Answer-The separation of negatively charged DNA
fragments by differential movement towards the anode through an agarose gel in an
electric field. The degree of movement is dependent on the mass of the DNA fragments
and their net charge.
DNA SEQUENCING - Answer-The process of determining the order of nucleotide bases
in samples of DNA. This is done by detecting the nucleotide bases A, T, C and G as
they are added to a template strand by a polymerase enzyme.
HIGH THROUGHPUT SEQUENCING - Answer-Any method in which the base
sequence in samples of DNA, including whole genomes are determined in a short
period of time.
SINGLE NUCLEOTIDE POLYMORPHISMS - Answer-[SNPs]. Sequences of DNA that
vary between people by a single nucleotide. They can occur in genes but they are much
more common in non-coding DNA. When SNP's occur in genes, they are referred to as
alleles. SNP's are caused by base substitution mutations. Substitution mutations in a
gene may not cause a change in the amino acid sequence of the protein as the genetic
code is degenerate.
HAPLOTYPE - Answer-A set of genes inherited together from one parent. Haplotypes
can provide insight into the history of human migrations. As a result of the founder
effect, people with the same ancestral origins tend to share SNP's and have very similar
haplotypes.
RECOMBINANT DNA [rDNA] - Answer-A type of DNA formed by combining DNA from
two different sources such as human and plasmid
ELECTROPORATION - Answer-A process where an electric shock is given to stimulate
cells to take up pieces of DNA such as plasmids and bacterial artificial chromosomes.
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