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CIE A Level Biology Genetic Technology Exam Questions with Correct Answers
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CIE A Level Biology Genetic Technology Exam Questions with Correct Answers
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CIE A Level Biology Genetic TechnologyExam Questions with Correct Answers
What are transcription factors? - Answer-Proteins that bind to a specific DNA sequence
and control the flow of information from DNA to RNA by controlling the formation of
mRNA.
What controls transcription of genes in both prokaryotes and eukaryotes? - Answer-
Transcription factors
What are structural genes? - Answer-Genes that code for proteins required by the cell.
Such proteins may form part of a cellular structure but may also have another role (e.g.
enzymes).
What are regulatory genes? - Answer-Genes that code for proteins that regulate the
expression of other genes.
How can the synthesis of a repressible enzyme be prevented? - Answer-By binding a
repressor protein to a specific site called an operator on a bacterium's DNA.
When does the synthesis of an inducible enzyme occur? - Answer-Only when its
substrate is present. Transcription of the gene occurs when the inducer (the enzyme's
substrate) interacts with the protein made by the regulatory gene.
What is an operon? - Answer-A length of DNA making up a unit of gene expression in a
bacterium.
What does an operon consist of? - Answer-One or more structural genes and also
control regions of DNA that are recognised by the products of regulatory genes.
What does the enzyme beta galactosidase do? - Answer-Hydrolyses the disaccharide
lactose to the monosaccharides galactose and glucose.
How does the number of beta galactosidase molecules vary within Escherichia coli
bacteria? - Answer-It varies according to the concentration of lactose in the medium in
which the bacterium is growing.
How does E.coli alter the concentration of beta galactosidase within the cell? - Answer-
It must regulate the transcription of the gene coding for beta galactosidase. Each
bacterium only has one copy of this gene.
What does the lac operon consist of? - Answer-Three structural genes and a length of
DNA including operator and promoter regions.
,What are the three structural genes in the lac operon? - Answer-lacZ, lacY, lacA
What does lacZ do? - Answer-Codes for beta-galactosidase
What does lacY do? - Answer-Codes for permease, which allows lactose to enter the
cell.
What does lacA do? - Answer-Codes for transacetylase
What is the sequence of events that occurs when no lactose is present in the medium
where the E.coli bacteria are growing? - Answer-The regulatory gene codes for a
repressor protein. The repressor binds to the operator region close to the gene for beta-
galactosidase. When the repressor is bound at the operator, RNA polymerase cannot
bind to DNA at the promoter region. No transcription of the three structural genes (lacZ,
lacY, lacA) can take place.
What does it mean if the repressor protein for the lac operon is allosteric? - Answer-It
has two binding sites. When it binds to a molecule at one binding site, its ability to bind
to another molecule at its other binding site is affected.
What happens when the repressor protein binds to the operator at the lac operon? -
Answer-The site of the protein that binds to DNA is separate from the site that binds to
lactose. When lactose binds to its site, the protein changes so that the DNA binding site
closes.
Describe the events that happen when the E.coli grow in a medium containing lactose?
- Answer-Lactose is taken up by the bacteria. Lactose binds to the repressor protein, so
that it changes shape is no longer binds to the DNA at the operator site. Transcription is
no longer inhibited and messenger RNA is produced from the three structural genes.
The genes have been switched on and are transcribed together.
What does the mechanism of switching the gene on and off for beta-galactosidase
mean? - Answer-Beta-galactosidase, permease and transacetylase are only produced
when lactose is available in the surrounding medium. The three enzymes are also
produced in equal amounts. This prevents the waste of energy and materials when
lactose is not available.
What kind of enzyme is beta galactosidase? - Answer-An inducible enzyme
As the size of a genome increases... - Answer-the number of different proteins that act
as transcription factors also generally increases.
Compare the number of ways of regulating genes eukaryotes have to prokaryotes? -
Answer-Eukaryotes have many more ways of regulating gene expression than
prokaryotes do.
, What may transcription factors in eukaryotes do? - Answer-They may bind to the
promoter region of a gene or increase or decrease the transcription of a gene. Their role
is to make sure that genes are expressed in the correct cell at the correct time and to
the correct extent.
What are some of the effects of transcription factors? - Answer-They are necessary for
transcription to occur because they form part of the protein complex that binds to the
promoter region of the gene concerned; activate appropriate genes in sequence,
allowing the correct pattern of development of body regions; determine the sex of
mammals; allow responses to environmental stimuli; regulate the cell cycle, growth and
apoptosis; give hormones their effects.
How does the plant hormone gibberellin control seed germination? - Answer-It
stimulates the synthesis of amylase. For example, in barley seeds the application of
gibberellin causes an increase in the transcription of mRNA coding for amylase.
How does gibberellin stimulate the synthesis of amylase? - Answer-It causes the
breakdown of DELLA proteins. DELLA proteins inhibit the binding of transcription
factors to a gene promoter. When the DELLA proteins are broken down, the factors can
bind to their target promoters, allowing transcription to take place.
What is the aim of genetic engineering? - Answer-To remove a gene from one organism
and transfer it to another so that the gene is expressed in its new host. The organism
that now expresses the gene is now a transgenic organism or a genetically modified
organism.
What is recombinant DNA? - Answer-DNA made by joining pieces from two or more
different sources.
Give an overview of the process of gene transfer - Answer-The gene that is required is
identified. It may be cut from a chromosome, made from mRNA by reverse transcription
or synthesised from nucleotides. Multiple copies of this gene are made by PCR. The
gene is then inserted into a vector, which delivers the gene into the cells of the
organism. The cells that have the new gene are identified and cloned.
What is needed to carry out gene transfer? - Answer-Enzymes - restriction enzymes,
ligase and reverse transcriptase. Vectors. Genes coding for easily identifiable
substances that can be used as markers.
Give examples of vectors - Answer-plasmids, viruses and liposomes
What are restriction endonucleases? - Answer-A class of enzymes from bacteria which
recognise and break down the DNA of invading viruses
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