Control of Gene Expression Flashcards
(39 cards)
Explain how a single base substitution causes a change in the structure of this polypeptide
Change in primary structure
Means different hydrogen/ionic/disulphide bonds
Which causes a change in tertiary structure
Increased methylation of the promoter region of a tumour suppressor gene
causes one type of human throat cancer.
In this type of throat cancer, cancer cells are able to pass on the increased
methylation to daughter cells. The methylation is caused by an enzyme called
DNMT.
Scientists have found that a chemical in green tea, called EGCG, is a
competitive inhibitor of DNMT. EGCG enables daughter cells to produce
messenger RNA (mRNA) from the tumour suppressor gene.
(b) Suggest how EGCG allows the production of mRNA in daughter cells.
ECCG binds to the active site of DNMT
This prevents it from methylating the promoter region of the tumour suppressor gene
This means that transcription factors can bind to promoter region
So RNA polymerase can also bind
Describe how alterations to tumour suppressor genes can lead to the
development of tumours
Increased methylation of tumour suppressor gene means it is no longer transcribed
A DNA mutation can mean that primary structure and tertiary structure is changed so it is no longer complementary to the active site
Results in uncontrolled cell division
Sometimes, a mutagenic agent causes DNA to break. A different enzyme called ATM binds to the broken DNA. This leads to the activation of a protein coded for by a tumour suppressor gene. The effect of ATM binding is to stop cell division until DNA is repaired. A mutation could result in a person having non-functional forms of the gene that produces ATM.
What can you predict about the possible effects of having a non-functional
form of ATM?
ATM is no longer complementary to the broken DNA so it will not bind.
This leads to cell division replicating the broken DNA
Tumour suppressor gene is not activated
May have no effect on heterozygous organism that still has a copy of the functional ATM gene
Define what is meant by epigenetics.
A heritable change in an organisms gene function
Without a change in DNA base sequence
Explain how increased methylation could lead to cancer
Increased methylation of a tumour suppressor gene
Transcription of tumour suppressor gene is inhibited
Which leads to uncontrolled cell division
Give one way in which benign tumours differ from malignant tumours
They cannot invade into neighbouring tissues
They cannot metastasize and spread to other parts of the body
MM is caused by a faulty receptor protein in cell-surface membranes. Cells in MM tumours can be destroyed by the immune system.
Suggest why they can be destroyed by the immune system
Receptor proteins are recognised by the immune system as foreign
T cells bind to faulty protein
Stimulate B cells to divide by clonal selection
B cells release antibodies against faulty protein
One method of transferring RNAi molecules into cells involves combining
these molecules with a lipid. Suggest why this increases uptake of RNAi
molecules into cells
Lipids can diffuse across the phospholipid bilayer so no need for channel protein
Steroid hormones are hydrophobic.
Explain why steroid hormones can rapidly enter a cell by passing through
its cell-surface membrane.
They are lipid soluble
They can diffuse through the phospholipid bilayer
In the cytoplasm, testosterone binds to a specific androgen receptor (AR).
An AR is a protein.
Suggest and explain why testosterone binds to a specific AR
Testosterone has a specific tertiary structure that makes is complementary to the structure of a specific AR
The binding of testosterone to an AR changes the shape of the AR. This
AR molecule now enters the nucleus and stimulates gene expression.
Suggest how the AR could stimulate gene expression.
It is a transcription factor
By binding to the promoter region of a gene it stimulates RNA transcriptase to bind and transcribe the gene
Suggest how the production of ‘antisense’ SUT1 mRNA in type A plants
would reduce the expression of the SUT1 gene
Antisense is complementary to sense mRNA
Antisense mRNA binds to sense mRNA
This prevents the mRNA from binding to a ribosome
This means the mRNA will not be translated into a protein
The first successful drug trial to reduce concentrations of huntingtin in the
brain used single-stranded DNA molecules (lines 13–14).
Suggest and explain how this drug could cause a reduction in the
concentration of the protein huntingtin.
DNA is complementary to mRNA
Binds to mRNA and becomes double stranded
Prevents mRNA from being translated
Suggest how the siRNA produced a reduction in protein production.
siRNA is complementary to mRNA for producing proteins
It binds to mRNA and makes it double stranded
This means it can no longer be translated as it will not bind to ribosomes
siRNA also allows enzymes to bind and hydrolyse mRNA to prevent translation
This decreases the levels of proteins produced by this gene
Myelodysplastic syndromes (MDS) are a group of malignant cancers. In MDS,
the bone marrow does not produce healthy blood cells.
Haematopoietic stem cell transplantation (HSCT) is one treatment for MDS. In
HSCT, the patient receives stem cells from the bone marrow of a person who
does not have MDS. Before the treatment starts, the patient’s faulty bone
marrow is destroyed.
(a) For some patients, HSCT is an effective treatment for MDS.
Explain how
The transplanted bone marrow can produce healthy blood cells to replace those effected by MDS
As the old bone marrow is removed there is no more MDS blood cells produced
Stem cells divide and replicate to replace old bone marrow
Current research into the treatment of red-green colour blindness involves
the use of induced pluripotent stem cells (iPS cells) (lines 17–19).
Suggest how iPS cells could correct red-green colour blindness.
iPS cells divide
and differentiate into green sensitive cone cells
The use of iPS cells could have advantages over the use of gene therapy to
correct red-green colour blindness (lines 19–20).
Using the information from the passage, suggest and explain reasons why
iPS are long term
They only require one surgery
There is a smaller chance of them being rejected by the body
Gene therapy has risks due to using viruses to transmit DNA
Suggest how transcription factors can reprogramme cells to form iPS
cells
Bind to promoter region
Stimulate RNA polymerase
Suggest how the growth of new blood vessels into damaged heart tissues
could increase the rate of repair of tissues
Increased blood flow means more oxygen and glucose
This means more respiration which produces ATP needed for protein synthesis and DNA replication to produce new cells to replace damaged ones
Also provides more amino acids for protein synthesis
Name two techniques the scientists may have used when analysing viral
DNA to determine that the viruses were closely related.
PCR
Genetic fingerprinting
Gel Electrophoresis
Genome sequencing
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.
Extract DNA and add restriction endonucleases
Separate fragments using gel electrophoresis
Treat DNA to form single strands
The probe will hybridise to the SUT1 gene
Use autoradiography to show bound probe
What is a DNA probe?
Short single strand of DNA
With bases complementary to a gene/allele
Describe how the DNA is broken down into smaller fragments.
Add restriction endonucleases to the DNA
They cut at specific recognition sequences
