The Control of Gene Expression (3.8) Flashcards
Mutations (AO1)
Define gene mutation
Random change in the base sequence of DNA.
Results in the formation of new alleles.
Mutations (AO1)
Gene mutations might occur spontaneously during _____________.
DNA replication
Mutations (AO1)
List the types of mutations
Addition of bases;
Deletion of bases;
Substitution of a base;
Inversion of bases;
Duplication of bases / genes;
Translocation of bases / genes’
Non-disjunction of chromosomes;
Mutations (AO1)
A change in the DNA base sequence may alter the [1] structure, this may alter the [2] of amino acids.
This may change the [3] of hydrogen, ionic and disulphide bonds between the [4] groups of amino acids.
This may change the [5] structure of the polypeptide.
[1] primary
[2] sequence
[3] position
[4] R
[5] tertiary
Mutations (AO1)
The mutation rate is __________ by mutagenic agents.
increased
Mutations (AO1)
List examples of mutagenic agents
High energy radiation e.g. x rays, gamma rays, ultraviolet light
Carcinogens e.g. benzene
Biological agents e.g. viruses
Mutations (AO1)
A __________ mutation may change only one triplet code.
substitution
Mutations (AO1)
Due to the ______________ nature of the genetic code, not all mutations result in a change to the encoded amino acid.
degenerate
Mutations (AO1)
3 key terms for the genetic code
degenerate
universal
non-overlapping
Mutations (AO1)
Define degenerate
More than one triplet / codon codes for a single amino acid
Mutations (AO1)
What is meant by the universal nature of the genetic code?
Same 3 bases used in DNA (triplets) / mRNA (codon) code for the same amino acids in all organisms
Mutations (AO1)
What is meant by the non-overlapping genetic code?
Each base is read only once in the triplet / codon
Mutations (AO1)
Additions and [1] of bases may change the nature of all base [2] downstream from the mutation.
This results in a [3] shift.
[1] deletions
[2] triplets
[3] frame
Mutations (AO1)
A base substitution may result in the formation of a [1] codon.
This signals to the [2] to detach from mRNA and polypeptide during translation.
This results in a [3] polypeptide.
[1] stop
[2] ribosome
[3] shorter
Mutations (AO1)
What happens during a translocation mutation?
Sections of DNA bases relocate from one area of the genome to another;
e.g., between non-homologous pairs of chromosomes;
Mutations (AO1)
Box 2
Inversions do not change the number of DNA bases
Mutations (AO2)
Sickle cell disease (SCD) is a group of inherited disorders. People with SCD have sickle-shaped red blood cells. A single base substitution mutation can cause one type of SCD. This mutation causes a change in the structure of the beta polypeptide chains in haemoglobin. Explain how (3 marks).
1. Change in primary structure OR sequence of amino acids;
2. Change in (position) of hydrogen / ionic / disulfide bonds;
3. Alters tertiary structure;
Stem Cells (AO1)
Cells become specialised through the process of cellular ______________.
differentiation
Stem Cells (AO1)
Functions of stem cells
Differentiation;
Mitosis;
Stem Cells (AO1)
4 types of stem cells
Totipotent
Pluripotent
Multipotent
Unipotent
Stem Cells (AO1)
________________ cells occur only for a limited time in early mammalian embryos.
Totipotent
Stem Cells (AO1)
Totipotent stem cells can divide by [1] and produce [2] type of body cell.
[1] mitosis
[2] ANY
Stem Cells (AO1)
TRUE or FALSE:
During development, totipotent cells translate only part of their DNA, resulting in cell specialisation.
TRUE
Stem Cells (AO1)
Pluripotent stem cells are found in ___________
embryos
Stem Cells (AO1)
Functions of pluripotent stem cells
1. Divide in unlimited numbers;
2. Produce MOST cell types
3. Used to treat human disorders
Stem Cells (AO1)
Stem cells found
in mature mammals
multipotent
unipotent
Stem Cells (AO1)
Multipotent stem cells produce ________ cell types
SOME
Stem Cells (AO1)
Unipotent stem cells in the heart can differentiate into ___________
cardiomyocytes
Stem Cells (AO2)
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.
For some patients, HSCT is an effective treatment for MDS. Explain how (3 marks).
1. Stem cells differentiate/produce healthy (blood) cells;
2. No MDS/faulty/cancerous (blood) cells;
3. Stem cells divide/replicate by mitosis;
Stem Cells (AO2)
Scientists have investigated the use of different types of stem cell to treat damage to the heart after a myocardial infarction. During a myocardial infarction, a number of different cell types in the heart die. This includes cardiomyocytes which are heart-muscle cells.
Embryonic pluripotent stem cells (ESCs) can divide and differentiate into a wide range of different cell types.
Using the information given, suggest one reason why ESCs might be suitable to treat damage to the heart.
(ESCs produce MOST types of cell)
So they can replace any type of heart cell;
Stem Cells (AO2)
Embryonic pluripotent stem cells (ESCs) have not yet been used to treat people who have had a myocardial infarction. This is because of concern that the use of ESCs might lead to more harm to the person.
Suggest how putting ESCs into a person’s heart might lead to more harm to the person (3 marks).
1. Differentiating into the wrong types of cells.
2. Might divide out of control;
3. Leading to tumour / cancer;
Stem Cells (AO2)
Haematopoietic stem cell transplantation (HSCT) is a long-term treatment for sickle cell disease (SCD). In HSCT, the patient receives stem cells from the bone marrow of a person who does not have SCD.
The donor is often the patient’s brother or sister. Explain why.
Less chance of rejection
by immune system
(from brother/sister);
Stem Cells (AO1)
What are iPS cells?
induced pluripotent stem cells
Stem Cells (AO1)
Induced pluripotent stem (iPS) cells can be produced from adult [1] cells using appropriate ‘reprogramming’ protein [2] factors.
[1] somatic
(e.g. keratinocytes in the skin)
[2] transcription
Stem Cells (AO1)
Suggest how transcription factors can reprogramme cells to form iPS cells (2 marks).
1. Bind to DNA promoter region;
2. Stimulate / inhibit RNA polymerase
3. Increase / decrease transcription
Stem Cells (AO1)
Advantages of using iPS cells
1. Somatic cells easy to obtain;
2. Divide in unlimited numbers;
3. Produce MOST cell types;
4. Used to treat human disorders;
5. Less chance of rejection by immune system
(as using somatic cells that originated from patient);
Stem Cells (AO1)
Disadvantages of using iPS cells
1. Takes a long time to differentiate into desired specialised cell;
2. Cells generated ‘in vitro’ (i.e. in cell culture) may not function when transplated back into humans;
Regulation of Transcription & Translation (AO1)
What binds to the DNA promoter region?
Transcription Factors
These are proteins with specific tertiary structures
Regulation of Transcription & Translation (AO1)
The promoter region is located BEFORE or WITHIN the gene?
Before
Sometimes this is referred to as ‘upstream’ of the gene
Regulation of Transcription & Translation (AO1)
Transcription factors are found in the [1] and upon activation can enter the [2].
[1] cytoplasm
[2] nucleus
Regulation of Transcription & Translation (AO1)
What happens after the transcription factor binds to the promoter region?
stimulates RNA polymerase;
transcription begins and mRNA increases;
Regulation of Transcription & Translation (AO1)
TRUE or FALSE:
Transcription factors binding to the promoter regions always increase transcription.
FALSE
Some transcription factors inhibit transcription
Regulation of Transcription & Translation (AO1)
How does oestrogen enter cells?
1. Lipid-soluble (steroid hormone);
2. Diffuses through the phospholipid bilayer;
Regulation of Transcription & Translation (AO1)
What does oestrogen bind to?
oestrogen receptor (ER alpha)
The receptor is a transcription factor
Regulation of Transcription & Translation (AO1)
What happens to the oestrogen receptor (ER alpha) upon binding with oestrogen?
Changes its tertiary structure;
The receptor now acts as a transcripton factor;
Regulation of Transcription & Translation (AO1)
TRUE or FALSE:
Oestrogen is a transcription factor
FALSE
Its receptor when activated by oestrogen binding = transcription factor
Regulation of Transcription & Translation (AO1)
Osterogen binds to its receptor becuase it has a _____________ shape
complementary
Regulation of Transcription & Translation (AO1)
The activiated ooestrogen receptor (ER alpha) is a [1] and binds to the [2] region.
This stimulates [3] and leads to transcription of a gene. This increases [4] and leads to more protein synthesis.
[1] transcription factor
[2] promoter
[3] RNA polymerase
[4] mRNA
Regulation of Transcription & Translation (AO2)
Steroid hormones are hydrophobic.
Explain why steroid hormones can rapidly enter a cell by passing through its cell-surface membrane [2 marks].
1. Lipid soluble;
2. Diffuse through phospholipid bilayer;
Regulation of Transcription & Translation (AO2)
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 (2 marks).
1. Testosterone has a specific tertiary structure;
2. This has a complementary shape to the receptor;
Many hormones are ‘modified’ proteins
Regulation of Transcription & Translation (AO2)
The binding of testosterone to the androgen receptor (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 (2 marks).
1. AR is a transcription factor;
2. Binds to DNA promoter region;
3. Stimulates RNA polymerase;
Regulation of Transcription & Translation (AO1)
RNA interference (RNAi) inhibits the ________________ of mRNA
translation
Regulation of Transcription & Translation (AO1)
Types of RNA interfering molecules
small interfering RNA (siRNA)
micro RNA (miRNA)
Regulation of Transcription & Translation (AO1)
Are siRNA and miRNAs single OR double stranded?
single stranded
Regulation of Transcription & Translation (AO1)
siRNA binds to specific [1] molecules via [2] base pairing.
This guides enzymes which [3] mRNA.
[4] is prevented.
[1] mRNA
[2] complementary
[3] destory
[4] translation
Regulation of Transcription & Translation (AO1)
If a specific protein is still produced in smaller quantities this could be because not all mRNA has been __________________ by RNA interference.
destroyed
Regulation of Transcription & Translation (AO2)
1. siRNA binds to mRNA for CENP-W;
(via complementary base pairing)
2. (mRNA for CENP-W) destroyed
3. Prevents translation of CENP-W;
4. As CENP-W reduces so does tubulin production;
Regulation of Transcription & Translation (AO1)
Define epigenetics
Inheritable changes in gene function;
without changes to the DNA base sequence;
Regulation of Transcription & Translation (AO1)
Types of epigenetic changes
Methylation
Acetylation
Regulation of Transcription & Translation (AO1)
TRUE or FALSE:
Changes in the environment lead to changes in methylation and acetylation which determine whether a gene is expressed.
TRUE
Regulation of Transcription & Translation (AO1)
During methylation, a methyl group is added to a ______ _______.
DNA base
typically cytosine or guanine in the promoter region
Regulation of Transcription & Translation (AO1)
Methylation of DNA bases in the [1] region, prevents transcription [2] from binding.
This [3] transcription.
[1] promoter
[2] factors
[3] decreases / inhibits
Regulation of Transcription & Translation (AO1)
Chromosomal DNA in eukaryotes is wrapped around _____________
histones
Regulation of Transcription & Translation (AO1)
**TRUE or FALSE: **
During acetylation DNA bases are modified
FALSE
Histone tails are modified by acetylation
Regulation of Transcription & Translation (AO1)
Acetylation of histone makes them [1] packed.
This makes the promoter region and target gene more accessible to transcription factors and [2].
This [3] transcription.
[1] loosely
[2] RNA polymerase
[3] increases
Regulation of Transcription & Translation (AO1)
Decreasing methylation,
________________ transcription
stimulates / increases
Regulation of Transcription & Translation (AO1)
Explain why decreasing acetylation of histones decreases transcription.
1. Histones are more tightly packed;
2. Prevents transcription factors from binding to the promoter region;
3. Prevents RNA polymerase from accessing the target gene;
Regulation of Transcription & Translation (AO1)
Gene expression and cancer (AO1)
Cancer is caused by [1] mitosis and this can lead to a abnormal mass of cells known as a [2].
[1] uncontrolled
[2] tumour
Gene expression and cancer (AO1)
Benign tumour characteristics
slow growing;
surrounded by a capsule;
do NOT metastasise;
Gene expression and cancer (AO1)
Malignant tumour characteristics
fast growing;
non-capsulated;
metastasise;
(spread to other parts of body)
Gene expression and cancer (AO1)
The rate of tumour development is controlled by which genes?
Tumour suppressor genes
Oncogenes
Gene expression and cancer (AO1)
Role of tumour suppressor genes
Slow down / regulate the rate of cell cycle
Gene expression and cancer (AO1)
Role of proto-oncogenes
Speed up the rate of the cell cycle
Gene expression and cancer (AO1)
Role of oncogenes
Speed up the rate of cell cycle;
Leads to uncontrolled cell cycle / mitosis;
Gene expression and cancer (AO1)
How do oncogenes arise?
Random mutations in proto-oncogenes
Gene expression and cancer (AO2)
BRCA1 and BRCA2 are human genes that code for tumour suppressor proteins.
Mutations in BRCA1 and BRCA2 can cause cancer. Explain how (3 marks).
1. Change in DNA base sequence;
2. Change in primary structure / sequence of amino acids
OR Change in tertiary structure
3. Results in rapid / uncontrollable cell division / mitosis;
Gene expression and cancer (AO1)
Increasing methylation of which gene could lead to the development of a tumour?
Tumour suppressor genes
As increasing methylation decreases transcription
Gene expression and cancer (AO1)
Increasing acetylation of histones near which gene could lead to the development of a tumour?
Oncogenes
Gene expression and cancer (AO2)
Treatment with drugs might be able to reverse the epigenetic changes that cause cancers.
Suggest and explain how (3 marks).
1. Increase methylation of oncogene(s);
2. Increasing methylation inhibits / decreases transcription;
3. Decrease methylation of tumour suppressor gene;
4. Decreasing methylation stimulates / increases transcription;
5. Increase acetylation of histones stimulates transcription / gene expression;
(e.g. of tumour suppressor gene)
Gene expression and cancer (AO2)
Myelodysplastic syndromes (MDS) are a group of malignant cancers of blood cells.
MDS can develop from epigenetic changes to tumour suppressor genes. In some patients, the drug AZA has reduced the effects of MDS. AZA is an inhibitor of DNA methyltransferases. These enzymes add methyl groups to cytosine bases.
Suggest and explain how AZA can reduce the effects of MDS in some patients (3 marks).
1. AZA reduces methylation of DNA/cytosine;
2. Tumour suppressor gene is transcribed/expressed;
Accept mRNA produced for transcription/transcribed.
3. Prevents rapid/uncontrollable mitosis
OR cell division can be controlled/stopped/slowed;
Gene expression and cancer (AO2)
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.
Suggest how EGCG allows the production of mRNA in daughter cells (3 marks).
1. EGCG binds to active site of DNMT;
2. DNMT cannot methylate / less methylation of promoter region of tumour suppressor gene;
3. Transcription factor(s) can bind to promoter region;
4. RNA polymerase stimulated;
Gene expression and cancer (AO1)
Increased concentration of which hormome are linked to the development of some breast cancers?
Oestrogen
Gene expression and cancer (AO2)
ER-positive breast cancers have receptors for the hormone oestrogen. These cancers develop as a result of increased oestrogen concentrations in the blood. Effective treatment of ER-positive breast cancers often involves the use of drugs which have a similar structure to oestrogen.
Suggest and explain how these drugs are an effective treatment of ER-positive breast cancers (3 marks).
1. Drug binds to oestrogen/ER receptor;
2. Prevents binding of oestrogen
3. No/fewer transcription factor(s) bind to promoter
OR RNA polymerase not stimulated
Genome projects (AO1)
Define genome
All the DNA in a cell
Genome projects (AO1)
TRUE or FALSE:
Some viruses have a RNA genome
TRUE
e.g. HIV
Genome projects (AO1)
____________ sequencing has allowed entire genomes of millions of organisms to be fully sequenced.
Automated
Genome projects (AO1)
To sequence a genome means to know the exact sequence of ___________ that make up the entire DNA of an organism.
bases
Genome projects (AO1)
List source(s) / location(s) of genomes
- Linear DNA (arranged as chromosomes) in eukaryotes
- Circular DNA in prokaryotes, chloroplasts, mitochondria
- Plasmids in bacteria
- Viral DNA or RNA (e.g. HIV)
Genome projects (AO1)
If researchers know which genes are present in a genome, they can determine which ______________ can be produced via gene expression.
proteins
Genome projects (AO1)
TRUE or FALSE: only 1% of the human genome contains genes that code for proteins
TRUE
Genome projects (AO1)
Define proteome
The full range of proteins produced by cells
Genome projects (AO1)
Applications of the proteome
The identification of potential antigens for use in vaccine production
Genome projects (AO1)
Knowledge of the genome has led to increased study of non-coding DNA and regulatory DNA such as…….
- promoters
- terminators
- enhancers
- siRNAs
- miRNAs
- tRNAs
Genome projects (AO1)
TRUE or FALSE:
Non-coding DNA is located in intergenic* DNA sequences and makes up most of the DNA.
*Intergenic means in between genes
TRUE
Genome projects (AO1)
Determining the genome of the viruses could allow scientists to develop a vaccine.
Explain how (2 marks).
1. Could identify the proteome;
2. Then identify potential antigens
(to use in the vaccine);
Genome projects (AO1)
Name two techniques the scientists may use when analysing viral DNA to determine whether two viruses are closely related.
- DNA/genome sequencing;
- The polymerase chain reaction;
- Genetic/DNA fingerprinting;
- Gel electrophoresis;
Recombinant DNA technology (AO1)
What is recombinant DNA technology?
The transfer of fragments of DNA from one organism / species, to another.
e.g. Bacteria with plasmids that continue a human gene
Recombinant DNA technology (AO1)
Give two reasons why bacteria are able to use human DNA to produce human proteins (2 marks).
1. The genetic code is universal
2. The mechanism of transcription is universal;
3. The mechanism of translation is universal;
Recombinant DNA technology (AO1)
List the 5 steps in recombinant DNA technology in the correct order
1. Isolation of DNA (usually contains a gene)
2. Insertion of DNA into a vector (e.g. a plasmid)
3. Transformation of cells (to produce a genetically modfied or transgenic organism with two or more sources of DNA).
4. Identification of cells that have taken up the DNA by using marker genes
5. Growth / cloning
- i.e. bacterial divide by binary fission
- amplify DNA using PCR
Recombinant DNA technology (AO1)
3 ways to isolate a DNA fragment
which typically contains a gene
1. Reverse transcriptase & mRNA
2. Restriction endonucleases
3. Gene machine
Recombinant DNA technology (AO1)
Enzyme required to convert
mRNA into cDNA
reverse transcriptase
Recombinant DNA technology (AO1)
Describe how isolated mRNA from a cell can be converted into DNA (3 marks).
1. mRNA is mixed with free DNA nucleotides AND reverse transcriptase.
2. Free DNA nucleotides bind to single stranded mRNA template via complementary base pairing.
3. Reverse transcriptase joins DNA nucleotides together to form a single stranded cDNA molecule.
4. DNA polymerase is required to make cDNA double stranded.
cDNA means copy DNA i.e. it is a copy based on mRNA
Recombinant DNA technology (AO1)
Advantages of using reverse transcriptase to isolate DNA fragments
- Introns have been removed
- Cells producing protein will contain many mRNA molecules
- mRNA is easy to isolate from cells
Recombinant DNA technology (AO1)
Disadvantages of using reverse transcriptase to isolate DNA fragments
- Many steps involving involving enzyme-controlled reactions
- Time consuming
- Requires more technical expertise
Recombinant DNA technology (AO1)
Name of enzyme that isolate a gene / section of DNA from a larger section of DNA e.g. a chromosome.
Restriction endonucleases
Recombinant DNA technology (AO1)
Restriction endonucleases are enzymes that [1] phosphodiester bonds at specific DNA base sequences called [2] sites.
- hydrolyse
- restriction
Recombinant DNA technology (AO1)
Restriction sites are often _______________
palindromic
Recombinant DNA technology (AO1)
What is the consequence if the restriction site for the restriction endonuclease occurs within the DNA fragment researchers wish to isolate.
This will cut the gene and it will not code for a functional protein.
Recombinant DNA technology (AO1)
What type of ends are produced after cutting DNA with restriction endonucleases.
Sticky ends
Blunt ends
Recombinant DNA technology (AO1)
What are sticky ends used for?
To insert a gene into a vector
(e.g. a plasmid)
Recombinant DNA technology (AO1)
What are blunt ends used for?
Can be amplified by the polymerase chain reaction;
Separated by size using gel electrophoresis;
Recombinant DNA technology (AO1)
Advantages of using restriction endonucleases to isolate DNA fragments
- Produce sticky and blunt ends
- 1000s of restriction endonucleases have been isolated that are each highly specific to different DNA sequences
Recombinant DNA technology (AO1)
Disadvantages of using restriction endonucleases to isolate DNA fragments
Contains introns
Enzymes may cut in the middle of the desired gene leading to a non-functional protein
Recombinant DNA technology (AO1)
Restriction endonucleases
Recombinant DNA technology (AO1)
Which method of DNA isolation is decribed below:
Desired sequence of nucleotide bases are entered into a computer and automated machinery synthesises the DNA fragment
Gene machine
Recombinant DNA technology (AO1)
Advantages of using gene machines to isolate DNA fragments
- Faster process owing to automated machinery and fewer enzyme controlled reactions
- Sequences contain no introns
- Blunt and sticky ends can be added
Recombinant DNA technology (AO1)
Disdvantages of using gene machines to isolate DNA fragments
If sequence of DNA is unknown, requires the primary structure of the polypeptide to be known.
Recombinant DNA technology (AO1)
Once a DNA fragment has been isolated, what must be added to enable gene expression?
- A promoter region
(allow transcription factors to bind) - A terminator region
(ensures only the DNA fragment is transcribed)
Recombinant DNA technology (AO1)
Suggest and explain one reason why bacteria might not be able to produce every human protein (1 mark).
Cannot splice pre-mRNA, so cannot remove introns
OR
Do not have Golgi apparatus, so cannot process/modify proteins;
OR
Do not have the required transcriptional factors, so cannot carry out transcription/produce mRNA;
Recombinant DNA technology (AO1)
A geneticist concluded it would be faster to create a human gene using a gene machine than by using reverse transcriptase to convert mRNA into cDNA.
Suggest why the geneticist reached this conclusion.
Faster to use gene machine than all the enzyme-catalysed reactions (involving reverse transcriptase);
Recombinant DNA technology (AO1)
M = promoter;
N = terminator;
Recombinant DNA technology (AO1)
Which methods of DNA isolation could used prior to insertion of the human gene into a bacteria to ensure the protein could be produced.
1. mRNA & reverse transcriptase AND gene machine
2. Produce DNA / human gene without introns;
3. Bacteria cannot remove introns / cannot splice mRNA / cannot splice pre-mRNA;
