Topic 8A: The Control of Gene Expression Flashcards
Describe how mRNA is formed by transcription. [5]
- Hydrogen bonds (between DNA bases) break;
- (Only) one DNA strand acts as a template;
- (Free) RNA nucleotides align by complementary base pairing;
- (In RNA) uracil is used instead of thymine;
- RNA polymerase joins (adjacent RNA) nucleotides;
- (By) phosphodiester bonds (between adjacent nucleotides);
- Pre-mRNA is spliced (to form mRNA)
OR
Introns are removed (to form mRNA)
Describe how a polypeptide is formed by translation of mRNA. [6]
- (mRNA attaches) to ribosome;
- (tRNA) anticodons (bind to) complementary (mRNA) codons;
- tRNA brings a specific amino acid;
- Amino acids joined by peptide bonds;
- with the use of ATP;
- tRNA released (after amino acid joined to polypeptide);
- The ribosome moves along the mRNA to form the polypeptide
Explain how a gene mutation can have no effect on an individual. [2]
- Genetic code is degenerate (so amino acids sequence may not change)
OR
Mutation is in an intron (so amino acid sequence may not change) - Does change amino acid but no effect in tertiary structure;
- (New allele) is recessive so does not influence phenotype
Explain how a gene mutation can have a positive effect on an individual. [2]
- Results in change in polypeptide that positively changes the properties (of the protein);
- May result in increased survival (chances)
Explain how a gene mutation can have a negative effect in an individual. [2]
- Results in change in polypeptide that negatively changes the properties (of the protein);
- May result in reduced survival (chances)
Suggest how a mutation can lead to the production of a protein that has one amino acid missing. [2]
Loss of 3 bases/triplet = 2 marks
Suggest how the production of a protein with one amino acid missing may lead to a genetic disorder. [2]
- Change in tertiary structure;
- (So) non-functioning protein
A mutation in a gene coding for an enzyme could lead to the production of a non-functional enzyme. Explain how. [3]
- Change in base sequence (of DNA) leading to change in primary structure (of enzyme);
- Change in hydrogen/ionic/disulphide bonds leading to change in tertiary structure (of enzyme);
- No enzyme-substrate complexes form
Explain how a single base substitution can cause a change in the structure of a polypeptide. [3]
- Change in primary structure;
- Change in hydrogen/ionic/disulphide bonds;
- Alters tertiary structure
Suggest why using stem cells for medical treatment could result in more harm to a patient. [2]
- Might divide out of control;
- Leading to cancer
Suggest how the growth of new blood vessels into damaged heart tissues could increase the rate of repair of tissues. [3]
- Greater blood supply;
- Bringing more oxygen/glucose for respiration;
- Brings more amino acids for protein synthesis;
- For cell repair/mitosis
The scientists used an optical microscope to measure the number of capillaries in thin sections cut from samples of heart muscle.
Describe the method they would have used to find the mean number of capillaries per mm². [4]
- Measure diameter of diameter of field of view and calculate area;
- Using stage micrometer slide and eyepiece graticule;
- Count number of capillaries in large number of fields of view and calculate mean;
- Select fields of view randomly
Explain the advantage of growing plants from tissue culture rather than from seeds. [1]
- Will be clones/genetically identical / all plants will have desired characteristics
Suggest how the growth of new blood vessels into damaged heart tissues could increase the rate of repair of tissues. [3]
Oestrogen is a hormone that affects transcription. It forms a complex with a receptor int he cytoplasm of target cells.
Explain how an activated oestrogen receptor affects the target cell. [2]
- (Transcriptional factor) binds to promoter which stimulates RNA polymerase;
- Transcribes gene
Oestrogen only affects target cells. Explain why oestrogen does not affect other cells in the body. [1]
- Other cells do not have (transcriptional factors with) oestrogen receptors
Suggest how transcriptional factors can reprogramme cells to form induced pluripotent stem cells. [2]
- Attach to promoter region;
- Stimulate/inhibit transcription
Huntington’s disease is a disorder caused when a protein called Huntington damages the brain. Huntington is produced because of a dominant, mutant allele.
Suggest and explain one way epigenetics may affect the age when symptoms of Huntington’s disease start. [2]
- Increased methylation of DNA/gene;
- Inhibits transcription;
OR - Decreased methylation of DNA/gene;
- Stimulates transcription;
OR - Decreased acetylation of histones;
- Inhibits transcription;
OR - Increased acetylation of histones;
- Stimulates transcription
The KRAS gene codes for a protein called K-Ras. The protein delays signals from outside a cell to a cell’s nucleus, stimulating cell division. An alteration in the KRAS gene produces an oncogene which can cause a tumour to develop.
Suggest and explain how an alteration in the KRAS gene can cause a tumour to develop. [3]
- Change in base sequence (of gene);
- Change in protein
OR
More protein produced; - (Results in) rapid/uncontrollable cell division
BRCA1 and BRCA2 are human genes that code for tumour suppressor proteins. Mutations in the genes can cause cancer. Explain how. [3]
- Change in DNA base sequence;
- Change in primary/tertiary structure (of tumour suppressor protein);
- (Results in) rapid/uncontrolled cell division
Define what is meant by epigenetics. [2]
- Heritable change in gene function;
- Without changes to the base sequence of DNA
Explain how increased methylation could lead to cancer. [3]
- Methyl groups added to a tumour suppressor gene;
- The transcription of tumour suppressor genes is inhibited;
- Leading to uncontrolled cell division
Describe how alterations of tumour suppressor genes can lead to the development of tumours. [3]
- (Increased) methylation (of tumour suppressor genes);
- Mutation (in tumour suppressor genes);
- Tumour suppressor genes not transcribes
OR
Primary structure altered; - (Results in) rapid/uncontrolled cell division
Scientist investigated the role of a protein called CENP-W in mitosis. Their method involved cell fractionation and ultracentrifugation.
The scientists began by lysing (breaking open) cells and organelles using a detergent that dissolved lipids in water.
Suggest how the detergent releases CENP-W from cells. [2]
- Cell membrane made from phospholipid;
- (Detergent) dissolves membrane/phospholipid bilayer
Scientist investigated the role of a protein called CENP-W in mitosis. Their method involved cell fractionation and ultracentrifugation.
Explain how ultracentrifugation separates CENP-W from other molecules. [2]
- Spin at very high speed;
- Molecules separate depending on density
Give two characteristic features of stem cells. [2]
- Will keep dividing;
- Undifferentiated / can different into other cells
Name the viral enzyme that makes a DNA copy from RNA. [1]
- Reverse transcriptase
Integrate inserts the DNA copy anywhere in the DNA of the host cell. It may even insert the DNA copy in one of the host cell’s genes.
The insertion of the DNA copy in one of the host cell’s genes may cause the cell to make a non-functional protein. Explain how. [2]
- Alters base sequence;
- Different primary structure, alters the tertiary structure
Integrate inserts the DNA copy anywhere in the DNA of the host cell. It may even insert the DNA copy in one of the host cell’s genes. The stem cells are then injected into the bone marrow of the patient.
Some of the patients developed cancer. How might the insertion of the DNA have caused cancer? [2]
- Affects tumour suppressor gene;
- Inactivates gene;
- Rate of cell division increased
