Mutations And Gene Expression Flashcards
What are the 2 types of gene that control gene division and what do they do?
Tumour suppressor genes and proto-oncogenes
TSG- slow cell division by producing proteins that stop cells dividing or cause them to self-destruct
Proto-oncogenes- Stimulate cell division by producing cells that make cells divide
What will happen to TSG if there is a mutation in the DNA sequence
Inactivated.
The protein that stops cell division/ makes cells self-destruct, isn’t produced so cells divide uncontrollably so tumour
What will happen to proto-oncogene if a mutation occurs in the DNA sequence?
Produces a mutated proto-oncogene called an oncogene
If a mutation occurs, this may result in an overactive gene which stimulates the cells to divide uncontrollably so tumour forms.
Identify and describe BAD tumours
Malignant tumours are cancers.
Usually grow rapidly, invade and destroy surrounding tissue’s.
Cells can break off the tumour and spread to other areas of the body via bloodstream or lymphatic system
Describe HARMLESS tumours :
Benign cancers aren’t cancerous. Usually gore slower than M and are often covered in fibrous tissue that stops cells invading other tissue’s.
Often harmless but cause blockages and out pressure on organs.
Can become malignant.
How are tumours different to normal cells?
- irregular shape
- nucleus is larger and darker
- different antigens on their surface
- Don’t respond to growth regulating processes
- divide by mitosis more frequently
Oestrogen is a substance produced by the enzyme aromatase. In females, the main source of oestrogen is the ovaries but aromatase is produced by many other organs in the body, including the lungs. Oestrogen can stimulate the development of some lung tumours. In these tumours, binding of oestrogen to cell-surface receptors stimulates cell division.
Scientists investigated whether two drugs could prevent lung tumours in female mice. First, they removed the ovaries from these mice. They then injected the mice with a tumour-causing chemical found in tobacco twice a day for 4 weeks. The mice were then randomly allocated to one of four groups. Each group contained 10 mice.
- Group Q was given a placebo. This placebo did not contain either drug.
- Group R was given the drug anastrozole. This inhibits the enzyme aromatase.
- Group S was given the drug fulvestrant. This binds to oestrogen receptors.
- Group T was given both anastrozole and fulvestrant.
The mice were given these drugs each week during weeks 5−15 of the investigation.
(a) The scientists removed the ovaries from the mice for the investigation. They also gave the mice injections of the substrate of aromatase each day.
Explain why these steps were necessary.
Removes (main / largest) source of oestrogen / (different) mice produce different amounts of oestrogen
(Allows) oestrogen to be controlled / oestrogen to be made by aromatase only / only oestrogen made in lungs to be involved.
Oestrogen is a substance produced by the enzyme aromatase. In females, the main source of oestrogen is the ovaries but aromatase is produced by many other organs in the body, including the lungs. Oestrogen can stimulate the development of some lung tumours. In these tumours, binding of oestrogen to cell-surface receptors stimulates cell division.
Scientists investigated whether two drugs could prevent lung tumours in female mice. First, they removed the ovaries from these mice. They then injected the mice with a tumour-causing chemical found in tobacco twice a day for 4 weeks. The mice were then randomly allocated to one of four groups. Each group contained 10 mice.
- Group Q was given a placebo. This placebo did not contain either drug.
- Group R was given the drug anastrozole. This inhibits the enzyme aromatase.
- Group S was given the drug fulvestrant. This binds to oestrogen receptors.
- Group T was given both anastrozole and fulvestrant.
The mice were given these drugs each week during weeks 5−15 of the investigation.
The scientists predicted that fulvestrant would be more effective when given with anastrozole than when given alone.
Use the information provided to suggest why they predicted this.
- (Anastrozole) prevents / reduces oestrogen production;
2. (Fulvestrant) stops remaining oestrogen binding / less oestrogen binds to receptors.
The scientists used tumour area as an indicator of tumour size.
Explain why tumour area may not be the best indicator of tumour size and suggest a more reliable measurement.
- Tumours may be different depths / area does not take depth into account / tumours are 3-D / are not 2-D
- Should (Measure) tumour volume / mass / weight.
The scientists repeated the investigation but this time they did not give the drugs until week 9.
Suggest why they gave the drugs at week 9, rather than at week 5.
- Allows tumours to grow / develop / form;
Neutral: gives drug more time to work.
- (So) can investigate treatment rather than prevention (of tumours) / when tumour / cancer is more advanced
Another group of scientists is currently using these drugs in human trials. However, the control group is not being given a placebo.
Suggest why a placebo is not being given and what is being given to this group instead.
- Unethical (not to treat patients) / may increase probability of patients dying / getting more ill;
- Use normal cancer drugs / treatment.
A mutation of a tumour suppressor gene can result in the formation of a tumour.
Explain how.
- (Tumour suppressor) gene inactivated / not able to control / slow down cell division;
Ignore: references to growth
- Rate of cell division too fast / out of control.
Not all mutations result in a change to the amino acid sequence of the encoded polypeptide.
Explain why.
- (Genetic) code degenerate;
2. Mutation in intron.
Some cancer cells have a receptor protein in their cell-surface membrane that binds
to a hormone called growth factor. This stimulates the cancer cells to divide.
Scientists have produced a monoclonal antibody that stops this stimulation.
Use your knowledge of monoclonal antibodies to suggest how this antibody stops the growth of a tumour.
- Antibody has specific tertiary structure
- Complementary (shape / fit) to receptor protein / GF
- Prevents GF binding (to receptor).
Explain how the methylation of tumour suppressor genes can lead to cancer.
- Methylation prevents transcription of gene;
- Protein not produced that prevents cell division / causes cell death / apoptosis;
- No control of mitosis.
The doctors compared median survival times for patients in each group.
How would you find the median survival time for a group of patients?
- Rank all STs (survival times) in ascending order;
2. Find value with same number (of people) above and below.
In many trials of new drugs, a control group of patients is given a placebo that does not contain any drug.
The control group in this investigation had been treated with dacarbazine. Suggest why they had not been given a placebo.
Not ethical to fail to treat cancer.
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.
- Faulty protein recognised as an antigen / as a ‘foreign’ protein;
- T cells will bind to faulty protein / to (this) ‘foreign’ protein;
- (Sensitised) T cells will stimulate clonal selection of B cells;
- (Resulting in) release of antibodies against faulty protein.
Alzheimer’s disease (AD) is a non-reversi
number of years. At the start of 2014 the number of Americans with AD was
estimated to be 5.4 million. Every 30 seconds another person in America
develops AD.
5 In the brain of a person with AD there is a lower concentration of acetylcholine.
This affects communication between nerve cells and initially results in memory
loss and confusion. Some of the symptoms of AD that are associated with
communication between nerve cells are reduced by taking the drug donepezil.
Donepezil inhibits the enzyme acetylcholinesterase.
10 A gene mutation called E280A found on chromosome 14 causes early-onset AD
at a mean age of 49 years. The age at which the E280A mutation is expressed
to cause AD varies.
Yaramul is a town in a historically isolated region of the Andes Mountains. The
population of this town has the highest frequency of the E280A mutation in the
15 world. The origin of the E280A mutation in this population has been traced back
to a common ancestor in the 17th century. Natural selection has not reduced
the frequency of the E280A mutation in the population.
This autosomal dominant mutation involves a change in triplet 280 from GAA to
GCA. Scientists analysed chromosome 14 from 102 individuals from Yaramul.
20 They recorded a sample size of 204 and detected 75 E280A mutations but only
74 potential AD cases. The scientists identified individuals with the mutation by
whole genome sequencing. They had decided that a DNA probe would not be a
suitable method to detect the E280A mutation.
(a) Assuming no one with AD died in 2014, calculate the annual percentage increase in AD cases in America for 2014 (lines 2–4).
Correct answer of 19.4 / 19.41%
OR
19.47 / 19.5% = 2 marks;
“loss and confusion. Some of the symptoms of AD that are associated with
communication between nerve cells are reduced by taking the drug donepezil.
Donepezil inhibits the enzyme acetylcholinesterase.”
Explain how donepezil could improve communication between nerve cells (lines 7–9).
- Less / no acetylcholine broken down;
- Acetylcholine attaches to receptors;
- (More) Na+ enter to reach threshold / for depolarisation / action potential / impuls
“Yaramul is a town in a historically isolated region of the Andes Mountains. The
population of this town has the highest frequency of the E280A mutation in the
15 world. The origin of the E280A mutation in this population has been traced back”
Suggest and explain two reasons why there is a high frequency of the E280A mutation in Yaramul
- Isolated so inbreeding / low genetic diversity / small gene pool;
- Allele inherited (through generations) from (common) ancestor
“to a common ancestor in the 17th century. Natural selection has not reduced
the frequency of the E280A mutation in the population.”
Explain why natural selection has not reduced the frequency of the E280A mutation in the population
- AD / symptoms develops late / at 49;
2. Have already reproduced
“at a mean age of 49 years. The age at which the E280A mutation is expressed
to cause AD varies.”
The age at which the E280A mutation is expressed to cause AD can vary (lines 11–12).
Suggest and explain one reason for this.
- Epigenetics / environment / named factor e.g. stress, alcohol, toxins, diet, exercise, smoking;
- methylation (of genes)
OR
acetylation (of histones)
One scientific study which analysed chromosome 14 involved 102 individuals. The scientists recorded a sample size of 204. In this sample they detected 75 E280A mutations but only 74 potential AD cases (lines 19–21).
Suggest explanations for the figures the scientists recorded.
- One person was homozygous dominant / has two dominant alleles = 2 marks;
- For one mark has two alleles / chromosomes
“whole genome sequencing. They had decided that a DNA probe would not be a
suitable method to detect the E280A mutation”
Suggest why a DNA probe for the mutated triplet was not considered a suitable method for detection of the E280A mutation
- (GCA / triplet) is common / found in other places;
- Would not know if it was the mutation / allele / gene
OR
Produces ‘false positives’
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.
(a) Using the information given, suggest one reason why ESCs might be suitable to treat damage to the heart.
(ESCs) can replace any type of (heart) cell;
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. One way that ESCs might lead to more harm is by differentiating into the wrong types of cells.
Suggest one other way that putting ESCs into a person’s heart might lead to more harm to the person.
- Might divide out of control;
2. Leading to tumour / cance
Suggest how the growth of new blood vessels into damaged heart tissues could increase the rate of repair of tissues.
- Greater blood supply (to damaged areas);
- Bringing more oxygen / glucose for respiration;
- Brings more amino acids for protein synthesis;
- For cell repair / mitosis / division
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.
- Measure diameter of field of view and calculate area;
- Using micrometer slide and eyepiece graticule;
Accept descriptions
- Count number of capillaries in large number of fields of view and calculate mean;
- Select fields of view randomly
“Plants require phosphate ions that they get from soil. These ions are often in poor supply and this results in poor growth of the plants.”
Suggest and explain two reasons why a poor supply of phosphate ions results in poor growth of plants
- (Required to) make ATP / glucose phosphate, so less respiration / less energy for growth;
- (Required to) make nucleotides, so less DNA / mRNA / tRNA for cell division / production of protein (for growth);
- (Required to) make RuBP / NADP, so less CO2 fixed / reduced into sugar;
- (Required to) make phospholipids for membrane
“Plants can defend themselves by producing defensive enzymes that destroy pathogens such as bacteria.”
Suggest how defensive enzymes produced by plants destroy bacteria
- Hydrolyse;
Accept digest
- murein / glycoprotein (in cell wall);
“Some plants express the genes for defensive enzymes in response to signal proteins secreted by other plants that are being attacked by a pathogen. These signal proteins can be released into the air.”
The signal proteins secreted into the air by a plant being attacked by a pathogen act as stimuli leading to the expression of genes for defensive enzymes in other plants (lines 9–12).
Suggest how they lead to the expression of these genes
- Bind to receptor (on target plant);
- Acts as / leads to production of a transcription factor;
- (Which) binds to promoter
“Some plants express the genes for defensive enzymes in response to signal proteins secreted by other plants that are being attacked by a pathogen. These signal proteins can be released into the air.”
“Scientists have discovered that tomato plants increase production of defensive enzymes if plants next to them become infected with a pathogen. These tomato plants were connected by a mycorrhizal network that can carry signal proteins between them.”
Suggest and explain the advantage to tomato plants of transmitting signal proteins through mycorrhizal networks, rather than releasing them into the air (
Direct plant-to-plant transmission;
- (So) localised response
OR
faster response
Define what is meant by epigenetics.
- Heritable changes in gene function;
2. Without changes to the base sequence of DNA;
Does oestrogen bind to DNA? PROTEIN?
Do methyl groups bind to DNA? PROTEIN?
Do acetyl groups bind to DNA?PROTEIN?
Oestrogen- protein
Methyl- DNA
Acetyl- protein
Explain how increased methylation could lead to cancer.
- Methyl groups (could be) added to (both copies of) a tumour suppressor gene;
- The transcription of tumour suppressor genes is inhibited;
- Leading to uncontrolled cell division
Give one way in which benign tumours differ from malignant tumours.
Cells of benign tumours cannot spread to other parts of the body / metastasise;
OR
Cells of benign tumours cannot invade neighbouring tissues.
What does degenerate mean?
More than one codon codes for a single amino acid
