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Myelodysplastic syndromes (MDS) are a group of malignant cancers - AQA - A-Level Biology - Question 6 - 2021 - Paper 2
Question 6
Myelodysplastic syndromes (MDS) are a group of malignant cancers. In MDS, the bone marrow does not produce healthy blood cells. Haematopoietic stem cell transplanta... show full transcript
Worked Solution & Example Answer:Myelodysplastic syndromes (MDS) are a group of malignant cancers - AQA - A-Level Biology - Question 6 - 2021 - Paper 2
Step 1
1. For some patients, HSCT is an effective treatment for MDS. Explain how.
Answer
Haematopoietic stem cell transplantation (HSCT) effectively treats MDS by replacing faulty bone marrow with healthy stem cells. This procedure consists of the following steps:
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Production of Healthy Cells: HSCT involves the generation of healthy blood cells by introducing stem cells that are not affected by MDS.
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Elimination of Faulty Cells: Before transplantation, the patient's own unhealthy bone marrow is destroyed, eliminating the source of defective blood cells.
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Stem Cell Replication: The transplanted stem cells replicate and differentiate, leading to the formation of functional blood cells, thereby restoring the hematopoietic function.
Step 2
2. Suggest and explain how AZA can reduce the effects of MDS in some patients.
Answer
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Reduction of Methylation: AZA reduces methylation of DNA, specifically targeting cytosine bases in the promoter region of tumour suppressor genes. This demethylation promotes the expression of these genes.
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Gene Activation: By allowing the transcription of tumour suppressor genes, AZA controls aberrant cell division, thus preventing the uncontrolled proliferation typical of MDS. This mechanism helps restore normal cell cycle regulation and reduces the severity of MDS.
Step 3
3. The control patients were treated with conventional drugs. Give two reasons why.
Answer
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Effectiveness Comparison: Conventional drugs are established treatments for MDS, providing a baseline for evaluating the effectiveness of AZA.
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Ethical Considerations: It is important to use a control group for ethical reasons, ensuring that patients in the study receive a recognized standard of care.
Step 4
4. Use Figure 6 and the information provided to calculate the difference in the number of patients surviving at 10 months after treatment with AZA compared with conventional drugs.
Answer
At 10 months, the proportion of patients surviving with AZA is 0.58 while the conventional drugs have 0.74.
To find the difference in the number of patients:
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Calculate Surviving Patients:
- For AZA: 0.58 of patients
- For Conventional Drugs: 0.74 of patients
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Difference in Proportions:
- Difference = 0.74 - 0.58 = 0.16
This indicates that there is a difference of 16% in survival rates after 10 months.