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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
For some patients, HSCT is an effective treatment for MDS. Explain how.
Answer
Haematopoietic stem cell transplantation (HSCT) is effective for MDS patients as it introduces healthy stem cells that can produce normal blood cells. This occurs after the patient's faulty bone marrow is destroyed, eliminating the diseased cells. The new stem cells can replicate and differentiate properly, replenishing the patient's blood cell supply with healthy cells.
Step 2
Suggest and explain how AZA can reduce the effects of MDS in some patients.
Answer
AZA reduces the methylation of DNA at the cytosine bases. This means that the genes responsible for tumor suppression, which may have been silenced due to excessive methylation, can be expressed again. By promoting the transcription of these genes, AZA helps to prevent the rapid and uncontrolled division of cells that characterizes MDS.
Step 3
Step 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
From Figure 6, at 10 months, approximately 58% of patients receiving AZA survived while about 74% of those on conventional treatments survived. Therefore, the difference in the proportion of patients surviving is: