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The flow chart shows a sequence for extracting DNA from peas - Edexcel - GCSE Biology - Question 4 - 2016 - Paper 1
Question 4
The flow chart shows a sequence for extracting DNA from peas. Dissolve 3 g of salt in 100 cm³ of detergent solution in a test tube. Add 50 g of crushed peas to the ... show full transcript
Worked Solution & Example Answer:The flow chart shows a sequence for extracting DNA from peas - Edexcel - GCSE Biology - Question 4 - 2016 - Paper 1
Step 1
Explain why the salt needs to be dissolved in detergent solution in a test tube.
Answer
The salt helps to stabilize the DNA by neutralizing the negatively charged phosphate groups in the DNA, which facilitates its separation from proteins and cellular debris. The detergent solution disrupts cell membranes, allowing the DNA to be released into the solution by breaking down lipids and proteins.
Step 2
Describe a difference in the appearance of the DNA after adding protease solution.
Answer
After adding protease solution, the DNA appears more distinct and visible compared to before. Protease enzymes break down proteins, which allows the DNA to aggregate and form visible strands, enhancing clarity against the solution.
Step 3
Describe the purpose of pouring ice cold ethanol down the side of the test tube.
Answer
Pouring ice cold ethanol down the side of the test tube helps to precipitate the DNA out of the solution. The cold temperature reduces the solubility of DNA in the alcohol, causing the DNA strands to come together and become visible as white strands. This process also helps to further purify the DNA by removing water solubles and other contaminants.