8 (a) DNA molecules contain base pairs - Edexcel - GCSE Biology - Question 8 - 2022 - Paper 1
Question 8
8 (a) DNA molecules contain base pairs.
Describe how the base pairs are bonded together in a DNA molecule.
(b) Figure 16 shows part of a DNA molecule.
T T G A T T ... show full transcript
Worked Solution & Example Answer:8 (a) DNA molecules contain base pairs - Edexcel - GCSE Biology - Question 8 - 2022 - Paper 1
Step 1
Describe how the base pairs are bonded together in a DNA molecule.
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Answer
Base pairs in a DNA molecule are held together by hydrogen bonds. Each base pairs with a complementary base: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). This pairing occurs due to specific base interactions, stabilizing the double-stranded structure of the DNA.
Step 2
Write the code for the complementary DNA strand in Figure 16.
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Answer
The complementary DNA strand for T T G A T T G C T G T A A is: A A C T A A C G A C A T T.
Step 3
Which is the maximum number of amino acids coded for by this strand of DNA?
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Answer
The maximum number of amino acids coded for by the strand of DNA shown is 4. This is because there are 12 bases in total, and since three bases code for one amino acid, the calculation is:
extMaximumAminoAcids=312=4
Step 4
What is the shape of a DNA molecule?
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Answer
The shape of a DNA molecule is a double helix. This structure consists of two strands that twist around each other, forming a helical configuration.
Step 5
Explain why the enzyme protease was added to the mixture.
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Answer
The enzyme protease was added to the mixture to break down proteins, which helps to release DNA from the cells by breaking down the proteins that are associated with the DNA. This facilitates the extraction process.
Step 6
State why ice-cold ethanol was poured into the filtrate.
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Ice-cold ethanol was poured into the filtrate to precipitate the DNA. The cold temperature helps to increase the efficiency of DNA precipitation by reducing its solubility, allowing it to form visible strands.
Step 7
Give two variables the student would need to control to make this a valid comparison.
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Answer
The student should control the following two variables:
The amount of fresh peas and beans used in the experiment.
The temperature at which the extraction process is carried out.
