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. Adenine pairs with thymine through two hydrogen bonds and cytosine pairs with guanine through three hydrogen bonds. This complementary base pairing is essential for the structure of DNA as it maintains the integrity of the genetic code.
Step 2
Write the code for the complementary DNA strand in Figure 16.
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Answer
The complementary DNA strand for the sequence given in Figure 16 (T T G A T T G C T G T A A) would be: 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
Since three bases on the strand of DNA code for one amino acid, and there are 12 bases in total from the DNA sequence, the maximum number of amino acids coded for would be:
extMaximumAminoAcids=312=4
Thus, the answer is B 4.
Step 4
What is the shape of a DNA molecule?
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Answer
The shape of a DNA molecule is best described as a double helix. This structure consists of two strands of nucleotides winding around each other.
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 and remove cellular debris that could inhibit the extraction of DNA. Protease helps to digest any proteins that are surrounding the DNA, allowing for a clearer extraction.
Step 6
State why ice-cold ethanol was poured into the filtrate.
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Answer
Ice-cold ethanol was poured into the filtrate to precipitate the DNA. DNA is soluble in water but becomes insoluble in the presence of alcohol, especially at low temperatures, thereby allowing the DNA to separate from the solution.
Step 7
Give two variables the student would need to control to make this a valid comparison.
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Answer
The mass of the plant material used (both peas and beans) must be the same.
The concentration of the solutions used during the extraction process should be held constant.
