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A DNA molecule consists of two strands coiled to form a double helix - Edexcel - GCSE Biology - Question 2 - 2012 - Paper 1
Question 2
A DNA molecule consists of two strands coiled to form a double helix. (a) Describe how the two strands of a DNA molecule are linked together. (b) The bar chart sho... show full transcript
Worked Solution & Example Answer:A DNA molecule consists of two strands coiled to form a double helix - Edexcel - GCSE Biology - Question 2 - 2012 - Paper 1
Step 1
Describe how the two strands of a DNA molecule are linked together.
Answer
The two strands of a DNA molecule are linked together by hydrogen bonds between nitrogenous bases. Each base pairs with its complementary base: adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). This complementary base pairing is crucial for the double helix structure and helps maintain the stability of the DNA molecule.
Step 2
Complete the bar chart to show the percentage of adenine and cytosine in the sample.
Answer
Since guanine and thymine are present at certain percentages, and based on Chargaff's rules, the percentage of adenine will be equal to that of thymine, and the percentage of cytosine will be equal to that of guanine. If guanine's percentage is represented as X, then the percentage of cytosine is also X. If thymine percentage is Y, adenine percentage is Y. Thus, the complete calculation will depend on the values given in the bar chart.
Step 3
Step 4
State the maximum number of amino acids that are coded for by this DNA strand.
Answer
The maximum number of amino acids coded for by this DNA strand can be determined by dividing the total number of codons (three nucleotide bases) in the mRNA by three. The provided DNA sequence has 8 bases, resulting in a maximum of 2 amino acids coded.
Step 5