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Figure 4 shows two complementary strands in part of a DNA double helix structure - AQA - A-Level Chemistry - Question 12 - 2019 - Paper 2
Question 12
Figure 4 shows two complementary strands in part of a DNA double helix structure. 1 2.1 Draw all the hydrogen bonds between the complementary strands shown in Figur... show full transcript
Worked Solution & Example Answer:Figure 4 shows two complementary strands in part of a DNA double helix structure - AQA - A-Level Chemistry - Question 12 - 2019 - Paper 2
Step 1
Draw all the hydrogen bonds between the complementary strands shown in Figure 4.
Answer
In Figure 4, the hydrogen bonds between complementary DNA bases are as follows:
- Two dashed lines between adenine (A) and thymine (T) indicate 2 hydrogen bonds.
- Three dashed lines between cytosine (C) and guanine (G) indicate 3 hydrogen bonds. Ensure that these dashed lines connect the corresponding bases appropriately.
Step 2
Draw a ring around each of the component parts that make up the cytosine nucleotide in the section of DNA shown in Figure 4.
Answer
To indicate the components of the cytosine nucleotide, draw a ring around the following parts:
- The cytosine base, which is present on the strand.
- The sugar (ribose or deoxyribose) connected to the cytosine base.
- The phosphate group linked to the sugar (upper phosphate is the one that connects to the next nucleotide).
Step 3
State the meaning of the term complementary when it is used to refer to DNA strands.
Answer
The term 'complementary' in reference to DNA strands means that the two strands have base sequences that must match according to specific pairings: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). This ensures the strands can form base pairs correctly.