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Question
Which of the following is not relevant to the structure of double helical DNA?
Which of the following is not relevant to the structure of double helical DNA?
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Solution
The correct option is D Each strand of helix has a backbone made up of alternating ribose sugar and phosphate
The Watson and Crick model shows that DNA is a double helix and each strand of helix has a backbone made up of alternating deoxyribose sugar and phosphate.
Ribose sugar-phosphate backbone is found in RNA.
The figure below shows deoxyribose sugar and phosphate making the backbone and paired bases that are projected inside.
Four types of nitrogenous bases occur in DNA. They belong to two groups, purines (9- membered double ring structure) and pyrimidines (six- membered single ring structure).
DNA has two types of purines (adenine and guanine) and two types of pyrimidines (cytosine and guanine).
Purines having double ring structure are large sized and pyrimidines on the other side with single ring structure are small sized.
Purines always pair up with pyrimidines with the help of hydrogen bonds. This generates a uniform distance between two strands of helix. The diameter of the DNA helix is 20 A°.
DNA double helix is coiled in right handed helical fashion. Each complete turn of the helix is called the pitch having length of 34 A° that consists of around 10 base pairs. Therefore, the distance between successive base pairs is 3.4 A°.
The figure below shows a double helix DNA with the diameter of the helix 20 A° and distance between successive base pairs of 3.4 A°.
Thus, it can be concluded that option d, each strand of DNA helix has a backbone made up of alternating ribose sugar and phosphate is not relevant.
The Watson and Crick model shows that DNA is a double helix and each strand of helix has a backbone made up of alternating deoxyribose sugar and phosphate.
Ribose sugar-phosphate backbone is found in RNA.
The figure below shows deoxyribose sugar and phosphate making the backbone and paired bases that are projected inside.
Four types of nitrogenous bases occur in DNA. They belong to two groups, purines (9- membered double ring structure) and pyrimidines (six- membered single ring structure).
DNA has two types of purines (adenine and guanine) and two types of pyrimidines (cytosine and guanine).
Purines having double ring structure are large sized and pyrimidines on the other side with single ring structure are small sized.
Purines always pair up with pyrimidines with the help of hydrogen bonds. This generates a uniform distance between two strands of helix. The diameter of the DNA helix is 20 A°.
DNA double helix is coiled in right handed helical fashion. Each complete turn of the helix is called the pitch having length of 34 A° that consists of around 10 base pairs. Therefore, the distance between successive base pairs is 3.4 A°.
The figure below shows a double helix DNA with the diameter of the helix 20 A° and distance between successive base pairs of 3.4 A°.
Thus, it can be concluded that option d, each strand of DNA helix has a backbone made up of alternating ribose sugar and phosphate is not relevant.
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