Students are studying a model fragment of a DNA double helix. In the model they can see nucleotides linked together by 16 phosphodiester bonds, 9 stacked pairs of nitrogenous bases and 3 of the nitrogenous bases are thymine.This DNA double helix fragment therefore contains:Select one alternative:16 deoxyribose molecules and 6 adenine nitrogenous bases.18 deoxyribose molecules and 6 adenine nitrogenous bases.9 deoxyribose molecules and 3 adenine nitrogenous bases.18 deoxyribose molecules and 3 adenine nitrogenous bases.
Question
Students are studying a model fragment of a DNA double helix. In the model they can see nucleotides linked together by 16 phosphodiester bonds, 9 stacked pairs of nitrogenous bases and 3 of the nitrogenous bases are thymine.This DNA double helix fragment therefore contains:Select one alternative:16 deoxyribose molecules and 6 adenine nitrogenous bases.18 deoxyribose molecules and 6 adenine nitrogenous bases.9 deoxyribose molecules and 3 adenine nitrogenous bases.18 deoxyribose molecules and 3 adenine nitrogenous bases.
Solution
The correct answer is: 18 deoxyribose molecules and 6 adenine nitrogenous bases.
Here's the step-by-step reasoning:
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In a DNA double helix, each nucleotide is composed of a deoxyribose sugar, a phosphate group, and a nitrogenous base.
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The phosphodiester bonds link these nucleotides together. So, if there are 16 phosphodiester bonds, that means there are 18 nucleotides (because the bonds are between the nucleotides, so there's always one more nucleotide at each end).
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Therefore, there are 18 deoxyribose molecules (one for each nucleotide).
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The nitrogenous bases in DNA are adenine (A), thymine (T), cytosine (C), and guanine (G). In a DNA double helix, adenine always pairs with thymine, and cytosine always pairs with guanine.
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If there are 9 stacked pairs of nitrogenous bases, that means there are 18 nitrogenous bases in total.
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If 3 of these are thymine, and adenine always pairs with thymine, then there must be 3 adenine bases to pair with them.
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However, this leaves 12 more nitrogenous bases (18 total minus the 6 accounted for). These must be evenly split between cytosine and guanine, because they always pair together. So, there are 6 more adenine bases.
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Therefore, in total, there are 6 adenine nitrogenous bases.
Similar Questions
Which two bases are present in equal amounts in a double-stranded DNA molecule? (1) cytosine and thymine (2) adenine and thymine (3) ade- nine and uracil (4) cytosine and uracil
Which of the following statements about DNA is incorrect?ANSWERThe alternating sugars and phosphate molecules of the DNA backbone bond together via phosphodiester bonds.DNA is a long, single-stranded molecule that curves into a helix, and the set pairings of the bases ensure that there is always a purine across from another purine and a pyrimidine across from another pyrimidine.The nitrogen base adenine always pairs with thymine, and guanine always pairs with cytosine.DNA has an antiparallel arrangement.
DNA double helix does not have which of the following?Group of answer choicescomplementary base pairingparallel configurationthyminemajor and minor grooves
How are the nitrogenous bases (A, G, C, T) joined to the DNA backbone?Group of answer choicesThey make covalent bonds with both the deoxyribose and the phosphate.They are covalently bound to the deoxyribose.They are covalently bound to the phosphate group.They interact through ionic interactions with the deoxyribose.They interact through ionic interactions with the phosphate group.
What is the structure of the DNA double helix
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