A nucleotide of DNA may contain_______. a. ribose, uracil, and a phosphate group b. deoxyribose, uracil, and a phosphate group c. deoxyribose, thymine, and a phosphate group d. ribose, thymine, and a phosphate group
The Correct Answer and Explanation is:
The correct answer is c. deoxyribose, thymine, and a phosphate group.
Explanation:
A nucleotide is the basic building block of DNA (deoxyribonucleic acid). It is composed of three main components:
- Deoxyribose: This is a 5-carbon sugar molecule that forms the backbone of the DNA strand. The “deoxy-” part of the name indicates that one oxygen atom is missing from the sugar compared to ribose (found in RNA). This absence of oxygen is a key difference between DNA and RNA.
- Thymine: This is one of the four nitrogenous bases found in DNA. Thymine is a pyrimidine base, and it pairs with adenine in the DNA double helix through two hydrogen bonds.
- Phosphate group: The phosphate group is attached to the sugar (deoxyribose) and is crucial for linking adjacent nucleotides together to form the DNA strand. The phosphate group forms a bond with the 3′ carbon of one sugar and the 5′ carbon of the next sugar, creating a sugar-phosphate backbone for the DNA molecule.
The other answer choices do not describe a nucleotide in DNA:
- a. Ribose, uracil, and a phosphate group: This describes RNA, not DNA. RNA contains ribose (a sugar with an extra hydroxyl group compared to deoxyribose) and uracil (a nitrogenous base that pairs with adenine in RNA).
- b. Deoxyribose, uracil, and a phosphate group: Uracil is found in RNA, not DNA. In DNA, uracil is replaced by thymine.
- d. Ribose, thymine, and a phosphate group: Ribose is a component of RNA, and thymine is found in DNA, but this combination is incorrect because ribose should not be present in DNA.
Thus, c. deoxyribose, thymine, and a phosphate group is the correct description of a nucleotide in DNA.
