mRNA is a polymer of:

Options

A. deoxyribonucleosides
B. ribonucleosides
C. deoxyribonucleotides
D. ribonucleotides

Explanation

To determine what mRNA is a polymer of, we need to analyze the options provided and understand the structure of mRNA.

### Step-by-Step Solution:

1. **Understanding mRNA**: mRNA stands for messenger RNA. It is a type of RNA that carries genetic information from DNA to the ribosome, where proteins are synthesized.

2. **Identifying the Components of mRNA**: mRNA is composed of three main components:
- A sugar (specifically ribose)
- A phosphate group
- Nitrogenous bases (adenine, uracil, cytosine, and guanine)

3. **Evaluating the Options**:
- **Option A: Deoxyribonucleosides**: These are components of DNA, not RNA. Therefore, this option is incorrect.
- **Option B: Ribonucleosides**: Ribonucleosides are similar to nucleotides but lack the phosphate group. Since mRNA contains phosphate groups, this option is also incorrect.
- **Option C: Deoxyribonucleotides**: These are the building blocks of DNA, not RNA. Thus, this option is incorrect as well.
- **Option D: Ribonucleotides**: Ribonucleotides are the building blocks of RNA, consisting of ribose sugar, a phosphate group, and a nitrogenous base. This option is correct.

4. **Conclusion**: Since mRNA is made up of ribonucleotides, the correct answer is **Option D: ribonucleotides**.

### Final Answer:
mRNA is a polymer of ribonucleotides.

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