The RNA components of ribosomes are synthesized in the __.
a. cytoplasm
b. nucleus
c. nucleolus
d. endoplasmic reticulum
The correct answer and explanation is :
The correct answer is:
c. nucleolus
Explanation:
Ribosomes are the cellular structures responsible for protein synthesis, and they consist of two main components: ribosomal RNA (rRNA) and proteins. The RNA components of ribosomes are synthesized in the nucleolus, a specialized region within the nucleus.
The Role of the Nucleolus
The nucleolus is the site where ribosomal RNA (rRNA) is transcribed, processed, and assembled with ribosomal proteins to form the ribosomal subunits. This process begins with genes encoding rRNA being transcribed by RNA polymerase I, producing a precursor rRNA (pre-rRNA). This pre-rRNA undergoes chemical modifications and cleavage to form the mature rRNA molecules that will be part of the ribosome.
Formation of Ribosomal Subunits
Once the rRNA is processed in the nucleolus, it combines with ribosomal proteins (imported from the cytoplasm) to form the small (40S) and large (60S) ribosomal subunits in eukaryotic cells. These subunits are then transported out of the nucleus through the nuclear pores into the cytoplasm, where they assemble into functional ribosomes and participate in protein synthesis.
Why the Other Options Are Incorrect?
- Cytoplasm (a): The ribosomal subunits function in the cytoplasm, but rRNA synthesis does not occur there.
- Nucleus (b): While the nucleolus is inside the nucleus, rRNA synthesis specifically occurs in the nucleolus, not the entire nucleus.
- Endoplasmic Reticulum (d): Ribosomes may attach to the rough ER for protein synthesis, but rRNA is not synthesized there.
Thus, the nucleolus is the correct answer as the site of rRNA synthesis and initial ribosome assembly.
