## **Core Concept**
Eukaryotic ribosomes are complex molecular machines responsible for protein synthesis in eukaryotic cells. They consist of two subunits, which are assembled from ribosomal RNA (rRNA) and proteins. The size and composition of these subunits are crucial for their function.

## **Why the Correct Answer is Right**
The correct answer, , indicates that eukaryotic ribosomes have large and small subunits, specifically referred to as 60S and 40S subunits. The 60S subunit is the large subunit, and the 40S subunit is the small subunit. These designations refer to their sedimentation coefficients (S), which reflect their size and density. The 60S subunit is composed of 28S, 5.8S, and 5S rRNA, along with numerous proteins, while the 40S subunit contains 18S rRNA and proteins.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because prokaryotic ribosomes, not eukaryotic, are characterized by 70S ribosomes, which dissociate into 50S and 30S subunits.
- **Option B:** This option is incorrect because it inaccurately represents the subunits of eukaryotic ribosomes. While it mentions 60S and 40S, which are correct, the inclusion of 30S and 50S refers to prokaryotic ribosomal subunits.
- **Option D:** This option is incorrect as it suggests 30S and 50S subunits, which are characteristics of prokaryotic ribosomes, not eukaryotic.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the difference in ribosomal subunits between prokaryotes (70S, with 50S and 30S subunits) and eukaryotes (80S, with 60S and 40S subunits) is crucial for understanding the mechanism of action of various antibiotics that target bacterial protein synthesis.

## **Correct Answer:** .