Ribosome Structure and Sedimentation — NEET Biology
✅ Asked in NEET 2025Ribosomes are the granular structures first observed under the electron microscope as dense particles by George Palade (1953). They are composed of ribonucleic acid (RNA) and proteins and are not surrounded by any membrane. The eukaryotic ribosomes are 80S while the prokaryotic ribosomes are 70S. Each ribosome has two subunits, larger and smaller subunits. The two subunits of 80S ribosomes are 60S and 40S while that of 70S ribosomes are 50S and 30S. Here 'S' (Svedberg's Unit) stands for the sedimentation coefficient; it is indirectly a measure of density and size. Both 70S and 80S ribosomes are composed of two subunits.
NTA tests whether students can distinguish between eukaryotic (80S) and prokaryotic (70S) ribosomes and their subunit compositions. The core concept is that the 'S' value (Svedberg's unit) measures sedimentation coefficient, which reflects size and density, not individual subunit summation. Students commonly make the mistake of thinking 80S = 60S + 40S mathematically equals 80, but S values don't add linearly due to different sedimentation properties. Remember: 80S ribosomes have 60S and 40S subunits (eukaryotes), while 70S have 50S and 30S subunits (prokaryotes). This distinction is critical for identifying cell types and understanding protein synthesis in different organisms.
From the statements given below choose the correct option: Statement A: The eukaryotic ribosomes are 80S and prokaryotic ribosomes are 70S. Statement B: Each ribosome has two sub-units. Statement C: The two sub-units of 80S ribosomes are 60S and 40S while that of 70S are 50S and 30S. Statement D: The two sub-units of 80S ribosomes are 60S and 20S and that of 70S are 50S and 20S. Statement E: The two sub-units of 80S are 60S and 30S and that of 70S are 50S and 30S. (NEET 2025)
Through deep analysis of NEET and NTA, 88 of 90 questions from the NEET 2026 paper were matched straight from the MedicNEET Biology question bank.
88/90MedicNEET's Biology question bank is built from the same NCERT lines NTA picks repeatedly. Not random MCQs — questions crafted exactly like NTA crafts them.