What are ribosomal subunit sizes in prokaryotes and eukaryotes and their general function?

• A. Prokaryotes have a 70S ribosome (50S+30S); Eukaryotes have an 80S ribosome (60S+40S); both synthesize lipids.
• B. Prokaryotes have a 70S ribosome (50S+30S); Eukaryotes have an 80S ribosome (60S+40S); both synthesize proteins.
• C. Prokaryotes have 80S ribosome; Eukaryotes have 70S; both make DNA.
• D. Prokaryotes have 60S and 40S; Eukaryotes have 50S and 30S; both replicate DNA.

Answer: (B)

Ribosome size and subunit composition reflect how different cells carry out protein synthesis. Prokaryotes have a 70S ribosome made up of a 50S large subunit and a 30S small subunit. Eukaryotes have an 80S ribosome made up of a 60S large subunit and a 40S small subunit. The “S” (Svedberg units) measures how the particle sediments during centrifugation, which relates to its size and shape rather than a direct linear size.

Both types of ribosomes are dedicated to making proteins by translating mRNA sequences into polypeptides, not producing lipids or DNA. The stated options that assign the wrong functions (lipid synthesis or DNA synthesis) clash with the fundamental role of ribosomes, and the subunit compositions in the other choices don’t align with the established prokaryotic versus eukaryotic sizes.