Question

Which of the following statement is correct for 70S ribosome?
(A) The 16S RNA belongs to small subunit.
(B) It also has 8S RNA.
(C) The 5S RNA belongs to 50S subunit.
(D) It can be dissociated into 40S and 30S subunit.
Choose the correct answer from the options given below:

• (A) and (B) only.
• (A) and (C) only.
• (B) and (C) only.
• (C) and (D) only.

Hint:

To remember ribosome composition:
- Prokaryotic 70S = 30S (16S rRNA) + 50S (5S & 23S rRNA).
- Eukaryotic 80S = 40S (18S rRNA) + 60S (5S, 5.8S, & 28S rRNA).
Note that the Svedberg (S) units do not add up mathematically because they depend on sedimentation rates, which are determined by both shape and mass.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Ribosomes are complexes composed of ribosomal RNA (rRNA) and proteins that carry out translation.
Prokaryotic ribosomes are 70S particles, while eukaryotic cytoplasmic ribosomes are 80S particles.
Each ribosome consists of a large subunit and a small subunit, which can dissociate under specific ionic conditions in vitro.

Step 2: Detailed Explanation:
Let us analyze each statement regarding the prokaryotic 70S ribosome:
Statement (A) is correct because the 70S ribosome contains a small 30S subunit and a large 50S subunit.
The 30S small subunit contains the 16S rRNA molecule alongside approximately 21 proteins.
Statement (B) is incorrect because there is no 8S RNA in prokaryotes.
The standard rRNAs in the 70S ribosome are 16S, 23S, and 5S rRNAs.
Statement (C) is correct because the 50S large subunit contains two rRNA molecules: the 23S rRNA and the small 5S rRNA.
Statement (D) is incorrect because the 70S ribosome dissociates into 50S and 30S subunits.
The 40S and 30S combination is incorrect; 40S is the small subunit of the eukaryotic 80S ribosome.
Evaluating the statements shows that only (A) and (C) are correct.

Step 3: Final Answer:
Statements (A) and (C) are correct.
This corresponds to Option (B).