Select the CORRECTLY matched pair.

Options

A. Ribozyme - part of smaller subunit of ribosome
B. P-site - Contributed by two ribosomal subunits
C. E-site - Face the tunnel between two subunits of ribosome
D. A-site - Part of smaller subunit of ribosome facing the tunnel site

Answer

To solve the question of selecting the correctly matched pair, we will analyze each option provided in the question step by step.

### Step 1: Understand the components mentioned in the options.
- **Ribozyme**: This is an RNA molecule that has catalytic properties, meaning it can catalyze biochemical reactions, similar to enzymes. However, it is not a part of the ribosome.
- **P-site**: This is one of the three sites on the ribosome (A-site, P-site, and E-site) involved in protein synthesis. The P-site is where the tRNA carrying the growing polypeptide chain is located.
- **E-site**: This is the exit site on the ribosome where the tRNA exits after its amino acid has been added to the growing polypeptide chain.
- **A-site**: This is the aminoacyl site on the ribosome where new amino acids are added during translation.

### Step 2: Analyze the correctness of each pair.
1. **Ribozyme - Part of small subunit of ribosome**: Incorrect. Ribozyme is not a structural part of the ribosome; it is a functional RNA molecule.

2. **P-site - Contributed by two ribosomal subunits**: Correct. The P-site is indeed formed by the interaction of the large and small ribosomal subunits and is crucial for forming peptide bonds.

3. **E-site - Face the tunnel between two subunits of ribosome**: Incorrect. The E-site is not in the middle; it is located at the edge of the ribosome.

4. **A-site - Part of smaller subunit of ribosome facing the tunnel side**: Incorrect. The A-site is not specifically part of the smaller subunit; it is located at the interface of both subunits.

### Step 3: Conclusion
Based on the analysis, the only correctly matched pair is **P-site - contributed by two ribosomal subunits**. Therefore, the correct answer is the second option.