Which is a true statement about ribosomes?

Options

A. Ribosomes contain DNA and protein
B. Ribosomes are active in carbohydrate synthesis
C. Ribosomal subunits leave the nucleus and form ribosomes in the cytoplasm
D. Polyribosomes are the subunits of ribosomes

Explanation

To determine which statement about ribosomes is true, let's evaluate each option step by step.

### Step 1: Analyze the First Statement
**Statement:** Ribosomes contain DNA and protein.
**Evaluation:** This statement is incorrect. Ribosomes do not contain DNA; they are made up of ribosomal RNA (rRNA) and proteins. Their primary function is to synthesize proteins based on the instructions provided by messenger RNA (mRNA), which is transcribed from DNA.

**Hint:** Remember that ribosomes are primarily composed of rRNA and proteins, not DNA.

### Step 2: Analyze the Second Statement
**Statement:** Ribosomes are active in carbohydrate synthesis.
**Evaluation:** This statement is also incorrect. Ribosomes are not involved in carbohydrate synthesis; they are specifically responsible for protein synthesis. They translate the genetic information carried by mRNA into polypeptide chains, which then fold into functional proteins.

**Hint:** Focus on the primary function of ribosomes, which is protein synthesis, not carbohydrate synthesis.

### Step 3: Analyze the Third Statement
**Statement:** Ribosomal subunits leave the nucleus and form ribosomes in the cytoplasm.
**Evaluation:** This statement is correct. Ribosomes are assembled in the nucleolus of the nucleus as two subunits (large and small). These subunits then exit the nucleus and come together in the cytoplasm to form functional ribosomes that participate in protein synthesis.

**Hint:** Consider the process of ribosome assembly and where it occurs in the cell.

### Step 4: Analyze the Fourth Statement
**Statement:** Polyribosomes are subunits of ribosomes.
**Evaluation:** This statement is incorrect. Polyribosomes (or polysomes) are not subunits of ribosomes; rather, they are structures formed when multiple ribosomes simultaneously translate a single mRNA strand. They consist of several ribosomes working together, but they are not a part of the ribosome structure itself.

**Hint:** Understand the difference between ribosomal subunits and polyribosomes.

### Conclusion
After analyzing all the statements, the true statement about ribosomes is: **Ribosomal subunits leave the nucleus and form ribosomes in the cytoplasm.**