Ribosomes are composed of

Options

A. DNA and protein
B. rRNA and protein
C. Nucleoproteins + `Mg^(++)` + tRNA
D. DNA, rRNA and proteins

Answer

### Step-by-Step Solution:

1. **Understanding Ribosomes**: Ribosomes are cellular structures that play a crucial role in protein synthesis. They are unique because they do not have a membrane, distinguishing them from many other organelles.

2. **Presence in Organisms**: Ribosomes are found in both prokaryotic and eukaryotic cells. This means they are essential for all forms of life, from simple bacteria to complex organisms like plants and animals.

3. **Structure of Ribosomes**: Ribosomes are composed of two subunits: a larger subunit and a smaller subunit. These subunits come together during protein synthesis.

4. **Composition of Ribosomes**: The ribosomal structure is made up of ribosomal RNA (rRNA) and proteins. The rRNA is crucial for the ribosome's function, as it helps in the assembly of amino acids into proteins.

5. **Role of tRNA**: Transfer RNA (tRNA) is also involved in the process of protein synthesis, as it brings the appropriate amino acids to the ribosome based on the sequence of the messenger RNA (mRNA).

6. **Absence of DNA**: It is important to note that ribosomes do not contain DNA. They also do not have nuclear proteins or magnesium ions within their structure, although magnesium ions are necessary for the interaction between the subunits.

7. **Final Answer**: Therefore, ribosomes are composed of ribosomal RNA (rRNA) and proteins.