Which of the following pairs of substances are found inside a mitochondrion?

Options

A. Single RNA molecule and 50S ribosomes
B. Single DNA molecule and 50S ribosomes
C. Single RNA molecule and 70S ribosomes
D. Single DNA molecule and 70S ribosomes

Answer

To solve the question "Which of the following pairs of substances are found inside a mitochondrion?", we need to analyze the options provided and understand the components typically found in mitochondria.

### Step-by-Step Solution:

1. **Understanding Mitochondria**:
- Mitochondria are known as the powerhouse of the cell. They are responsible for producing ATP (adenosine triphosphate), which is the energy currency of the cell.
- They are semi-autonomous organelles, meaning they have their own DNA and ribosomes, which allow them to synthesize some proteins independently.

2. **Identifying Components**:
- Mitochondria contain a **single DNA molecule**. This DNA is circular and resembles bacterial DNA, which supports the endosymbiotic theory of their origin.
- Mitochondria also contain **70S ribosomes**, which are similar to those found in prokaryotes (bacteria). This is in contrast to the 80S ribosomes found in the cytoplasm of eukaryotic cells.

3. **Evaluating the Options**:
- **Option A**: Single RNA molecules and 50S ribosomes - Incorrect. Mitochondria do not contain 50S ribosomes; they have 70S ribosomes.
- **Option B**: Single DNA molecule and 50S ribosomes - Incorrect. While the single DNA molecule is correct, the ribosome type is incorrect.
- **Option C**: Single RNA molecule and 70S ribosomes - Incorrect. Mitochondria do not contain RNA molecules in this context; they contain DNA and 70S ribosomes.
- **Option D**: Single DNA molecule and 70S ribosomes - Correct. This accurately describes the contents of mitochondria.

4. **Conclusion**:
- The correct answer is **Option D: Single DNA molecule and 70S ribosomes**.