Question

The mitochondrial matrix contains which of the following
(A) Linear double stranded DNA
(B) Circular double stranded DNA
(C) RNA
(D) Ribosomes
Choose the correct answer from the options given below:

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

Hint:

Always associate mitochondrial DNA (mtDNA) with a circular structure, resembling bacterial plasmids.
This circular configuration, along with the presence of unique ribosomes and RNA within the matrix, provides strong evidence for the bacterial origin of mitochondria.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
As proposed by the endosymbiotic theory, mitochondria contain their own genetic material and the machinery required to synthesize some of their own proteins.
This entire genetic apparatus is housed within the innermost compartment of the organelle, known as the mitochondrial matrix.

Step 2: Detailed Explanation:
Let us analyze the genetic and biochemical contents of the mitochondrial matrix:
- Circular double-stranded DNA (mtDNA) (B): Unlike eukaryotic nuclear DNA (which is linear), mitochondrial DNA is a circular, double-stranded molecule. This circular structure is highly characteristic of prokaryotes.
- RNA (C): The matrix contains the transcription machinery to produce its own messenger RNAs (mRNAs), transfer RNAs (tRNAs), and ribosomal RNAs (rRNAs).
- Ribosomes (D): Mitochondria contain their own ribosomes ($55\text{S}$ in mammals, $70\text{S}$ in plants/yeast) to translate the mitochondrially encoded mRNAs into functional proteins.
Therefore, the mitochondrial matrix contains circular double-stranded DNA, RNA, and ribosomes, but it does not contain linear double-stranded DNA (A).

Step 3: Final Answer:
The correct combination is (B), (C), and (D) only, which corresponds to option (D).