Question

Mitochondrial DNA A. is circular. B. is self-replicating. C. is important in the synthesis of mitochondrial ribosomes. D. both (A) and (B).

Short answer

D. both (A) and (B).

Step-by-step solution

Understand the Statements

First, review each statement about mitochondrial DNA to understand what they imply.

Evaluate Statement A

Statement A: 'Mitochondrial DNA is circular.' Evaluate this statement. Mitochondrial DNA in most organisms is indeed circular, similar to bacterial DNA.

Evaluate Statement B

Statement B: 'Mitochondrial DNA is self-replicating.' Evaluate this statement. Mitochondrial DNA has the machinery needed for replication independent of nuclear DNA, so this statement is true.

Evaluate Statement C

Statement C: 'Mitochondrial DNA is important in the synthesis of mitochondrial ribosomes.' Evaluate this statement. While mitochondrial DNA codes for some mitochondrial proteins and RNA, it does not directly synthesize ribosomes.

Combine the True Statements

Since both Statement A and Statement B are true, we need to check for options that include both A and B. Option D states 'both (A) and (B),' which is the correct combination.

Key concepts

circular DNA

In most organisms, mitochondrial DNA (mtDNA) is circular. This means that the DNA forms a closed loop, unlike the linear DNA found in the nucleus. This circular structure is similar to the DNA found in bacteria, indicating a common evolutionary origin. The circular nature of mtDNA helps protect it from degradation and ensures the efficient replication of the entire genome during cell division.
In summary, mitochondrial DNA is unique in its circular formation, contrasting with the linear strands of nuclear DNA and facilitating its specific roles within the cell.

self-replicating DNA

Mitochondrial DNA is self-replicating. This means it has its own machinery to replicate independently of the cell's nuclear DNA. Here are some key points about its self-replicating nature:

• It ensures that mitochondria can duplicate their DNA during cell division without relying on nuclear DNA.
• This capability is crucial for producing enough mitochondria to meet the energy demands of the cell.

The self-replication of mitochondrial DNA supports the idea that mitochondria evolved from free-living bacteria that had their own DNA and replication mechanisms.

mitochondrial ribosomes

While mitochondrial DNA codes for some proteins and RNA necessary for mitochondrial function, it does not directly synthesize ribosomes. Mitochondrial ribosomes (mitoribosomes) are specialized structures within the mitochondria responsible for protein synthesis. Here are a couple of details about them:

• Mitoribosomes are similar to bacterial ribosomes but are adapted to meet the needs of the mitochondria.
• Mitochondrial DNA contributes to the production of RNA components that become part of these ribosomes.

In conclusion, mitochondrial DNA is essential but works indirectly in the process involving mitochondrial ribosomes, highlighting the interplay between different cellular components in sustaining mitochondrial function.