Question

Some of the unique features of the human mitochondrial genome are
A. The rRNA genes are among the smallest known, with a sedimentation coefficient of 16S and 12S for large and small subunits respectively
B. There are only 13 protein-coding genes each of which takes part in the electron transport chain
C. There are no intergenic regions in the genome
D. The genes are present only for 22 tRNAs
Choose the correct answer from the options given below:

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

Hint:

Human mtDNA: 16.5 kb circular dsDNA $\rightarrow$ 37 genes total: 13 respiratory proteins + 2 rRNAs (12S, 16S) + 22 tRNAs. No introns.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The human mitochondrial genome (mtDNA) is a circular, compact, non-intronic double-stranded 16,569 bp genome encoding 37 essential genes.

Step 2: Detailed Explanation:
Key architectural features of human mitochondrial DNA (mtDNA):
1. A (True): Encodes two ribosomal RNAs: 12S rRNA (small subunit) and 16S rRNA (large subunit).
2. B (True): Encodes exactly 13 essential polypeptide subunits of the respiratory chain (Complexes I, III, IV, and ATP synthase).
3. C (True): Highly economical with virtually no non-coding intergenic spacer sequences and no introns (polycistronic transcripts).
4. D (True): Encodes 22 tRNA genes (sufficient to translate all codons via extended wobble rules).
Thus, statements A, B, C, and D are all correct.

Step 3: Final Answer:
Hence, the correct answer is A, B, C and D, matching option (D).