This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of nucleic acids, Subject name: Biochemistry
True about mitochondrial DNA 
Select and explain. 
A. UGA codes for arginine, B. Codes for 13 protein, C. High content of untranslated sequence, D. Circular double stranded DNA
A: UGA codes for arginine
Answer: A: UGA codes for arginine 
Explanation: The protein synthesizing machinery of mitochondria is distinct from that in the cytoplasmThere are only about 22 tRNA in mitochondria but there are 31 tRNA species in cytoplasm The discovery of difference in codons representing different amino acids in mitochondria has now changed the universal nature of the genetic code For example, UGA is a terminator codon in nuclear DNA but codes for arginine in mitochondrial DNARef: DM Vasudevan, 7th edition, page no: 599