How do the standard and the mammalian mitochondrial genetic codes differ in term
ID: 167543 • Letter: H
Question
How do the standard and the mammalian mitochondrial genetic codes differ in terms of their tRNAs?
- (1) Wobble rules permit 22 tRNAs to decode the standard code, whereas different rules require at least 32 tRNAs for the mammalian mitochondrial code; (2) when a single amino acid is four-fold degenerate (i.e., specified by four codons that differ only in the third codon position), a single tRNA is used in the mitochondrial code, whereas a minimum of two tRNAs would be needed to decode the standard code.
- (1) Wobble rules require at least 32 tRNAs to decode the standard code, whereas different rules permit only 22 tRNAs for the mammalian mitochondrial code; (2) when a single amino acid is four-fold degenerate (i.e., specified by four codons that differ only in the third codon position), a single tRNA is used in the standard code, whereas a minimum of two tRNAs would be needed to decode the mitochondrial code.
- (1) Wobble rules permit 22 tRNAs to decode the standard code, whereas different rules require at least 32 tRNAs to decode the mammalian mitochondrial code; (2) when a single amino acid is specified by four codons that differ only in the third codon position, a single tRNA is used in the standard code, whereas a minimum of two tRNAs would be needed to decode the mitochondrial code.
- (1) Wobble rules require at least 32 tRNAs to decode the standard code, whereas different rules permit only 22 tRNAs for the mammalian mitochondrial code; (2) when a single amino acid is four-fold degenerate (i.e., specified by four codons that differ only in the third codon position), a single tRNA is used in the mitochondrial code, whereas a minimum of two tRNAs would be needed to decode the standard code.- (1) Wobble rules require at least 32 tRNAs to decode the standard code, whereas different rules permit only 22 tRNAs for the mammalian mitochondrial code; (2) when a single amino acid is four-fold degenerate (i.e., specified by four codons that differ only in the third codon position), a single tRNA is used in the standard code, whereas a minimum of two tRNAs would be needed to decode the mitochondrial code.
- (1) Wobble rules permit 22 tRNAs to decode the standard code, whereas different rules require at least 32 tRNAs to decode the mammalian mitochondrial code; (2) when a single amino acid is specified by four codons that differ only in the third codon position, a single tRNA is used in the standard code, whereas a minimum of two tRNAs would be needed to decode the mitochondrial code.
Explanation / Answer
Choice 1 is correct.
Reason: The mitochondria inside a eukaryotic cell are considered to be endo-symbiotic bacteria by evoltionary trend. The mitochondria have their double-stranded circular genome of own which undergoes replication and traslates for specific mitochondrial proteins. Most of these proteins are regulatory proteins and unique to the mitochondria only. However, the mitochondrial genome follows a different set of Wobble rules as compared to the nuclear genome and hence, the codon sequences often code of different amino acids compared to nuclear codons. For example, the codon UGA refers to a stop codon in eukaryotes as it does not encode for any amino acid but in prokaryotes and mitochondria, it indeed encodes for amino acid tryptophan. Thus, whereas eukaryotes do not contain any amino-acyl tRNA for UGA codon, mitochondrial machinery does contain it. This is why there occurs a difference between number of codons in the nuclear and mitochondrial genome and accounts for difference in number of tRNAs in these two genomes.
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