30. Imagine the following RNA sequence is translated in the mammalian cytosol and mitochondria. RNA sequence:
    
    AUG AUA CUG UGA CUU AGG CUC UAA
    Following are some putative peptide sequences

CytosolMitochondria

(a) Met-Ile-Leu             (i) Met-Ile-Leu-Trp-
Leu-Arg- Leu
(b) Met-Ile-Leu-Trp-     (ii) Met-Met-Leu-Trp-
Leu-Arg- LeuLeu

Find out the correct combination of peptides made in the cytosol and mitochondria.
(1) (a) (i)                     (2) (a) (ii)
(3) (b) (i)                     (4) (b) (ii)

Differences in Peptide Translation from the Same RNA Sequence in Mammalian Cytosol and Mitochondria

The translation of a given RNA sequence can differ significantly between the mammalian cytosol and mitochondria due to variations in genetic codes, initiation mechanisms, and ribosomal machinery. Understanding these differences is crucial for interpreting protein synthesis in different cellular compartments.

Given RNA Sequence:

AUG AUA CUG UGA CUU AGG CUC UAA

Step 1: Translation in the Cytosol

• Start Codon: AUG (Methionine, Met)

• Codons and Amino Acids:

  • AUG = Met

  • AUA = Ile

  • CUG = Leu

  • UGA = Stop codon (translation terminates here)

• Resulting Peptide: Met-Ile-Leu

• The downstream codons after UGA are not translated because UGA is a stop codon in the cytosol.

Step 2: Translation in Mitochondria

• Differences in Mitochondrial Genetic Code:

  • UGA codes for tryptophan (Trp) instead of a stop codon.

  • AUA codes for methionine (Met) instead of isoleucine.

  • UAA and UAG are stop codons as usual.

• Codons and Amino Acids:

  • AUG = Met

  • AUA = Met

  • CUG = Leu

  • UGA = Trp

  • CUU = Leu

  • AGG = Arg

  • CUC = Leu

  • UAA = Stop codon

• Resulting Peptide: Met-Met-Leu-Trp-Leu-Arg-Leu

Matching the Given Options

The correct combination is:

• Cytosol: Met-Ile-Leu (translation stops at UGA)

• Mitochondria: Met-Met-Leu-Trp-Leu-Arg-Leu (UGA codes for Trp, AUA codes for Met)

This corresponds to option (1) (a) (i).

Keywords for SEO Optimization

• Mammalian cytosolic vs mitochondrial translation

• Mitochondrial genetic code differences

• UGA codon in mitochondria

• Protein synthesis in mitochondria

• Translation termination codons

• Mitochondrial ribosome function

• Cytosolic ribosome translation

• Amino acid codon reassignment

• Mitochondrial protein synthesis

• RNA translation differences

Conclusion

The RNA sequence AUG AUA CUG UGA CUU AGG CUC UAA translates into Met-Ile-Leu in the mammalian cytosol, where UGA acts as a stop codon. In contrast, mitochondrial translation interprets UGA as tryptophan and AUA as methionine, producing a longer peptide Met-Met-Leu-Trp-Leu-Arg-Leu. Thus, the correct peptide combination is:

(1) (a) (i) — Cytosol: Met-Ile-Leu; Mitochondria: Met-Ile-Leu-Trp-Leu-Arg-Leu.