Asked by Sam
what determines the genetic code that specifies which protein will be made
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GPT-5 mini
AI
Two related things determine which protein is made:
1) The genetic code (codon table)
- The genetic code is the mapping of three-base codons in mRNA to specific amino acids (plus start and stop signals). That mapping is essentially universal and tells the ribosome which amino acid to add for each codon during translation.
2) The nucleotide sequence and gene-expression control
- Which protein actually gets made in a cell depends on the DNA sequence of a particular gene (the order of codons that becomes the mRNA) and the cellular machinery that expresses that gene. Key steps:
- Promoters, enhancers and transcription factors determine whether and how much a gene is transcribed into mRNA.
- mRNA processing (splicing, 5' cap, poly-A tail) and RNA stability affect which mRNA isoforms are available.
- The ribosome and tRNAs translate the mRNA codons into an amino-acid sequence; start codons set the reading frame and stop codons terminate translation.
- Alternative splicing, RNA editing, and translational regulation can produce different protein isoforms from the same gene.
- Post-translational modifications (phosphorylation, glycosylation, cleavage) can further change the final protein.
Other factors that change the outcome
- Mutations (point, insertion/deletion) can alter codons and change amino acids, create premature stops, or shift the reading frame.
- Codon usage bias, availability of tRNAs, and organelle-specific code variants (e.g., mitochondria) can influence translation efficiency or slightly different codon assignments.
- Epigenetic states and cell-type–specific transcription programs determine which genes are turned on in a given cell.
Short summary: the codon table defines how triplets map to amino acids, but the actual protein produced is determined by which gene’s DNA sequence is transcribed and translated and by the regulatory processes that control transcription, RNA processing, translation and post-translational modification.
1) The genetic code (codon table)
- The genetic code is the mapping of three-base codons in mRNA to specific amino acids (plus start and stop signals). That mapping is essentially universal and tells the ribosome which amino acid to add for each codon during translation.
2) The nucleotide sequence and gene-expression control
- Which protein actually gets made in a cell depends on the DNA sequence of a particular gene (the order of codons that becomes the mRNA) and the cellular machinery that expresses that gene. Key steps:
- Promoters, enhancers and transcription factors determine whether and how much a gene is transcribed into mRNA.
- mRNA processing (splicing, 5' cap, poly-A tail) and RNA stability affect which mRNA isoforms are available.
- The ribosome and tRNAs translate the mRNA codons into an amino-acid sequence; start codons set the reading frame and stop codons terminate translation.
- Alternative splicing, RNA editing, and translational regulation can produce different protein isoforms from the same gene.
- Post-translational modifications (phosphorylation, glycosylation, cleavage) can further change the final protein.
Other factors that change the outcome
- Mutations (point, insertion/deletion) can alter codons and change amino acids, create premature stops, or shift the reading frame.
- Codon usage bias, availability of tRNAs, and organelle-specific code variants (e.g., mitochondria) can influence translation efficiency or slightly different codon assignments.
- Epigenetic states and cell-type–specific transcription programs determine which genes are turned on in a given cell.
Short summary: the codon table defines how triplets map to amino acids, but the actual protein produced is determined by which gene’s DNA sequence is transcribed and translated and by the regulatory processes that control transcription, RNA processing, translation and post-translational modification.
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