Shown here are the amino acid sequences of the wild-type and three mutant forms of a short protein.
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Wild-type: Met-Trp-Tyr-Arg-Gly-Ser-Pro-Thr
Mutant 1: Met-Trp
Mutant 2: Met-Trp-His-Arg-Gly-Ser-Pro-Thr
Mutant 3: Met -Cys-Ile-Val-Val-Val-Gln-His
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Use this information to answer the following questions:
Another mutation (mutant 4) is isolated. Its amino acid sequence is unchanged from the wild type, but the mutant cells produce abnormally low amounts of the wild-type proteins. As specifically as you can, predict where this mutation exists in the gene.

검증된 단계별 안내

Understand that the amino acid sequence of mutant 4 is identical to the wild-type protein, indicating that the mutation does not change the protein's primary structure.

Since the protein sequence is unchanged but the amount of protein produced is abnormally low, consider mutations that affect gene expression rather than protein coding, such as mutations in regulatory regions.

Identify key regulatory regions in the gene that control transcription and translation, including the promoter, enhancer, and possibly the 5' untranslated region (5' UTR) or sequences affecting mRNA stability.

Predict that the mutation likely exists in the promoter or other regulatory elements upstream of the coding sequence, which would reduce transcription efficiency and thus lower protein production without altering the amino acid sequence.

Conclude that the mutation is not in the coding region but in a regulatory region of the gene that controls the amount of protein synthesized.

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주요 개념

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Gene Expression and Protein Synthesis

Gene expression involves transcribing DNA into mRNA and translating mRNA into a protein sequence. Mutations can affect protein quantity or quality by altering transcription, mRNA stability, or translation efficiency, even if the amino acid sequence remains unchanged.

Types of Mutations Affecting Protein Levels

Mutations outside the coding region, such as in promoters, enhancers, or regulatory sequences, can reduce protein production without changing the amino acid sequence. These regulatory mutations impact transcription initiation or mRNA processing, leading to lower protein amounts.

Relationship Between DNA Sequence and Protein Sequence

The amino acid sequence is determined by the coding DNA sequence, but mutations in non-coding regions or synonymous codons can affect gene expression levels. Thus, unchanged protein sequences can still result from mutations that alter gene regulation rather than protein structure.