The mRNA formed from the repeating tetranucleotide UUAC incorporates only three amino acids, but the use of UAUC incorporates four amino acids. Why?

Verified step by step guidance

1. Step 1: Understand that the mRNA sequence is read in sets of three nucleotides called codons, each codon specifying one amino acid during translation.
2. Step 2: Analyze the repeating tetranucleotide sequence UUAC. When this sequence is repeated, the reading frame divides the sequence into codons, but due to the repetition pattern, only three unique codons (and thus three amino acids) are formed.
3. Step 3: Examine the sequence UAUC repeated. Because of the different nucleotide order, the reading frame produces four distinct codons, resulting in four different amino acids being incorporated.
4. Step 4: Recognize that the difference arises because the reading frame shifts the grouping of nucleotides into codons differently depending on the sequence, affecting how many unique codons are generated from the repeating pattern.
5. Step 5: Conclude that the number of amino acids incorporated depends on how the repeating sequence is divided into triplet codons, which is influenced by the specific nucleotide order in the tetranucleotide repeat.

Key Concepts

Genetic Code and Codons

The genetic code consists of triplet codons, each made of three nucleotides, that specify particular amino acids during protein synthesis. The sequence of codons in mRNA determines the order of amino acids in a polypeptide chain.

Reading Frame and Frame Shifts

The reading frame is the way nucleotides are grouped into codons starting from a specific nucleotide. Shifting the reading frame by one or two nucleotides changes the grouping of codons, potentially altering the number and identity of amino acids incorporated.

Repeating Nucleotide Sequences and Codon Overlap

Repeating sequences like UUAC can produce overlapping codons depending on the reading frame, which affects how many unique amino acids are encoded. Different tetranucleotide repeats can shift codon boundaries, leading to variations in amino acid incorporation.