Question

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

Short answer

Answer: The UUAC sequence incorporates two unique amino acids (Leucine and Tyrosine), while the UAUC sequence incorporates three unique amino acids (Tyrosine, Isoleucine, and Serine). The difference in the number of amino acids incorporated is due to the extra codon (UCU) present in the UAUC sequence, which adds an additional amino acid (Serine) to the mix.

Step-by-step solution

Break the sequence into triplet codons

In this step, we will break down the given mRNA sequences into codons. Recall that codons consist of three nucleotides each. So, let's break the tetranucleotide UUAC and UAUC into codons: For UUAC, the possible codons are UUA and UAC, and for UAUC, the possible codons are UA, UCU, and AUC.

Use the genetic code table to find corresponding amino acids

Now that we have the codons for each sequence, we can use the genetic code table to determine which amino acids are incorporated by each sequence. Below are the corresponding amino acids for each codon: UUAC: - UUA: Leucine (Leu) - UAC: Tyrosine (Tyr) UAUC: - UAU: Tyrosine (Tyr) - AUC: Isoleucine (Ile) - UCU: Serine (Ser)

Count the amino acids incorporated in each sequence

Now that we have determined the amino acids for the codons in each sequence, we can count the number of unique amino acids incorporated by each sequence: - UUAC: Leucine and Tyrosine (2 unique amino acids) - UAUC: Tyrosine, Isoleucine, and Serine (3 unique amino acids)

Analyze the difference

With all the unique amino acids incorporated by each sequence counted, we can see that the UUAC sequence incorporates only two amino acids, not three as mentioned in the question. The UAUC sequence incorporates three amino acids as mentioned. The difference between the two sequences is due to the fact that the UAUC sequence has one additional codon (UCU) compared to the UUAC sequence, which adds an extra amino acid into the mix (Serine). The question seems to have a small error, as the UUAC sequence incorporates only two amino acids, not three.

Key concepts

mRNA sequences

mRNA sequences are crucial components of the genetic code. They are essential for protein synthesis. These sequences are formed during transcription, where DNA serves as the template to create a complementary RNA strand. mRNA stands for "messenger RNA", reflecting its role in conveying genetic information.
The sequence of nucleotides in mRNA directly determines the sequence of amino acids in a protein. Each set of three nucleotides, known as a "triplet codon," codes for a specific amino acid. This is true except for stop codons, which signal the end of protein synthesis. In the exercise example, the mRNA sequences are UUAC and UAUC. These sequences determine the sequence of amino acids to be incorporated into a protein.

codons

Codons are the basic building blocks of the genetic code. Each codon is a sequence of three nucleotides. During translation, these codons guide the synthesis of proteins by determining which amino acids are added. It's like reading instructions through a 3-letter code.
For example, in the sequence UUAC, the codons are UUA and UAC. In the UAUC sequence, the codons are UAU and AUC. Each codon corresponds to a specific amino acid, and the genetic code chart allows you to find this correspondence. This is how DNA sequences ultimately determine protein structures.

amino acids

Amino acids are the building blocks of proteins. They are organic compounds essential for various life functions. Each amino acid is assigned to specific codons. This assignment happens in a process called translation, using the mRNA template to determine the order of amino acid residues in a protein. In the exercise, different mRNA codons result in different amino acids.
For illustration, UUA translates to leucine and UAC to tyrosine in the genetic code. In contrast, the codons in the UAUC sequence, UAU, and AUC, code for tyrosine and isoleucine, respectively. The additional codon, UCU, determines the inclusion of serine as an amino acid. This variation highlights how sequences of codons result in different protein structures.

tRNA

tRNA, or transfer RNA, acts as the translator between mRNA and amino acids. Each tRNA molecule carries a specific amino acid and recognizes specific codons through its anticodon loop. This recognition is vital for assembling amino acids into the correct order based on the mRNA instructions.
When a ribosome reads the codons from the mRNA strand, tRNA molecules bring the corresponding amino acids to the growing protein chain. In the process, tRNA matches its anticodon to the complementary mRNA codon. This mechanism ensures that proteins are built accurately according to the genetic information. Without tRNA, the connection between mRNA codons and amino acid sequences would be lost.