Question

What is the anticodon on tRNA for each of the following codons in mRNA? a. \(A G C\) b. UAU c. \(\mathrm{CCA}\)

Short answer

a. UCG, b. AUA, c. GGU.

Step-by-step solution

Understanding Codons and Anticodons

Codons are sequences of three nucleotides in mRNA that specify an amino acid. The anticodon is a complementary sequence of three nucleotides in tRNA that pairs with the mRNA codon during translation.

Determine the Complementary Sequence

To find the anticodon for each mRNA codon, identify the complementary RNA base pairing. Remember that Adenine (A) pairs with Uracil (U), Cytosine (C) pairs with Guanine (G), Guanine (G) pairs with Cytosine (C), and Uracil (U) pairs with Adenine (A).

Find the Anticodon for Codon a. AGC

The mRNA codon is AGC. Using the base pairing rules: A pairs with U, G pairs with C, and C pairs with G. Therefore, the anticodon is UCG.

Find the Anticodon for Codon b. UAU

The mRNA codon is UAU. Using the base pairing rules: U pairs with A, A pairs with U, and U pairs with A. Therefore, the anticodon is AUA.

Find the Anticodon for Codon c. CCA

The mRNA codon is CCA. Using the base pairing rules: C pairs with G, C pairs with G, and A pairs with U. Therefore, the anticodon is GGU.

Key concepts

mRNA Codons

Messenger RNA (mRNA) codons are crucial in the process of protein synthesis. A codon is a sequence of three nucleotides in mRNA that corresponds to a specific amino acid or stop signal during translation. Each codon is like an instruction, telling the cellular machinery what building blocks are needed to construct a protein. There are 64 possible codons, but only 20 standard amino acids, so some amino acids are specified by more than one codon.
For example, the codon sequence 'AUG' is unique because it serves as the start codon, signaling the beginning of translation. It also codes for the amino acid methionine. This dual function makes it essential for the initiation of protein synthesis.

Base Pairing Rules

Base pairing rules are fundamental to understanding how information is transferred from DNA to mRNA and then to tRNA. These rules dictate how nucleotides interact based on their chemical structures. In the context of RNA, the primary bases are Adenine (A), Uracil (U), Cytosine (C), and Guanine (G). According to the base pairing rules:

• Adenine (A) pairs with Uracil (U)
• Cytosine (C) pairs with Guanine (G)
• Guanine (G) pairs with Cytosine (C)
• Uracil (U) pairs with Adenine (A)

These pairs are formed because of hydrogen bonds between the complementary bases, which stabilizes the RNA structure. For instance, if an mRNA codon is AGC, the respective anticodon on tRNA will be UCG, following these base pairing rules. This complementary interaction ensures that the correct amino acids are brought to the ribosome during protein synthesis.

Translation Process

The translation process is the final step in decoding mRNA into a functional protein. This complex process occurs in the ribosome and involves several key stages:

• Initiation: The ribosome assembles around the mRNA to be read and the first tRNA. The start codon (AUG) on mRNA signals the beginning of translation.
• Elongation: During this phase, tRNAs bring amino acids to the ribosome in the sequence specified by the mRNA codons. Each anticodon on the tRNA pairs with the corresponding codon on the mRNA. The ribosome then links the amino acids together to form a growing polypeptide chain.
• Termination: When the ribosome encounters a stop codon (like UAA, UAG, or UGA), the translation process ends. The completed polypeptide chain is released to undergo folding and modifications to become a functional protein.

Proper translation depends on the accurate pairing of tRNA anticodons with mRNA codons. If this pairing were incorrect, the wrong amino acids could be incorporated, potentially leading to malfunctioning proteins. This precision highlights the importance of both codons and anticodons in cellular functions.