Question

What amino acid sequence is coded by the following mRNA base sequence? CUU-AUG-GCU-UGG-CCC-UAA

Short answer

Leucine, Methionine, Alanine, Tryptophan, Proline.

Step-by-step solution

Determine the Codons

Break the mRNA base sequence into codons (groups of three nucleotides). The given sequence is CUU-AUG-GCU-UGG-CCC-UAA, so the codons are: CUU, AUG, GCU, UGG, CCC, and UAA.

Find the Amino Acid for Each Codon

Use the genetic code chart to identify the amino acid corresponding to each mRNA codon: - CUU codes for Leucine (Leu) - AUG codes for Methionine (Met) — this is also the start codon - GCU codes for Alanine (Ala) - UGG codes for Tryptophan (Trp) - CCC codes for Proline (Pro) - UAA is a stop codon, which signals the termination of translation.

Translate Codons to Amino Acid Sequence

Translate the sequence of codons into an amino acid sequence, ignoring the stop codon since it marks the end of translation. The amino acid sequence is: Leucine, Methionine, Alanine, Tryptophan, Proline.

Key concepts

Genetic Code

The genetic code is an essential system that allows cells to translate mRNA sequences into proteins. It is the set of rules used by living cells to convert the triplet nucleotides of mRNA, known as codons, into specific amino acids.
This code is nearly universal among all organisms, meaning the same codon sequences tend to specify the same amino acids. This universality underlines the theory of a common evolutionary origin for all life on Earth.

• Each set of three nucleotides in mRNA corresponds to one codon.
• There are 64 codons in total, and they encode 20 different amino acids.
  
• Some codons serve specific functions, such as starting or stopping protein synthesis.

Breaking down the genetic code helps scientists understand how genes dictate the synthesis of proteins, the workhorses of the cell.

Codon Recognition

Codon recognition is a key step in protein synthesis where the ribosome identifies the three-nucleotide sequence in an mRNA molecule and matches it with the appropriate amino acid. Each codon is recognized by a specific molecule called tRNA, or transfer RNA, which carries the corresponding amino acid.
During translation, the mRNA is read in a 5' to 3' direction. The ribosome facilitates the base pairing between the mRNA codon and the tRNA anticodon, ensuring the correct amino acid is added to the growing polypeptide chain.

• The ribosome reads mRNA codons sequentially, one at a time.
• Correct recognition is crucial because even a single error can lead to a faulty protein.
• An AUG codon serves as the start signal for protein synthesis.

Through precise codon recognition, the cellular machinery ensures the accurate translation of a protein's blueprint.

Amino Acid Sequence

The amino acid sequence refers to the specific order of amino acids in a protein. This sequence determines the protein's structure and function, and is directly encoded by the sequence of codons in the mRNA.
The order of amino acids is crucial because it determines how a protein will fold into its three-dimensional shape. The interaction between amino acids causes the protein to take on a specific structure which is essential for its activity.

• Proteins can consist of hundreds or even thousands of amino acids.
• Each protein performs distinct functions, from catalyzing reactions to providing structural support.
  
• Mutations in the mRNA sequence can alter the amino acid sequence, potentially leading to diseases.

Understanding the amino acid sequence is key to comprehending how proteins carry out their biological roles.

Stop Codon

Stop codons play a critical role in protein synthesis by signaling the end of translation. In the genetic code, there are three stop codons: UAA, UAG, and UGA. These codons are distinct because they do not correspond to any amino acid.
When the ribosome encounters a stop codon during mRNA reading, it halts the addition of amino acids, effectively bringing the process of protein synthesis to a conclusion. This termination is essential to ensure that proteins are produced in the correct size and sequence.

• Stop codons prevent the continuation of a polypeptide chain beyond a certain point.
• They provide quality control by ensuring proteins are not too lengthy or short.
• A mutation that changes a regular codon to a stop codon can result in a truncated protein.

Stop codons are crucial for properly regulating when translation should cease, thereby influencing the final structure of proteins.

Translation Termination

Translation termination is the final stage of protein synthesis. It occurs when a stop codon is reached. Unlike elongation, this phase doesn't involve adding another amino acid but rather involves releasing the newly made protein from the ribosome.
Once a stop codon enters the ribosome, release factors bind to it, prompting the release of the polypeptide chain from the tRNA in the P-site. The newly synthesized protein is then free to undergo folding and post-translational modifications to become functional.

• Release factors are specialized proteins that aid in associating stop codons with translation termination.
• The ribosome dissociates and mRNA is released once the protein is complete.
  
• Changes in translation termination can affect protein stability and function.

Understanding translation termination is vital for grasping how protein synthesis is meticulously controlled within the cell.