Question

What amino acid sequence is coded for by the following mRNA base sequence? (5') CUA-GAC-CGU-UCC-AAG-UGA (3')

Short answer

Leu-Asp-Arg-Ser-Lys

Step-by-step solution

Understanding Codon Structure

mRNA sequences are read in sets of three nucleotides known as codons. Each codon corresponds to a specific amino acid. So, let's first divide the sequence into codons: (5') CUA-GAC-CGU-UCC-AAG-UGA (3') becomes CUA, GAC, CGU, UCC, AAG, UGA.

Referencing the Genetic Code

Using the genetic code chart, find the amino acids corresponding to each codon in the sequence. - CUA codes for Leucine (Leu) - GAC codes for Aspartic acid (Asp) - CGU codes for Arginine (Arg) - UCC codes for Serine (Ser) - AAG codes for Lysine (Lys) - UGA is a stop codon and does not code for an amino acid, indicating the end of the protein synthesis.

Listing the Amino Acid Sequence

Combine the amino acids from the codons to form the amino acid sequence: Leu-Asp-Arg-Ser-Lys. The presence of UGA as a stop codon means the sequence ends there.

Key concepts

Amino Acid Sequence

An amino acid sequence is a series of amino acids that are linked together in a specific order, forming the building blocks of a protein. When mRNA is translated during the process of protein synthesis, the sequence of nucleotides in the mRNA strand dictates the sequence of amino acids. This is achieved by reading the mRNA in groups of three nucleotides, called codons.
Each codon codes for a specific amino acid or provides a signal to stop translation, known as a stop codon.
For example, given the mRNA sequence (5') CUA-GAC-CGU-UCC-AAG-UGA (3'):

• CUA translates to Leucine (Leu)
• GAC translates to Aspartic acid (Asp)
• CGU translates to Arginine (Arg)
• UCC translates to Serine (Ser)
• AAG translates to Lysine (Lys)
• UGA is a stop codon

The resulting amino acid sequence would be: Leu-Asp-Arg-Ser-Lys. The sequence ceases translation upon encountering the stop codon UGA.

Genetic Code Chart

The genetic code chart is a crucial tool that determines which amino acid corresponds to each mRNA codon. This chart effectively converts the genetic information stored in the mRNA into the language of proteins.
The code is made up of 64 possible three-nucleotide combinations (codons), with each one specifying either an amino acid or a stop signal.
With only 20 different amino acids to code for, the genetic code is said to be redundant or degenerate, meaning several codons can encode the same amino acid. For instance, the codons CUA, CUG, CUU, and CUC all code for the amino acid Leucine (Leu).

• The chart is universally applicable across most organisms.
• It's indicative of the evolutionary importance of protein synthesis.
• The chart also signals when to begin and end protein synthesis.

Hence, by consulting the genetic code chart, scientists and students alike can accurately translate nucleotide sequences into their respective amino acid sequences.

Stop Codon

Stop codons are essential for indicating the termination of protein synthesis. In the genetic code, there are three stop codons: UAA, UAG, and UGA. These codons signal the end of the transcription of mRNA into a protein. Unlike other codons, they do not code for an amino acid.
When the ribosome encounters a stop codon during translation, it understands that the protein synthesis is complete, resulting in the release of the newly formed polypeptide chain.

• Stop codons are necessary to prevent the protein chain from mistakenly extending.
• The absence of a stop codon could lead to incomplete, malfunctioning proteins.

It's interesting to note that while stop codons function as a halt signal, certain cellular environments can re-interpret them, extending protein synthesis under specific conditions. Understanding the role of stop codons is fundamental for grasping how the genetic instructions are translated into functional proteins.

Protein Synthesis

Protein synthesis is the process by which cells build proteins, an essential component for cell structure and function. This complex procedure involves two main stages: transcription and translation.

Transcription:
In this step, the DNA sequence of a gene is transcribed to produce mRNA. The mRNA carries the genetic blueprint from the cell nucleus to the ribosomes, the cellular machinery responsible for protein production.

Translation:
Translation is where the actual protein synthesis occurs. The ribosome deciphers the mRNA sequence, reading it as codons, and matches each one with its corresponding amino acid using tRNA molecules. This process continues until a stop codon is reached, resulting in the release of a completed polypeptide chain.

• Protein synthesis is vital for growth, repair, and maintenance of cells.
• The sequence and structure of proteins determine their function within living organisms.

Without efficient protein synthesis, cells would be unable to perform necessary biological tasks or respond to changes within their environment.