Question

If the DNA coding sequence -CAA-CCG-GAT- were miscopied during replication and became -CGA-CCG-GAT", what effect would there be on the sequence of the protein produced?

Short answer

The protein sequence changes from Glutamine-Proline-Aspartic acid to Arginine-Proline-Aspartic acid.

Step-by-step solution

Identify Original Codons

The original DNA sequence consists of the codons: -CAA-CCG-GAT-. Each group of three nucleotides represents a codon that corresponds to a specific amino acid.

Determine Amino Acids for Original Codons

Using a codon table, translate the original codons: \(-\text{CAA}-\) codes for Glutamine, \(-\text{CCG}-\) codes for Proline, and \(-\text{GAT}-\) codes for Aspartic acid. So, the original protein sequence is Glutamine-Proline-Aspartic acid.

Identify Mutated Codons

In the mutated DNA sequence, the codons are: -CGA-CCG-GAT-. We need to identify how this change affects the protein sequence.

Determine Amino Acids for Mutated Codons

Translate the mutated codons using a codon table: \(-\text{CGA}-\) codes for Arginine, \(-\text{CCG}-\) codes for Proline, and \(-\text{GAT}-\) codes for Aspartic acid. The mutated protein sequence is Arginine-Proline-Aspartic acid.

Compare Original and Mutated Protein Sequence

Compare the two protein sequences. The original sequence is Glutamine-Proline-Aspartic acid, while the mutated sequence is Arginine-Proline-Aspartic acid. Note that the first amino acid has changed from Glutamine to Arginine.

Key concepts

Codon Translation

In biology, the process of codon translation is crucial for converting genetic information from DNA to the creation of proteins. Each sequence of three nucleotides, or codon, represents a specific amino acid. This process begins with the transcription of DNA into messenger RNA (mRNA). Once the mRNA is formed, ribosomes read the codons in sequences of three nucleotides. Each triplet corresponds to one of the 20 amino acids used to build proteins.
By reading these codons, the ribosome adds the correct amino acid to the growing protein chain. For example, the DNA sequence "CAA" is transcribed to mRNA as "GUU", which translates to the amino acid Glutamine in protein coding. The specific matching of each codon to its respective amino acid is determined by the genetic code, a set of rules shared by almost all organisms.

Amino Acid Sequence

The amino acid sequence is the order in which amino acids are linked to form a protein. Each protein's unique function and characteristics come from its specific sequence of amino acids. The primary structure, or sequence, defines how the protein folds into its final 3D form.
When a DNA sequence is altered, like from a replication error, it can lead to a change in the amino acid sequence. In our exercise, the original amino acid sequence was Glutamine-Proline-Aspartic acid, derived from the DNA codons CAA-CCG-GAT. After mutation, this sequence becomes Arginine-Proline-Aspartic acid because the first codon changes from CAA to CGA.

• Glutamine becomes replaced by Arginine due to this codon change.
• The rest of the sequence remains the same.
• This alteration can affect the protein's function, depending on the role of the replaced amino acid.

Protein Synthesis

Protein synthesis is the intricate process of building proteins from amino acids, guided by the information encoded in DNA. This process involves two main stages: transcription and translation. Transcription takes place in the cell nucleus, where DNA is transcribed to mRNA. This mRNA then moves out of the nucleus into the cytoplasm where translation begins.
During translation, ribosomes interpret the mRNA codons to string together a protein. Transfer RNA (tRNA) molecules bring specific amino acids corresponding to each codon. This detailed process ensures the amino acids are added in the correct sequence. The final protein emerges once all the relevant amino acids are linked and folded properly, ready to perform its biological function.
In this exercise context, the mutation in DNA from CAA to CGA impacted protein synthesis by changing the initial amino acid from Glutamine to Arginine. Such changes can affect a protein's function, potentially leading to differing biological effects.

Genetic Replication Errors

Genetic replication errors occur when the DNA sequence is incorrectly copied during cell replication. These errors can result in mutations which may lead to changes in the protein produced. In most cases, cells have mechanisms to correct such errors, but occasionally they slip through.
Errors often involve small changes, such as a single nucleotide substitution like in this exercise. The change from "CAA" to "CGA" in the DNA leads to the production of Arginine instead of Glutamine at the start of the protein sequence. These single nucleotide changes can have significant effects if they alter key functional sites in proteins or change protein stability.

• Mispaired nucleotides can escape detection and cause persistent genetic variations.
• Such mutations can result in non-functional or malfunctioning proteins.
• However, not all replication errors lead to severe outcomes; some are neutral or even beneficial.

Understanding these errors is important for both genetic research and the study of diseases linked to DNA mutations. It serves as the basis for developing gene-based therapies and diagnostic tools.