Question

An alanine residue exists at position 180 of a certain plant protein. If the codon specifying alanine is GCU, how many singlebase substitutions will result in an amino acid substitution at position \(180,\) and what are they?

Short answer

Answer: There are 5 single base substitutions that will result in an amino acid substitution at position 180. The resulting amino acids are Aspartic acid, Glutamic acid, Glycine, and Valine.

Step-by-step solution

Identify the codon and its constituent bases

The given codon for alanine is GCU, which consists of three bases: Guanine (G), Cytosine (C), and Uracil (U).

Determine possible single base substitutions

For each base in the codon, there are three possible substitutions as there are four nucleotide bases (A, U, C, and G) in total. We will list down the possible substitutions for each base in the GCU codon: - First base (G): GAU, GAA, GGU - Second base (C): GAU, GUU, GCA - Third base (U): GCA, GCC, GCG, GCU

Identify which substitutions result in amino acid changes

Now, we will identify which of these codons code for a different amino acid than alanine. To determine this, we can refer to the genetic code table: - First base (G): GAU (Aspartic acid), GAA (Glutamic acid), GGU (Glycine) - Second base (C): GAU (Aspartic acid), GUU (Valine), GCA (Alanine - not a substitution) - Third base (U): GCA (Alanine - not a substitution), GCC (Alanine - not a substitution), GCG (Alanine - not a substitution)

Count the base substitutions and list the resulting amino acids

There are a total of 5 single base substitutions that result in an amino acid substitution at position 180, and they are: 1. GAU (Aspartic acid) 2. GAA (Glutamic acid) 3. GGU (Glycine) 4. GAU (Aspartic acid) 5. GUU (Valine) Therefore, 5 single base substitutions will result in an amino acid substitution at position 180, and the resulting amino acids are Aspartic acid, Glutamic acid, Glycine, and Valine.

Key concepts

Codon

A codon is a sequence of three nucleotides found in messenger RNA (mRNA) that corresponds to a specific amino acid or serves as a start or stop signal during protein synthesis. This trio of bases forms the foundation of the genetic code in living organisms. For example, in the provided exercise, the codon GCU is responsible for encoding the amino acid alanine.
Each codon is unique to its corresponding amino acid, which means that any change to a codon can potentially alter the amino acid it codes for. This can lead to variations in the protein chain, potentially affecting its structure and function.
Understanding codons is crucial because they are the basic units of the genetic code, representing DNA's instructions translated into proteins needed for life.

Amino Acid Substitution

Amino acid substitution occurs when a specific codon in the mRNA sequence changes, resulting in a different amino acid being incorporated into the protein sequence. This substitution can potentially alter the protein's function or structure, sometimes leading to significant biological consequences. For example, in the exercise, a substitution at position 180 in the plant protein could change what amino acid is present.
When the codon GCU (for alanine) undergoes a change, this substitution may introduce amino acids like aspartic acid, glutamic acid, glycine, or valine, resulting in a new protein variant. These amino acids have different properties and interactions due to changes in their side chains, which can impact the protein's role in the organism.
Amino acid substitutions are essential for understanding genetic mutations and their effects, having implications in various fields such as genetics, molecular biology, and medicine.

Single Base Substitution

Single base substitution, also known as point mutation, involves changing just one nucleotide base in a codon. These tiny changes can have significant effects on the resulting protein structure. For example, in the GCU codon, altering just one of its bases (such as G to A) can lead to the formation of a different codon, effectively changing the amino acid sequence.
In our exercise, we explore various substitutions like changing GCU to GAU or GGU, which results in coding for different amino acids. These changes illustrate the precision and complexity of genetic coding, where even a single nucleotide shift can alter biological outcomes.
Understanding single base substitutions helps in the study of genetic mutations, which may be harmless, beneficial, or detrimental, impacting areas such as genetic disorders and evolutionary biology.

Genetic Code Table

The genetic code table is a crucial tool for decoding the genetic instructions written in DNA and RNA into proteins. This table maps each mRNA codon to its corresponding amino acid or signaling function (start/stop) during protein synthesis. For example, using this table, we can determine that the codon GCU corresponds to alanine.
The genetic code is noted for being redundant, meaning some amino acids are specified by more than one codon. For instance, alanine can be coded by GCU, GCC, GCA, and GCG. This redundancy can serve as a buffer against certain mutations, as seen in the exercise where some substitutions do not lead to an amino acid change.
Learning to use the genetic code table paves the way for understanding how genetic information is translated into proteins, enabling advances in genetics, biotechnology, and medicine, helping us comprehend cellular functions and genetic mutations effectively.