Question

When the amino acid sequences of insulin isolated from different organisms were determined, differences were noted. For example, alanine was substituted for threonine, serine for glycine, and valine for isoleucine at corresponding positions in the protein. List the single-base changes that could occur in codons of the genetic code to produce these amino acid changes.

Short answer

Answer: 1. Alanine (A) for Threonine (T): - GCU to ACU - GCC to ACC - GCA to ACA - GCG to ACG 2. Serine (S) for Glycine (G): - GGU to AGU - GGC to AGC - GGA to UCA - GGG to UCG 3. Valine (V) for Isoleucine (I): - GUU to AUU - GUC to AUC - GUA to AUA

Step-by-step solution

Find the codons for the given amino acids

To determine the possible single-base changes, we first need to identify the codons for the amino acids mentioned in the problem. The codons for the amino acids are as follows: Alanine (Ala, A): GCU, GCC, GCA, GCG Threonine (Thr, T): ACU, ACC, ACA, ACG Serine (Ser, S): UCU, UCC, UCA, UCG, AGU, AGC Glycine (Gly, G): GGU, GGC, GGA, GGG Valine (Val, V): GUU, GUC, GUA, GUG Isoleucine (Ile, I): AUU, AUC, AUA

Identify possible single-base changes for each amino acid substitution

Now let's look at each amino acid substitution and find the possible single-base changes that could produce the given substitution: 1. Alanine (A) for Threonine (T): Possible single-base changes: GCU to ACU, GCC to ACC, GCA to ACA, GCG to ACG 2. Serine (S) for Glycine (G): Possible single-base changes: GGU to AGU, GGC to AGC, GGA to UCA, GGG to UCG 3. Valine (V) for Isoleucine (I): Possible single-base changes: GUU to AUU, GUC to AUC, GUA to AUA

Organize the results

Finally, let's list down the single-base changes that would result in the given amino acid substitutions: 1. Alanine (A) for Threonine (T): - GCU to ACU - GCC to ACC - GCA to ACA - GCG to ACG 2. Serine (S) for Glycine (G): - GGU to AGU - GGC to AGC - GGA to UCA - GGG to UCG 3. Valine (V) for Isoleucine (I): - GUU to AUU - GUC to AUC - GUA to AUA These are the single-base changes in codons that could produce the given amino acid substitutions in the insulin protein.

Key concepts

Codons

Codons are the language of your genetic code. Each codon is a sequence of three nucleotides in our DNA or RNA. These nucleotides are made up of the bases adenine (A), cytosine (C), guanine (G), and thymine (T) in DNA, or uracil (U) in RNA. The combination of these bases in a sequence of three forms a codon.

Every triplet of bases corresponds to one specific amino acid. Amino acids are the building blocks of proteins, and proteins are vital for our cells' structure and function. For example, the codon "GCU" in mRNA translates to the amino acid alanine. This translation is facilitated by the ribosome during the process of protein synthesis.

• Our genetic code has 64 possible codons.
• Only 20 amino acids are encoded by these codons.
• Some codons signal for the process to start or stop.

Understanding codons is crucial because it helps in predicting the effects of mutations, which are changes in the genetic material.

Amino Acid Substitution

Amino acid substitution occurs when one amino acid in a protein is replaced with another amino acid. This can happen due to small changes in the DNA code (mutations). Some substitutions do not affect protein function, while others can cause diseases or alter protein activity.

In our example, changes at the genetic code level can result in different substitutions:

• Alanine (Ala) being replaced by Threonine (Thr)
• Serine (Ser) swapped for Glycine (Gly)
• Valine (Val) substituted with Isoleucine (Ile)

These changes are deeply tied to the codons, as a shift from one codon to another can switch the corresponding amino acid. This variability is a part of what gives evolution its creative power in generating new traits and forms of life.

Single-Base Changes

Single-base changes, also known as point mutations, are alterations affecting just one nucleotide base in a DNA sequence. These subtle mutations can have significant consequences, especially when they involve a codon. A single nucleotide change, like from GCU to ACU, can lead to the production of a different amino acid—such as from Alanine to Threonine.

There are various types of point mutations, such as:

• Silent mutations, which do not affect the amino acid sequence.
• Missense mutations, which result in a different amino acid.
• Nonsense mutations, which create an early stop codon, terminating protein synthesis prematurely.

In our scenario, understanding which single-base changes occur allows us to predict possible impacts on the protein, such as altering its shape or function.

Protein Synthesis

Protein synthesis is the biological process where cells create proteins. It involves two main steps: transcription and translation. Let's break it down simply.

During transcription, the DNA code is copied into mRNA (messenger RNA). The mRNA takes the code out of the nucleus to the ribosomes, where the real action happens—the translation.

In translation, the mRNA code is 'read' by the ribosome. Transfer RNA (tRNA) molecules bring the correct amino acids to the ribosome, based on the sequence of codons in the mRNA. The amino acids are joined together in the order dictated by the mRNA to form a protein.

• Ribosomes are the cell's protein factories.
• Each tRNA has an anticodon matching the mRNA codon.
• This matching ensures that proteins are built accurately.

Protein synthesis is essential because proteins perform nearly every function within biological organisms, making it a cornerstone of life itself.