Question

Consider the peptides Ser Glu-Gly His-Ala and Gly-His-Ala-Glu-Ser. How do these two peptides differ?

Short answer

The two peptides differ in the sequence of their amino acids.

Step-by-step solution

- Understand the Peptide Sequences

Examine the given peptide sequences. The first peptide is Ser-Glu-Gly-His-Ala, and the second peptide is Gly-His-Ala-Glu-Ser.

- Identify the Amino Acids

List out the amino acids for each peptide. The first peptide: Serine (Ser), Glutamic acid (Glu), Glycine (Gly), Histidine (His), Alanine (Ala). The second peptide: Glycine (Gly), Histidine (His), Alanine (Ala), Glutamic acid (Glu), Serine (Ser).

- Compare the Amino Acid Order

Observe the sequence of the amino acids. The first peptide's order is Ser-Glu-Gly-His-Ala, while the second peptide's order is Gly-His-Ala-Glu-Ser.

- Analyze the Differences

Note the specific order differences. The first peptide starts with Ser and ends with Ala, whereas the second peptide starts with Gly and ends with Ser.

Key concepts

Amino Acids

Amino acids are the building blocks of proteins. Each amino acid has a specific side chain, which determines its properties. There are 20 standard amino acids, and they can be classified based on the characteristics of their side chains, such as being acidic, basic, hydrophilic, or hydrophobic.

In the peptides given in the exercise, we have:
- Serine (Ser): has a polar side chain.
- Glutamic acid (Glu): an acidic amino acid with a negatively charged side chain.
- Glycine (Gly): the simplest amino acid with a hydrogen atom as its side chain, making it quite flexible.
- Histidine (His): a basic amino acid with an imidazole side chain, which can be positively charged.
- Alanine (Ala): has a nonpolar, hydrophobic side chain. Understanding the properties of these amino acids helps in predicting how they interact within a peptide and its overall structure.

Peptide Structure

Peptides are short chains of amino acids linked by peptide bonds. The sequence and chemical properties of the amino acids determine the structure and function of the peptide.

A peptide bond forms between the carboxyl group of one amino acid and the amino group of another, releasing a molecule of water. This is a dehydration synthesis reaction.

In the example exercise, the peptides Ser-Glu-Gly-His-Ala and Gly-His-Ala-Glu-Ser are both composed of the same amino acids but in different arrangements. This difference in sequence can lead to different structural conformations and properties.

Sequence Analysis

Sequence analysis involves comparing the order of amino acids in two or more peptides or proteins. This can provide insights into their function and evolutionary relationships.

The primary structure of a peptide is its amino acid sequence. Even small changes in the sequence can significantly impact the peptide's properties.

In the provided exercise, the peptides' sequences are:
- First peptide: Ser-Glu-Gly-His-Ala
- Second peptide: Gly-His-Ala-Glu-Ser

By comparing these sequences, we see that they contain the same amino acids but in different orders. This is a prime example of how sequence variation, even with identical amino acid content, can result in different peptides. Understanding these differences is crucial in fields like bioinformatics and molecular biology<.