Question

A polypeptide on partial hydrolysis gave the following \(d i\) and tripeptides: Ser-Met-Ile; Ile-Tyr; Ile-Ser-Met; Met-Ile; Ile-Ser. Identify the sequence of amino acids in peptide chain.

Short answer

The polypeptide sequence is Ile-Ser-Met-Ile-Tyr.

Step-by-step solution

Identify starting point

Examine the given peptides and search for a peptide that can potentially be the start of the sequence. The dipeptide 'Ile-Ser' could be a starting point since its components don't appear as an ending in any other peptide.

Extend from the starting point

Using 'Ile-Ser' as a starting point, look for peptides that can follow or extend it. The tripeptide 'Ile-Ser-Met' matches with this start, extending it to 'Ile-Ser-Met'.

Search for continuation

Next, we see if there is any peptide that continues from 'Ile-Ser-Met'. We find 'Ser-Met-Ile', so placing it after 'Ile-Ser-Met' provides the sequence 'Ile-Ser-Met-Ile'.

Connect remaining fragments

There remains the dipeptide 'Met-Ile' which is already incorporated, and the dipeptide 'Ile-Tyr'. Attach 'Ile-Tyr' to 'Ile-Ser-Met-Ile' to complete the sequence.

Final sequence

The completed sequence is 'Ile-Ser-Met-Ile-Tyr'. Double-check each connection is valid by confirming overlapping segments in identified peptides.

Key concepts

Polypeptide Sequence

Polypeptides are chains of amino acids linked together by peptide bonds. They are the building blocks of proteins, which play crucial roles in biological functions. Each polypeptide sequence is unique and determines the specific properties and functions of the protein it forms. These sequences are written from the amino end (N-terminus) to the carboxyl end (C-terminus) of the chain.
Understanding the polypeptide sequence is essential in biochemistry and molecular biology. It helps grasp how proteins are constructed and how they function at a molecular level. In some instances, solving polypeptide sequences resembles assembling a puzzle where smaller peptides must fit together to form a complete chain. This understanding is vital for many applications, including drug design and genetic research.

Hydrolysis of Peptides

Hydrolysis is a chemical process that breaks down compounds by the addition of water. In the case of peptides, hydrolysis cleaves peptide bonds between amino acids, resulting in smaller peptide fragments or individual amino acids. This reaction is crucial for digestion and the recycling of proteins within organisms.
During hydrolysis, water molecules break the peptide bond, leading to the formation of either dipeptides, tripeptides, or even single amino acids. This process can be partial, yielding di- and tripeptides that help in identifying the sequence of amino acids. Hydrolysis is a common technique used in laboratories to determine the primary structure of proteins, as demonstrated by the initial exercise with our polypeptide fragments. It provides insight into the functional and structural characteristics of proteins by revealing their amino acid sequence.

Dipeptides and Tripeptides

Dipeptides and tripeptides are short sequences of two and three amino acids, respectively, linked by peptide bonds. They are derived from the partial hydrolysis of polypeptides, where longer chains are broken down into smaller fragments. These smaller peptides are crucial for studying peptide sequences as they provide clues to the order of amino acids in a longer chain.
Dipeptides and tripeptides play an essential role in the process of reconstructing a polypeptide sequence. By analyzing overlapping segments, scientists can determine how these small peptides fit together in a complete sequence. They act as intermediate units in metabolic processes and are also important in pharmaceuticals for their therapeutic properties. For instance, certain di- and tripeptides can modulate enzyme activities or act as neurotransmitters.

Step-by-Step Peptide Sequencing

Determining the sequence of peptides involves a systematic approach to match fragments from partial hydrolysis into a complete polypeptide chain. In the exercise provided, a logical step-by-step method identified the sequence through connecting overlapping dipeptides and tripeptides.

• **Step 1**: Identify a potential starting fragment which, in our example, was the dipeptide 'Ile-Ser'.
• **Step 2**: Extend the sequence using matching peptides, like adding 'Ile-Ser-Met' to continue the chain.
• **Step 3**: Search for further extension possibilities, such as incorporating 'Ser-Met-Ile'.
• **Step 4**: Connect remaining peptides, completing the sequence with 'Ile-Tyr'.
• **Step 5**: Confirm the sequence by ensuring each connection is logical, considering overlaps.

This sequencing method is foundational in biochemistry, allowing the determination of protein primary structures, which paves the way for understanding their function and interaction in biological systems.