Question

When an unknown peptide containing five amino acids is treated with an enzyme that hydrolyzes only the serine-leucine peptide bond, the fragments Leu-Gys, Ser, Leu-Ser are formed. What was the original amino acid sequence in the peptide?

Short answer

Original peptide sequence: Leu-Gys-Ser-Leu-Ser.

Step-by-step solution

Understand the Problem

We are given fragments of a peptide after it has been treated with an enzyme that specifically breaks the bond between serine (Ser) and leucine (Leu). The fragments given are: Leu-Gys, Ser, Leu-Ser. Our task is to piece these fragments together to identify the sequence of amino acids in the original peptide.

Analyze the Fragments

The fragments provided are 'Leu-Gys', 'Ser', 'Leu-Ser'. We need to recognize the key part of the problem: the hydrolysis affects only the bond between Ser and Leu. This means the original sequence was cut at a point where Ser precedes Leu.

Piece Together Fragments

Start by identifying the fragment that logically follows each cut. Since Ser and Leu-Ser fragments are mentioned, we can deduce Ser should follow Leu in one instance. Place 'Leu' in a position where it follows 'Ser', giving us part of the sequence `...Ser-Leu-...`. Looking at the remaining fragments 'Leu-Gys', we place Leu-Gys before the first break since Gly follows Leu logically. So, the sequence starts with 'Leu-Gys'.

Confirm the Sequence

Combine the logic: 'Leu-Gys' precedes 'Ser', and then follows by 'Leu-Ser'. This means the full sequence is 'Leu-Gys-Ser-Leu-Ser'. Double check where Ser-Leu breaks occur, ensuring that the enzyme-treated fragments could plausibly lead to 'Leu-Gys', 'Ser', and 'Leu-Ser'.

Construct Original Sequence

Given the combination explained above, the amino acid sequence before enzyme treatment was 'Leu-Gys-Ser-Leu-Ser'. This sequence ends with a Ser, and there are two Ser-Leu breaks explaining the fragments.

Key concepts

amino acid sequence

Amino acid sequences are fundamental to understanding how proteins work. Proteins are made of chains of amino acids, and the specific order—or sequence—of these acids determines the protein's structure and function. Every protein's unique sequence is determined by gene coding.
The exercise here asks us to figure out the amino acid sequence of a peptide after it was broken down into fragments. By arranging amino acids, we can predict the overall shape and also the biological activity of the protein in question.

• Sequence influences structure and function
• Determined by specific genetic instructions
• Provides insight into biological mechanisms

In this problem, the challenge lies in taking peptide fragments and recombining them correctly to find the original sequence. Understanding the nature of amino acid sequences is key to solving such problems.

enzyme hydrolysis

Enzyme hydrolysis is a process where enzymes catalyze the breaking down of peptide bonds in proteins. This is achieved by the addition of a water molecule, a process crucial for digestion and many biological functions.
In the given exercise, an enzyme specifically hydrolyzes or breaks the bond between serine and leucine, resulting in smaller peptide fragments. This specificity is due to the unique active site of the enzyme, which only reacts with certain bonds.

• Catalyzes breaking of peptide bonds
• Works by adding a water molecule
• Highly specific in action

The enzyme uniquely breaking the serine-leucine bond provides critical clues to determining the original peptide sequence.

serine-leucine peptide bond

A peptide bond is a covalent bond that links two amino acids in a protein. In this exercise, the focus is on the peptide bond between serine (Ser) and leucine (Leu). This bond is broken by the enzyme, creating different protein fragments.
The serine-leucine bond is a point of cleavage during enzyme hydrolysis. Understanding this helps position fragments within the original sequence.

• Links amino acids in proteins
• Can be targeted by specific enzymes
• Crucial for identifying sequence breaks

These directional breaks are critical in piecing back the puzzle of protein structure from fragments, illustrating the precise control of biochemical processes.

protein fragments

Protein fragments are the pieces created when a protein chain is broken down. These fragments give us pieces of the original sequence, much like pieces of a puzzle.
In enzyme hydrolysis, as exemplified in this exercise, the fragments formed (Leu-Gys, Ser, Leu-Ser) arise from specific break points, aiding in reconstructing the original chain.

• Broken pieces of the original peptide
• Result from specific bonds being hydrolyzed
• Help deduce the original sequence

Working with these fragments, particularly knowing the specific enzymatic activity, allows us to reconstruct the complete amino acid sequence by careful deduction.