Lesson 8:
Peptide Bond Formation
🔹 Definition
Let’s start with the basics:
A peptide bond is a special type of chemical bond. It is a strong covalent bond (a type of chemical bond formed when atoms share electrons) that links two amino acids together.
🧠 Think of it like a button on a shirt that joins two pieces of fabric (amino acids). Without that button (peptide bond), the shirt pieces won’t hold together.
🔹 Mechanism of Peptide Bond Formation
Every amino acid has two important groups:
- Amino group (-NH₂) → this is like a “head”
- Carboxyl group (-COOH) → this is like a “tail”
When two amino acids come close to each other:
- The amino group of one amino acid reacts with the carboxyl group of another.
- One molecule of water (H₂O) is removed in this reaction.
- This process is called dehydration synthesis (also called a condensation reaction).
💧**”Dehydration”** = removal of water
🧵**”Synthesis”** = building or joining
- As a result, a new peptide bond is formed between the carbon (C) of the carboxyl group and the nitrogen (N) of the amino group.
📌 Peptide Bond = C–N bond between two amino acids
💡 Analogy: It’s like two Lego blocks snapping together. The connector piece (peptide bond) holds them tight by removing a small piece (water).
🔹 Peptides and Polypeptides
✔️ Peptide
Once two or more amino acids are linked by peptide bonds, we call the resulting chain a peptide.
- Dipeptide = 2 amino acids joined
➤ Example: Glycylalanine (formed from glycine + alanine) - Tripeptide = 3 amino acids
- Polypeptide = many amino acids (hundreds or thousands) linked together
✍️ Important: Even in a dipeptide, the chain still has one free amino group at one end and one free carboxyl group at the other end.
🔁 So it can keep growing into a longer chain.
🔹 Proteins from Polypeptides
A protein is made when one or more polypeptide chains are folded and combined in specific ways.
🧬 Examples:
- Insulin = made of 2 polypeptide chains
- Hemoglobin = made of 4 polypeptide chains
(Found in red blood cells, helps carry oxygen)
📌 Key Point: The number of chains and their folding gives each protein a unique shape and function.