The Basics
Amino acids, peptide bonds, protein folding, and the peptide-protein spectrum
The Tiny Molecules Running Your Body
Peptides are short chains of amino acids -- the building blocks of life. They act as messengers, hormones, and defenders throughout your body. From insulin keeping your blood sugar stable to endorphins giving you a runner's high, peptides are everywhere.
What Are Amino Acids?
Think of amino acids as letters in an alphabet. Just as 26 letters can create any word, your body uses 20 amino acids to build every protein and peptide it needs. Each amino acid has the same basic structure but a unique side chain that gives it special properties.
How Amino Acids Connect
When two amino acids link together, they form a peptide bond through a condensation reaction -- releasing a water molecule in the process. This bond is what creates the chain that becomes a peptide.
From Chain to Shape
A peptide chain doesn't stay flat -- it folds into a 3D shape that determines what it does. Like origami, the same chain can fold into completely different structures, each with a unique function.
Peptides vs Proteins
There's no hard line between peptides and proteins -- it's a spectrum. Generally, chains under 50 amino acids are called peptides, and longer ones are proteins. But the real difference is complexity: proteins fold into intricate 3D structures with multiple subunits.
Oxytocin
9 amino acids
The "bonding hormone" -- small but powerful
Insulin
51 amino acids (2 chains)
Right at the peptide/protein boundary
Hemoglobin
574 amino acids (4 subunits)
A full protein carrying oxygen in your blood
Titin
34,350 amino acids
The largest known protein, found in your muscles
Knowledge Check
Test what you learned in this module.
Practice Exercises
Reinforce your understanding with interactive exercises.