All proteins in all known life forms are built from the same 20 amino acids — a biochemical alphabet billions of years old. The extraordinary diversity of protein function comes not from new building blocks, but from different sequences and structures.
Each amino acid contains:
All amino acids are chiral except glycine. Only L-amino acids are used in proteins.
Examples: Gly, Ala, Val, Leu, Ile, Met, Pro, Phe, Trp
Special cases:
Examples: Ser, Thr, Tyr, Cys, Asn, Gln
Special:
These residues:
The exact amino acid sequence of a protein.
The amino acid sequence:
🧠 One amino acid change can cause disease Example:
📌 Insulin is a classic example: two chains linked by disulfide bonds.
Common in:
📌 Every third residue must be glycine → Only glycine fits in the crowded center
Replacing glycine with a larger residue:
The complete 3D structure of a single polypeptide chain.
Water-soluble proteins fold into compact structures with hydrophobic cores
📌 Only two histidines inside — essential for oxygen binding.
Proteins fold via sharp transitions:
This is an “all-or-none” process.
Random search would take longer than the age of the universe (Levinthal paradox).
Proteins fold by:
Some proteins misfold into amyloid fibrils:
Diseases:
Smaller oligomers may be more toxic than large aggregates.
Examples:
These:
Proteins are often made as inactive precursors:
Cleavage activates or diversifies function.
Protein structure is hierarchical:
Structure → function → regulation → disease.
To study:
Proteins differ in:
Methods:
Advanced forms:
Used in:
Measures mass-to-charge ratio (m/z)
Ionization methods:
Analyzers:
Central to:
Cleavage agents:
DNA sequence:
Protein analysis:
➡️ Both are complementary, not interchangeable.
Proteins:
Understanding protein structure is essential to understanding life itself.