Ch. 19: Amino Acids and Proteins

Chem 106

Biological functions of proteins?

Enzymes, structure, transport, signaling, immune defense, movement.

Basic structure of an amino acid?

Central C with –NH₂, –COOH, –H, and R group.

What is a polypeptide?

Chain of amino acids joined by peptide bonds.

What is a protein?

One or more polypeptides folded into a functional structure.

How to distinguish D and L amino acids?

In Fischer projection, –NH₂ on left = L (naturally occurring); right = D.

How does pH affect amino acids?

Low pH = positive charge (protonated); high pH = negative charge (deprotonated).

Primary protein structure?

Sequence of amino acids (peptide bonds).

Secondary protein structure?

α-helix or β-sheet (hydrogen bonding).

Tertiary protein structure?

3D folding from side chain interactions (H-bonds, ionic, disulfide, hydrophobic).

Quaternary protein structure?

Multiple polypeptides forming a functional unit (e.g., hemoglobin).

How to draw a dipeptide or tripeptide?

Join amino acids via peptide bonds –CO–NH–, removing water between each.

Types of proteins by shape?

Fibrous = structural (e.g., collagen); Globular = functional (e.g., enzymes); Membrane = embedded in cell membranes.

Difference between hydrolysis and denaturation?

Hydrolysis = breaks peptide bonds (chemical); Denaturation = unfolds protein (no bond breaking, just shape change).