Protein Structures

Describe Globular Proteins

Compact, Spherical proteins, soluble in water, perform diverse functions (ex. enzymes and hormones)

Fibrous Proteins

Long, thread-like proteins, insoluble in water, provide structural support (ex. collagen and keratin)

Membrane Proteins

proteins embedded in cell membranes, involved in transport, signaling, and structure (ex. receptors and channels)

Primary structure:

Sequence of amino acids in a polypeptide chain, determines proteins identity.

Secondary structure:

Local-folding patterns of polypeptide (alpha helix and beta sheet) formed by hydrogen bonds.

Tertiary Structure:

Overall 3D shape of the protein due to interactions between side chains (hydrophobic, ionic, etc.)

Quaternary structure:

Arrangement of multiple polypeptide chains into a functional protein complex.

Hydrogen bonding/side chains distribution in a helix:

Hydrogen bonds: Between the carbonyl oxygen of one amino acid and the amide hydrogen of nother, 4 resides apart

Side chains: Project outward, not involved in hydrogen bonds

Hydrogen bonding/side chains distribution in B-strand/sheet

Hydrogen bonds: between the carbonyl oxygen of one strand and the amide hydrogen of another strand, forming sheets

Side chains: alternate above and below the plane of the sheet

Factors that stabilize protein structure

Hydrogen bonds, hydrophobic interactions, ionic bonds( salt bridges), disulfide bonds, and Van der Waals forces.

Factors that destabilize Protein Structures

Heat (denaturation), pH changes (disrupts ionic bonds), High concentrations of salts, Chemical denaturants

How do you find Protein Molar Mass calculations:

Average molecular weight of an amino acid = 110 Da

multiply the number of amino acids by 110 Da to estimate molar mass in Daltons (Da)

Convert to kDa by dividing by 1000.