Proteins & Amino Acids

Protein Structure Levels

Primary, Secondary, Tertiary, Quaternary

Primary Structure

Amino acid sequence

Secondary Structure

Alpha helices and beta sheets

Tertiary Structure

3D folding of protein

Quaternary Structure

Multiple protein subunits

Amino Acid Structure

Central carbon with NH2, COOH, H, and R group

Canonical Amino Acids

20 standard amino acids

Zwitterion

Molecule with both positive and negative charges

Isoelectric Point (pI)

pH where net charge is zero

Hydrophobic Amino Acids

Nonpolar, water-fearing

Polar Amino Acids

Form hydrogen bonds

Glycine

Flexible amino acid

Proline

Causes bends in proteins

Cysteine

Forms disulfide bonds

Disulfide Bond

Covalent bond stabilizing protein structure

Protein Denaturation

Loss of structure due to heat/pH

Chaperones

Help proteins fold correctly

Proteolysis

Breakdown of proteins

Amino Acid Charge at Low pH

Positive.

Amino Acid Charge at High pH

Negative.

Charged Amino Acids Role

Enable catalysis and solubility.

Protein π-cation Interactions

Aromatic residues participate in these interactions.

UV Absorption (280 nm)

Used to estimate protein concentration.

Protein Folding Occurs Co-Translationally

Folding begins during synthesis.

Heat Shock Proteins

DnaK and DnaJ assist folding under stress.

Protease Examples (E. coli)

Lon, ClpXP, HflB.

Proteolysis Benefit

Recycles amino acids and removes damaged proteins.

Ubiquitination

Targets proteins for degradation in eukaryotes.

X-ray Crystallography

Used to determine protein structure.