Levels of Protein Structure16.5

Peptide/Protein Formation

• Peptide: small, up to 50 AA • Proteins: large, several 100 AA and/or multiple

peptide chains grouped together• Ribosomes translates m-RNA into AA

sequence: 3 nucleotide = 1 AA

1o Primary Structure

• Number and order of AA• Reflected by peptide name• Example: Alanylglycylserine• 1o structure is the basis for all other levels of

peptide/protein structure

2o Secondary Structure

• Interaction between Amino- and Carboxyl groups residues from the peptide backbone forming

• H-Bonds N-H…….O=C

a) Alpha Helix b) Beta pleated sheet

collagen, wool silk

3o - Tertiary Structure

• Governed by R-side chain interactions1. Hydrophobic interactions: At the center of a protein – two non-polar side chains are attracted (Ex: Ala and Leu)2. Hydrophilic interactions: at the outskirts of a protein – two polar side chains, H-bonds (Ex: Ser with Thr)

3o structure

3. Salt Bridges (ionic bonds):attraction between acidic and basic side chains (Ex: Lys with Glu)

4. Disulfide Bridges: -S-S- covalent bond formation, two Cystein react, stabilizes the 3-D confirmation of large proteins, strongest

4o – Quaternary Structure

• Multiple peptide chains aggregate together to form a large functional unit

• Governed by R-side chain interactions (see 3o structure…)

• Not all proteins have it

Globular Proteins

• Have a compact, spherical 3-D shape• Very stable, function as enzymes and

transport molecules Hemoglobin Enzyme

Fibrous Proteins

• Long, thin, fiber like shapes• Used as structural components: wool, skin,

scales, feathers

keratin

collagen

Denaturation

• Change in 3-D structure of a protein when exposed to heat/acids/bases/heavy metals/ organic solvents/agitation

• Disrupts all levels of protein structure Exception: Dissulfide bridges remain, or new ones form…

Denaturation

Homework

• Pgs 550 – 551 • #16.22 – #16.34 (even)• Skip #16.28• Print the Enzyme Lab