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Levels of Protein Structure 16.5. 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. 1 o Primary Structure. Number and order of AA - PowerPoint PPT Presentation
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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