BCH 380 1st Edition Lecture 10 Outline of Last Lecture I. Beta Sheets A. Common motifsII.Cytochrome cProteins Outline of Current Lecture III. Protein foldingB. How and WhyIV. Forces in Protein folding and stabilityV. Hydrophobic EffectCurrent LectureAssociation constants and protein concentration- Assuming the concentration of the other component is in excess, the concentrations at which half the molecules are in complex and half are free corresponds to the reciprocal of the association constant  the dissociation constant (Kd)Why do proteins fold into these shapes rather than simply existing as a long strand?- That they do adapt there structures indicates that these are the lowest energy states for the protein – it is thermodynamically favorable for them to adopt these structuresEnergy well of protein folding- The funnels represent the free-energy potential of the folding proteins- Two possible pathways to the low-energy native protein are shown- In order to unfold a protein we need to add energy, lifting it form N to A or BHow to unfold proteins:- Heat- ChemicalsHypothetical protein folding pathways- The initially extended polypeptide chains form partial secondary structures, then approximate tertiary structures, and finally the unique native conformationsForces In Protein Folding and Stability1. Hydrophobic Effect2. Hydrogen Bonding3. Van der Waals Interactions4. Charge-Charge Interactions– Protein folding is also assisted by molecular chaperonesThe Hydrophobic Effect- The major driving force for protein folding- The oily side chains of hydrophobic amino acids are sequestered in the interior of the protein, while the hydrophilic side chains remain solvent exposed on the surface of the protein- The order induced in the protein is less that the resulting disorder in the water- ∆G =∆H – T∆S2 Categories of Proteins:1. Fibrous proteins: Structural proteins such as Collagen, Keratin, ect. 2. Globular proteins: Myoglobin, Hemoglobin, most