cell bio notes

cell bio notes - Pka is 50:50. Pka is a constant same way...

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Pka is 50:50. Pka is a constant same way free energy change is constant. Equal number of molecules A to B, B to A if let go spontaneous exergonic in direction of B, in direction of A endergonic. Does reaction go forward? Atp to Adp + P have less energy so must go in direction. A reaction runs to equilbiruim which direction does it go? Pka =- log K. Acid form base + proton. Acid dissociation problems. Ph goes down, proton goes up, pushing reaction to the left, favor the conjugatre acid. Pka above point, direction goes to conjugate base. The more conjugate acid holds This matters because charges in the cell matter. If Nh3 +, go high give up to become Nh2. Then favor the hyuprobilic group and changes the conformation of the protein. Aspirin cant enter intestine because Ph = 7 is above Pka so it has a charge on it. However, it can easily pass through the stomach because the ph =2 when the Pka is Ph =3. A heix immouno nitrogen, ketono oxygen, hydrogen bonds forms to make helix stable. Just as stable in water because hydrogen bonds forms from water. Proteins start to unfold with heat energy. Beta peelted sheet, max h bonds. Ratio of con a and con base is important because it determines what is hydrop and hydrophi which determines structure of protein. Hyprohobic is no charge (non-polar) and can’t make hydrogen bond, Hydrophilic has polar colvalent bond. Can form hydrogen bond. Can be charged or uncharged. Competing for water with hydrogen bonds but both are stable as same because of hydrogen bond. 9/15 – Henderson equation – ph of the systems affects the con a and b. Related to pKa.
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Acid dissociation At low ph all proteins are folded (protonated) Ph changes can cause proteins to unfold. The deprotonation of surface histidines at higher ph starts the denaturation process. Uncharged will try to get on the inside. The pka of aa residues is not the same as free aa. Charged likes the outside Hydrophobic groups inside. How do proteins work? They bind to other molecules (ligand). Fit together ike hand and glove. Protein changes shape when ligand goes into contact w/ protein. Binding or active site, non-covalent bonds form b/t them. The eqilibirium constant is high, most of active site is filed. Free energy change is negative. Lig and prtein become more stable because of nc bonds that form. Substrate – ligand that binds to enzymes. When protein binds, it changes shape a little bit. Aa sequence could be far apart but are brought together by folding. Imino group is part of peptide bond which plays role in a hhelix shape. Cant rotate around pep bond. H bond fits into the substrate, that bonds to it. Forms covalent bonds (h bond and 1 ionic bond). Changes in charged aa side chains is the primary reason protein activity changes with ph. Changes in Ph (small), change charge of aa side chain which changes ability to bind to substrate. Large Changes in ph, change the structure of the protein. Enzymes increase rate in which reaction reaches equilibrium. How does that happen? 1.) Transition stage
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This note was uploaded on 10/27/2010 for the course BIO 101 taught by Professor Cadigan during the Spring '10 term at DeSales.

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cell bio notes - Pka is 50:50. Pka is a constant same way...

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