Biochem Chapter 12 part II

Biochem Chapter 12 part II - Chapter Seven Chapter 12 Part...

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Unformatted text preview: Chapter Seven Chapter 12 Part II Chapter Twelve Translation of RNA: The Genetic Code and Protein Metabolism Concepts in Biochemistry 3rd Edition Dr. Joe Davis Dr. Joe Davis Chapter Seven Chapter 12 Homework #1 (Definitions), 2, 5 - 8, 11 - 15, 17, 22 - 24, 25 and 31. 12.3 Post-translational Processing of Protein Most proteins/polypeptides are made in the cytoplasm and thus must be transported to their site of function. Most polypeptides / proteins are not initially in a biologically active form immediately after synthesis. Extensive modifications of the polypeptide chain (from a random coil to its final native structure) is often required. Protein Folding (Review) Recall: Initially, most proteins need to fold into their native conformation (can start before synthesis is completed). Folding Process is dictated by the primary structure and AA sequence. 12.3 Post-translational Processing of Protein Protein Folding (cont.) The protein initially assumes its local 2 o structure [-helix & -sheet conformations] and a seed nucleus of subsequent folding activity is initiated. The rest of the chain then begins folding (process labelled as a cooperativity process). During the folding process, proteins attempt to maximize the number of favorable/strong interactions (hydrogen bonds, hydrophobic bonds and ionic interactions & some vanderwaals) forming a stable 3-D structure. Molecular Chaperones assist the process (Recall Chapter 4). 12.3 Post-translational Processing of Protein Protein Folding (cont.) Protein disulfide isomerases modify locations of covalent disulfide bonds [-SS-], which cross-link and lock the conformation in place once all the other, noncovalent, stabilizing interactions are completed. However, some proteins still cannot fold into their final conformation until additional biochemical modifications take place. 12.3 Post-translational Processing of Protein Biochemical Modifications required for optimal Protein (biological) activity 1. Proteolytic Cleavage 1. 1. F-Met is usually the first thing cleaved F-Met is usually the first thing cleaved 2. Amino Acid Modification 3. Covalent attachment of Carbohydrates 4. Attachment of Prosthetic Groups 12.3 Post-translational Processing of Protein Biochemical Modification of Proteins 1. Proteolytic Cleavage All prokarytotic proteins have the amino acid N-formyl methionine as their N-/(amino)-terminus AA. About ~ 50% of these proteins must remove this AA by hydrolysis. Eukaryotic proteins also remove this methionine from their amino-terminus AA prior to function. Many eukaryotic proteins then add an acetyl group to the amino terminal amino acid CH 3 CNHpeptide II O 12.3 Post-translational Processing of Protein Proteolytic Cleavage (2) Example: Chymotrypsin , an enzyme (catalyzes the hydrolysis of peptide bonds between Phe, Tyr, etc.), is initially derived from a precursor form (zymogen) called Chymotrypsinogen. Chymotrypsinogen....
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Biochem Chapter 12 part II - Chapter Seven Chapter 12 Part...

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