Phosphate groups on proteins are hydrolyzed off by

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Phosphate groups on PROTEINS are hydrolyzed off by (phospho)protein phosphatases Protein- O PO 3 2- + H 2 O → Protein- OH + P i Phosphorylated protein protein phosphatase
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Phosphorylation/Dephosphorylation Phosphorylation/Dephosphorylation Example: glycogen phosphorylase (breaks down glycogen when your body needs glucose) Phosphorylation vs. dephosphorylation shifts conformational equilibrium modified enzyme (E- P ) is more active. 2 specific Ser residues (1 per subunit) modified by phosphorylase kinase De modifying enzyme: phosphorylase phosphatase (a phospho- protein phosphatase) Phosphorylase phosphatase Phosphorylase kinase Glycogen phosphorylase a (more active) Glycogen phosphorylase b (less active) P P Ser 14 side chain Ser 14 side chain
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Irreversible Regulation: Irreversible Regulation: Proteolytic Cleavage of Zymogens Proteolytic Cleavage of Zymogens
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Catalytic task of all kinds of proteases is to make that normally unreactive carbonyl group more susceptible to nucleophilic attack by H 2 O . Overall reaction: 2 separate "half reactions" (2 "phases" of catalysis), with a metastable covalent intermediate ("acyl-enzyme intermediate") between the 2 half reactions. 1st half-reaction (acylation): Serine residue OH acts as nucleophile, His helps by being a general base and later a general acid, and Asp helps keep it all aligned/oriented. Amine half of substrate is released as first product, and carboxylic acid half of substrate is covalently attached to enzyme (Ser) in an ester bond (acyl-enzyme intermediate). 2nd half reaction (deacylation): H 2 O (or OH ) acts as nucleophile, His helps by being a general base and later a general acid, and Asp helps keep it all aligned/oriented. Carboxylic acid half of substrate is released as second product. CHYMOTRYPSIN: CHYMOTRYPSIN: Mechanism of Peptide Bond Hydrolysis Mechanism of Peptide Bond Hydrolysis general base nucleophile .. catalytic triad
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Coenzyme Coenzyme (or “ (or “ cofactor cofactor ” if ” if inorganic inorganic ): ): a non-protein molecule/ion that participates in an enzymatic rxn and is regenerated for another reaction NAD + /NADH- coenzyme of biological redox rxns R N CNH 2 O + + H + + 2 e - R N CNH 2 O H H NAD + (oxidized form) NADH (reduced form) (from a reduced substrate) (oxidized substrate) +
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Fatty Acids Fatty Acids Carboxylic acids with long hydrocarbon chains amphipathic (polar “head” group + hydrophobic tail) Shorthand: # of carbons : # of double bonds in chain (e.g., 18:2 = 18 C with 2 double bonds), and positions of double bonds (counting from carboxyl C) indicated as (superscripts) : Palmitic acid: 16:0 Oleic acid: 18:0 Linoleic acid: 18:2 9,12
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Regulation of Membrane Fluidity Regulation of Membrane Fluidity Regulation of fluidity by lipid composition (especially in organisms that don’t rigorously control their body temperature): 1. fatty acid chain length (shorter more fluid) 2. number of double bonds (more d.b. more fluid) 3. Cholesterol ( animal cells) "stiffens" membrane by packing between unsaturated HC tails, but also disrupts close packing
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