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Enzymes

Enzyme Location. Extracellular (secreted)IntracellularCytosolic (soluble)Membrane-associatedIntegralPeripheral. Definitions of Enzyme Activity. Unit: amount of enzyme that catalyzes the formation of 1 mmol of product per minSpecific activity: units per mg proteinTurnover number: moles of substrate converted to product per sec by 1 mol of enzyme.

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Enzymes

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    1. Enzymes Enzymes are biological catalysts responsible for supporting almost all of the chemical reactions that maintain biological homeostasis. The macromolecular components of almost all enzymes are composed of protein, except for a class of RNA modifying catalysts known as ribozymes. Ribozymes are molecules of ribonucleic acid that catalyze reactions on the phosphodiester bond of other RNAs.

    2. Enzyme Location Extracellular (secreted) Intracellular Cytosolic (soluble) Membrane-associated Integral Peripheral

    9. Definitions of Enzyme Activity Unit: amount of enzyme that catalyzes the formation of 1 mmol of product per min Specific activity: units per mg protein Turnover number: moles of substrate converted to product per sec by 1 mol of enzyme

    10. Enzyme Measurement Chemical: analysis of protein Activity: conversion of substrate to product Loss of substrate Formation of product Change in cofactor

    11. e.g., Lactate Dehydrogenase Pyruvate + NADH ? lactate + NAD Measure decrease in absorbance at 340 nm and calculate decrease in NADH concentration using the extinction coefficient (?NADH = 6.22 x 103 M-1 cm-1) Concentration = absorbance/extinction coefficient

    20. Michaelis-Menton Kinetics E + S <---> ES <---> ES* <---> EP <---> E + P

    21. Lineweaver-Burk Plot

    34. Types of Inhibitors

    36. Enzyme Kinetics and Food Quality Freezing and dehydration (concentration of solutes) Substrates Cofactors Enzymes Inhibitors Activators

    37. Processing and Enzyme Kinetics E + S <---> ES <---> ES* <---> EP <---> E + P

    39. Temperature and Food Quality Fish: Enzyme activity at low temperature Bacteria: Enzyme activity at high temperature Consider the source of enzyme

    40. Lipases Triacylglycerol ? diacylglycerol + fatty acid Diacylglycerol ? monoacylglycerol + fatty acid Monoacylglycerol ? glycerol + fatty acid Flavor generation, emulsifier, rancidity

    41. Phospholipases Phospholipase A1 Phospholipid ? 2-lysophospholipid + fatty acid Phospholipase A2 Phospholipid ? 1-lysophospholipid + fatty acid Membrane disruption, flavor, rancidity, cell signaling

    42. Phospholipases Phospholipase C Phospholipid ? diacylglycerol + X-phosphate Phospholipase D Phospholipid ? phosphatidic acid + X Membrane disruption, cell signaling (loss of food quality)

    43. Lipoxygenase Unsaturated fatty acid ? free radicals (cis, cis- 1,4-pentadiene double bond system) Lipid oxidation, rancidity, bleaching (color, flavor, texture, nutrition)

    44. Carboxyprotease Aminoprotease Acid protease

    46. Cellulase Cellulose ? oligosaccharides, glucose Softening, sweetener

    47. Pectinases Pectin methylesterase Pectin ? demethylated pectin Pectin lyase Pectin ? hydrolyzed pectin Juice clarification, prevents gelling, softening

    48. Amylases a-Amylase Amylose (Amylopectin) ? oligosaccharides b-Amylase Amylose (Amylopectin) ? b-Maltose Malting, baking, starch degradation

    53. Deleterious Reactions Flavor: proteases, lipases, lipoxygenase Color: phenolase, invertase, amylase, maltase Texture: phospholipases, proteases, pectinase, cellulase

    54. Enzymes and Food Processing Natural, nontoxic, and specific Active at low concentrations Active under mild conditions Can control reactions by knowing enzyme properties

    55. Analytical Tools Acetic acid (cheese, mayonnaise) Ascorbic acid (potatoes, flour) Cholesterol (noodles, egg liqueur) Citric acid (bread, meat, cheese) Lactose (cheese, ice cream) Lecithin (egg, noodles) Triacylglycerol (margarine, salad oil)

    56. Biotechnology Immobilized enzymes Batch process Continuous process Recombinant DNA Technology Gene cloning Enzyme expression (flavor, color, texture, nutrition)

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