Chapter 3 Cell Metabolism Glucose Carbohydrates Fats and Proteins The types of reac ons that provide cells the energy needed to perform their work Where are we going Metabolism Reac ons in Cells How individual cells use oxida ve phosphoryla on to acquire the energy they need Whole Body Metabolism The way the body stores and u lizes energy controlled through the endocrine system Food intake is intermiCent so the body must store nutrients during periods of intake and then break down stores in between meals The brain depends on glucose as its primary energy source so glucose levels must be maintained at all mes even between meals Types of Metabolic Reac ons Oxida on Reduc on Reac ons Overview of Glucose Oxida on In cells glucose is oxidized through a long series of carefully controlled redox reac ons The resul ng change in free energy is used to synthesize ATP from ADP and Pi The carbon atoms of glucose are oxidized to form carbon dioxide and the oxygen atoms in oxygen are reduced to form water C6H12O6 6 O2 6 CO2 6 H2O energy Glucose oxygen carbon water dioxide Stages of Glucose Oxida on 1 Glycolysis glucose is broken down to two molecules of pyruvate 2 Pyruvate processing pyruvate is oxidized to form acetyl CoA 3 Citric acid cycle Krebs Cycle acetyl CoA is oxidized to CO2 4 Electron transport and chemiosmosis compounds that were reduced in steps 1 3 are oxidized in reac ons leading to ATP produc on The Role of Enzymes in Chemical Reac ons Cells contain a wide variety of enzymes each specialized to catalyze a par cular reac on or group of reac ons Enzymes help to stabilize the transi on state thereby decreasing the ac va on energy barrier and speeding up the rate of reac ons Step 1 Glycolysis Glycolysis is comprised of 10 reac ons each catalyzed by a di erent cytosolic enzyme Only 2 ATP directly from glycolysis No oxygen is consumed and no CO2 is produced Pyruvate is moved into the mitochondria matrix All 8 Reac ons of the Krebs Cycle occur in the mitochondrial matrix outside the cristae Step 2 Pyruvate Processing Step 3 Krebs Cycle CAC By the end of each turn total of two CO2 molecules are generated as end products Only 2 ATP directly from Krebs Cycle However 8 of the 12 reduced electron carriers are produced by the Krebs Cycle Step 4 Electron Transport Chain In oxida ve phosphoryla on the reduced electron carriers NADH and FADH2 generated in previous steps serve as the energy source for making ATP As electrons pass through these carriers they u lize the released energy to move hydrogen ions against their gradient to create a store of poten al energy ATP Synthase The protons then move through the enzyme protein synthase driving the produc on of ATP from ADP and Pi Because this mode of ATP produc on links the phosphoryla on of ADP with NADH and FADH2 oxida on it is called oxida ve phosphoryla on ATP Synthase Anima on hCp www sigmaaldrich com sigma aldrich areas of interest life science metabolomics learning center metabolic pathways atp synthase atp anima on html 1 molecule of glucose yields 38 molecules ATP Cells also metabolize other monosaccharides such as fructose galactose and mannose Exercise and Cell Metabolism Because oxygen is the ul mate electron acceptor if the rate of oxygen supply is lower than the metabolic demand the en re process will slow and possibly even Exercise and Cell Metabolism Fortunately cells are able to convert pyruvate to lactate which ensures NAD is produced feeding glycolysis and ensuring ATP can s ll be produced Anaerobic Glycolysis Metabolism of Carbohydrates Metabolism of Fats Metabolism of Proteins