Overview of Cell Metabolism PDF

Cellular Metabolism PARA 1002 1 Introduction to Cellular Metabolism Metabolism: total cellular chemical changes – Anabolism: process of building up – Catabolism: process of breaking down Calorie: measure of energy contained in food ATP:...

Cellular Metabolism PARA 1002 1 Introduction to Cellular Metabolism Metabolism: total cellular chemical changes – Anabolism: process of building up – Catabolism: process of breaking down Calorie: measure of energy contained in food ATP: energy source available to the cell PARA 1002 2 1  Cellular Respiration Organic molecules from the food we eat are broken down by digestion into their simplest components (catabolism) ATP is produced in the cells from the further breakdown of these organic components ** glucose is the primary source of energy but other molecule can be modified to be used as well This process of Cellular Respiration (cellular metabolism) can be looked at in 3 steps… PARA 1002 3 Cellular Respiration 1. Glycolysis 2. Pyruvate Oxidation 3. Krebs Cycle (Citric Acid Cycle) 4. Electron Transport Chain (ETC) PARA 1002 4 2  Glycolysis PARA 1002 5 Glycolysis First step in breakdown of glucose Beginning of both anaerobic and aerobic processes Glucose is sequentially broken down into several other “intermediate” molecules Final outcome: 2 pyruvate molecules 2 ATP molecules (anaerobic) 2 NADH PARA 1002 6 3  The Krebs/Citric Acid Cycle PARA 1002 7 The Krebs/Citric Acid Cycle Starts with Pyruvic Acid from Glycolysis which is oxidized (Pyruvate Oxidation) Converted into Acetic Acid Converted into Acetyl-CoA Acetyl-CoA enters Krebs cycle in mitochondria Final outcome: 6 CO2 8 NADH (2 from pyruvate oxidation) 2 FADH2 2 ATP ** total for 2 pyruvate molecules (1 glucose molecule) PARA 1002 8 4  PARA 1002 9 Electron Transport Chain (ETC) Series of reduction/oxidation reactions Requires O2 Makes use of “electron carriers” Number of ATP molecules dependent on electron carrier Water is a waste product Oxygen is the “Terminal Electron Acceptor” PARA 1002 10 5  Summary of ATP Production ** You may see estimates of ATP production ranging from 30 – 38 per glucose End result of glycolysis, the citric acid cycle, and electron transport: PARA 1002 11 Anaerobic Respiration Occurs when oxygen is not present Produces less ATP than aerobic respiration Fermentation Occurs in yeast cells Final products are CO2, ethanol, and ATP Anaerobic muscle metabolism Occurs in certain muscles when oxygen is in limited supply When does this occur? PARA 1002 12 6  Fermentation Yeast breaks down glucose anaerobically Pyruvic acid still produced by glycolysis Pyruvic acid broken down by decarboxylase – Forms carbon dioxide and acetaldehyde Final products: 2 ATP CO2 ethyl alcohol (ethanol) PARA 1002 13 Anaerobic Muscle Metabolism PARA 1002 14 7  Anaerobic Metabolism (Muscle) Pyruvic acid converted to lactic acid (lactate) – Does build up of lactate / lactic acid cause muscle soreness and burning? – When oxygen is present, lactate can be converted back into pyruvate and enter the Krebs Cycle – Lactate may also be converted into glucose in the liver (gluconeogenesis) *What is oxygen debt? 2 ATP produced per glucose molecule PARA 1002 15 Lactate and Gluconeogenesis PARA 1002 16 8  Do we have to start with glucose? Do we always eat glucose in its raw form? What type of biological molecule is glucose? What other biological macromolecules do we consume? What are these other molecules broken down into during digestion? PARA 1002 17 Other Energy Sources Carbohydrates: Complex carbohydrates are broken down into simple sugars such as glucose May be stored in liver or converted to fat if not needed immediately Fit into cellular furnace at same level as glucose PARA 1002 18 9  Other Energy Sources Fats (Lipids): Digested into fatty acids and glycerol Glycerol enters at PGA stage of glycolysis Fatty acids enter Krebs Cycle (Beta Oxidation) Proteins: Digested into amino acids Enter into Krebs cycle at different stages Dependent on chemical structure PARA 1002 19 Ketogenesis Occurs when cells lack a carbohydrate source for fuel Acetyl CoA builds up (β-oxidation of fats / amino acid oxidation) Acetyl CoA cannot enter Krebs Cycle (Why?) Liver converts Acetyl CoA into various Ketone Bodies Ketone Bodies may be used as an energy source by some cells The body can tolerate a certain degree of ketone metabolism (ketosis) but prolonged ketosis or ketosis under certain conditions is very harmful ** Ketoacidosis PARA 1002 20 10