An Overview of Cellular Respiration Cellular respiration occurs at the mitochondria: Parts of the Mitochondria • Outer Membrane: contains many pore proteins to allow materials in and out of the mitochondria. • Inner Membrane: contains enzymes essential for cell respiration. • Cristae: the folded sections of the inner membrane. • Inner membrane is about 5 times larger than the outer membrane (increases surface area and rate of respiration) • The inner membrane must be folded to fit inside An Overview of Cellular Respiration • Intermembrane Space: space between the inner and outer membrane of the mitochondria. • Matrix: the area inside of the inner membrane. • Contains proteins, cytosol, and mitochondrial DNA. An Overview of Cellular Respiration • Cellular respiration happens slowly and in many steps. • If all the energy was released in one step . . . Most would be lost as light and heat. • Three steps of cellular respiration 1. Glycolysis 2. Krebs Cycle 3. Electron Transport Chain Oxygen and Energy • Glycolysis is an ANAEROBIC processes. It does not directly require oxygen, nor does it rely on an oxygen-requiring process to run. • Glycolysis is still considered part of cellular respiration. • Glycolysis takes place in the cytoplasm of a cell. Oxygen and Energy • Pathways of cellular respiration that require oxygen are called AEROBIC. • The Krebs cycle and electron transport chain are both aerobic processes. • Both processes take place inside the mitochondria. Overview of Cellular Respiration NADH High-energy electrons carried by NADH NADH FADH2 and Stage 1 Stage 3 Stage 2 OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) GLYCOLYSIS Glucose CITRIC ACID CYCLE Pyruvate Krebs Mitochondrion Cytoplasm ATP Substrate-level phosphorylation CO2 CO2 ATP ATP Substrate-level phosphorylation Oxidative phosphorylation Step 1: Glycolysis • Location: In the cytosol just outside the mitochondria • Purpose: Splits glucose into two molecules of pyruvic acid. • To begin glycolysis the cell needs to invest two ATP • Glycolysis produces 4 ATP and 2 NADH (NADH is similar to NADPH in photosynthesis) Glycolysis ________ ↓ GLUCOSE ___________ → → ↓ 2 PYRUVIC ACID _____________ ATP ATP ATP ATP NADH ____________________ + _______________ Put in 2 ATP and get back 4 ATP Net gain of 2 ATP and 2 NADH NADH Step 2: Krebs Cycle • Location: The mitochondrial matrix • Pyruvic acid from glycolysis enters the mitochondria. • Purpose: To break down the pyruvic acid into CO2. • Every turn of the Krebs Cycle produces: • • • • 3 CO2 1 ATP 1 FADH2 (similar to NADH) 4 NADH The Krebs Cycle •Pyruvic acid from glycolysis enters the matrix, the innermost compartment of the mitochondrion. The Krebs Cycle • During the Krebs cycle, the 2nd stage of cellular respiration, pyruvic acid produced in glycolysis is broken down into carbon dioxide in a series of energy-extracting reactions. • The Krebs Cycle is also known as the Citric Acid Cycle because citric acid is the first compound formed in this series of reactions. Citric Acid Cycle An Overview (3:17) KREBS CYCLE KREBS CYCLE PRODUCES 3 ____ 1 ____ 1 ____ 4 ____ Krebs Cycle Animation The Krebs Cycle • Energy released by the breaking and rearranging of carbon bonds is captured in the forms of ATP, NADH, and FADH2. • For each turn of the cycle, 1 ADP molecule is converted into ATP. • ATP can directly power the cell’s activities. • NADH and FADH2 are used in the electron transport chain to generate ATP. Energy Extraction • Remember! Each molecule of glucose results in 2 molecules of pyruvic acid, which enter the Krebs cycle. So each molecule of glucose results in 2 complete “turns” of the Krebs cycle. • Therefore, for each glucose molecule, 6 CO2 molecules, 2 ATP molecules, 8 NADH molecules, and 2 FADH2 molecules are produced. Step 2: Krebs Cycle What happens to the products of the Krebs cycle? Carbon dioxide is lost to the atmosphere ATP can be used directly to supply energy for the cell High energy electron carriers move to the electron transport chain.