Cellular Respiration 7.3 Aerobic Respiration

Stages Aerobic Respiration Stage 1: Glycolysis Stage 2: Pyruvate Oxidation Stage 3: Krebs Cycle Stage 4: Electron Transport Chain and Chemiosmosis Glycolysis occurs in cytoplasm Stage 2 – 4 occurs in mitochondria - possess double membrane: outer membrane as well as an inner membrane (highly folded) - intermembrane space between both membranes (fluid filled) - inner membrane contains mitochondrial matrix (protein-rich liquid that fills interior)

Aerobic cellular respiration: Overview

Aerobic respiration: An overview A series of enzyme controlled reactions Oxygen is used to oxidize glucose Glucose is oxidized to form carbon dioxide Oxygen is reduced to form water During the oxidation of glucose: Electrons transferred to electron carriers, NAD+ and FAD+ Glycolysis and Kreb’s cycle Electrons then passed through an electron transport chain. The energy from the electrons will be used to pump protons. The energy from the diffusion of protons will be used to make ATP.

Stage 2: Pyruvate Oxidation Recall: reactions of glycolysis produced TWO pyruvates, TWO ATP’s, and 2 NADH’s - does not require O2 ; occurs in cytoplasm Pyruvate Oxidation: chemical pathway that connects glycolysis to Krebs cycle 2 pyruvate molecules are moved from the cytoplasm to the matrix of the mitochondria CO2 is removed from each pyruvate molecule and released as a waste product (1/3 of what you exhale)

Stage 2: Pyruvate Oxidation Cont. The remaining 2-carbon portions are oxidized by NAD+; As a result, the NAD+ molecule gains two hydrogen atoms and the remaining 2- carbon molecule becomes acetic acid Coenzyme A (Co-A) attaches and forms acetyl-CoA Acetyl-coA enters stage 3 (Krebs cycle) and NADH goes to stage 4 (ETC) 2 CO2 diffuses out of the mitochondria and cell.

Stage 3: Krebs Cycle This is an 8 step and cyclic stage cyclic because one of the products of step 8, is a reactant in step 1 At the end of the Krebs Cycle, all six carbons have been oxidized to CO2 and released from the cell as metabolic waste All that remains is some free energy in the form of ATP and high energy NADH and FADH2 These energy carriers enter the ETC

Krebs Cycle: The Details Cycle occurs twice for each acetyl-CoA molecule Acetyl CoA adds 2-carbons to oxaloacetate, producing citrate Citrate loses a CO2 molecule, and the resulting compound is oxidized, reducing NAD+ to NADH Another CO2 is lost, and the resulting compound is oxidized, reducing NAD+ to NADH ADP is phosphorylated to ATP Two hydrogen's are transferred to FAD+ to form FADH2 Kreb Cycle

Krebs Cycle Overview 1 Glucose= 2 ATP 6 NADH 2 FADH2 4 CO2 EACH pyruvate molecule produced in glycolysis (2) must enter the Krebs Cycle Therefore the cycle occurs twice for every glucose molecule

Stage 4: ETC NADH and FADH2: release the electrons they received during glycolysis and the Kreb’s cycle to ETC - proteins of the ETC transfer the electrons and use the energy released to pump hydrogen ions (protons) Hydrogen ions (protons) are pumped from the matrix to the intermembrane space Creates a concentration gradient

Stage 4: ETC Cont. Oxygen: final electron acceptor at the end of the ETC - oxygen accepts the electrons, combines with protons and become water The accumulated hydrogen ions (protons) diffuse back into the matrix through ATP synthase complex - The energy released from the diffusion fuels the formation of ATP (by pumping H+ ions into intermembrane space) ETC: an ongoing process - NADH delivers electrons continuously - FADH2 delivers lower energy electrons in different place than NADH (cannot pump as many H+ ions) Electron Transport Chain animation Electron Transport Chain

Stage 4 Cont: Chemiosmosis H+ ions accumulate in intermembrane space from ETC - creates an electrochemical gradient H+ ions (protons) move from intermembrane space to ATP synthase complex - energy in gradient forces them through Energy released as H+ ions pass through = binds ADP with Pi to produce ATP! Energy removed from 1 NADH = 3 ATP’s; 1 FADH2 = 2 ATP’s Oxidative phosphorylation: Because the energy needed to add the Pi group to ADP is derived from the oxidation of a glucose molecule aka oxidative ATP synthesis

Final Points… ATP is now sent to the cytoplasm to be utilized by the cell All stages are dependent on glycolysis for the production of pyruvate Last stages are dependent on the availability of electrons (from food– glucose) and oxygen