Cellular Respiration Chapter 8

Cellular Respiration There are two pathways for cellular respiration. Anaerobic Pathway-glycolysis and fermentation Aerobic pathway-glycolysis paired with aerobic respiration in the mitochondria. Carbohydrates produced in photosynthesis are converted into the energy of the cell, ATP. Overall Equation: C6H12O6 + 6O2 6CO2 + 6H2O + energy (ATP)

Respiration is a Redox Reaction Oxidation-reduction LEO the lion says GER Oxidation is e- loss Reduction is e- gain Reducing agent is the e- donor Oxidizing agent is the e- acceptor

Oxidizing Agent in Respiration NAD+ (nicotinamide adenine dinucleotide) NAD+ is reduced to NADH Enzyme action: dehydrogenase Oxygen is the eventual e- acceptor

NAD+ Only a small amount of NAD+ is needed in cells; each NAD+ is used over and over. Electrons received by NAD+ are high-energy electrons and are usually carried to the electron transport system.

FAD FAD coenzyme of oxidation-reduction can replace NAD+. FAD accepts two electrons and becomes FADH2.

How Cells Acquire ATP Glucose is high-energy CO2 & H2O are low-energy Process is exergonic and releases energy. Glucose is oxidized and O2 is reduced. Buildup of ATP is an endergonic rxn that requires energy. Breakdown of glucose yields synthesis of 36 or 38 ATP, preserving 39% of energy in glucose.

Cellular Respiration Glycolysis: occurs in cytosol; degrades glucose into pyruvate Kreb’s Cycle: occurs in the mitochondrial matrix; converts pyruvate into carbon dioxide Electron Transport Chain: inner membrane of mitochondrion; electrons are passed to oxygen

Order of Events and how it leads into Aerobic Respiration. * First we will look at Glycolysis and how it leads into Aerobic Respiration. * Second we will look at our other pathway of Glycolysis into Fermentation.

Glycolysis Glycolysis is the breakdown of glucose to two pyruvate. Enough energy is released for immediate buildup of two ATP. Two NADH are also produced. Glycolysis takes place outside the mitochondria and does not utilize oxygen (anaerobic).

ATP Production in Glycolysis

Glycolysis Glucose (C6) splits into two C3 molecules each with a phosphate group. 4 total ATP are produced but two are used to phosphorylate glucose so there is a net gain of 2 ATP. The C3 molecules, pyruvate, enter the mitochondria if O2 is available to continue with aerobic respiration. If no O2 is available, glycolysis becomes part of fermentation. Let’s look at an aerobic environment first…

Inside The Mitochondria Glucose breakdown involves the transition rxn, the Krebs cycle, and the electron transport system. A mitochondrion has a double membrane with an intermembrane space between the outer and inner membrane.

Inside the Mitochondria

Inside the Mitochondria Outer Membrane Intermembrane space Inner Membrane Cristae Folds of inner membrane. Increases surface area for chemiosmosis ETS occurs here Matrix Jelly-like substance Transition Reaction and Kreb’s Cycle occur here.

The Mitochondria

Transition Reaction The Transition Reaction links Glycolysis and the Krebs cycle. Pyruvate is oxidized to an acetyl group attached to co-enzyme A and CO2 is removed. This happens twice for each glucose molecule.

The Krebs Cycle The Krebs cycle is a series of reactions that give off CO2 and producing ATP. It occurs in the matrix of the mitochondria. The Krebs cycle produces two immediate ATP molecules per glucose molecule. 6 NADH and 2 FADH2 are also formed and carry electrons to the ETS. CO2 is released- we exhale it.

The Electron Transport System Electron transport system is located in cristae of mitochondria. Consists of carriers that pass electrons. Electrons pass from higher to lower energy states, energy is released and stored for ATP production. Electrons that enter the electron transport system are carried by NADH and FADH2 NADH gives up electrons, becoming NAD+ System accounts for 32 to 34 ATP depending on the cell.

The Electron Transport System At each sequential oxidation-reduction rxn, energy is released to form ATP. O2 serves as a terminal electron acceptor and combines with hydrogen to form water. Because O2 must be present for system to work, it is called oxidative phosphorylation.

The Electron Transport System At each sequential oxidation-reduction rxn, energy is released to form ATP. O2 serves as a terminal electron acceptor and combines with hydrogen to form water. Because O2 must be present for system to work, it is called oxidative phosphorylation.

Cristae of Mitochondria NADH dehydrogenase complex, cytochrome b-c complex, and cytochrome oxidase complex all pump H+ ions into the intermembrane space. Energy released from flow of electrons down electron transport chain is used to pump H+ ions, carried by NADH and FADH2, into intermembrane space.

ATP Production in the Mitochondria ATP synthase complexes are channel proteins that also serve as enzymes for ATP synthesis. As H+ ions flow from high to low concentration, ATP synthase synthesizes ATP (Chemiosmosis). Once formed, ATP molecules diffuse out of the mitochondrial matrix through channel proteins.

Energy Yield From Glucose Breakdown Source FADH2 NADH ATP Glycolysis 2 ATP 2 NADH 4-6 ATP Transition 6 ATP Kreb’s 6 NADH 18 ATP 2 FADH2 4 ATP TOTAL: 36-38 ATP

Anaerobic Pathway If O2 is not available to the cell, fermentation, an anaerobic process, occurs. During fermentation, glucose is incompletely metabolized to lactate or CO2 and alcohol. Fermentation results in a net gain of only 2 ATP per glucose molecule.

Fermentation Fermentation consists of glycolysis plus reduction of pyruvate to either lactate or alcohol and CO2. NADH passes its electrons to pyruvate instead of to an electron transport system. NAD+ is then free to return and pick up more electrons during earlier rxns of glycolysis.

Fermentation Examples Anaerobic bacteria produce lactic acid when we manufacture some cheeses. Anaerobic bacteria produce industrial chemicals: isopropanol, butyric acid, etc. Yeasts use CO2 to make bread rise and produce ethyl alcohol in wine-making. Animals produce pyruvate to lactate when it is produced faster than it can be oxidized by Krebs cycle.

Advantages and Disadvantages of Fermentation Fermentation provides quick bursts of ATP energy for muscular activity. Disadvantage is that lactate is toxic to cells. When blood can’t remove lactate from muscles, lactate changes pH and causes muscles to fatigue. Individual is in oxygen debt b/c oxygen is still needed after exercising. Recovery occurs after lactate goes to liver.

Efficiency of Fermentation Two ATP produced per glucose molecule during fermentation . Fermentation is much less efficient than complete breakdown of glucose in oxidative phosphorylation..