Cellular Respiration Cellular Respiration AKA Respiration The metabolic

Cellular Respiration

Cellular Respiration – AKA Respiration The metabolic pathways by which carbohydrates are broken down into ATP n The formula for respiration is: n C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O + ATP n Respiration allows the gradual build up of ATP, n If a cell used all the potential energy in glucose at once, too much heat would be released, and not all the energy would be harvested. n

Three Steps of Respiration 1. Glycolysis Yields 2 molecules of ATP 2. Citric Acid Cycle (Krebs Cycle) Yields 2 molecules of ATP 3. Electron Transport Chain (Oxidative phosphorylation) Yields 32 molecules of ATP Though 36 molecules of ATP are produced, it is only 39% of the total energy in a molecule of glucose

The Process in General Electrons carried via NADH and FADH 2 Electrons carried via NADH Glycolysis Glucose Pyruvate ATP Substrate-level phosphorylation 0% Citric acid cycle ATP Substrate-level phosphorylation Oxidative phosphorylation: electron transport and chemiosmosis ATP Oxidative phosphorylation

Glycolysis Glyco- of or relating to glucose n Lysis- to split or burst n Changes one molecule of glucose to 2 three Carbon molecules called pyruvate n Occurs in the cytosol (cytoplasm) n Does not require Oxygen n

Glycolysis Glucose 2 pyruvate n 2 NADH n 2 ADP 4 ATP n 2 ATP n Net gain of 2 ATP molecules (top=input, bottom= n outputs) 2 ATP 2 ADP n P + 2 NADH Glucose Fructose PGAL PGA PEP pyruv 2 ATP H 2 O 2 ATP

Glycolysis When Oxygen is present, glucose / pyruvate can be broken down further in a process called the Krebs cycle. n However, when Oxygen is not present pyruvate can be broken down through the process of fermentation. n Aerobic respiration- respiration with Oxygen n Anaerobic respiration- respiration with out Oxygen n

The Evolutionary Significance of Glycolysis occurs in nearly all organisms n Glycolysis probably evolved in ancient prokaryotes before there was oxygen in the atmosphere n Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fermentation Glycolysis + the reduction of pyruvate to lactic acid, alcohol, or CO 2 n Fermentation is inefficient. But when O 2 is not present it is better than nothing. n n n Glycolysis yields 2 ATP, fermentation yields 2 more Fermentation yields only 14. 6 Kcal of a possible 686 Kcal from 1 molecule of glucose that is about 2. 1% efficient.

Fermentation n In yeast produces alcohol and CO 2 death In humans produces lactic Acid soreness In athletes : n n n because of training more mitochondria are produced in the muscle cells. b/c of higher # of mito. , they utilize more O 2 and can produce more ATP (less O 2 wasted) Means less Oxygen debt or deficit Less fermentation Less soreness

Types of Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis n Two common types are alcohol fermentation and lactic acid fermentation n Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

In alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO 2 n Alcohol fermentation by yeast is used in brewing, winemaking, and baking n Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -18 2 ADP + 2 Pi Glucose 2 ATP Glycolysis 2 Pyruvate 2 NAD+ 2 NADH + 2 H+ 2 CO 2 2 Acetaldehyde 2 Ethanol (a) Alcohol fermentation 2 ADP + 2 Pi Glucose 2 ATP Glycolysis 2 NAD+ 2 Lactate (b) Lactic acid fermentation 2 NADH + 2 H+ 2 Pyruvate

Fig. 9 -18 a 2 ADP + 2 P i Glucose 2 ATP Glycolysis 2 Pyruvate 2 NAD+ 2 Ethanol (a) Alcohol fermentation 2 NADH + 2 H+ 2 CO 2 2 Acetaldehyde

In lactic acid fermentation, pyruvate is reduced to NADH, forming lactate as an end product, with no release of CO 2 n Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt n Human muscle cells use lactic acid fermentation to generate ATP when O 2 is scarce n Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -18 b 2 ADP + 2 P i Glucose 2 ATP Glycolysis 2 NAD+ 2 Lactate (b) Lactic acid fermentation 2 NADH + 2 H+ 2 Pyruvate

Fermentation and Aerobic Respiration Compared Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate n The processes have different final electron acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermentation and O 2 in cellular respiration n Cellular respiration produces 38 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule n Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Obligate anaerobes carry out fermentation or anaerobic respiration and cannot survive in the presence of O 2 n Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration n In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes n Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -19 Glucose CYTOSOL Glycolysis Pyruvate No O 2 present: Fermentation O 2 present: Aerobic cellular respiration MITOCHONDRION Ethanol or lactate Acetyl Co. A Citric acid cycle

Aerobic Respiration Occurs when Oxygen is present n Produces 36 ATP molecules n Begins after glycolysis n The Transition reaction connects glycolysis to the Aerobic pathways (Krebs cycle & Electron transport chain). n

Transition Reactions Connects glycolysis to the Krebs cycle n The pyruvate from glycolysis is converted to a 2 Carbon compound called an acetyl group. n The acetyl group is attached to Coenzyme A n The resulting complex is Acetyl Coenzyme A (Acetyl Co. A) n Coenzyme- protein that acts as a carrier molecule in biochemical processes. n

Transition Reaction Occurs twice for each glucose molecule n Occurs in the matrix of the mitochondria n 2 NADH + H- 2 pyruvate + 2 Co. A 2 Acetyl Co. A + 2 CO 2 n Mitochondrial structure n Cristae - location of the electron transport chain n Cytosol – location of glycolysis n Matrix- location of the transition reactions and the Krebs cycle. n

Fig. 9 -10 CYTOSOL MITOCHONDRION NAD+ NADH + H+ 2 1 Pyruvate Transport protein 3 CO 2 Coenzyme A Acetyl Co. A

Krebs Cycle n n n The products of the Transition RXN are the reactants of the Krebs Cycle. The Krebs Cycle is also known as the Citric Acid Cycle. Citrate is the first metabolite produced in the Krebs Cycle. During the Krebs Cycle: n n n the acetyl group on Acetyl Co. A is oxidized to CO 2. Some of the electrons (H ions) are accepted by NAD, but 1 is picked up by another electron carrier, FAD. Some ATP is produced by phosphorylation like in glycolysis. The Krebs Cycle turns twice for each original molecule of glucose.

Krebs Cycle n. Inputs 2 acetyl groups n 2 ADP + 2 P n 6 NAD n 2 FAD n n. Outputs 4 CO 2 n 2 ATP n 6 NADH n 2 FADH 2 n See Figure 9. 7

Acetyl Co. A—SH NADH H 2 O NAD+ Oxaloacetate Isocitrate Malate Citrate NAD+ Citric acid cycle NADH CO 2 H 2 O Fumarate Co. A—SH -Ketoglutarate Co. A—SH FADH 2 NAD+ FAD Succinate NADH P Succinyl Co. A ADP ATP CO 2

Fig. 9 -7 Substrate-level phosphorylation: • Use of an enzyme to produce ATP and another product Enzyme + ADP P Substrat e ATP Product

The Electron Transport Chain Located in the cristae n Series of electron carriers that pass an electron from one to another. n The electrons in the electron transport chain come from NADH and FADH 2 in the Krebs Cycle n Drives the process that generates most of the ATP. n The process that generates most of the ATP is called oxidative phosphorylation because it n

Electrons are transferred from NADH or FADH 2 to the electron transport chain n Electrons are passed through a number of proteins including cytochromes (each with an iron atom) to O 2 n The electron transport chain generates no ATP n The chain’s function is to break the large free-energy drop from food to O 2 into smaller steps that release energy in manageable amounts n Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -13 NADH 50 2 e– NAD+ FADH 2 2 e– Free energy (G) relative to O 2 (kcal/mol) 40 FMN FAD Multiprotein complexes FAD Fe • S Q Cyt b 30 Fe • S Cyt c 1 IV Cyt c Cyt a 20 10 0 Cyt a 3 2 e– (from NADH or FADH 2) 2 H+ + 1/2 O 2 H 2 O

Chemiosmosis: The Energy. Coupling Mechanism n n Electron transfer in the electron transport chain causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space H+ then moves back across the membrane, passing through channels in ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ATP This is an example of chemiosmosis, the use of energy in a H+ gradient to drive cellular work

The energy stored in a H+ gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis n The H+ gradient is referred to as a protonmotive force, emphasizing its capacity to do work n Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -14 INTERMEMBRANE SPACE H+ Stator Rotor Internal rod Catalytic knob ADP + P i ATP MITOCHONDRIAL MATRIX

Oxidative Phosphorylation n The process by which ATP production is tied to an electron transport system that uses Oxygen as a final electron receptor. After Oxygen accepts the electron it binds with Hydrogen from the matrix and form H 2 O n Figure 9. 8 n

Complexes of the Electron Transport Chain NADH dehydrogenase - causes the oxidation of NADH. n Cytochrome b-c complex - the complex which receives electrons and pumps H ions into the inter-membrane space. n Cytochrome oxidase complex - receives electrons and passes them to oxygen. n

Electron Transport Chain

The Process in General Electrons carried via NADH and FADH 2 0% Glycolysis Glucose Pyruvate ATP Substrate-level phosphorylation Citric acid cycle ATP Substrate-level phosphorylation Oxidative phosphorylation: electron transport and chemiosmosis ATP Oxidative phosphorylation

The process with details Electron shuttles span membrane CYTOSOL 2 NADH MITOCHONDRION 2 NADH Glycolysis Glucose 2 NADH or 2 FADH 2 2 Pyruvate 2 Acetyl Co. A + 2 ATP 6 NADH Citric acid cycle + 2 ATP Maximum per glucose: About 36 or 38 ATP 2 FADH 2 Oxidative phosphorylation: electron transport and chemiosmosis + about 32 or 34 ATP

Concept 9. 6: Glycolysis and the citric acid cycle connect to many other metabolic pathways n Gycolysis and the citric acid cycle are major intersections to various catabolic and anabolic pathways Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

The Versatility of Catabolism Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration n Glycolysis accepts a wide range of carbohydrates n Proteins must be digested to amino acids; amino groups can feed glycolysis or the citric acid cycle n Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fats are digested to glycerol (used in glycolysis) and fatty acids (used in generating acetyl Co. A) n Fatty acids are broken down by beta oxidation and yield acetyl Co. A n An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate n Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -20 Proteins Amino acids Carbohydrates Sugars Glycolysis Glucose Glyceraldehyde-3 - P NH 3 Pyruvate Acetyl Co. A Citric acid cycle Oxidative phosphorylation Fats Glycerol Fatty acids

Regulation of Cellular Respiration via Feedback Mechanisms n Feedback inhibition is the most common mechanism for control n If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down n Control of catabolism is based mainly on regulating the activity of enzymes at strategic points in the catabolic pathway Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings