CHAPTER 8 Cellular Respiration

I. Intro. to Cell Respiration A. Respiration 1. Obtaining O2 from environment & releasing CO2 B. Cellular Respiration 1. Harvesting of energy from food molecules by cells 9/18/2018

II. Cell Respiration banks ATP A. Equation for Aerobic Respiration C6H12O6 + 6O2 --> 6CO2 + 6H2O + ATP oxidation reduction 9/18/2018

B. Glucose contains much chemical energy (10 g = 40 kcal) 1. Cell only turns about 40% of glucose’s energy into ATP 2. Rest is lost as heat C. Average adult needs to eat food with the equivalent of 2200 kcal of energy per day 9/18/2018

D. Energy in 1 glucose molecule is too great for any cell job 1. Respiration breaks down glucose in a series of small steps. a. Bonds are broken b. Electrons move from places with more energy to places with less energy c. Energy released stored as ATP 9/18/2018

III. NAD+ and FAD as electron shuttles 1. NAD+ - Nicotinamide adenine dinucleotide Coenzyme of oxidation-reduction reactions that is used over and over again a. NAD+ removes H atoms and electrons from compounds. Becomes NADH. ●The compounds are oxidized ● The NAD+ is reduced and has become an electron or hydrogen carrier 9/18/2018

b. NADH molecules are loaded with energy ● NADH delivers its electrons to an electron carrier that is part of an electron transport chain ● NADH gives up electrons. Becomes NAD+ (it is oxidized) ● Electron carrier gains electrons and is thus reduced. 9/18/2018

NAD+ Cycle

2. FAD (flavin adenine dinucleotide) ● Also a coenzyme of oxidation- reduction ● Sometimes used instead of NAD+ ● Accepts two electrons and two hydrogen ions (H+) to become FADH2 9/18/2018

IV. Two mechanisms generate ATP in cellular respiration A. Chemiosmosis 1. Uses protein complexes found in membranes (ATP synthases) 2. The synthases use the energy stored in H+ concentration gradients across membranes 3. ATP is synthesized as H+ ions flow across the membrane down their concentration gradients 9/18/2018

B. Substrate-level phosphorylation 1. An enzyme transfers a phosphate group from an organic substrate molecule to ADP a. Occurs because bond holding phosphate group in substrate is less stable than new bond holding it in ATP P = phosphate group 9/18/2018

V. Respiration in 4 Main Stages A. Glycolysis 1. Breaks glucose in half to pyruvate 2. Produces some ATP B. Preparatory step 1. Produces NADH & some CO2 C. Krebs Cycle (Citric Acid Cycle) 1. Completes the breakdown of glucose to CO2 molecules 2. Produces NADH & FADH2 3. Produces some ATP D. Electron Transport Chain & Chemiosmosis 1. NADH and FADH2 energy is turned into many ATP molecules by chemiosmosis 9/18/2018

Glucose Breakdown: Overview of 4 Phases

VI. Glycolysis (Stage I - Aerobic Respiration) A. Takes place in cytoplasm B. Steps of glycolysis: 1. ATP donates to glucose, forming C6- (glucose-6- phosphate) P P P 2. Another ATP donates to glucose to form -C6- (fructose 1,6-diphosphate) P P 9/18/2018

3. This splits in half to form 2 G3P molecules = C3- 4. 2 G3P are oxidized by NAD+ 1. 2 NADH produced, which will store energy 5. G3P is phosphorylated; becomes -C3- P P 9/18/2018

6. This molecule then transfers to ADP to form ATP (This is an example of substrate-level phosphorylation) a. This happens twice = 2 ATPs 2 -C3- + 2ADP --> 2 -C3 + 2ATP P P P 9/18/2018

Substrate-level Phosphorylation

7. -C3 transfers to another ADP to form ATP once again 2 -C3 + 2ADP ---> 2 C3 + 2 ATP pyruvate  Net profit of 2 ATPs + 2NADH at end P P P 9/18/2018

10. However, most cannot so there are further reactions that happen. 8. 2 ATPS of glycolysis represent only 5% of energy a cell can harvest from glucose a. 2 NADHs account for 16%, but their stored energy is not available in absence of O2 9. A few organisms (yeasts in an anaerobic environment) can get sufficient ATP by glycolysis 10. However, most cannot so there are further reactions that happen. 9/18/2018

Mitochondrion Structure

VIII. Preparatory Reaction (Stage II) A. Pyruvate diffuses from cytoplasm into mitochondrial matrix B. Things that happen to pyruvate: 1. Carbon is removed & released as CO2. Leaves 2-C acetyl group 2. 2-C acetyl group gets attached to Coenzyme A to form acetyl CoA 3. Pyruvate electron picked up by NAD+ which becomes NADH 9/18/2018

Preparatory Reaction

IX. Krebs (Citric Acid) Cycle (Stage III) A. Occurs in matrix of mitochondria B. Acetyl CoA combines with C4 (oxaloacetic acid) to form C6 (citric acid) C. C6 becomes C5 which becomes C4 giving off 2 CO2 molecules D. C4 will eventually convert back to the original C4 (oxaloacetic acid) E. Takes two turns of Krebs cycle to metabolize 1 glucose molecule 9/18/2018

The Citric Acid Cycle

E. Energy molecules in Krebs a. Each turn of Krebs cycle produces:  1 ATP molecule by substrate- level phosphorylation  3 NADH molecules  1 FADH2 b. But need to double those numbers because each acetyl CoA represents half of one glucose molecule 9/18/2018

Balance Sheet

F. Total Energy Molecules per Glucose so Far Glycolysis = 2 ATP + 2 NADH Prep Step = 0 ATP + 2 NADH Krebs Cycle = 2 ATP + 6 NADH + 2 FADH2 Totals = 4 ATP + 10 NADH + 2 FADH2 9/18/2018

Summary of Cell Respiration

X. ETC & Chemiosmosis (Stages IV & V) A. Electron Transport Chain (IV) 1. Transport proteins are arranged in the inner membrane of the mitochondrion (cristae) 2. Many of these carrier proteins are cytochromes (respiratory proteins) 3. This process sets up the cell to convert the NADH and FADH2 into ATP 9/18/2018

4. Steps of Electron transport: a. NADH brings its electrons to the first protein complex in the membrane. Becomes NAD+. b. Protein complex uses energy released from electrons to actively transport H+ ions to other side of membrane  H+ transported out from inner matrix to outer compartment 9/18/2018

c. Electrons are then passed to next complex in the membrane  H+ ions once again are pumped to other side of membrane; raising the H+ concentration in the outer compartment.  This continues down the chain of proteins, transferring electrons and releasing energy at each step. 9/18/2018

Organization of Cristae

d. The final electron acceptor is O2  Each of the oxygen atoms in O2 combines with 2 electrons & 2 H+ ions to form H2O. e. If O2 is not present, NADH cannot release its H and turn back into NAD+. ● This NAD+ is needed in order for the earlier stages of cellular respiration to function. ● Also, the Hs are needed for O2 to bind to them to create water. 9/18/2018

f. At end, all the NADH & FADH2. have been utilized, but no ATP f. At end, all the NADH & FADH2 have been utilized, but no ATP has been made.  Instead, concentration gradient has been built up over the mitochondrial membrane g. Oxidative phosphorylation – production of ATP as a result of release of energy by ETC. 9/18/2018

B. Chemiosmotic Production of ATP (Stage V) 1. H+ ions now highly concentrated in outer compartment 2. These H+ ions will now be allowed to flow through the ATP synthase complex a. This flow drives the synthesis of ATP by causing the phosphorylation of ADP 9/18/2018

3. Conversion of NADH & FADH2 into ATPs a. Each NADH transfers a pair of electrons to electron transport chain & contributes to the mitochondrion’s H+ gradient to create 3 ATP, on average b. Each FADH2 yields 2 ATPs, on average c.  Maximum yield of ATPs = 38 9/18/2018

Overall Energy Yielded per Glucose

XI. Respiration & Photosynthesis A. ALL organisms use cellular respiration to harvest energy from organic fuel molecules 1. Includes humans, animals, fungi, protists, plants, bacteria B. NOT ALL organisms have the ability to make organic molecules from CO2 and H2O 1. Only photosynthetic organisms 9/18/2018

XII. Fermentation A. Yeast normally use aerobic resp. However, they can also survive anaerobically by using only the 2 ATPs generated by glycolysis. B. Not efficient; but they can thrive on it if there is plenty of glucose C. One catch: 1. Without oxygen, cells will run out of NAD+ (needed for glycolysis) because NADH can’t rid itself of its hydrogens 9/18/2018

D. Two Types of Fermentation 1. Yeasts & certain bacteria can convert the pyruvic acid produced during glycolysis into other molecules plus NAD+ 2. Two types are: a. Alcoholic fermentation b. Lactic acid fermentation 9/18/2018

Two Types of Fermentation

3. Alcoholic Fermentation a. CO2 is removed from pyruvate b. NADH is oxidized back to NAD+ This recharges cell with NAD+ c. 2-C ethanol is produced This is still energy rich Ethanol is toxic, however.  If concentrations get too high the yeast will die. 9/18/2018

Products of Fermentation

4. Lactic Acid Fermentation a. Pyruvate is converted into 3-C lactic acid. b. NADH is oxidized back to NAD+  Used to make cheese & yogurt  Occurs in human muscle cells when O2 is in short supply  Lactic acid builds up in muscles & causes cramps  Liver converts it back later 9/18/2018

5. Efficiency of Fermentation a. The 2 ATPS produced per glucose during glycolysis plus fermentation are equivalent of only 2.1% of the energy available via aerobic respiration b. However, fermentation is sometimes essential to certain animals and tissues ● Red-eared slider turtles ● Human muscles when exercising very strenuously. Build up an oxygen debt and muscles may cramp until you get enough oxygen once again. 9/18/2018

Efficiency of Fermentation InLine Figure 143 These ATP are actually from glycolysis, NOT fermentation

The Metabolic Pool Concept 9/18/2018

XIII. Metabolic Pool A. Catabolism 1. Exergonic reactions that break down molecules 2. Breakdown products of food catabolism (carbs, fats, proteins) can enter into respiratory pathways as intermediates and then be converted into ATP. a. Deamination – when the amino groups are removed from proteins. 9/18/2018

B. Anabolism 1. Endergonic reactions that build up molecules 2. All metabolic reactions are part of the metabolic pool a. Intermediates from respiratory pathways can be used for anabolism 9/18/2018