Complex Organic Molecules Simpler waste products w/ less energy catabolic pathway ADP + P ATP + H2O

LEO says GER Xe- + Y  X + Ye- Reduction = gain of e- Oxidation = loss of e- Y is being reduced (oxidizing agent) Xe- + Y  X + Ye- X is being oxidized (reducing agent)

Cellular Respiration Reduction C6H12O6 + 6 O2  6 CO2 + 6 H2O + E Oxidation C6H12O6 is oxidized to form CO2 O2 is reduced to form H2O e- are used to form ATP

NAD+ Enzymes lower EACT so glucose is oxidized slowly. Hydrogens stripped from glucose are not transferred directly to oxygen, but are passed to a special e- acceptor NAD+

NAD+ (nicotinamide adenine dinucleotide) Acts as a coenzyme in the redox reaction functions as an oxidizing agent by trapping e- Reactions are catalyzed by enzymes called dehydrogenases

R–C–R’ + NAD+  R-C-R’ + NADH + H+ H reduction R–C–R’ + NAD+  R-C-R’ + NADH + H+ H OH O dehydrogenase oxidation NAD+ = oxidized coenzyme NADH = reduced coenzyme

Steps of Cellular Respiration: 1. GLYCOLYSIS occurs in cytosol partially oxidizes glucose (6C) into two pyruvate (3C) molecules Energy investment phase = requires to ATP to start

GLUCOSE (6C) 2 ATP 2 ADP FRUCTOSE DIPHOSPHATE (6C) 2 PGAL

2 NAD 2 NADH 2 P 2 DPGA 2 ADP 2 ATP 2 PGA

2 ADP 2 ATP 2 H2O PYRUVIC ACID Kreb’s Cycle

Chemical energy from glucose is still stored in the pyruvate molecules. Fate depends on presence or absence of oxygen If O2 is present  pyruvate enters the mitochondrion where it is completely oxidized

2. KREBS CYCLE occurs in mitochondrial matrix complete glucose oxidation by breaking down a pyruvate derivative (acetyl Co-A) into CO2 a small amount of ATP is produced by substrate-level phosphorylation NADH formed by transfer of e- from substrate to NAD+

Formation of Acetyl-CoA CH3 OH CO2 C=O S-CoA CH3 NAD+ NADH + H+ pyruvate Acetyl CoA

A multienzyme complex catalyzes: the removal of CO2 from the carboxyl group of pyruvate the oxidation of the 2C fragment to acetate while reducing NAD+ to NADH the attachment of coenzyme A to the acetyl group forming acetyl CoA

Krebs Cycle (Citric Acid Cycle) oxidizes remaining acetyl fragments of Acetyl-CoA to CO2 For every turn of the Krebs cycle: 2 C enter in the acetyl fragment 2 different C are oxidized and leave as CO2 coenyzymes are reduced 3 NADH and 1 FADH2 1 ATP produced by s-l phosphorylation oxaloacetate is regenerated

(6C) (4C) (4C) H2O (5C) (4C) ATP

It takes 2 turns of the Krebs cycle for complete oxidation of 1 glucose molecule.

CH2 COO- succinate CH2 C=O S-CoA COO- succinyl CoA CoA-SH P + ADP ATP GDP GTP P + ADP ATP

3. ELECTRON TRANSPORT CHAIN occurs at the inner membrane of the mitochondrion accepts energized e- from reduced coenzymes (NADH and FADH2) O2 pulls the e- down the ETC to a lower energy state couples the exergonic slide of e- to ATP synthesis (oxidative phosphorylation – makes 90% of all ATP)

NADH FADH2 FMN FeS FeS CoQ NADH=3 ATP FeS FADH2=2 ATP Cyt b NADH=3 ATP FeS Cyt c FADH2=2 ATP Cyt c3 Cyt a Cyt a1 Final e- acceptor (forms water) ½ O2

ETC does not make ATP directly. It generates a proton gradient across the inner mitochondrial membrane.

KREBS CYCLE net: (2 turns) 2 ATP by s-l phosphorylation 6 NADH 2 FADH2 4 CO2 *** most energy found in NADH and FADH2 in high energy bonds

TOTAL Process ATP by S-L Phos. Reduced Co-Enzyme ATP by Ox Phos. TOTAL Glycolysis Net 2 ATP 2 NADH 4-6 ATP 6-8 ATP Oxidation of Pyruvate 6 ATP Krebs Cycle 2 ATP 6 NADH 2 FADH2 18 ATP 4 ATP 24 ATP 36-38 ATP TOTAL

* Prokaryotes usually get a better yield of 38 ATP because there is no membrane separating glycolysis from the ETC. * Eukaryotes usually only get 2 ATP per NADH in glycolysis.

Respiratory Poisons: Cyanide – blocks e- from cyt a3 to O2 Oligomycin (antibiotic) – inhibits ATP synthase Dinitrophenol (DNP) – uncouples the chemiosmotic reaction so protons leak across the membrane

Anaerobic Respiration: occurs if O2 is not present there is no final e- acceptor used by plants, fungi (yeasts) and bacteria occurs in the cytoplasm alongside glycolysis

2 PYRUVATE 2 CO2 2 ACETYLALDEHYDE 2 NADH 2 NAD+ 2 ETHANOL Alcohol Fermentation 2 ACETYLALDEHYDE 2 NADH 2 NAD+ 2 ETHANOL

2 PYRUVATE 2 NADH Lactic Acid Fermentation 2 NAD+ 2 LACTATE

ANAEROBIC RESPIRATION: does not require O2 uses ETC to make ATP uses a substance other than O2 as the final e- acceptor ex. NO3 or SO4-2 produces ATP by oxidative phosphorylation ** occurs in only a few bacterial groups that exist in anaerobic environments

Strict (obligate) aerobes: organisms that require O2 for growth and as the final e- acceptor Strict (obligate) anaerobes: organisms that only grow in the absence of O2, and are poisoned by it

FACULATIVE ANAEROBES: organisms can grow in either aerobic or anaerobic environments Cells can make ATP by fermentation if O2 is not available or ATP by cellular respiration if O2 is available. PYRUVATE is common to both fermentation and respiration.

GLUCOSE no O2 O2 PYRUVATE reduced to ethanol or lactate and NAD+ is recycled as NADH is oxidized oxidized to acetyl CoA and oxidation continues into the Krebs cycle

RESPIRATION CONTROLS: Third step in glycolysis is catalyzed by the allosteric enzyme phosphofructokinase. Ratio of ATP to ADP reflects energy status of the cell. PFK is sensitive to changes in this ratio. Citrate and ATP are allosteric inhibitors of PFK. When concentration rises, enzyme slows glycolysis.

ADP is an allosteric activator of PFK so when ADP rises, enzyme speeds up glycolysis