Complex Organic Molecules Simpler waste products w/ less energy catabolic pathway ATP + H 2 O ADP + P

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

Cellular Respiration C 6 H 12 O O 2  6 CO H 2 O + E Oxidation Reduction C 6 H 12 O 6 is oxidized to form CO 2 O 2 is reduced to form H 2 O e- are used to form ATP

Enzymes lower E ACT 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 OH O oxidation reduction NAD+ = oxidized coenzyme NADH = reduced coenzyme dehydrogenase

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) FRUCTOSE DIPHOSPHATE (6C) 2 PGAL 2 ATP2 ADP

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

2 H 2 O 2 ADP 2 ATP 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 O 2 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 CO 2  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 C=O CH 3 OH C=O S-CoA CH 3 CO 2 NAD+ NADH + H + pyruvateAcetyl CoA

A multienzyme complex catalyzes: the removal of CO 2 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 CO 2 For every turn of the Krebs cycle: 2 C enter in the acetyl fragment 2 different C are oxidized and leave as CO 2 coenyzymes are reduced 3 NADH and 1 FADH 2 1 ATP produced by s-l phosphorylation oxaloacetate is regenerated

(6C) (5C) (4C) ATP H2OH2O

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

GDPGTP P + ADPATP CoA-SH CH 2 C=O S-CoA COO - succinyl CoA CH 2 COO - succinate

3. ELECTRON TRANSPORT CHAIN occurs at the inner membrane of the mitochondrion accepts energized e- from reduced coenzymes (NADH and FADH 2 ) O 2 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)

FMN CoQ FeS Cyt b Cyt c FeS Cyt c 3 Cyt a Cyt a 1 ½ O 2 NADH FADH 2 Final e- acceptor (forms water) NADH=3 ATP FADH 2 =2 ATP

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 FADH 2 4 CO 2 *** most energy found in NADH and FADH 2 in high energy bonds From glycolysis and Krebs

ProcessATP by S-L Phos. Reduced Co- Enzyme ATP by Ox Phos. TOTAL Glycolysis Net 2 ATP 2 NADH4-6 ATP6-8 ATP Oxidation of Pyruvate 2 NADH6 ATP Krebs Cycle 2 ATP 6 NADH 2 FADH 2 18 ATP 4 ATP24 ATP 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 a 3 to O 2 Oligomycin (antibiotic) – inhibits ATP synthase Dinitrophenol (DNP) – uncouples the chemiosmotic reaction so protons leak across the membrane

Anaerobic Respiration: occurs if O 2 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 ACETYLALDEHYDE 2 ETHANOL 2 CO 2 2 NADH 2 NAD+

2 PYRUVATE 2 LACTATE 2 NADH 2 NAD+

ANAEROBIC RESPIRATION: does not require O 2 uses ETC to make ATP uses a substance other than O 2 as the final e- acceptor ex. NO 3 or SO 4 -2 produces ATP by oxidative phosphorylation ** occurs in only a few bacterial groups that exist in anaerobic environments

Strict (obligate) aerobes: organisms that require O 2 for growth and as the final e- acceptor Strict (obligate) anaerobes: organisms that only grow in the absence of O 2, and are poisoned by it

FACULATIVE ANAEROBES: organisms can grow in either aerobic or anaerobic environments Cells can make ATP by fermentation if O 2 is not available or ATP by cellular respiration if O 2 is available. PYRUVATE is common to both fermentation and respiration.

GLUCOSE 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 no O 2 O2O2

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