Cellular Respiration

Cellular Respiration Producing ATP from the energy in food

An Overview • ATP is immediate source of energy used by cells • Energy in ATP held in phosphodiester bonds • Most energy release in cells results from redox rxns. involving Glucose • C6H12O6 + O2 --> 6 CO2 + 6 H2O + energy

40% of energy in Glucose is converted to usable energy in ATP • Production of ATP and other organic molecules is endergonic and require a constant input of energy to continue. • The source of that energy is the sun. • Photosynthesis is essentially the opposite of Cellular Respiration. • Energy flows from sun to autotrophs to heterotrophs. • All energy is lost eventually as work or heat.

Cellular Respiration THE BEGINNING * GLYCOLYSIS

Glycolysis • Activation of Glucose • 1 ATP used to add “P” to Glucose • forms Glucose Phosphate • Fructose Phosphate then formed • 1 ATP - P = 1 ADP + P

Formation of Sugar Diphosphate • 1 ATP used to add “P” to Fructose Phosphate • Forms Sugar Diphosphate (sugar and two “P”’s) • 1 ATP - P = 1 ADP + P

Formation and Oxidation of G3P • Sugar Diphosphate (6 C) into two 3 C molecules • 1 into G3P • Other 3 C becomes a different 3 C, but is then converted into G3P • Both G3P’s lose an H • Accepted by NAD to make 2 NADH’s • High energy level e-’s carried by the H’s • Some of the energy used to make 2 ATP’s

Formation of Pyruvate • 3 more reactions make two Pyruvate molecules • The energy released from these reactions used to make 2 ATP’s • Two C3H4O3 = 6 C’s, 8 H’s, 6 O’s (just 4 H’s removed from Glucose, C6H12O6.

Summary of Glycolysis • Glucose split into two 3 C’s • 2 ATP’s used for activation energy • 2 molecules NADH produced (+ 2 H+) • 4 ATP’s made (net gain of 2 ATP’s) • Pyruvate is the 3 C made • Will next enter Kreb’s Cycle if Oxygen is available • Will undergo fermentation if no Oxygen is available • Occurs in cytoplasm • No oxygen required (but can be present)

The Oxidation of Pyruvate A necessary first step prior to either The Citric Acid Cycle or Fermentation

Oxidation of Pyruvate • 2 e - and their associated H released • 1 e - from each Pyruvate • Accepted by 2 NAD’s to form 2 NADH’s • A C also released from each pyruvate • forms two CO2’s • Results in formation of two acetyl groups

The Citric Acid Cycle • Occurs in mitochondria • An aerobic process • Begins with acetyl (or Pyruvate if you include the oxidation of pyruvate as part of this process) • Ends with CO2 ,H2O, NADH and FADH2 and some ATP being produced

The process • Acetyl groups combine with a coenzyme • the coenzyme is CoA • just “hanging around” in mitochondria • forms AcetylCoA • AcetylCoA joins a 4C compound already present • The 4 C is oxaloacetic Acid • forms Citric Acid (6C) • Citric Acid undergoes two rxns to form isocitric acid

Isocitric Acid is oxidized • The H’s released are accepted by NAD and FAD • forms 4 NADH and two FADH2 • some of the energhy used to form two more ATP molecules • Forms Fumaric Acid • Fumaric Acid undergoes 2 rxns • Forms Oxaloacetic Acid • Combines with AcetylCoA to form Citric Acid • The whole darn thing happens again! • Two more NADH’s produced

2NADH produce in the Oxidation of Pyruvate • 2ATP’s produced in Citric Acid Cycle • 6 NADH and 2 FADH2 also produced in Citric Acid Cycle • Add that to the net gain of 2 ATP and 4 NADH produced in glycolysis • 4ATP • 10 NADH • 2 FADH2

Electron Transport Chain • Utilizing the energy held in NADH and FADH2 previously produced to make ATP • Produced by chemiosmosis • Gradient produced b/w the area within the inner and outer mitochondrial membrane and inside the mitochondria • 2 NADH from glycolysis were actively transported in (required 1 ATP each)

The ETC • High energy e - ’s carried by NADH and FADH2 transported out of inner mitochondrial membrane into area b/w inner and outer membrane by cytochromes embedded in the membrane. • protons follow • e - accepted by Oxygen to form H2O • creates proton conc. gradient • Protons move back across membrane in response to gradient • Movement coupled to production of ATP

The Balance Sheet from ETC • Each NADH drives synthesis of 3 ATP • 10 NADH from glycolysis, oxidation of pyruvate and the citric acid cycle • 30 ATP • but the NADH’s from glycolysis cost 1 ATP each to transport (- 2 ATP) • Each FADH2 drives synthesis of 2 ATP • 2 FADH2 ‘s from Citric acid cycle • 4 ATP • Net gain from ETC = 32 ATP

Overview of Oxidative Metabolism • Glycolysis • 2ATP (net gain), 2 NADH • anaerobic, in cytoplasm • Oxidation of Pyruvate • 2 NADH • Citric Acid Cycle • 2ATP, 6 NADH, 2 FADH2 • aerobic, in mitochondria • ETC • 32 ATP (net gain), H2O • in christae of mitochondria

Fermentation Anaerobic Respiration: allowing Glycolysis to continue without O2

Alcoholic Fermentation • Pyruvate from glycolysis is oxidized • forms acetyl • CO2 also formed • Acetyl combines with H from NADH (from gly) • forms ethyl alcohol • also forms NAD to be used in glycolysis • Alcohol becomes toxic @ 12 % • ceases fermentation • thats why fermented drinks have max alcohol of 12% • Uses: wine, brewing, baking

Lactic Acid Fermentation • Pyruvate from glycolysis doesnt get oxidized • an enzyme helps to bond H from NADH to pyruvate • forms Lactic Acid - “Ooooh feel the burn!” • makes NAD available for glycolysis to continue • Occurs in aerobic cells under O2 stress - muscle • Also occurs in certain other microorganisms • sour cream, yogurt • vinegar

Cellular Respiration