Cellular Respiration

 CR is the process by which cells convert the energy in food, in the form of glucose, into usable energy (ATP)  Terms to know  Oxidation=the loss of electrons, compound becomes more positive  Reduction=the gain of electrons, compound becomes more negative  Electrons and protons (H+) travel TOGETHER, 2 electrons for every 1 H+(Proton)

 Two types of cellular respiration include aerobic (with O2) and anaerobic (without O2)  “glucose-breaking  Glycolysis is the first step in both forms of CR, thus it does not need oxygen Glycolysis

 Big Picture  Glucose, C6H12O6 (a 6 carbon molecule) is broken down into 2 molecules of (a 3 carbon molecule) pyruvate  Occurs in the cytosol  Releases about 2% of the energy in glucose

 Input  2 ATP, ”charged batteries” to use  2 NAD  Glucose, energy storage molecule from food, C6H12O6  Output:  4 ATP ( 2 net ATP )  2 NADH from NAD+  2 pyruvates – also known as pyruvic acid  Glucose breaks in half forming 2, 3 carbons chains

 If oxygen is absent, anaerobic respiration occurs  Fermentation  If plants, bacteria, or yeast is alcoholic fermentation  If animals is lactic acid fermentation  If oxygen is present, aerobic respiration occurs

Anaerobic Respiration: Fermentation  2 major types: alcoholic and lactic acid  Fermentation is used as a way to dispose of H+ produced during glycolysis  If the supply of NAD+ runs out, then glycolysis would stop  Thus the purpose of fermentation is to recycle NAD

Anaerobic Respiration: Fermentation  Alcoholic Fermentation Occurs in plans, bacteria, and yeast -Normal process -Carbon dioxide is released from pyruvate (3C) forming acetaldehyde (2C) -Acetaldehyde is reduced by NADH (gains an electron) forming ethyl alcohol (ethanol) -NAD+ is regenerate allowing glycolysis to continue -Used to produce beer and wine

Anaerobic Respiration: Fermentation  Lactic Acid Fermentation  Occurs in animal cells  Normal process  Pyruvate is reduced by NADH (gains an electron), forming lactic acid  NAD+ is regenerated allowing glycolysis to continue  Occurs in muscle cells, causing muscle pain and fatigue during rapid exercise when the body cannot supply enough oxygen to tissues

Aerobic Respiration  After glycolysis, most of the energy from glucose remains “locked” in 2 molecules of pyruvate  If oxygen is present, pyruvate enters the mitochondrial matrix to complete the Kreb’s Cycle/The Citric Acid cycle (TCA)  First pryuvate gets “groomed” in the mitochondria by removing 1 C (CO2) and adding Coenzyme A

Aerobic Respiration

 Kreb’s Cycle  The next step in aerobic respiration occurring in the matrix of the mitochondria  It’s a series of redox reactions starting with Acetyl CoA  Acetyl CoA (2C) binds with oxaloacetate (4C) forming a 6C compound.  Eventually the carbons from acetyl CoA get released as CO2, allowing oxaloacetate to go through the cycle again

Aerobic Respiration  Kreb’s Cycle  Named after Hans Krebs, Nobel prize winner 1953 for discovering the cycle  Also called the citric acid cycle  Yields per pyruvate molecule:  4 NADH, 1 FADH2, 1 ATP  Yields per glucose:  8 NADH, 2 FADH2, 2 ATP

Aerobic Respiration

 Electron Transport Chain and Chemiosmosis  The ETC is the last step in aerobic respiration  It receives all the electron carriers (NADH, FADH2) from glycolysis and Kreb’s cycle  It then converts NADH and FADH2 into NAD+ and FAD+  Occurs in the inner membrane of the mitochondria

Aerobic Respiration  Electron Transport Chain and Chemiosmosis  1 NADH -> 3 ATP  1 FADH2 -> 2 ATP  The electrons from NADH and FADH2 are passed from one electron acceptor protein to another  Oxygen is the final electron acceptor and makes water when it combines with hydrogens

Aerobic Respiration  Chemiosmosis  The energy the electrons lose along the way moves H+ (off of NADH and FADH2) out of the matrix and into the intermembrane space of the mitochondria  As H+ ions diffuse through the membrane, the enzyme ATP synthase uses the energy to join ADP and a phosphate group -> ATP

Aerobic Respiration  Electron Transport Chain  38% efficient (some energy lost as heat)  62% is released as heat (why you feel warmer after exercise)  1 glucose yields ATP  ATP made from glucose provides energy to sleep, exercise, eat, and study – allows cells to function  Glycolysis: 2 ATP, 2 NADH -> 6 ATP in ETC  Kreb’s: 2 ATP, 8 NADH-> 24 ATP in ETC, 2 FADH2 -> 4 ATP in ETC