Cellular Respiration

the atoms of glucose together. When those I. Introduction NRG is stored in the chemical bonds that hold the atoms of glucose together. When those bonds are broken, the NRG can be captured and used to do work One of the major types of work done is the synthesis of ATP. Coupled RXNS play an important role (FIGURE 1) The ATP will provide energy for a variety of biochemical rxns in the cell.

Breakdown of any other phosphate ester releases less than half the NRG of what ATP releases (7.3 Kcal)

The process that involves the breakdown of Cellular Respiration The process that involves the breakdown of glucose to produce ATP. Occurs anaerobically (when oxygen is NOT present) or aerobically (when oxygen IS present). It can be summarized by the equation: C6H12O6 + 6O2  6CO2 + 6H2O + ATP

II. Understanding Glucose Breakdown REDOX reaction (a.k.a. oxidation-reduction rxn) – a chemical rxn in which one molecule is OXIDIZED (i.e. losses e-) and another molecule is REDUCED (i.e. gains e-) These terms also apply to the gain/loss of H atoms b/c that involves the transfer of e- Example: next slide

Each half of the rxn has specific characteristics 1. Oxidation half a. Releases a pair of e-, becomes oxidized b. Releases NRG, thus is exergonic 2. Reduction half a. Accepts a pair of e-, becomes reduced b. Gains NRG, thus endergonic

Coenzymes whose sole purpose is to carry D. NAD+ and FAD Coenzymes whose sole purpose is to carry H atoms to the E.T.C. to produce high amounts of ATP In the process: NAD+ is reduced to (NADH + H+) FAD is reduced to FADH2 FIGURE 2 http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__how_the_nad__works.html

III. Overview of glucose breakdown (NRG release) A. The breakdown occurs in several stages Glycolysis (stage 1): Universal 2. Aerobic Respiration (if oxygen IS present)  Transition Reaction  Kreb’s Cycle (stage 2)  Electron Transport Chain 3. Anaerobic Respiration (if no oxygen)  Lactic Acid Fermentation  Alcoholic Fermentation

IV. The breakdown of glucose (FIGURE 3) Glycolysis (1st stage): (a.k.a. Substrate-level phosphorylation) 1. Occurs in the cytoplasm of your cells 2. Anaerobic – no oxygen is required 3. Steps: a. Two molecules of ATP are broken down in order to begin this process b. The P group from each is added to glucose (6C) At this point, there’s an NRG debt of 2 ATP

c. The glucose is split in half forming two molecules, each w/ 3-C and 1 P group (this is the “substrate”) d. 2 P groups enter from cytoplasm and are attached to each molecule (now have 2 molecules, each w/ 3 C & 2 P groups). This also causes 2 H atoms from each molecule to be transferred to NAD+ to form (NADH + H+) (2 TOTAL)  they will go to E.T.C e. Each molecule transfers both P groups to an ADP to form 2 ATP (4 TOTAL). Left with 2 molecules of pyruvate (3C) f. So, 4 ATP have been produced, but 2 are used to repay NRG debt, thus 2 NET ATP are produced

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One of two things can now happen: a. Aerobic respiration – if oxygen is present b. Anerobic respiration – no oxygen available

B. Aerobic Respiration (requires oxygen) REMEMBER: The following steps happen twice, once for each pyruvate from glycolysis Transition Reaction (takes place in mitochondria) *** (requires 2 ATP) a. Pyruvate (3C) from glycolysis enters the mitochondria – double membrane organelle 1. Matrix – gel-like material; site of Krebs cycle 2. Cristae – The internal folds; the site of E.T.C.

combine w/ CoEnzyme-A to form Acetyl Co-A (2C) b. One of the C is released as CO2, the other 2 C combine w/ CoEnzyme-A to form Acetyl Co-A (2C)  This produces one molecule of (NADH + H+) which goes to E.T.C.

2. Krebs Cycle (Citric Acid Cycle) a. The Acetyl Co-A (2C) enters the Kreb’s cycle and combines w/ a 4C molecule to form Citric Acid (1st molecule made in cycle) b. The rest of the cycle is a series of rxns  One turn of the cycle produces: -- 2 CO2 molecules -- 3 (NADH + H+)  goes to E.T.C. -- 1 FADH2  goes to E.T.C. -- 1 ATP REMEMBER, this is for ONE pyruvate molecule; happens 2x)

The Transition RXN & Kreb’s cycle occur for each REMEMBER: The Transition RXN & Kreb’s cycle occur for each pyruvate that was made during glycolysis. So now, every C from the original glucose molecule has been utilized (turned into CO2) You get twice as many products as stated in the notes http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__how_the_krebs_cycle_works__quiz_1_.html

3. Electron Transport Chain – Oxidative Phosphorylation Each (NADH + H+) and FADH2 that was created will release their e- into the chain Chemiosmosis: e- pass from molecule to molecule in the chain. As that happens, H+ protons are pumped into the intermembrane space of the mitochondria (proton motive force). They diffuse back into the matrix thru ATP Synthase channels, producing ATP. When the e- reaches the end of the chain, they are picked up by O2 (the final e- acceptor) to form H2O  NAD+ and FAD are now reoxidized FIGURE 4

NOTE: Every pair of e- from (NADH + H+) = 3 ATP Every pair of e- from FADH2 = 2 ATP Thus, 34 ATP (32 NET) are produced from co-enzymes NAD and FAD in E.T.C. *** 2 ATP used to get NADH made during glycolysis from cytoplasm into mitochondria

C. Summary of ATP production (FIGURE 5) -- To start glycolysis: -- From glycolysis directly: -- From (NADH + H+) made during glycolysis: from transition rxn: -- From Krebs cycle directly: during Krebs cycle: -- From FADH2 made during Krebs cycle: _______ -- TOTAL -2 ATP 4 ATP {2 NET} 6 ATP {4 NET} 6 ATP 2 ATP 18 ATP 4 ATP 38 ATP (36 NET}

4 CO2 2 CO2 H2O

ANIMALS http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__electron_transport_system_and_atp_synthesis__quiz_1_.html BACTERIA http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__electron_transport_system_and_formation_of_atp__quiz_1_.html

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Anaerobic Respiration (Fermentation) *** Energetically less efficient!!! The E.T.C. can fxn properly as long as O2 is present to act as the last e- acceptor. If no O2, the Kreb’s cycle & E.T.C. can’t be utilized  no ATP produced If O2 supply is cut off, the result is death for cells (b/c they don’t reoxidize NADH or FADH2, thus they can’t produce ATP from glycolysis (EX: brain cells) However, some cells (ex. muscle cells) have special enzymes allowing them to use fermentation to reoxidize NADH into NAD+; this allows more glucose break down in glycolysis, producing minimal ATP, but enough for the cell to live

1. Lactic Acid (FIGURE 6) After glycolysis, (NADH + H+) will pass e- to pyruvate This will regenerate NAD+ and produce: Lactic acid and 4 ATP (NET of 2 ATP) c. Muscles feel sore (strenuous exercise, no oxygen present)

2. Alcoholic (FIGURE 7) Single-celled organisms (e.g. yeast) can ferment glucose After glycolysis, (NADH + H+) will pass e- to pyruvate This will regenerate NAD+ and produce: Ethanol and CO2 and ATP d. This is responsible for beer, wine, bread rising

FIGURE 8 (Processes combined) V. The Metabolic Pool Describes all the rxns involved in cell.resp. Catabolic rxns – Those that degrade molecules and release NRG (exergonic) B. Anabolic rxns – Those that require NRG to synthesize molecules (endergonic)