Ch 9: Cellular Respiration

The Big Picture Cellular respiration sole purpose is to produce ATP. Its an exergonic (catabolic)reaction. Can be summarized as a whole as: Organic Compound+OxygenCO2+Water +ATP + heat

Glycolysis, Krebs Cycle, and Oxidative Phosphorylation 1. Glycolysis is the decomposition of glucose to pyruvate (or pyruvic acid) 2. Krebs Cycle takes pyruvate (2 pyruvate per glucose molecule) and yields electron acceptors and ATP. 3. Oxidative phosphorylation extracts ATP from NADH and FADH2.

Reminder on ATP ATP (adenosine triphosphate) is a nucleotide with unstable phosphate bonds that the cell hydrolyzes for energy. The cell taps energy stored in ATP by enzy- matically transferring terminal phosphate groups from ATP to other compounds. The compound receiving the phosphate group is said to be phosphoralated and is more reactive as a result. Cells use ATP to continue cellular work. But they must replenish the ATP supply to continue cellular work. Respiration does this.

Simply put – cellular respiration is a redox process that transfers hydrogen from sugar to oxygen. Valence electrons of carbon and hydrogen lose potential energy as they shift toward electronegative O. Released energy is used by cells to produce ATP.

Redox reactions These are the energy-shuttling mechansisms of metabolism Partial or complete gain of electrons=reduction Partial or complete loss of electron=oxidation They are always coupled…so in order for a material to lose an electron, another molecule must accept it

The NAD+, NADH, FAD+, FADH NAD+ and FAD+ are coenzymes that function in the redox reactions and are found in all cells. Traps energy-rich electrons from the organic compound. NAD+= oxidized coenzyme NADH= reduced coenzyme Why isn’t glucose oxidized in one explosive step?

During oxydation of glucose, NAD+ functions as an oxidizing agent by trapping energy-rich electrons from glucose. These reactions are catalized by enzymes called dehydrogenases which: - Remove a pair of hydrogen atoms (2 e,2p) from substrate. Deliver the two electrons and one proton to NAD+ Release the remaining proton into the surrounding solution.

Cellular Respiration

Glyclolysis (per glucose molecule) Takes place in cytosol. Mutiple steps (9 or 10 depending on source) in the process of decomposing glucose into pyruvate. Mg2+ ions are cofactors to help. 2 ATP go IN 4 ATP PRODUCED (so what is NET gain?) 2 NAD+ go IN 2 NADH PRODUCED 2 Pyruvate (Pyruvic acid) PRODUCED

Glycolysis………. - occurs whether O is present or not - no CO2 is released as glucose is oxidized to pyruvate; all C in glu – cose can be accounted for in the 2 molecules of pyruvate. - occurs in 2 phases

Glycolysis: Energy Investment Phase includes 5 preparatory steps in which glucose is split in two. consumes ATP….why? The cell uses ATP to phosphorylate the intermediates of glycolysis. End result of this phase is 2 molecules of glyceraldehyde phosphate (3 C each) for each glucose molecule.

Glycolysis: Energy – Yielding Phase two 3 carbon intermediaries (PGAL) are oxidized becoming pyruvate. there’s a net gain of 2 ATPs by substrate phosphorylation 2 molecules of NAD+ are reduced to NADH

Glycolysis The products are: Breaks down “Glucose” (6-carbon sugar) into 2 molecules of “Pyruvic Acid” (3-carbon compound) The products are: 2 Pyruvic Acid molecules 2 ATP molecules 2 NADH molecules

Glycolysis has 2 pathways… If Oxygen is present (Aerobic) ...“Krebs Cycle”… then to Electron Transport Chain If Oxygen is absent (Anaerobic) …….. “Fermentation”occurs

KREBS Cycle (per pyruvate) Takes place in mitochondrial matrix. Pyruvate combines with CoA (coenzyme A) to make acetyl CoA. This makes 1 NADH and 1 CO2. Acetyl CoA combines with OAA to form citric acid. (8 steps yielding intermediate products). 3 NADH and 1 FADH2 are made and CO2 released. 1 ATP is made. How much total ATP then for the Krebs cycle?

Junction between gly- colysis and Krebs Cycle Is the oxidation of Pyru- vate to acetyl CoA. - CO2 is removed from the carboxyl group of pyruvate changing it from a 3 carbon to a 2 carbon compound. CO2 is released. 2 NADH molecules are produced Coenzyme A attaches to the acetyl group – very unstable-reactive

KREBS CYCLE (Aerobic Pathway) Krebs Cycle oxidizes the remaining acetyl fragments of Acetyl – CoA to CO2. Energy released from this exergonic process is used to reduce co – enzymes, NAD and FAD, and phosphory – late ATP. How many ATPs are produced here? 2 NADH molecules are produced Coenzyme A attaches to the acetyl group – very unstable-reactive

ETC (Oxidative Phosphorylation) Takes place in inner mitochondrial membrane Involves a passing of electrons through a series of membrane associated electron carriers in the mitochondria to ultimately produce ATP You shuffle electrons to pump protons across the mitochondiral membrane against a concentration gradient to help establish a proton gradient

The ETC transports electrons from NADH and FADH2 along a transport chain The respiratory chain is composed of 4 enzyme complexes and carriers called cytochrome c and ubiquinone (Q). The 1st two complexes shuttle the electrons of NADH + H+ and FADH2 to Q. The third complex moves electrons from Q to chytochrome c. The final complex passes electrons to O2, an ultimate acceptor, which results in H20 as a by-product

The chain is an energy converter that pumps H+ across the membrane. How? Certain members along the electron transport chain accept and release protons along with electrons. A gradient is created that is referred to as the proton-motive force Now this H+ has the capacity to do work

The electron transport chain made no ATP directly, but it did ease the fall of electrons from food to oxygen So now, by chemiosmosis, it will couple this electron transport and energy release to ATP Synthase ATP Synthase is an enzyme that catalyses ATP from ADP and an inorganic phosphate Each NADH produces 3 ATP Each FADH produces 2 ATP

To summarize, for each glucose molecule… Glycolysis makes 2 NET ATP and 2 NADH and 2 pyruvate 2 acetyl CoA = 2 NADH Krebs Cycle: 6 NADH, 2 FADH2, 2 ATP Since each NADH produces 3 ATP during oxidative phosphorylation and each FADH2 produces 2 ATP…how many ATP total?

Wait…but what if there is no oxygen? What will be affected? Well now there is no electron acceptor to accept electrons at the end of the ETC. NADH will accumulate. Once all NAD+ has been made to NADH, Krebs and glycolysis will eventually stop. We have to free NAD+ to allow glycolysis to continue! We must release some NAD+ for use by glycolysis

FERMENTATION (Aanerobic Pathway) Alcoholic : Yeast & other microorganisms use this to produce alcohol & CO2 as wastes. Beer is a beverage made by alcoholic fermentation 2 TYPES: Alcoholic & Lactic Acid

Alcoholic Fermentation Commonly done by yeast in an anaerobic environment. 1) Glycolysis is done as normal. And then, to regenerate the NAD+… 2) Pyruvate  acetaldehyde 3) Acetaldehyde ethanol…the energy in NADH is used to drive this reaction and this will release NAD+. For each acetaldehyde, 1 ethanol is made and 1 NAD+ is produced. Now we have made 2 ATP from glyocolysis for each 2 converted pyruvate

Or…we can do Lactic Acid Fermentation (Aanerobic Pathway) Lactic Acid: Exercise causes the body needs more oxygen for respiration to make more ATP Body resorts to lactic acid fermentation to make ATP Lactic Acid is also produced causing burning sensation in muscles

Lactic Acid Fermentation Commonly done by: Muscle cells during oxygen debt. Same thing as before: - do glycolysis - but then to regenerate NAD+, a byproduct called lactate is made instead of acetylaldehydeethanol.

Diagram Assignment You will diagram the major pathways to respiration in color in a way that is understandable to you. Use websites and the book to help you form diagrams for each section of respiration. It must be in color, complete, and have words on it to describe what is happening in the process for full credit. Also must have an input/output chart by each stage: glycolysis, krebs, + ETC