Ch 9: Respiration

1. Ch 9: Respiration

2. The Big Picture • Cellular respiration has the sole purpose to produce ATP. • Its an exergonic reaction. • Can be summarized as a whole as: Glucose + Oxygen CO2 + Water+ ATP

3. Reminder on ATP • ATP (adenosine triphosphate) is a nucleotide with unstable phosphate bonds that the cell hydrolyzes for energy. • Cells use ATP to continue cellular work. But they must replenish the ATP supply to continue cellular work. Respiration does this.

5. Redox reactions • These are the energy-shuttling mechansisms of metabolism • Gain a Proton or Electron=reduction • Loss of an Electron=oxidation • LEO GER • They are always coupled…so in order for a material to lose an electron, another molecule must accept it

6. The NAD+, NADH, FAD+, FADH • NAD+ and FAD+ are coenzymes that functions in the redox reactions and is found in all cells. • It traps energy-rich electrons from glucose or food. • NAD+= oxidized coenzyme (lost an electron) • NADH= reduced coenzyme (gained a proton)

7. Why glucose? C6H12O6 • It’s the energy source used most often by living organisms. • Keep in mind that fats and proteins could also be considered but glucose is the “hallmark” molecule to use in cellular respiration

8. Respiration is divided into three parts: Glycolysis, Krebs Cycle, and Oxidative Phosphorylation • 1. Glycolysis is the decomposition of glucose to pyruvate (or pyruvic acid). • 2. Krebs Cycle (oxidative phosphorylation) takes pyruvate (1 pyruvate) and yields electron acceptors and ATP. • 3. ETC (Oxidative phosphorylation) extracts ATP from NADH and FADH2.

9. Glyclolysis (per glucose molecule) • Takes place in cytosol. • There are 9 intermediate steps is the process of decomposing glucose into pyruvate. Mg2+ ions are cofactors to help. • One molecule of glucose goes IN • 2 ATP go IN • 4 ATP PRODUCED (so what is NET?) • 2 NAD+ go IN • 2 NADH PRODUCED • 2 Pyruvate (Pyrivic acid) PRODUCED

10. KREBS Cycle (per pyruvate) • Takes place in mitochondrial matrix. • Pyruvate combines with CoA (coenzyme A) to make acetyl CoA. This makes 2 NADH and CO2. • Acetyl CoA combines with OAA to form citric acid…which is why Krebs can also be the Citric Acid Cycle. (7 intermediate products). 6 NADH and 2 FADH2 are made and CO2 released. 2 ATP is made. • How much total ATP then for Krebs?

11. 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

13. 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

14. That chain is an energy converter that pumped 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

15. http://www.sci.uidaho.edu/bionet/biol115/t4_energy/etc.htm

16. This 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 actually MAKES ATP from ADP and inorganic phosphate • Each NADH produces 3 ATP • Each FADH produces 2 ATP

18. To summarize… • Glycolysis makes 2 NET ATP and 2 NADH • 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?

19. In Reality… • It would appear we get 38 ATP. But we don’t in reality. This is because glycolysis only occurs in the cytoplasm and each NADH produced there must be transported into the mitochondria for oxidative phosphorylation. The transport of NADH across the mitochondrial matrix reduces the yield of these NADH in glycolysis to only 2 ATP. • That means in reality 36 ATP only.

20. 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

21. 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

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