7.2 Glycolysis

1. 7.2 Glycolysis

2. Glycolysis • Process for harnessing energy in which a glucose molecule is broken into pyruvate molecule in the cytoplasm of a cell • The carbon backbone of glucose is essentially split in half • 6 carbon 2 3-carbon • Although it occurs in both types of cellular respiration, glycolysis itself is an anerobic process (it does not require O2)

3. Stage 1: Glycolysis • No oxygen required • Thus it is the first step for both aerobic and anaerobic respiration • Starts with glucose (6-carbon sugar) • 2 ATP molecules are used in the first stages of glycolysis (“investment phase”) • 2 NAD+ removes H+ ions and forms 2 NADH • Later enough energy is released to form 4 ATP, which will be available to be used in cellular functions • Glycolysis produces TWO 3-carbon pyruvate molecules • Net production of 2 ATP

4. Glycolysis

5. Glycolysis • Relatively inefficient • Only transfers about 2.2% of free energy available in glucose to ATP • Some released as heat, but remainder tied up in pyruvate and 2 NADH molecules • NOTE: the 2 NADH molecules produced are eventually converted into 2 FADH2 molecules BEFORE they are transferred to the ETC • glycolysis

6. Glycolysis Review: Reactants: 1 Glucose 4 ADP 4 Pi 2 ATP 2 NAD+ 2 H+ Products: 2 Pyruvate 4 ATP (therefore, net gain of 2 ATP) 2 ADP 2 NADH

7. Cellular Respiration 7.3 Aerobic Respiration

8. Stages Aerobic Respiration • Stage 1: Glycolysis • Stage 2: Pyruvate Oxidation • Stage 3: Krebs Cycle • Stage 4: Electron Transport Chain and Chemiosmosis • Glycolysis occurs in cytoplasm • Stage 2 – 4 occurs in mitochondria- possess double membrane: outer membrane as well as an inner membrane (highly folded)- intermembrane space between both membranes (fluid filled)- inner membrane contains mitochondrial matrix (protein-rich liquid that fills interior)

10. Aerobic cellular respiration: Overview

11. Aerobic respiration: An overview A series of enzyme controlled reactions • Oxygen is used to oxidize glucose • Glucose is oxidized to form carbon dioxide • Oxygen is reduced to form water During the oxidation of glucose: • Electrons transferred to electron carriers, NAD+ and FAD+ • Glycolysis and Kreb’s cycle • Electrons then passed through an electron transport chain. • The energy from the electrons will be used to pump protons. • The energy from the diffusion of protons will be used to make ATP.

13. Stage 2: Pyruvate Oxidation • Recall: reactions of glycolysis produced TWO pyruvates, TWO ATP’s, and 2 NADH’s- does not require O2 ; occurs in cytoplasm • Pyruvate Oxidation: chemical pathway that connects glycolysis to Krebs cycle • 2 pyruvate molecules are moved from the cytoplasm to the matrix of the mitochondria • CO2 is removed from each pyruvate molecule and released as a waste product (1/3 of what you exhale)

14. Stage 2: Pyruvate Oxidation Cont. • The remaining 2-carbon portions are oxidized by NAD+; As a result, the NAD+ molecule gains two hydrogen atoms and the remaining 2-carbon molecule becomes acetic acid • Coenzyme A (Co-A) attaches and forms acetyl-CoA • Acetyl-coA enters stage 3 (Krebs cycle) and NADH goes to stage 4 (ETC) • 2 CO2 diffuses out of the mitochondria and cell.

16. Stage 3: Krebs Cycle • This is an 8 step and cyclic stage • cyclic because one of the products of step 8, is a reactant in step 1 • At the end of the Krebs Cycle, all six carbons have been oxidized to CO2 and released from the cell as metabolic waste • All that remains is some free energy in the form of ATP and high energy NADH and FADH2 • These energy carriers enter the ETC

17. Krebs Cycle: The Details • Cycle occurs twice for each acetyl-CoA molecule • Acetyl CoA adds 2-carbons to oxaloacetate, producing citrate • Citrate loses a CO2 molecule, and the resulting compound is oxidized, reducing NAD+ to NADH • Another CO2 is lost, and the resulting compound is oxidized, reducing NAD+ to NADH • ADP is phosphorylated to ATP • Two hydrogen's are transferred to FAD+ to form FADH2 Kreb Cycle

19. Krebs Cycle Overview 1 Glucose= 2 ATP 6 NADH 2 FADH2 4 CO2 EACH pyruvate molecule produced in glycolysis (2) must enter the Krebs Cycle Therefore the cycle occurs twice for every glucose molecule

20. Stage 4: ETC • NADH and FADH2: release the electrons they received during glycolysis and the Kreb’s cycle to ETC- proteins of the ETC transfer the electrons and use the energy released to pump hydrogen ions (protons) • Hydrogen ions (protons) are pumped from the matrix to the intermembrane space • Creates a concentration gradient

22. Stage 4: ETC Cont. • Oxygen: final electron acceptor at the end of the ETC- oxygen accepts the electrons, combines with protons and become water • The accumulated hydrogen ions (protons) diffuse back into the matrix through ATP synthase complex- The energy released from the diffusion fuels the formation of ATP (by pumping H+ ions into intermembrane space) • ETC: an ongoing process- NADH delivers electrons continuously- FADH2 delivers lower energy electrons in different place than NADH (cannot pump as many H+ ions) • Electron Transport Chain animation • Electron Transport Chain • Electron Transport Chain

24. Stage 4 Cont: Chemiosmosis • H+ ions accumulate in intermembrane space from ETC- creates an electrochemical gradient • H+ ions (protons) move from intermembrane space to ATP synthase complex- energy in gradient forces them through • Energy released as H+ ions pass through = binds ADP with Pi to produce ATP! • Energy removed from 1 NADH = 3 ATP’s; 1 FADH2 = 2 ATP’s Oxidative phosphorylation: Because the energy needed to add the Pi group to ADP is derived from the oxidation of a glucose molecule aka oxidative ATP synthesis

26. Final Points… • ATP is now sent to the cytoplasm to be utilized by the cell • All stages are dependent on glycolysis for the production of pyruvate • Last stages are dependent on the availability of electrons (from food– glucose) and oxygen