1. Cellular Respiration
7.3
Aerobic Respiration

2. 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)

4. Aerobic cellular respiration: Overview

5. 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.

7. 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)

8. 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.

10. 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

11. 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

13. 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

14. 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

16. 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

18. 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

20. 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