Cellular Respiration and Electron Transport PDF

Overview: The ETS is the final step in cellular respiration. It consists of protein complexes and mobile electron carriers. Process: Electrons from NADH and FADH2 are transferred through the ETS like a bucket brigade. Electrons move from carriers with lower redox potential...

Overview: The ETS is the final step in cellular respiration. It consists of protein complexes and mobile electron carriers. Process: Electrons from NADH and FADH2 are transferred through the ETS like a bucket brigade. Electrons move from carriers with lower redox potential to those with higher redox potential. Four main types of electron carriers: ○ Cytochromes ○ Flavoproteins ○ Iron-sulfur proteins ○ Quinones Aerobic Respiration: The final electron acceptor is oxygen (O2), which is converted to water (H2O). Cytochrome oxidase is the last carrier and varies among bacteria, helping in their identification (e.g., Pseudomonas aeruginosa vs. Vibrio cholerae). When Aerobic Respiration Isn't Possible: Lack of genes for the right cytochrome oxidase. Lack of genes to manage harmful oxygen radicals (like hydrogen peroxide). Insufficient oxygen availability. Alternative: Anaerobic Respiration Uses inorganic molecules (not oxygen) as final electron acceptors. Denitrifiers use nitrate (NO3-) and nitrite (NO2-) to produce nitrogen gas (N2). Some bacteria (like E. coli) can switch to using nitrate when oxygen is low. Electron Transfer and Energy Loss: ○ Electrons lose energy when transferred through the electron transport system (ETS). ○ Some energy is used to pump hydrogen ions (H+) across a membrane. Hydrogen Ion Pumping: ○ In prokaryotic cells: H+ is pumped outside the cytoplasmic membrane (periplasmic space). ○ In eukaryotic cells: H+ is pumped from the mitochondrial matrix to the intermembrane space. Electrochemical Gradient: ○ An uneven distribution of H+ creates an electrochemical gradient. ○ Higher H+ concentration on one side leads to a proton motive force (PMF).  ○ The side with more H+ is more acidic. Uses of Proton Motive Force: ○ PMF is used to make ATP and drive other processes like nutrient transport and flagella movement. Chemiosmosis: ○ H+ diffuses across membranes through a channel via ATP synthase. ○ This movement is similar to water flowing through a dam. ATP Synthase: ○ ATP synthase acts like a generator, turning as H+ flows through it. ○ In prokaryotes, H+ moves into the cytoplasm; in eukaryotes, it moves into the mitochondrial matrix. ○ This process regenerates ATP from ADP and inorganic phosphate (Pi) through oxidative phosphorylation. Key Points ETS: Electrons lose energy, pumping H+ across membranes. PMF: Created by uneven H+ distribution, used for ATP production and other functions. Chemiosmosis: H+ movement through ATP synthase generates ATP. ATP yield from glucose catabolism varies by species. In aerobic respiration: 1 NADH produces 3 ATP. 1 FADH2 produces 2 ATP. From 1 glucose: 10 NADH = 30 ATP. 2 FADH2 = 4 ATP. Theoretical maximum yield of ATP from 1 glucose: 38 ATP total. ○ 4 ATP from substrate-level phosphorylation. ○ 34 ATP from oxidative phosphorylation. Actual ATP yield typically ranges from 1 to 34 ATP. Energy is lost when transporting molecules into mitochondria, affecting yield.