Cellular Respiration Process

• Cellular respiration breaks down nutrient molecules and produces ATP.
• Cellular respiration consumes oxygen and produces carbon dioxide.
• The process usually involves the breakdown of glucose to CO₂ and H₂O, with the production of ATP.
• Cellular respiration requires oxygen and gives off CO2.
• Step-by-step breakdown of glucose produces 36 or 38 ATP molecules, which is 39% of the energy in glucose.
• NAD+ and FAD are redox coenzymes.
• NAD+ + 2H+ + 2e- becomes NADH+H
• FAD +2H+ + 2e- becomes FADH₂
• O₂ and glucose enter cells, which releases H₂O and CO₂.
• Mitochondria use energy from glucose to form ATP from ADP and P.

Four Phases of Cellular Respiration:

• Glycolysis occurs in the cytoplasm, with or without O₂ where glucose becomes 2 pyruvate + 2NADH + 2ATP.
• Preparatory reaction occurs in the matrix of mitochondria where 2 pyruvate is oxidized into 2 Acetyl-CoA group + 2NADH + 2CO₂.
• Citric acid cycle occurs in the mitochondrial matrix where 6 NADH+ 2 FADH₂ + 4 CO₂ + 2ATP become 2 Acetyl-CoA.
• Electron transport system occurs in the inner membrane where carriers accept e- from NADH and FADHS and transport them to O₂+H becoming H₂O, and produces 32-34 ATP.
• Four phases of cellular respiration include
• Glycolysis where glucose becomes pyruvate
• A transition reaction
• The citric acid cycle
• The electron transport system and chemiosmosis.

Glycolysis:

• Glycolysis takes place in the cytoplasm.
• One glucose molecule breaks down into 2 pyruvate molecules.
• The first step, the energy investment step, involves 2 ATP activating glucose: Glucose (C6) + 2 ATP becomes 2C₃ (G3P).
• Each C₃ undergoes the same series of reactions.
• In the energy harvesting steps, e- are removed from G3P and picked up by NAD+, resulting in NADH which transports e- to e chain.
• In Substrate-level phosphorylation 4 ATP are produced as P passes to ADP becoming ATP.

Substrate-Level ATP Synthesis:

• BPG uses an enzyme and with ADP forms ATP and 3PG
• Glycolysis has an energy-investment step and energy-harvesting steps.
• Two ATP are used to get started in the energy investment step.
• Splitting produces two 3-carbon molecules.
• Oxidation of G3P occurs as NAD+ receives high-energy electrons.
• Substrate-level ATP synthesis.
• Oxidation of 3PG occurs by removal of water.
• Two molecules of pyruvate are the end products of glycolysis.
• Glycolysis inputs 6C glucose and 2 NAD+ which produces outputs of 2 (3C) pyruvate, 2NADH, 2 ADP, and 4 ADP+4P= 2ATP (net gain).

The Mitochondria:

• Has two membranes with an intermembrane space.
• Cristae are folds of the inner membrane.
• Transition reaction and citric acid cycle enzymes are in the matrix.
• The e transport system is in the cristae.
• Most ATP is produced within mitochondria.
• The transition (prep) phase in mitochondria connects glycolysis to the citric acid cycle.
• The end product of glycolysis, pyruvate, enters the mitochondrial matrix.
• Pyruvate is converted to a 2-carbon acetyl group which attaches to Coenzyme A to form acetyl-CoA.
• Electrons are picked up as hydrogen atom by NAD+.
• CO₂ is released and transported out of mitochondria into the cytoplasm.
• During the preparatory reaction, pyruvate loses CO₂, converting to acetyl that attaches to Coenzyme A to form acetyl-CoA.
• Electrons are picked up by NAD+.

Citric Acid Cycle:

• Krebs Cycle occurs in the matrix of mitochondria.
• Begins adding a two-carbon acetyl group (from acetyl-CoA) to a four-carbon molecule (oxaloacetate), forming a six-carbon molecule (citric acid).
• NADH and FADH₂ capture energy rich electrons.
• ATP is formed by substrate-level phosphorylation.
• Turns twice for one glucose molecule (once for each pyruvate).
• Produces 4 CO₂, 2 ATP, 6 NADH and 2 FADH₂ per glucose molecule.
• The citric acid cycle begins when a C₂ acetyl group carried by CoA combines with a C4 molecule to form citrate.
• Twice over, substrates are oxidized as NAD+ is reduced to NADH, and CO₂ is released.
• ATP is produced as an energized phosphate is transferred from a substrate to ADP.
• Inputs include 2 (2c) acetyl groups. Output is 4 CO₂.
• Includes 6 NAD+ and 6 NADH.
• Includes 2 FAD and 2 FADH₂.
• Includes 2 ADP +2 P, with 2ATP.
• Summarized, there are 2 NADH , 2 ATP , 6 NADH ,2 ATP, and total 32,34 ATP

Electron Transport Chain (ETC):

• Eukaryotes are located in the cristae of the mitochondria
• Aerobic prokaryotes are located in the plasma membrane
• ETC consists of a series of carrier molecules
• The chain Passes energy-rich electrons successively from one to another
• The chain Contains complex arrays of protein and cytochrome (Proteins with heme groups with central iron atoms)
• The ETC receives electrons from NADH and FADH2 and produces ATP by oxidative phosphorylation Oxygen is the final electron acceptor, and combines with hydrogen ions to form water
• Three protein complexes = NADH-Q reductase complex, cytochrome reductase complex, and cytochrome oxidase complex.
• Pumps H from matrix (intermembrane space, cytochrome c).
• Also consists of 2 electron carrier molecules that transport e between complexes = Coenzyme Q.
• High E electrons carried by NADH and FADH2 enter ETC, and low E electrons leave it.
• The complexes use the energy released to pump protons from matrix to intermembrane space against their concentration gradient.
• H+ becomes more concentrated in the intermembrane space, creating an electrochemical gradient.
• ATP synthase allows H+ to flow down its gradient, which drives the synthesis of ATP from ADP and inorganic phosphate by ATP synthase.

Energy Yield from Glucose Metabolism:

• 2 net ATP result from glucose becoming 2 pyruvate in Glycolysis
• Two NADH from Glycolysis leads on to 4 or 6 ATP in electron train transport
• Glucose results in 2 Net ATP in Glycolysis, two NADH and further along process
• 2 NADH, 2 Acetyl, 2CO2 , 6 NADH,2 ATP, 2 FADH2, H+

Fermentation:

• Pyruvate is a pivotal metabolite in cellular respiration.
• If O₂ is absent, the cell will ferment, an anaerobic process in the cytoplasm.
• Glucose is incompletely metabolized either to:
• Lactatic acid fermentation (e.g.:lactic-acid bacteria and some animal cells)
• Alcoholic fermentation: alcohol and CO₂ (e.g.: yeast).
• Fermentation advantages include providing a quick burst of ATP, which is low but rapid, and regeneration of NAD+.
• Disadvantages are alcohol and lactate are toxic.
• Lactate causes changes in pH and fatigue in muscles.
• Other issues include oxygen debt and yeast die off
• Fermentation takes Glucose inputs resulting in 2 ATP, 2 ADP + 2 P = 2 lactate or 2 alcohol and 2 COO₂.

Metabolic Reactions:

• Catabolism involves Degradative reactions, is exergonic, and catabolism produces molecules that can be used for anabolism of other compounds.
• Anabolism involves Synthetic reactions, is endergonic.
• Both catabolism and anabolism utilize the same pools of metabolites.
• The metabolic pool concept includes amino acids creating proteins, glucose creating carbohydrates and glycerol and fatty acids creating fats. Excess CHO results in formation of fat, and Extra G3P is converted to glycerol and FA.