Cellular Respiration and Fermentation
A catabolic process that is the partial degradation of sugars or other organic fuel that occurs without the use of oxygen -> Makes ATP.
The most efficient catabolic pathway in which oxygen is consumed as a reactant along with the organic fuel (aerobic is from the Greek aer, air, and bios, life) -> Makes ATP.
Cellular Respiration Diagram
glucose→NADH→electron transport chain→oxygen.
Electron transfer from NADH to oxygen is an exergonic reaction with a free-energy change of −53 kcal/mol(−222 kJ/mol). Instead of this energy being released and wasted in a single explosive step, electrons cascade down the chain from one carrier molecule to the next in a series of redox reactions, losing a small amount of energy with each step until they finally reach oxygen, the terminal electron acceptor, which has a very great affinity for electrons. Each “downhill” carrier has a greater affinity for electrons than, and is thus capable of accepting electrons from (oxidizing), its “uphill” neighbor, with O2 at the bottom of the chain. Therefore, the electrons transferred from glucose to NAD+, reducing it to NADH, fall down an energy gradient in the electron transport chain to a far more stable location in an electronegative oxygen atom from O2. Put another way, O2 pulls electrons down the chain in an energy-yielding tumble analogous to gravity pulling objects downhill.
Stages of Cellular Respiration
Glycolysis, which occurs in the cytosol, begins the degradation process by breaking glucose into two molecules of a compound called pyruvate. In eukaryotes, pyruvate enters the mitochondrion and is oxidized to a compound called acetyl CoA, which enters the citric acid cycle. There, the breakdown of glucose to carbon dioxide is completed. (In prokaryotes, these processes take place in the cytosol.) Thus, the carbon dioxide produced by respiration represents fragments of oxidized organic molecules.
Production of ATP using energy derived from the redox reactions of an electron transport chain; The third major stage of cellular respiration.
In eukaryotic cells, the inner membrane of the mitochondrion is the site of electron transport and another process called chemiosmosis, together making up oxidative phosphorylation. (In prokaryotes, these processes take place in the plasma membrane.) Oxidative phosphorylation accounts for almost 90% of the ATP generated by respiration.
A smaller amount of ATP is formed directly in a few reactions of glycolysis and the citric acid cycle by this mechanism.
How much ATP is typically made by cellular respiration?
Glycolysis can be divided into two phases: the energy investment phase and the energy payoff phase. During the energy investment phase, the cell actually spends ATP. This investment is repaid with interest during the energy payoff phase, when ATP is produced by substrate-level phosphorylation and NAD+ is reduced to NADH by electrons released from the oxidation of glucose. The net energy yield from glycolysis, per glucose molecule, is 2 ATP plus 2 NADH.
The Steps of Glycolysis