Adenosine triphosphate (ATP) has physical properties such as Adenine and Ribose PP. It is useful because it releases energy in small, usable amounts, thus reducing energy waste as heat. A single hydrolysis reaction is involved in releasing energy, which means one bond is broken. ATP can be quickly reformed from ADP + Pi. It phosphorylates other molecules to make them more reactive, and it cannot pass out of the cell, hence providing the cell with an immediate energy supply.
Aerobic respiration, which occurs in the presence of oxygen, involves the following steps:
- Glucose + oxygen -> carbon dioxide + water + ATP
- Triose phosphate (3C) is produced, with each triose phosphate oxidized to pyruvate
- A hydrogen reduces the coenzyme NAD to NADH
- 2 ATP molecules are produced for each triose phosphate oxidized
- Krebs Cycle occurs in the matrix and involves several steps, including the oxidation of a 6C molecule into a 5C molecule and then back to a 4C molecule, with the production of CO2 and 2 ATP molecules
- The Link Reaction takes place in the matrix, where pyruvate is oxidized to acetate, releasing a hydrogen to produce acetyl coenzyme A
- Oxidative Phosphorylation takes place on the inner membrane of the mitochondria, where reduced NAD and FAD are oxidized, releasing energy to form ATP
In the absence of oxygen, the link reaction, Krebs cycle, and oxidative phosphorylation stop. To regenerate NAD and continue glycolysis, reduced NAD is oxidized and the released hydrogen reduces pyruvate to form lactic acid in animals or ethanol + carbon dioxide in plants, fungi, and yeast. Oxygen is then used to oxidize the lactic acid back to pyruvate, allowing for the continuation of aerobic respiration to form more ATP.
Aerobic respiration requires oxygen, produces 38 ATP per glucose, and uses the link reaction, Krebs cycle, and oxidative phosphorylation. It occurs in the cytoplasm and mitochondria and produces CO2. NAD is regenerated by oxidizing NADH at the electron transfer chain.
Anaerobic respiration does not require oxygen, produces 2 ATP per glucose, and only uses glycolysis. It occurs in the cytoplasm, produces CO2 in the form of lactic acid in animals or ethanol + carbon dioxide in plants, fungi, and yeast. NAD is regenerated by oxidizing reduced NAD to continue glycolysis.
The rate of respiration in yeast can be measured using a gas syringe to measure the volume of CO2 produced in a certain time.
Lipids are hydrolyzed to fatty acids and glycerol. Glycerol is phosphorylated and converted to triose phosphate to enter glycolysis. Fatty acids are hydrolyzed into 2C fragments and are converted to acetyl coenzyme A to enter the Krebs cycle. The oxidation of these lipid products yields many reduced NAD and FAD molecules that can be fed into the electron transport chain to produce large amounts of ATP.
Proteins are hydrolyzed into amino acids. The amine group is removed from the amino acids (deamination) and the products enter respiration at different points, with 3C molecules being converted to pyruvate.
In summary, ATP possesses physical properties such as Adenine and Ribose PP, and its importance lies in the fact that it releases energy in small, usable amounts. Aerobic respiration, which occurs in the presence of oxygen, involves various steps including glycolysis, Krebs cycle, and oxidative phosphorylation. Anaerobic respiration occurs in the absence of oxygen and regenerates NAD to continue glycolysis. Lipids and proteins can also be used as sources for respiration, yielding large amounts of ATP. Various methods can be used to measure the rates of respiration, and the respiration of lipids and proteins follows different pathways in comparison to carbohydrates.
