Cellular Respiration: ATP Production and Energy Release

Posted on Feb 7, 2025 in Biology

Cell Respiration: ATP Production and Energy Release

Cell respiration is the controlled release of energy from organic compounds to produce ATP.

Organic compounds from the food we eat, such as glucose, contain stored energy within their covalent bonds.
All living organisms carry out cell respiration in order to convert stored energy into a form that can be used by the cell.
When organic molecules are broken down, the energy released is eventually stored in a high-energy molecule called ATP.
Cell respiration is the controlled release of energy from organic compounds in cells to produce ATP.

ATP from cell respiration is immediately available as a source of energy in the cell.

Energy for all types of cellular processes is immediately supplied by ATP.
The main types of cellular activity include synthesizing large molecules (e.g., DNA, RNA, and protein), pumping ions across membranes by active transport, and moving things around the cell, such as vesicles and chromosomes. Muscle contractions also use ATP.
Energy is released by splitting ATP into ADP + Pi (inorganic phosphate).

Anaerobic cell respiration yields a small amount of ATP from glucose.

Glucose (6C) is broken down into two pyruvate molecules (3C) in the cytoplasm by the process of glycolysis.
There is a net gain of 2 ATP molecules.
Glycolysis does not require oxygen.
Anaerobic respiration (without oxygen) occurs in the cytoplasm.
During glycolysis, glucose is converted into pyruvate with a net gain of 2 ATP.
After glucose is converted to pyruvate, if no oxygen is available, pyruvate is further converted into lactate or ethanol, depending on the organism.
When no oxygen is available, humans convert pyruvate into lactate (lactic acid) with no further gain of ATP.
No CO₂ is produced because, like pyruvate, lactate is also a 3-carbon molecule.
In yeast and plants, pyruvate is converted into ethanol (2C) and carbon dioxide with no further yield of ATP.
Ethanol and CO₂ are excreted as waste products.

Anaerobic cell respiration in yeasts is used to produce ethanol and carbon dioxide in baking.

Lactate production occurs in humans when anaerobic respiration is used to maximize the power of muscle contractions.

Aerobic cell respiration requires oxygen and yields a large amount of ATP from glucose.

Aerobic respiration also begins with glycolysis, which produces 2 pyruvate molecules per glucose.
Aerobic respiration occurs in the mitochondria.
Aerobic respiration is much more efficient than anaerobic respiration, as the glucose molecule is fully oxidized.
The products created in the redox reactions of the Krebs cycle, plus oxygen (the terminal electron acceptor), produce large quantities of ATP through oxidative phosphorylation (phosphate added to ADP to form ATP) in the electron transport chain (ETC), with water being released.
Overall, in aerobic respiration, glucose + oxygen produces carbon dioxide + water with a large yield of ATP.
About 32-34 molecules of ATP are produced by aerobic respiration, whereas, in anaerobic respiration, only 2 ATP molecules are produced.