Question

Water is the most abundant molecule in the body, but it is not a biomolecule. Neither are    carbon dioxide, ethanol, or methane. Review the definition of a biomolecule and the structure of these biomolecules compared to glucose and alanine, and explain why glucose and alanine are important and common molecules are not biomolecules.

Answer 1

By definition, a biomolecule is that which is synthesized by a living organism. So, water, carbondioxide are external sources using which living organisms synthesize biomolecules to meet their energy requirements.

Living plants fix atmospheric carbon dioxide during photosynthesis in their leaves where 6 molecules of carbon dioxide with 6 molecules of water gets converted to glucose, a 6 carbon compound and 6 molecules of oxygen. Here, the water and carbon dioxide are the sources using which the plant is able to synthesize its own food, glucose. Therefore, glucose is a biomolecule whereas carbondioxide and water are not.

During respiration, this glucose is then broken down by the process of glycolysis to give rise to pyruvic acid, which is the source for the synthesis of Alanine. alanine is synthesized from pyruvic acid throuogh the enzyme aminotransferase, where an amino group is added to pyruvate. The amino and methyl groups are acquired externally for the synthesis of pyruvate, so methane and ammonia are not biomolecules, whereas alanine is a biomolecule as it is not only used as a building block for protein synthesis, along with other amino acids , but also as a molecule involved in stress signaling.