The building blocks of life

The "Building Blocks of Life" refer to the fundamental molecules and processes that make up all living organisms. A key concept is that the variety of life, both past and present, is extensive, but the biochemical basis of life is remarkably similar for all living things, suggesting a common ancestor.

• Essential Elements

  • Life on Earth is carbon-based.

  • The four most abundant elements in living organisms are carbon, hydrogen, oxygen, and nitrogen, which together account for over 99% of the atoms found in all living things.

  • Carbon is particularly vital because its atoms can join together to form long chains or ring structures. These carbon structures act as the fundamental skeletons of organic molecules. All organic molecules inherently contain carbon and hydrogen.

• Chemical Evolution and Biological Molecules

  • It is believed that, before life evolved, there was a period of chemical evolution where simple carbon-based biological molecules originated from even simpler molecules that existed on the early Earth.

  • These relatively simple biological molecules serve as the building blocks for the larger, more complex biological molecules necessary for life.

  • The close relationship between the structure of molecules and their functions is a striking principle in molecular biology.

• Monomers, Polymers, and Macromolecules

  • Monomers are small, basic molecular units from which larger molecules are constructed. Many monomers are joined together by covalent bonds.

  • Polymers are large, complex molecules formed when a large number of monomers are joined together.

  • Macromolecules are giant molecules. Many biological polymers are macromolecules.

  • The three main types of macromolecules in living organisms are polysaccharides, proteins (also called polypeptides), and nucleic acids (also called polynucleotides).

  • Lipids are also key biological molecules but are not polymers.

• Formation and Breakdown of Polymers

  • Most biological polymers are formed from their monomers by condensation reactions. A condensation reaction joins two molecules together, forming a chemical bond and eliminating a molecule of water.

  • Biological polymers can be broken down into monomers by hydrolysis reactions. A hydrolysis reaction breaks the chemical bond between monomers by using a water molecule, effectively being the opposite of a condensation reaction.

• Specific Examples of Building Blocks

  • Monosaccharides (e.g., glucose) are the monomers of carbohydrates, which form polysaccharides like starch, glycogen, and cellulose.

  • Amino acids are the monomers of proteins. A condensation reaction between two amino acids forms a peptide bond. Proteins can be made of one or more polypeptide chains.

  • Nucleotides are the monomers that make up DNA and RNA. A condensation reaction between two nucleotides forms a phosphodiester bond.

  • Lipids include triglycerides (formed from glycerol and three fatty acids) and phospholipids (glycerol, two fatty acids, and a phosphate group). A condensation reaction between glycerol and a fatty acid forms an ester bond. Triglycerides are non-polar hydrophobic molecules.