Biomolecules in the Cell

From Cells to Biomolecules

Life on Earth spans an enormous range of forms -- from unicellular organisms such as bacteria and yeast to complex multicellular plants and animals -- yet every one of them is built from cells as their basic structural and functional unit. Inside every cell sits the protoplasm, a living substance packed with a huge variety of chemical compounds. These chemical compounds of living systems are collectively called biomolecules, and the branch of biology that studies them -- the chemical composition of cells and the reactions and molecular changes taking place inside plants, animals and micro-organisms -- is called biochemistry. Biochemistry underlies our understanding of nearly every biological process: how cells communicate with one another, the chemical basis of inheritance, and how disease arises at the molecular level.

When the tissue of any living organism is chemically analysed, the same handful of elements shows up again and again, each present in a characteristic proportion per unit mass of tissue:

• Prime elements (drawn mainly from air and water): Carbon (C), Hydrogen (H), Oxygen (O)
• Macro elements (needed in comparatively larger amounts): Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), Sulfur (S)
• Trace elements (needed only in minute amounts): Boron (B), Chlorine (Cl), Zinc (Zn), Copper (Cu), Iron (Fe), Sodium (Na), Molybdenum (Mo), Nickel (Ni), Silicon (Si), Cobalt (Co)

Building Blocks: Monomers and Macromolecules

Chemically, every living organism is built around three basic classes of macromolecules, each a polymer assembled by linking together many small repeating subunits, or monomers:

• Polysaccharides (carbohydrates) -- polymers of monosaccharides
• Polypeptides (proteins) -- polymers of amino acids
• Polynucleotides (nucleic acids) -- polymers of nucleotides

Alongside these three macromolecule classes, cells also contain lipids -- compounds that are water-insoluble and of comparatively small molecular weight next to the true macromolecules -- and secondary metabolites (alkaloids, phenolics, terpenoids, essential oils, toxins, lectins and more), which are not required for basic growth but play specialised roles, particularly in plants. Taken together, biomolecules are classed as organic (carbon-based -- the macromolecules and smaller "micromolecules" like lipids) or inorganic (the mineral elements listed above).

Biomolecules in the Cell …