ABSTRACT
A cell is the basic unit of any living being. Within a biological cell, there are tens of thousands of different biochemical species that interact in a highly organized manner. A cell looks like a “molecular ecosystem.” Within this “microscopic ecosystem,” proteins play essential roles. They are involved in metabolic processes, sensing functions, signaling, and epigenetic events. Proteins are dynamic soft polymers, made of semi-rigid domains and subunits. They exist as complex statistical ensembles of conformers, and they unfold and fold continuously in localized regions by adapting to their local microenvironment. There are even proteins or regions of proteins that are structurally disordered in their functional state. The interaction of a protein with a substrate can be described by either the Michaelis-Menten or the Hill model. The Hill model regards allosteric proteins that are characterized by nonlinear responses, such as positive and negative feedback actions. Allosteric proteins can originate bistability and oscillations. Biochemical oscillations are responsible for the biological ultradian, circadian, and infradian rhythms.
