● Tens and thousands of chemical compounds in a `color{violet}("living organism,")` otherwise called `color{brown}("metabolites, or biomolecules,")` are present at concentrations characteristic of each of them.

● For example, the `color{violet}("blood concentration of glucose")` in a normal healthy individual is `color{brown}("4.5-5.0 mM,")` while that of hormones would be `color{brown}("nanograms/ mL.")`

● The most important fact of `color{violet}("biological systems")` is that all `color{violet}("living organisms")` exist in a `color{brown}("steady-state")` characterised by concentrations of each of these `color{brown}("biomolecules.")`

● These `color{violet}("biomolecules")` are in a `color{brown}("metabolic flux.")`

● Any chemical or physical process moves spontaneously to `color{brown}("equilibrium.")`

● The steady state is a `color{brown}("non-equilibirium state.")`

● One should remember from physics that `color{violet}("systems at equilibrium")` cannot perform work.

● As `color{violet}(" living organisms")` work continuously, they cannot afford to reach `color{violet}("equilibrium.")`

● `color{brown}("Hence the living state is a non-equilibrium steady-state to be able to perform work;")`

● `color{violet}("Living process")` is a constant effort to prevent falling into equilibrium.

● This is achieved by `color{brown}("energy input.")`

● `color{violet}("Metabolism")` provides a mechanism for the `color{violet}("production of energy. ")`

● Hence the `color{brown}("living state and metabolism")` are `color{violet}("synonymous. ")`

● Without `color{violet}("metabolism")` there cannot be a `color{violet}("living state.")`

● Almost all `color{violet}("enzymes")` are `color{brown}("proteins.")`

● There are some `color{violet}("nucleic acids")` that behave like `color{violet}("enzymes.")` These are called `color{brown}("ribozymes.")`

● One can depict an enzyme by a `color{violet}("line diagram.")`

● An enzyme like any protein has a `color{brown}("primary structure,")` i.e., `color{violet}("amino acid")` sequence of the `color{violet}("protein.")`

● An `color{violet}("enzyme")` like any protein has the `color{brown}("secondary")` and the `color{brown}("tertiary structure.")`

● Looking at a `color{violet}("tertiary structure")` one will notice that the backbone of the `color{violet}("protein chain")` folds upon itself, the chain criss-crosses itself and hence, many `color{brown}("crevices or pockets")` are made.

● One such pocket is the `color{brown}("‘active site’.")`

● An active site of an enzyme is a crevice or pocket into which the `color[brown}("substrate fits.")`

● Thus enzymes, through their active site, `color{brown}("catalyse reactions")` at a high rate.

● `color{violet}("Enzyme catalysts")` differ from `color{violet}("inorganic catalysts")` in many ways, but one major difference needs mention.

● `color{violet}("Inorganic catalysts")` work efficiently at `color{brown}("high temperatures and high pressures")`, while enzymes get damaged at high temperatures (say above `"40°C"`).

● However, `color{violet}("enzymes isolated")` from organisms who normally live under extremely high temperatures (e.g., hot vents and `color{brown}("Sulphur springs")` ), are stable and retain their `color{violet}("catalytic power ")` even at high temperatures (upto `color{brown}("80°-90°C")` ).

● `color{brown}("Thermal stability")` is thus an important quality of such enzymes isolated from `color{brown}("thermophilic organisms.")`