(N/A) $\rightarrow$ Almost all enzymes are proteins.
$\rightarrow$ There are some nucleic acids that behave like enzymes. These are called ribozymes.
$\rightarrow$ An enzyme can be depicted by a linear diagram. An enzyme,like any protein,has a primary structure,i.e.,the amino acid sequence of the protein.
$\rightarrow$ An enzyme,like any protein,has secondary and tertiary structures. The backbone of the protein chain folds upon itself,the chain criss-crosses itself,and hence,many crevices or pockets are formed.
$\rightarrow$ One such pocket is the 'active site'. An active site of an enzyme is a crevice or pocket into which the substrate fits.
Thus,enzymes,through their active site,catalyse reactions at a higher rate.
$\rightarrow$ Enzyme catalysts differ from inorganic catalysts in many ways. One major difference is that inorganic catalysts work efficiently at high temperatures and high pressures,while enzymes get damaged at high temperatures (above $40^{\circ}C$).
$\rightarrow$ Enzymes isolated from thermophilic organisms that live under extremely high temperatures (e.g.,hot vents and sulphur springs,etc.) are stable and retain their catalytic power at high $(80^{\circ}-90^{\circ}C)$ temperatures. Thermal stability is thus an important quality of such enzymes isolated from thermophilic organisms.