What is enzyme?

Answer 1

EnzymesEnzymes are biological catalysts, mainly proteins, generated by an organism to speed up chemical reactions. They have an active site on which the substrate is attached, and then broken up or joined.

Contrary to the generally accepted belief, an enzyme is not necessarily a protein molecule (although an overwhelming amount of them are). An enzyme is simply a biological catalyst; it speeds up the rates of reaction for a specific chemical reaction in a cell. It does this by attaching a substrate (molecule it acts upon) into its highly specific active site. In this active site, certain environmental factors (pH, temperature, space etc) will significantly lower activation energy of the reaction, this will therefore speed up the reaction. Since enzymes are catalysts, they are not consumed by the reactions they catalyze.

Some enzymes operate independently; their presence is enough for the reaction to occur. Other enzymes however must be phosphorylated: They are coupled with the highly exothermic hydrolysis of adenosine triphosphate (ATP) and this energy provides the necessary activation energy for the reaction to take place.

Most enzymes are made up of proteins; however, some types of RNA can act as enzymes (see spliceosomes and RNAi). Spliceosomes are present in eukaryotic nuclei, they "sort" the introns and exons of pre-mRNA and account for the ability of one gene to encode for several different proteins. RNAi is a newly discovered phenomenon in which a cell will destroy mRNA in its cytoplasm if a complementary strand of RNA is introduced (RNAi stands for RNA interference, the complementary strand is referred to as interfering RNA because it binds to the mRNA and effectively interferes with ribosomal activity). This new RNAi discovery shows high hopes for the treatment of unimmunizable and drug resistant viruses.