Biology

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.

This process occurs in the cytoplasm. In a series of chemical reactions, glucose breaks into two pyruvates. The energy released from glucose is trapped in AtP molecules. The process release 2 AtP molecules and 2 NADH (nicotinamide adenine dinucleotide) that is an electron carrier molecule that temporarily stores energy.

The second major step in glucose breakdown takes placed in the mitochondria, specifically, in the area enclosed by the inner membrane. Initially, pyruvate moves from the cytoplasm into the mitochondria and forms acetyl coenzyme A. Acetyl CoA enters the Krebs Cycle which produces several substances. Several of these are recycled by moving continuously in the cycle. Others, such as CO2(Carbon Dioxide) and energy-storing compounds of NADH(Nicotinamide Adenine Dinucleotide) and FADH2(Flavin Adenine Dinucleotide), moves out of it. CO2 leaves the cell while NADH and FADH2 participate in the third step, the Electron Transport.

The electrons in NADH and FADH2 flow through a series of electron transport acceptors. These are located in the inner membrane of the mitochondria. The flow of electrons and H+ result in AtP formolation. The last electron acceptor in the chain is oxygen. The electrons, hydrogen ions, and oxygen combined to form water.