Nanotechnology-Enabled Sensors

422 Chapter 7: Organic Nanotechnology Enabled Sensors
enzymatic process. Alternatively, when a molecule other than the substrate
binds to an enzyme, at a special regulatory site outside the active site, it
can alter the conversion rate of the substrate. This is a negative feedback
process which is called a feedback inhibition, and its role is to prevent an
enzyme from functioning. Alternatively, enzymes can also be subjected to
positive regulations where the activity is stimulated by a regulatory molecule.
92 The shapes of the regulatory molecules are totally different from the
shape of the enzyme molds and are called allostery (means other-solid in
Greek language). Enzymes have at least two different binding sites on their
surfaces. These two binding sites can communicate with each other, when
binding occurs at one site of the enzyme it causes a change in the protein’s
structure.
The competitive inhibitor can be directly placed into the main binding
site (to fill and block the enzyme) or it can be placed in the secondary
bonding site to alter the dimensions of the main ones (also called a noncompetitive
inhibitor).
Many proteins are allosteric. It means that they can adopt two or more
different conformations. By changing from one conformation to another
they are able to regulate their activities. The chemistry is simple as each
molecule that binds the enzyme brings about a slight change in the overall
forces within the molecule hence which produces a new conformation.
The other method of regulating the activities of proteins involves the attachment
of phosphate groups, which covalently bonds to one of the amino
acids in the protein. The phosphate group carries two negative charges and
as a result, its attachment can cause a major conformational change in the
protein. For instance, it can attract a cluster of positively charged amino
acid side chains thus greatly altering the protein’s activity. This process is
reversible and is called protein phosphorylation. The addition or removal
of a phosphate group to or from a specific protein often occurs in response
to signals that specify changes in a cell’s state. Many of these signals are
generated by hormones and neurotransmitters and carried out from within
the cell’s membrane by a cascade of phosphorylation events.
Protein phosphorylation is conducted by a catalyst protein called kinase.
It transfers the terminal phosphate group of an adenosine triphosphate
(ATP) molecule to the hydroxyl group of an amino acid. The removal of
the phosphate group, which is the reverse reaction, is catalysed by the protein
phosphatase.
ATP is a nucleotide, which is a molecule that consists of a nitrogencontaining
ring that is linked to a five-carbon sugar: either ribose or deoxyribose.
Nucleotides can act as short-term carriers of chemical energy. ATP
participates in the transfer of energy in molecular interactions. ATP is
formed in the process of the generation of energy using the oxidative