Nanotechnology-Enabled Sensors

7.4 Proteins in Nanotechnology Enabled Sensors 409
the primary structure of the protein. The next level up is the secondary
which is concerned with the shape of the protein in localized areas and
takes into account the α-helix and β-sheets that forms within certain segments
of the polypeptide chain. The full three-dimensional protein structure
is the tertiary structure and it consists of all α-helix and β-sheets,
coils, loops and folds in the protein. The quaternary structure of a protein
is the overall structure in the case that the protein comprises more polypeptide
chain. An example of this is hemoglobin which has four polypeptide
chains in its quaternary structure.
7.4.2 The Analysis of Proteins
When analyzing a protein, the fundamental process is that cell should be
broken open, all of the soluble proteins should be separated by centrifugation,
and then passed through a column matrix that contains the pure target
protein. Isolating these proteins by electrophoresis through a polymer gel
can be the next step, which separates polypeptides on the basis of their
size. 92 Once the protein has been identified, we are ready to determine its
amino acid sequence. In order to do this, the protein is broken up into
smaller pieces by using selective enzyme called protease. For instance, the
enzyme trypsin cleaves polypeptide chains on the carboxyl side of any lysine
or arginine units.
Mass spectrometry (Chap. 5) can be utilized to determine the exact mass
of each peptide fragment. This method allows identifying the first finger
print. For structural analysis generally a large amount of the protein is
needed. Using the recombinant DNA method the proteins can be inserted
into cells of bacteria to get the cell to produce large amounts of the protein.
To determine the proteins’ structure using X-ray crystallography, they
have to be stacked together to form crystals which are large, highly ordered
arrays. The patterns are generally very complex and computer programs
are required to analyse these patterns. If the protein is small the
structure can also be determined by using nuclear magnetic resonance
(NMR) spectroscopy.
7.4.3 The Role of Proteins in Nanotechnology
Proteins represent an exciting area in nano-biotechnology as they have
ideal properties for engineering tasks such as processing sophisticated architectures
at nanoscale dimensions, have rich chemistry and provide us
versatile functionalities. By employing the knowledge of biochemical