Biomedical Engineering Reference
In-Depth Information
tissue culture cells derived from
Mus musculus
(house mouse). Various derivatives
of this strain have been widely used as model systems in bone biology. The subline
MC3T3-E1 is one of the most convenient and physiologically relevant systems for
the study of transcriptional control in calvarial osteoplasts.
Kim
et al
. tried to understand the biochemical reaction of RANKL in re-
sponse to mechanical loading. The MC3T3-E1 cells were biequiaxially stretched.
A murine RANKL cDNA with double epitopes, pEF6 HARANKL-V5His, was
transfected into MC3T3-E1 cells, which were then stretched. They found that
endogenous RANKL protein expression increased in response to mechanical
loading. Membrane-bound RANKL (HA-RANKL-V5His) increased in cell lysates
while soluble RANKL (RANKL-V5His) decreased in the conditioned media after
mechanical loading. This may have resulted from the decreased activity of TACE
after mechanical loading. Increased membrane-bound RANKL may be one of the
mechanisms through which osteoblasts adapt to mechanical loading by regulating
osteoclastogenic activity, [196].
1.3.6
Proteins and Amino Acids
An amino acid is a molecule containing both amine and carboxyl functional groups.
There are about 200 amino acids in nature. Protein amino acids or alpha amino
acids are the building blocks of proteins. In these amino acids, the amine and
carboxyl functional groups are linked to the same atom of carbon, cf. [197-199].
Proteinogenic amino acids are those 22 amino acids that are found in proteins
and that are coded for in the standard genetic code. Proteinogenic literally means
protein building
. Proteinogenic amino acids are assembled into a polypeptide (the
subunit of a protein) through a process known as
translation
(the second stage of
protein biosynthesis, part of the overall process of gene expression).
Peptides (Greek:
πεπτιδια
, small digestibles) are short polymers formed from
the linking, in a defined order, of
α
-amino acids. The link between one amino-acid
residue and the next is called an
amide bond
or a
peptide bond
. Proteins are
polypeptide molecules or consist of multiple polypeptide subunits. The distinction
is that peptides are short and proteins (polypeptides) are long. Proteins are defined
by their sequence of amino-acid residues; this sequence is the primary structure of
the protein. It is the genetic code that specifies 20 standard amino acids.
Since the works of Hofmeister (1850-1922) and Fischer (1852-1919), it has been
regarded that the proteins are in some fundamental fashion chainlike, that they
are constructed from polypeptides of the general formula, given in Figure 1.30,
in which
R
, and so on, stand for various univalent groups - 22
different kinds are known - which act as side chains to a common main chain
(backbone). Two of these can be specified by the genetic code, but are rare in
proteins.
The
−
R
,
R
,
−
−
-amino acids from which the proteins are formed, and into which they are
resolved again on digestion, have the general formula H
2
NCHRCOOH, where R
is an organic substituent, cf. Figure 1.31. In the
α
α
-amino acids, the amino and
