The
biosynthesis
of
this
peptidyl
chain
does
not
involve
ribosomes,
m-RNA,
etc.
The
amino
acids
are
added
sequentially
to
UDP-NAMA.
The
peptide
sequence
of
L-alanine,
D-glutamate,
a
di
amino
acid
(lysine,
mesodiaminopimelic
acid,
ornithine)
ends
with
D-alanine,
which
is
a
general
feature
of
most
bacterial
peptidoglycans.
In
the
second
set
of
reactions,
the
UDP-NAMA-pentapeptide
is
transferred
to
a
lipid
carrier
(C55
isoprenoid
alcohol)
in
the
cell
membrane.
Subsequently,
two
other
additions
are
made
to
the
lipid
bound
NAMA-pentapeptide
before
polymerization
into
the
peptidoglycan.
The
first
is
the
addition
of
NAG
from
UDP-n-acetyl
glucosamine
to
yield
a
disaccharide
unit
and
the
second
is
the
addition
of
amino
acids
to
form
an
interpeptide
cross
link.
The
amino
acid
composition
and
the
number
of
amino
acids
it
cross
link
vary
with
different
bacteria.
In
S.aureus,
this
consists
of
a
pentaglycine
bridge.
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