From Wikipedia,
the free encyclopedia.
-
This article is about anabolism
and catabolism as types of
metabolism. For steroids with
anabolic properties, see
Anabolic steroid.
Anabolism is the part of
metabolism that builds larger
molecules. One way of categorizing
metabolic processes, whether
at the
cellular, organ or organism
level is as anabolic or
catabolic.
Anabolic processes tend toward
"building up" organs and tissues.
These processes produce growth and
differentiation of cells and
increase in body size, a process
that involves
synthesis of complex
molecules. Examples of
anabolic processes include growth
and mineralization of
bone and increase of
muscle mass.
Catabolism is the part
of
metabolism that partitions
molecules into smaller units. It
is made up of degradative chemical
reactions in the living cell.
Large polymeric molecules (polysaccharides,
nucleic acids and
proteins) are processed into
their constituent monomeric units
(i.e.
monosaccharides,
nucleotides and
amino acids, respectively).
Cells use monomers to construct
new polymeric molecules and
disassemble them to simple
cellular metabolites (lactic acid,
acetic acid, carbon dioxide,
ammonia, urea, etc.). The creation
of cellular metabolites is an
oxidation process involving a
release of chemical free energy,
not all of which is lost as heat,
but some of which is partially
conserved through the coupled
synthesis of adenosine
triphosphate. The hydrolysis of
this compound is subsequently used
to drive almost every
energy-requiring reaction in the
cell. Catabolism provides the
chemical energy necessary for the
maintenance of the living cell.
Examples of catabolic processes
include breakdown of muscle
protein in order to use
amino acids as
substrates for
gluconeogenesis and breakdown
of
fat in
adipose to
fatty acids.
Because it is counterproductive
to have anabolic and catabolic
processes occurring in cells
simultaneously, there are many
signals that switch on anabolic
processes while switching off
catabolic processes and vice
versa. Most of the known signals
are
hormones and the molecules
involved in metabolism itself.
Endocrinologists have
traditionally classified many of
the hormones as anabolic or
catabolic.
- Classic anabolic hormones
include
- Classic catabolic hormones
include
- Newer hormones associated
with the balance of the
catabolic and anabolic states
include
