Question

How are proteins renewed?

Answer 1

Clinicians with interests in endocrinology, and in
nutrition, have been among those with a concern
for how the body builds and renews itself. Growth
and renewal depend upon protein synthesis, for
which food is necessary, for food provides amino
acids. The biochemical controls for cellular protein
synthesis, however, are similar for all organisms,
and not immediately dependent on diet.
We ourselves have an interest in sleep and share
the common man’s belief that sleep is in some way
restorative. If the belief is correct, then one must
ask what the link with restoration or renewal may
be. Studies of cell and tissue kinetics confm that
there are circadian (i.e. about 24h) variations in
protein synthesis and in cellular proliferation [ 11.
Indeed, endogenous ‘clocks’ govern the function
of every living tissue and in the whole body the
clocks are co-ordinated by the brain, directly or
indirectly.
The chief human circadian rhythm is that of
sleep-wakefulness. Entrained to it is, for example,
a rhythm of plasma amino acids, the timing of the
peaks and troughs being independent of feeding,
and there are also 24h rhythms in intracellular
amino acid levels that bear no simple relation to
feeding or to plasma amino acid levels, which is
not surprising, for amino acids are actively trans-
ported. As a feature of the sleep-wakefulness
rhythm there are 24h variations too in bodily
activity and in the concomitant degradation of
body fuels. Since amino acids provide one source
of fuel, it will be realized that if activity durin