Question:
Why is it that humans circulate the monosaccharide,
glucose, in their blood, rather than employing a disaccharide like
sucrose as a transport sugar, as plants do?
I understand that plants convert this glucose into a disaccharide for the
reason that it is less readily metabolized during transport in this form,
and normal glucose-utilizing enzymes of the organism cannot break the
bond linking the two monosaccharide subunits. The enzymes where the
energy is needed are able to break this bond. What I do not quite
understand is why humans do not perform this process as well. I know
this question probably relates a lot to evolution, but I would appreciate
any ideas.
Replies:
Given that humans and many other animals have active circulatory systems,
there is little need for targeting sugars for specific parts of the body.
The entire body would rapidly reach equilibrium with the glucose level of
the bloodstream, and thus there likely never evolved the need to target
specific organs to receive sugars via disaccharides.
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