Structure Determines Function
Monosaccharides are frequently depicted in Fischer projections to highlight the stereochemical differences. However, in solution, these molecules adopt a cyclic hemiacetal or hemiketal structure; this structure is best seen in a Haworth projection.
Polysaccharides can be broadly characterized by function as being energy stores or structural.
Energy storing polysaccharides can either be linear (e.g. amylose) or highly branched (e.g. amylopectin or glycogen). The branched forms enable the mobilization of monosaccharides at a higher rate, because release can happen simultaneously from several sites.
Structural polysaccharides are generally linear molecules, with multiple places where the strands can interact with one another through weak forces (typically hydrogen bonding, dipole–dipole and electrostatic interactions).
The structure of many enzymes is conserved throughout biology, and many of the same chemical reactions are employed in the breakdown and biosynthesis of carbohydrates in divergent species.
Evolution's Outcomes are Conserved
In contrast to some genes discussed in other chapters (e.g. the genes involved in eicosanoids and steroid metabolism), the genes coding for the enzymes involved in glycolysis are found throughout biology, and are therefore more ancient in origin. All of these pathways are conserved throughout evolution.
Because glycolysis is so basic to the existence of an organism, mutations that disrupt this pathway are often lethal or put organisms at such an evolutionary disadvantage that they generally fail to pass on these genes.