Biochemical Information is Transferred, Exchanged, Stored
Carbohydrate metabolism is regulated by several allosteric regulators and kinases that inhibit or activate key enzymes in the glycolytic pathway.
Biomolecules are Altered Through Pathways Involving Transformations of Energy and Matter
Energetically unfavorable reactions become favorable when coupled to energetically favorable reactions. Although we typically think of this in terms of ATP hydrolysis or phosphate transfer, other bonds with a large negative free energy of hydrolysis (e.g. thioesters) are also common in biochemistry.
Reactions that have ΔG° values close to 0 can be tipped to proceed in either direction by changing the concentrations of substrates or products.
The synthesis of glucose through gluconeogenesis and the degradation of monosaccharides via glycolysis use similar reactions but different pathways. Key steps are different, and compartmentalization is important. The same theme is seen in beta oxidation and fatty acid biosynthesis.
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.