= Biochemistry
{wiki}
<Biochemistry> studies the <chemistry> of living systems: what their <molecules> are, how they recognize one another, and how their <chemical reactions> support the organization of a <biological cell>. It connects <biology> to <chemical kinetics>, <stoichiometry> and <thermodynamics>. A useful biochemical explanation follows both material and <energy>: which <substrate> becomes which <reaction product>, what sets the <reaction rate>, and how the transformation is driven.
Consider three connected examples. The <stereochemistry> of a <sugar> helps determine how it interacts with an <enzyme>'s <active site>; the <molecular formula> alone cannot describe that recognition. Selective <enzymes> then direct material through <metabolism>, while <ATP> can participate in <energy coupling> that drives otherwise unfavourable transformations. These are different questions about the same working system, rather than three names for its <energy> supply.<Chemistry 2e by Paul Flowers and others>[§12.7, Enzyme Structure and Function, Figure 12.25: substrate recognition and induced fit]{ref}
This viewpoint is useful because it separates possible explanations for a stopped process. Missing <substrate>, inactive <enzyme>, depleted <ATP> and accumulated <reaction product> call for different interventions. Studying a <cell-free extract> can isolate some of those causes while leaving a substantial <chemical reaction network> intact.
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