text: In biochemistry, several important enzymatic cascades and signal transduction cascades participate in metabolic pathways or signaling networks, in which enzymes are usually involved to catalyze the reactions. For example, the tissue factor pathway in the coagulation cascade of secondary hemostasis is the primary pathway leading to fibrin formation, and thus, the initiation of blood coagulation. The pathways are a series of reactions, in which a zymogen (inactive enzyme precursor) of a serine protease and its glycoprotein co-factors are activated to become active components that then catalyze the next reaction in the cascade, ultimately resulting in cross-linked fibrin.
  Another example, sonic hedgehog signaling pathway, is one of the key regulators of embryonic development and is present in all bilaterians. Different parts of the embryo have different concentrations of hedgehog signaling proteins, which give cells information to make the embryo develop properly and correctly into a head or a tail. When the pathway malfunctions, it can result in diseases like basal cell carcinoma. Recent studies point to the role of hedgehog signaling in regulating adult stem cells involved in maintenance and regeneration of adult tissues. The pathway has also been implicated in the development of some cancers. Drugs that specifically target hedgehog signaling to fight diseases are being actively developed by a number of pharmaceutical companies. Most biochemical cascades are series of events, in which one event triggers the next, in a linear fashion.
  Biochemical cascades include: 
  *The Complement system
  *The Insulin Signaling Pathway
  *The Sonic hedgehog Signaling Pathway
  *The Wnt signaling pathway
  *The JAK-STAT signaling pathway
  *The Adrenergic receptor Pathways
  *The Acetylcholine receptor Pathways
  *The Mitogen-activated protein kinase cascade
  Conversely, negative cascades include events that are in a circular fashion, or can cause or be caused by multiple events. Negative cascades include:
  *Ischemic cascade