Biochemical Processes


Most chemical changes in a cell result from chains and cycles of biochemical reactions, with each step controlled by a separate, specific enzyme

Metabolism is the totality of the chemical reactions which occur within a cell, and can be divided into two types:

  • Anabolic reactions involve the synthesis of complex molecules from simpler ones and usually require energy to form new bonds (endergonic)
  • Catabolic reactions involve the breakdown of complex molecules into simpler ones and usually release energy from breaking bonds (exergonic)


Overview of Metabolism


Energy Transformations

  • Energy in living cells is stored and released in the chemical form of ATP (adenosine triphosphate)
  • ATP is made up of an RNA nucleotide (base = adenine) bonded to two additional phosphate groups (three in total)
  • These additional phosphates are connected by high energy bonds that release a large amount of free energy when hydrolysed
  • The energy released from the hydrolysis of ATP (into ADP + Pi) can be used by the cell to fuel biochemical processes


ATP Hydrolysis


  • ATP can be synthesised by the transmembrane enzyme ATP synthase (via both photosynthesis and cell respiration)
  • Photosynthesis uses light energy to synthesise ATP, which is then hydrolysed in order to synthesise organic molecules (anabolic reaction)
  • Cell respiration breaks down organic molecules to release energy which is used to synthesise ATP for use in cell processes (catabolic reaction)


Functions of ATP

ATP provides an immediate source of energy when hydrolysed and functions as the energy currency of the cell

Biochemical processes that utilise ATP include:

  • Growth and repair:  Increase cell size and replace damaged tissue requires ATP
  • Movement:  The contraction of muscle fibres in order to generate movement in organisms requires ATP
  • Nerve transmissions:  The generation and transmission of a nerve impulse (action potential) requires ATP
  • Active transport:  Moving molecules against their concentration gradient, or by cytosis, requires ATP
  • Biosynthesis of macromolecules:  Building complex organic molecules from simpler subunits (anabolism) requires ATP
  • Emission of light:  Some cells may be capable of luminescence, and this process requires ATP


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