Reversible & irreversible steps

• Metabolic processes can have reversible, irreversible steps and alternative pathways which keep the process under strict control.
• Pathways can be modified and contain alternative routes, so steps can be bypassed.
• • Glucose diffuses from a high concentration outside the cell to a low concentration inside the cell, then converted to intermediate 1.

  • This reaction is irreversible

  • It is of benefit to the cell as it maintains a low concentration of glucose inside the cell and therefore allows glucose to diffuse constantly into the cell.
• • The conversion of Intermediate 1 to Intermediate 2 is reversible.

  • If more intermediate 2 is formed than the cell needs for the next step then some can be changed back into intermediate 1 and used in an alternative pathway, e.g to build glycogen in animal cells or starch in plant cells.

  
• A pathway often has reversible & irreversible steps. This allows process to be kept under precise control.