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Cell Biology
Biological Energy
Linking reactions together
Linking Reactions Together How cells in the sugar cane plant set about synthesizing sucrose.

  1. Food molecules in the plant cell contain a lot of organized energy in their covalent bonds.

  2. This energy can be released in a spontaneous reaction with oxygen, but the rate of the reaction will be very slow because of the activation energy barrier.

  3. Catalysts lower the activation energy barrier and speed up the reaction. Enzymes are biological catalysts.

  4. Using enzymes, cells break down food molecules by reacting them with oxygen. In doing so, electrons are moved closer to the oxygen atoms, which releases a lot of energy.

  5. With different enzymes, cells use some of the released energy to make nonspontaneous synthetic reactions take place. Glucose is joined with fructose for form sucrose in the sugar cane plant.

This is the secret. Living organisms link these two types of reactions together to achieve spectacular results.

Spontaneous reactions that liberate energy are linked with nonspontaneous reactions that need energy.

By taking the energy from food, organisms are able to synthesize proteins, carbohydrates, nucleic acids, and lipids, all the major macromolecules vital to life.

From the tiniest bacterium to the largest redwood tree, all the building blocks and all the components of every cell are made by nonspontaneous reactions that get their energy from that given off by spontaneous reactions.

The entire body of a giant whale is made by pushing around electrons!

Figure legend: The Secret of Life. All living organisms on earth manipulate energy to stay alive. Large food molecules are fuels that are broken down into carbon dioxide and water, liberating a lot of energy.

Cells then use this liberated energy to drive highly nonspontaneous reactions, such as the formation of sucrose, or even larger molecules such as protein or DNA.

© 2001, Professor John Blamire