1. Energy Flow in the Cell What is energy? Capacity to do work... 1. Kinetic Energy - energy of movement (e.g. light, heat, electricity, movement of large objects) 2. Potential Energy - stored energy (e.g. chemical energy in bonds of molecules, electrical energy in a battery, positional energy) Living organisms use energy to maintain homeostasis. They do so by chemical reactions that either build more complex and orderly molecules, or break down larger molecules to gain access to the potential energy within those molecules.

2. Energy Flow in the Cell Exergonic versus endergonic reactions:

3. Energy Flow in the Cell Exergonic versus endergonic reactions: The energy released by the cell is converted to ATP which can later be used to “do work”.

4. Energy Flow in the Cell Exergonic and endergonic reactions can be coupled to “do work”... Note that such reactions are not very efficient.

5. Energy Flow in the Cell ATP acts as the energy carrier in the cell:

6. Energy Flow in the Cell Other electron carriers also carry energy in the cell, but more on them later...

7. Energy Flow in the Cell Enzymes act as catalysts in living systems. 1. Catalysts speed up reactions 2. Catalysts speed up reactions that are “energetically favorable” 3. Catalysts are not consumed in the reaction Note that sometimes, enzymes can use energy molecules to make a reaction “energetically favorable”.

8. Energy Flow in the Cell Structure of enzymes help with the catalysis.

9. Energy Flow in the Cell Cells regulate chemical reactions by regulating the enzymes: 1. Regulate synthesis of enzymes 3. Regulate the activation of enzymes. 4. Feedback inhibition 5. Allosteric inhibition 2. Regulate breakdown of enzymes 6. Competitive inhibition 7. Other?