General ---------Biology----------------------------------------------------- ------------------Online-------------------------wilcox@sunline.net Ch. 6  Metabolism of carbohydrates, fats, proteins, nucleic acids

The cell is home to thousands of chemical reactions making up hundreds of chemical pathways.  Each individual  reaction must be sped up or slowed down depending on the needs of the moment.

Different pathways are kept physically apart by the complex structure of organelles such as mitochondria, chloroplasts, endoplalsmic reticulum, etc.  

9.1  Pathway Regulation (Feedback Regulation)

Chemical pathways are often regulated (turned on/off, sped up/slowed down) by "feed back inhibition."  The mechanism is similar to the thermostat that controls the room temperature within a comfortable range. Read Figure 6.19 Feedback inhibition, in your text.

9.2 Cellular Structure

Inside cells are tiny structures called "organelles."  These are often folded phospholipid membranes.  These membranes form partitions between chemical pathways. Channels through the membranes allow chemical pathways on one side to be linked to pathways on the other side when channels are open and kept partitioned when the channels are closed.  Mitochondria are such membrane organelles.  Read Figure 7.17 The mitochondrion, site of cellular respiration, in your text.  Observe how this organelle might "partition" chemical reactions to regulate them.

The various chemical reactions that breakdown food and release energy occur in and around mitochondria.  These reactions can be kept apart by the numerous membranes and membrane folds in the mitochondria.  The reactions can be linked to one another through protein channels through the membranes.