Introduction to Metabolism
and Energetics

Friday:

Monday:

Reading: Campbell and Reece, 2002: Chapter 6 - Introduction to Metabolism

Student Objectives: As a result of this lecture and the assigned reading, you should understand the following:

Despite the organized structure of cells, all living things tend toward disorder. To maintain order, living things and the cells they are made up of depend on a continual flow of energy from the environment.

Metabolism is the sum total of an organism's chemical processing; some chemical processes degrade complex molecules into simpler molecules (catabolic pathways), and some chemical processes synthesize complex molecules from simpler molecules (anabolic pathways).

Energy can only be described and measured by how it affects matter. Energy is the capacity to perform work - all organisms require energy to stay alive, and all organisms transform energy.

There are two (2) forms of energy: potential energy and kinetic energy.

The first law of thermodynamics (law of energy conservation) = the total amount of energy in the universe is constant and energy can be transferred and transformed, but it cannot be created or destroyed.
The second law of thermodynamics = energy conversions reduce the order of the universe. Heat, which is due to random molecular motion, is one form of disorder. The second law has direct applications to cellular activities - as explained in this law, energy cannot be transferred or transformed by the cell with 100% efficiency.

Chemical reactions in living organisms - the starting substances of chemical reactions are called reactants; reactants interact with one another to form new substances called products.

Chemical reactions, including those in cells, are of two types: endergonic (energy-requiring) and exergonic (energy-releasing). In an endergonic biosynthetic reaction, the electrons forming the chemical bonds of the product are at a higher energy level than the electrons of the reactants (i.e., the reaction requires input of energy). Cells supply this energy through coupled reactions in which endergonic reactions are linked to exergonic reactions.
Enzymes act as catalysts (i.e., they participate in the reaction but are not reactants; enzymes are not consumed or transformed chemically in reactions they catalyze). Enzymes are proteins that increase the speed of the reaction by lowering the activation energy necessary for the reaction.

Enzymes combine briefly with reactants during enzyme-catalyzed reactions (a single enzyme molecule can catalyze thousands of reactions/sec).

Enzymes are relatively unchanged after catalyzing the conversion of reactants to products.

Enzymes are specific in their activity; each enzyme catalyzes the reaction of a single type of molecule or a group of closely related molecules.

Enzymes are saturated by high substrate concentrations.

Many enzymes require non-protein groups, cofactors. Inorganic cofactors are metallic ions. Organic cofactors, coenzymes, are complex groups derived from vitamins.

Conditions affecting enzyme activity include: 1) substrate concentration; 2) temperature; 3) pH; 4) cofactors.

Enzyme inhibitors can interfere with the activity of enzymes; the inhibitors may be of two types: 1) competitive inhibitors or 2) noncompetitive inhibitors.

Oxidation-reduction reactions (redox reactions) - Oxidation = the loss of electrons by a molecule, while reduction = gain of electrons. In living systems, the energy-capturing reactions (photosynthesis) and energy-releasing reactions (glycolysis and respiration) are oxidation-reduction reactions.

ATP is the cell's main energy carrier. Most frequently, coupled reactions use ATP, and ATP is renewable energy cells that cells regenerate.