| Enzymes & Photosynthesis |
UNIT TOPICS: Biological chemical reactions involve energy systems, principally
enzymes,
photosynthesis, and respiration (i.e., biological oxidation; aerobic
respiration).
Inherent in these systems are laws of thermodynamics (i.e., First and Second Laws).
First Law of Thermodynamics: Energy is not created or destroyed, but
may be transformed
(converted, changed) from one form to another.
Examples of various forms of energy: Heat, electricity, sunlight, mechanical, etc. Any one of these forms may be converted to another (i.e., mechanical to electrical). No system of conversion is 100 % efficient; always some “loss”. In this example, not all of the mechanical energy will be converted to electrical; some will be “lost” as heat. Understand, we do not really mean "lost", but not available in the form needed, or expected in the conversion process. Recall my (Bailey's) rendition-ENERGY IS!!
The Second Law of Thermodynamics deals with energy dispersion, or the dispersion of matter, from a concentrated form to a less concentrated form. The concept deals with the ever expansion of the universe and associated matter; it is termed ENTROPY. We will not deal with this concept at great length in this unit. Our center of focus will be on the First Law of Thermodynamics and will be referenced a number of times throughout the discussions in this unit.
Note that the SUN is the primary source of energy within this solar system, and therefore provides for much of the energy required in various systems, both biological and non-biological (i.e., air mass movements, wind, ocean currents, etc.). Even though a great deal of the sun energy is dispersed, reflected, and otherwise does not reach the surface of the earth, sufficient supply is available for biological systems. The sun (electromagnetic energy) provides the energy for PRIMARY PRODUCERS to convert (transform) sunlight energy to a form of stored chemical energy-GLUCOSE-which may be used as an energy source by various organisms. Ultimately, these organisms convert (transform) the energy contained in glucose to another form of chemical energy-ATP (adenosine triphosphate).
ATP is a universal form of energy-a common energy currency if you will, much the same as Gold is recognized by most all societies and cultures as a common economic currency-and is recognized by all living systems as a useful form of chemical energy. Also, recall that the energy available in the ATP molecule is provided by the bond between the 2nd and 3rd phosphate groups, and amounts to about 7,000 calories of energy. [NOTE: a CALORIE is defined as the amount of energy required to raise the temperature of one (1) cubic centimeter (cc) of water one (1) degree Centigrade]
When ATP releases a phosphate group, it forms ADP (adenosine diphosphate),
plus an inorganic form of phosphorus. It is at this point that the
7,000 calories of energy is released, and is available to do WORK in the
cell. Type of work: building cell parts, protein synthesis, muscle
cell contraction, etc.
TYPES OR FORMS OF ENERGY:
POTENTIAL ENERGY-stored, available, unused, has the ability, to do WORK. ENERGY AT REST.
KINETIC ENERGY-energy that is accomplishing (has accomplished) WORK. ENERGY IN MOTION.
CHEMICAL REACTIONS (Rx) take place all of the time. Some reactions
require an additional source of energy in order to take place (EDERGONIC),
while others require no additional energy to occur-they just seem to 'happen'
when the right substances are placed in close enough proximity (EXERGONIC).
Regardless, note that Rx take place because atoms or molecules are moving,
and collide together with sufficient force in order to form the necessary
bonds to hold them together.
The speed with which atoms and molecules move is a function of their energy content. One of the ways in which the energy may be increased is by raising temperature--adding heat to the "system" in question.
In any chemical Rx, the material which enters into the reaction is called a REACTANT. The result of the reaction is termed the PRODUCT.
It should be clear that an increase in temp (energy) increases the speed with which molecules are moving, and thus increase the chance of more collisions. In addition, the as the energy increases, so does the speed with which molecules are moving, and thus the FORCE of a collision is greater. Both of these factors increase the rate at which a Rx takes place, and thus the rate at which products are formed. In biological systems, however, the Rx's take place in a much more controlled, sequential manner, and the speed with which Rx's occur is not governed by temp. As much as the presence of a specific catalyst, generally and enzyme. In general, these Rx's are called metabolic Reactions. Examples: Photosynthesis
A CATALYST, reduces the energy (lowers the temp.) required for a Rx to occur, or LOWERS THE ENERGY OF ACTIVATION of a Rx. In biological systems, catalysts are most often enzymes.
The enzyme has an ACTIVE SITE, which binds with a SUBSTRATE(S), i.e., reactants, as illustrated in Text
Thus, all enzymes are:
