CONCEPTS IN BIOLOGY
PART II. CORNERSTONES: CHEMISTRY, CELLS, AND METABOLISM
5. Enzymes, Coenzymes, and Energy
Man Survives Body Temperature of 115.7!
Alcohol, drugs, and high temperatures just don’t mix.
Fifty-two-year-old Willie Jones of Atlanta, Georgia, has been documented as having survived the highest body temperature ever recorded. Jones’s core body temperature reached 115.7°F (46.5°C). He was admitted to the hospital with heatstroke (hyperthermia) on July 10, 1980, when the outside temperature reached 90°F (32.2°C). Hyperthermia may be caused by a combination of environmental exposure, physical exertion, infection, malfunction of temperature regulation mechanisms in the brain, and/or by various drugs.
The Centers for Disease Control and Prevention (CDC) reported that from 1999-2003 there were 1,203 deaths associated with hyperthermia; 345 (29%) were associated with “external causes (e.g., unintentional poisonings).” Willie suffered from environmental heatstroke, made worse by alcohol consumption. In fact, this patient’s peak body temperature was probably higher, since an accurate measurement was not made until 25 minutes after body-cooling devices were used. Other drugs that can cause this condition include amphetamines, cocaine, atropine, diphenhydramine, antidepressants, and antipsychotics.
Heatstroke victims commonly develop multisystem organ failure, resulting from damage to the body’s proteins, breakdown of muscle, and a bleeding disorder of the body’s clotting and anti-clotting mechanisms. Willie never developed the clotting disorder or muscle breakdown despite extreme hyperthermia, thanks to the actions of emergency department personnel.
• How are the body’s proteins affected by high temperatures?
• What happens to proteins when the environmental temperature drops?
• Will such information influence people to use alcohol and drugs more carefully?
ü Background Check
Concepts you should already know to get the most out of this chapter:
• The different ways that chemicals can react with one another (chapter 2)
• How atoms and molecules bond together (chapter 2)
• The variety of shapes proteins can take (chapter 3)
• The molecular structure of cellular membranes (chapter 4)
5.1. How Cells Use Enzymes
All living things require energy and building materials in order to grow and reproduce. Energy may be in the form of visible light, or it may be in energy-containing covalent bonds found in nutrients. Nutrients are molecules required by organisms for growth, reproduction, and repair. The formation, breakdown, and rearrangement of molecules to provide organisms with essential energy and building blocks are known as biochemical reactions. Most reactions require an input of energy to get them started; this energy is referred to as activation energy. Activation energy is used to make reactants unstable and more likely to react (figure 5.1).
FIGURE 5.1. The Lowering of Activation Energy
Enzymes operate by lowering the amount of energy needed to get a reaction going—the activation energy. When this energy is lowered, the nature of the bonds is changed, so they are more easily broken. Although the figure shows the breakdown of a single reactant into many end products (as in a hydrolysis reaction), the lowering of activation energy can also result in bonds being broken so that new bonds may be formed in the construction of a single, larger end product from several reactants (as in a synthesis reaction).
If organisms are to survive, they must obtain sizable amounts of energy and building materials in a very short time. Experience tells us that the sugar in candy bars contains the potential energy needed to keep us active, as well as building materials to help us grow (sometimes to excess!). Yet, random chemical processes alone could take millions of years to break down a candy bar. Of course, living things cannot wait that long. To sustain life, biochemical reactions must occur at extremely rapid rates. One way to increase the rate of any chemical reaction and make its energy and component parts available to a cell is to increase the temperature of the reactants. In general, the hotter the reactants, the faster they will react. However, this method of increasing reaction rates has a major drawback when it comes to living things: Organisms die because cellular proteins are denatured before the temperature reaches the point required to sustain the biochemical reactions necessary for life. This is of practical concern to people who are experiencing a fever. Should the fever stay too high for too long, major disruptions of cellular biochemical processes could be fatal.
Organisms have evolved a way of increasing the rate of chemical reactions without increasing the temperature. This involves using a catalyst, a chemical that speeds the reaction but is not used up in the reaction. It can be recovered unchanged when the reaction is complete. Catalysts lower the amount of activation energy needed to start the reaction (refer to figure 5.1). A cell manufactures specific proteins that act as catalysts. An enzyme is a protein molecule that acts as a catalyst to speed the rate of a reaction. Enzymes are found throughout the cell and can be used over and over again until they are worn out or broken. The production of these protein catalysts is under the direct control of an organism’s genetic material (DNA). The instructions for the manufacture of all enzymes are found in the genes of the cell. How the genetic information is used to direct the synthesis of these specific protein molecules will be discussed in chapter 8.
5.1. CONCEPT REVIEW
1. What is the difference between a catalyst and an enzyme?
2. How do enzymes increase the rate of a chemical reaction?