Chapter 2, part 1
The Chemical Level of Organization
Learning Objectives
Describe an atom and compare the ways atoms combine to form molecules.
Distinguish among the types of chemical reactions that are important to physiology.
Describe the role of enzymes in metabolism.
Distinguish between organic and inorganic compounds.
Explain the importance of water, pH and buffers to living systems.
Discuss the structures and functions of carbohydrates, lipids, proteins, nucleic acids and high energy compounds.
SECTION 2-1 Atoms, Molecules and Bonds
Atoms are the smallest stable units of matter
Subatomic particles
Protons = positive charge; weight of approximately 1 Dalton
Neutrons = no charge; weight similar to protons
Electrons = negative charge; weigh 1/1836th Dalton
Protons and neutrons are found in the nucleus; electrons occupy electron cloud
Atomic number = proton number; atomic mass = protons and neutrons
Isotopes are elements with similar numbers of protons but different numbers of neutron
Figure 2.1 Hydrogen Atoms
Electrons occupy a series of energy levels or electron shells.
The outermost electron shell determines the reactivity of the element.
Figure 2.2 Atoms and Energy Levels
Atoms combine through chemical reactions
Molecule = a chemical structure consisting of molecules held together by covalent bonds
Compound = a chemical substance composed of atoms of two or more elements
There are three types of bond: Ionic, covalent, and hydrogen
Ionic = attraction between positive cations and negative anions
Figure 2.3 Ionic Bonding
Covalent bonds exist between atoms that share electrons to form a molecule
Double covalent bond
Non-polar covalent bond
Polar covalent bond
Hydrogen bonds are weak forces that affect the shape and properties of compounds
Polar covalent bonds that occur when hydrogen covalently bonds with another element
Figure 2.5 Polar Covalent Bonds and the Structure of Water
Figure 2.6 Hydrogen Bonds
Matter and chemical notation
Matter can exist as a solid, liquid or gas
Depends on the interaction of the component atoms or molecules
Molecular weight is the sum of the atomic weights of the component atoms
Chemical notation
Short-hand that describes chemical compounds and reactions
See table 2.2 for examples of chemical notation
SECTION 2-2 Chemical Reactions
A chemical reaction occurs when reactants combine to generate one or more products
All chemical reactions in the body constitutes metabolism
Metabolism provides for the capture, storage and release of energy
Basic energy concepts
Work = movement of an object or change in its physical structure
Energy = the capacity to perform work
Kinetic energy is energy of motion
Potential energy is stored energy resulting from position or structure
Conversions are not 100% efficient, resulting in release of heat
Metabolism
Types of reaction
Decomposition
Synthesis
Exchange
Metabolism is the sum of all reactions
Through catabolism cells gain energy (break down of complex molecules)
Anabolism uses energy (synthesis of new molecules)
Reversible reactions
All reactions are theoretically reversible
At equilibrium the rates of two opposing reactions are in balance
Anabolism = catabolism
Enzymes, energy and chemical reactions
Activation energy is the amount of energy needed to begin a reaction
Enzymes are catalysts
Reduce energy of activation without being permanently changed or used up
Promote chemical reactions
Figure 2.7 Enzymes and Activation Energy
SECTION 2-3 Inorganic Compounds
Nutrients and Metabolites
Nutrients are essential chemical compounds obtained from the diet
Metabolites are molecules synthesized or broken down inside the body
These can be classified as organic or inorganic compounds
Organic compounds have carbon and hydrogen as their primary structural component
Inorganic compounds are not primarily carbon and hydrogen
Water and its properties
Water is the most important constituent of the body
Solution is a uniform mixture of two or more substances
Solvent is the medium in which molecules of solute are dispersed
Water is the solvent in aqueous solutions
Figure 2.8 Water molecules and solutions
Electrolytes undergo ionization
Compounds that interact readily with water are hydrophilic
Compounds that do not interact with water are hydrophobic
pH is a measure of the concentration of hydrogen ions solution
Neutral
Acidic
Basic
Acids and Bases
Acids release hydrogen ions into solution
Bases remove hydrogen ions from solution
Strong acids and strong bases ionize completely
Weak acids and weak bases do not ionize
Figure 2.9 pH and Hydrogen Ion Concentration
Salts and buffers
Salt = an electrolyte whose cation is not hydrogen and whose anion is not hydroxide
Buffers remove or replace hydrogen ions in solution
Buffer systems maintain the pH of body fluids
