Bài 63. Cơ sở khoa học của các biện pháp tránh thai

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
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
Atoms are the smallest stable units of matter
Figure 2.1 Hydrogen Atoms
Figure 2.1
The outermost electron shell determines the reactivity of the element.
Electrons occupy a series of energy levels or electron shells.
Figure 2.2 Atoms and Energy Levels
Figure 2.2
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
Atoms combine through chemical reactions
Figure 2.3 Ionic Bonding
Animation: Formation of Ions
PLAY
Figure 2.3
Double covalent bond
Non-polar covalent bond
Polar covalent bond
Covalent bonds exist between atoms that share electrons to form a molecule
Figure 2.4a, b
Polar covalent bonds that occur when hydrogen covalently bonds with another element
Hydrogen bonds are weak forces that affect the shape and properties of compounds
Figure 2.5
Figure 2.5 Polar Covalent Bonds and the Structure of Water
Figure 2.6
Figure 2.6 Hydrogen Bonds
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
Matter and chemical notation
SECTION 2-2
Chemical Reactions
All chemical reactions in the body constitutes metabolism
Metabolism provides for the capture, storage and release of energy
A chemical reaction occurs when reactants combine to generate one or more products
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
Basic energy concepts
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)
Metabolism
All reactions are theoretically reversible
At equilibrium the rates of two opposing reactions are in balance
Anabolism = catabolism
Reversible 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
Enzymes, energy and chemical reactions
Figure 2.7 Enzymes and Activation Energy
Figure 2.7
SECTION 2-3
Inorganic Compounds
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
Nutrients and Metabolites
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
Water and its properties
Figure 2.8 Water molecules and solutions
Figure 2.8
Compounds that interact readily with water are hydrophilic
Compounds that do not interact with water are hydrophobic
Electrolytes undergo ionization
Neutral
Acidic
Basic
pH is a measure of the concentration of hydrogen ions solution
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
Acids and Bases
Figure 2.9 pH and Hydrogen Ion Concentration
Figure 2.9
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
Salts and buffers