Chemistry Highlights for Physiology From Marieb Human Anatomy and Physiology

Composition of Matter  Elements  Cannot be broken down by ordinary chemical means; consists of only one type of atom  Atoms  Unique building blocks for each element  Atomic symbol: one- or two-letter chemical shorthand for each element ; for example: – Ca = calcium – H = hydrogen

Major Elements of the Human Body Oxygen (O) Carbon (C) Hydrogen (H) Nitrogen (N) About 96% of body mass

Lesser Elements of the Human Body  Make up ~3.9% of body mass:  Calcium (Ca), phosphorus (P), potassium (K), sulfur (S), sodium (Na), chlorine (Cl), magnesium (Mg), iodine (I), and iron (Fe) Trace Elements of the Human Body  Make up < 0.01% of body mass:  Part of enzymes, e.g., chromium (Cr), manganese (Mn), and zinc (Zn)

Identifying Elements Atomic number = number of protons Mass number = mass of protons and neutrons Atomic weight = average of the mass numbers of all isotopes for a particular element Isotope – atoms with same number of protons but a different number of neutrons Radioisotopes – atoms that undergo spontaneous decay called radioactivity

Radioisotopes  Valuable tools for biological research and medicine  Cause damage to living tissue: – Useful against localized cancers – Radon from uranium decay causes lung cancer

Mixtures  Most matter exists as mixtures  Mixtures – two or more components physically intermixed (not chemically bonded)  Three types of mixtures: – Solutions – Colloids – Suspensions

Concentration of Solutions  Expressed as  Percent, or parts per 100 parts  Milligrams per deciliter (mg/dl)  Molarity, or moles per liter (M) 1 mole = the atomic weight of an element or molecular weight (sum of atomic weights) of a compound in grams 1 mole of any substance contains 6.02  molecules (Avogadro’s number)

Types of Chemical Bonds Ionic Covalent Hydrogen

Ionic Bonds  Ions are charged atoms resulting from the gain or loss of electrons – Anions (– charge) have gained one or more electrons – Cations (+ charge) have lost one or more electrons  Attraction of opposite charges results in an ionic bond

Covalent Bonds – Equal Sharing of Electrons  Sharing of electrons may be equal or unequal – Equal sharing produces electrically balanced nonpolar molecules CO 2

Covalent Bonds – Unequal Sharing Unequal sharing by atoms with different electron-attracting abilities produces polar molecules (H 2 O) Atoms with six or seven valence shell electrons are electronegative, e.g., oxygen Atoms with one or two valence shell electrons are electropositive, e.g., sodium

Figure 2.9 Comparison of Bonds

Figure 2.9 Comparison of Bonds

Hydrogen Bonds  Attractive force between electropositive hydrogen of one molecule and an electronegative atom of another molecule – In water, these hydrogen bonds constantly form and break apart and hold the water molecules together – Responsible for surface tension in water – Also act as intramolecular bonds, holding a large molecule in a three-dimensional shape

(a) The slightly positive ends (  + ) of the water molecules become aligned with the slightly negative ends (  – ) of other water molecules. ++ –– –– –– –– –– ++ ++ ++ ++ ++ Hydrogen bond (indicated by dotted line) Figure 2.10a Polar covalent bond between H and O

Figure 2.10b (b) A water strider can walk on a pond because of the high surface tension of water, a result of the combined strength of its hydrogen bonds.

Hydrogen Bonds This example illustrates the conditions needed for a hydrogen bond to form O δ - —H δ+ ---N δ - —H δ + dipoles hydrogen bond polar covalent bond Dipole = partial charge due to uneven sharing of electrons between atoms Both O and N are more electronegative than H

Chemical Reactions  Occur when chemical bonds are formed, rearranged, or broken  Represented as chemical equations  Chemical equations contain: – Molecular formula for each reactant and product – Relative amounts of reactants and products, which should balance

Major Chemical Reactions Synthesis (combination) reactions: Bonds form to produce larger molecules (anabolic) A + B  AB Decomposition reactions: Molecules are broken down into smaller molecules (catabolic) AB  A + B Exchange reactions: Bonds are both made and broken AB + C  AC + B

Figure 2.11a Example Amino acids are joined together to form a protein molecule. (a) Synthesis reactions Smaller particles are bonded together to form larger, more complex molecules. Amino acid molecules Protein molecule

Figure 2.11b Example Glycogen is broken down to release glucose units. Bonds are broken in larger molecules, resulting in smaller, less complex molecules. (b) Decomposition reactions Glucose molecules Glycogen

Figure 2.11c Example ATP transfers its terminal phosphate group to glucose to form glucose-phosphate. Bonds are both made and broken (also called displacement reactions). (c) Exchange reactions GlucoseAdenosine triphosphate (ATP) Adenosine diphosphate (ADP) Glucose phosphate + +

Oxidation-Reduction (Redox) Reactions  Reactants losing electrons are electron donors and are oxidized – Become more positive since losing negative charge of electrons  Reactants taking up electrons are electron acceptors and become reduced – Become more negative since gaining negative charge of electrons

Energy Flow in Chemical Reactions  All chemical reactions are either exergonic or endergonic  Exergonic reactions – reactions that release energy Catabolic reactions  Endergonic reactions – reactions whose products contain more potential energy than did reactants Anabolic reactions

Reversibility in Chemical Reactions  All chemical reactions are theoretically reversible A + B  AB AB  A + B  Chemical equilibrium is reached if neither a forward nor reverse reaction is dominant  Many biological reactions are essentially irreversible due to – Energy requirements – Removal of products

Factors Influencing Rate of Chemical Reactions  Rate of reaction is influenced by: –  temperature   rate –  particle size   rate –  concentration of reactant   rate  Catalysts:  the rate of a reaction without being chemically changed – Enzymes are biological catalysts