Chapter 2 – Chemical Composition of the Body “Because living things, including humans, are composed only of chemicals, it is absolutely essential for a (physiology) student to have a basic understanding of chemistry.” Sylvia Mader..

Atoms – smallest unit of an element that can undergo a chemical change. Composed of subatomic particles: Protons = (+ charge) found in the nucleus Neutrons = (no charge) found in the nucleus Electrons = (e-,- charge) found orbiting the nucleus in the electron cloud The number of protons determines the atom’s identity, e.g. 6 P = carbon..

The number of N and/or e- can change. Isotope = change the number of N Ion = change the number of e-  cation = positive ion (how does it become positive?)  anion = negative ion (how does it become negative?).. Atomic number = sum of P Atomic mass = sum of P and N

The position of an atom’s e- is the electron configuration. We will not study configurations except for the outermost level of e- = valence shell The e- found there are the valence e-. The valence e- are the ones involved in ordinary chemical reactions..

Bonding is accomplished by interactions between two atom’s valence e-. –If e- are shared between two atoms that forms a covalent bond. Single bonds = one shared pair Double bonds = two shared pairs Triple bonds = three shared pairs –If e- are transferred from one atom (ion) to another that forms an ionic bond. Hydrogen bonds are special (polar) covalent bonds that are very important to physiology. Covalent Animation Ionic AnimationIonic Animation..

Electronegativity is the property that describes an atom’s attraction for a shared pair of e-. If two atoms with different electro- negativity values share e-, i.e. form a covalent bond, one of the atoms will have a “larger share” of the e-. This produces a molecule with differently charged ends (poles). This type of molecule is called polar..

Bonds formed between the hydrogen end (+ charged) of a polar molecule and the – end of any other polar molecule or highly electronegative atom (e.g. P, N, O) are called hydrogen bonds. These hydrogen bonds are very important because they alter the physical and chemical properties of many molecules (especially water)..

Molecules that are formed by polar covalent bonds have a tendency to break apart when the electron from the hydrogen is transferred to the more electronegative atom. This is called dissociation or ionization. Water ionizes to form equal amounts of hydroxyl (OH-) and hydrogen (hydro- nium, H+) ions..

An acid is a molecule that can release protons (H + ). –Proton donor. A base is a molecule that can combine with H + and remove it from solution. Bases are also defined as releasing OH-. –Proton acceptor..

pH = log _1__ [H + ] –[H + ] = molar concentration of H +. –pH inversely related to [H + ]. Because of logarithmic relationship, a solution with 10 times [H + ] of H 2 0 has a pH = 6; solution with 0.1 the [H + ] has a pH = 8. Hydrogen plus hydroxide molar concentrations will always equal

A buffer is a system of molecules and ions that act to prevent changes in [H + ] and stabilizes pH of a solution. In blood: * H C0 2 H 2 C0 3 H + + HC0 3 - –Reaction can proceed in either direction (depending upon the concentration of molecules and ions)..

Arterial blood pH remains remarkably stable at 7.35 – 7.45 because of buffering systems especially the bicarbonate/carbonic acid system. HC0 3 - and H 2 C0 3 act as buffer pair. Acidosis = pH < Alkalosis = pH >

Organic Molecules Composed primarily of H, C, O, & N. Look at the common functional groups.

Carbohydrates Organic molecules that contain carbon, hydrogen and oxygen. –C n H 2n 0 n. Monosaccharides = simple sugars. –Structural isomers: Glucose, fructose, galactose.

Disaccharide: –2 monosaccharides joined covalently. Sucrose (glucose and fructose), lactose (glucose and galactose), maltose (2 glucose). Polysaccharide: –Numerous monosaccharides joined covalently. Starch (thousands of glucose joined), glycogen (repeating glucose joined that are highly branched)..

Organic molecules are built by dehydration synthesis: C 6 H 12 O 6 + C 6 H 12 O 6 C 12 H 22 O 11 + H 2 O

Organic Molecules are broken down by hydrolysis C 12 H 22 O 11 + H 2 O C 6 H 12 O 6 + C 6 H 12 O 6

Lipids Insoluble in water because of nonpolar molecules –Triglycerides = 3 fatty acids + glycerol Saturated = joined by only single bonds Unsaturated = joined by at least one double bond Hydrolysis of triglycerides in adipose tissue releases free fatty acids. –Free fatty acids can be converted in the liver to ketone bodies. –Excess ketone bodies can lower blood pH..

–Phospholipids = phosphate + fatty acid phosphate end is polar = hydrophilic fatty acid end is nonpolar = hydrophobic –Steroids = aromatic rings = three 6-carbon rings joined to a 5-carbon ring Steroid hormones are cholesterol derivitaves..

Proteins Large molecules composed of long chains of amino acids. –20 different amino acids can be used in constructing a given protein. –Each amino acid contains an amino group (NH 2 ) at one end and carboxyl group (COOH) at the other end. Differences between amino acids are due to differences in functional groups (“R”). Amino acids are joined by peptide bonds..

Protein Structure Levels Primary structure is the sequence of the amino acids in the protein. Secondary structure is produced by weak hydrogen bonds between hydrogen of one amino acid and the and oxygen of a different amino acid nearby.   -helix or  -sheet..

Tertiary structure is formed when polypeptide chains bend and fold to produce 3 -dimensional shape. –Formed and stabilized by weak chemical bonds between functional groups. Each type of protein has its own own characteristic tertiary structure. Quaternary structure is produced when a number of polypeptide chains covalently linked together..

Nucleic Acids Include DNA and RNA. Nucleic acids are composed of nucleotides to form long polynucleotide chains. –Each nucleotide is composed of 3 smaller units: 5-carbon sugar (deoxyribose or ribose). Phosphate group attached to one end of sugar. Nitrogenous base attached to other end of sugar..

The “backbone” of the nucleic acid is formed by the sugar and phosphate pairs. The “rungs” are formed by paired nitrogenous bases. –Nitrogenous bases complementary pair A + T (U) C + G..