Chapter 2 – Chemical Composition of the Body

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

2. 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..

4. Atomic number = sum of P • Atomic mass = sum of P and N • 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?)..

5. 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..

6. Bonding is accomplished by interactions between two atom’s valencee-. • 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 Animation..

8. 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..

10. 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)..

12. 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..

13. 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..

14. 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 H20 has a pH = 6; solution with 0.1 the [H+] has a pH = 8. • Hydrogen plus hydroxide molar concentrations will always equal 10-14..

16. A buffer is a system of molecules and ions that act to prevent changes in [H+] and stabilizes pH of a solution. • In blood: • H20 + C02 H2C03 H+ + HC03- • Reaction can proceed in either direction (depending upon the concentration of molecules and ions)..

17. Arterial blood pH remains remarkably stable at 7.35 – 7.45 because of buffering systems especially the bicarbonate/carbonic acid system. HC03- and H2C03 act as buffer pair. • Acidosis = pH < 7.35. • Alkalosis = pH > 7.45..

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

19. Organic molecules that contain carbon, hydrogen and oxygen. CnH2n0n. Monosaccharides = simple sugars. Structural isomers: Glucose, fructose, galactose. Carbohydrates

20. 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)..

21. Organic molecules are built by dehydration synthesis: C6H12O6 + C6H12O6 C12H22O11 + H2O

22. Organic Molecules are broken down by hydrolysis C12H22O11 + H2O C6H12O6 + C6H12O6

23. 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..

26. 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..

28. 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 (NH2) 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..

31. 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. • a-helix or b-sheet..

32. 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..

35. 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..

37. 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..