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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 nucleusNeutrons = (no charge) found in the nucleusElectrons = (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 NIon = 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 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 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..
• 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)..
• 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..
Carbohydrates
• Organic molecules that contain carbon, hydrogen and oxygen.– CnH2n0n.
• 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)..
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
(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..
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..