Biology 231
Human Anatomy and Physiology
Chapter 2 Lecture Outline
Chemical Level of Organization
elements – building block of matter; cannot be split into a simpler substance by
ordinary chemical means
92 occur naturally
chemical symbol – 1 or 2 letters representing an element (eg. C for carbon)
atom – smallest unit of an element
nucleus – dense core of atom;
protons – positively charged particles
neutrons – uncharged particles
electrons – negatively charged particles; surround nucleus
electron shells – regions where electrons are usually found
# of protons = # of electrons (electrically neutral)
atomic number – number of protons (different for each element)
mass number – number of protons + neutrons
isotopes – atoms of an element with different numbers of neutrons;
electrical charge is the same (same chemical properties)
radioactive isotopes – unstable nuclei; decay and release radiation
(eg. C-14) decay at different rates
molecule – 2 or more atoms held together by chemical bonds
Chemical Bonds – forces that hold atoms of a molecule together; depends on
arrangement of electrons
valence shell – outer, reactive electron shell
octet rule – 8 electrons in the valence shell is most stable; allows
prediction of reactivity
(in some small atoms the valance shell has only 2 electrons)
Ionic Bonds – one atom loses valence electrons to another; held together by
electrical attraction of opposite charges
ion – charged particle
anion – gains electrons (negatively charged)
cation – loses electrons (positively charged)
ionic compounds break into ions in water
Covalent Bonds – atoms share valence electrons; most common bonds in body
single bond (share 1 pair of electrons) – hydrogen molecule
double bond (share 2 pairs of electrons) – oxygen molecule
nonpolar covalent bond – electrons shared equally
polar covalent bond – unequal electron sharing; produces partial electrical
charges on atoms sharing electrons
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Hydrogen Bonds – weak bonds between hydrogen atoms (partial positive charge)
and neighboring atoms with partial negative charges (eg. O or N)
too weak to form molecules; form attractions between molecules or parts
of molecules
Chemical Reactions – foundation of all life processes
metabolism – sum of all chemical reactions occurring in the body
reactants – starting substances
products – ending substances
Types of Reactions:
synthesis reactions (anabolism) – 2 or more atoms, ions, or molecules
combine to form new, larger molecules
decomposition reactions (catabolism) – larger molecules split into smaller
atoms, ions, or molecules
exchange reactions – concurrent synthesis and decomposition (old bonds
break and new ones form)
reversible reactions – reaction may proceed in either direction, usually
depending on conditions in the environment
Energy of Chemical Reactions (energy = ability to do work)
kinetic energy - energy of motion
activation energy – energy investment needed to start a reaction;
makes valence electrons unstable so they can react
factors affecting reaction rate:
concentration of reactants – more = faster
temperature – higher = faster
catalysts – lower activation energy so reaction proceeds faster
(enzymes – biological catalysts)
potential energy – stored energy
chemical energy – stored energy in chemical bonds; cannot be created or
destroyed, but can be converted into other forms (other chemical
bonds, mechanical energy, heat)
exergonic reaction – reaction that releases energy; products have less
chemical energy that reactants (catabolism)
endergonic reaction – reaction that requires energy input; products have
more chemical energy than reactants (anabolism)
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INORGANIC COMPOUNDS – usually lack carbon and are structurally simple
(eg. water, oxygen, carbon dioxide)
Water – most important inorganic compound in body
polar covalent molecule – biological solvent
(solvent + solutes = solution)
hydrophilic (water-loving) – dissolves easily in water (ions and
polar covalent molecules)
hydrophobic (water-fearing) – dissolve poorly in water (mainly
nonpolar covalent molecules)
participates in metabolic reactions
hydrolysis reaction – using water to break down larger molecules
dehydration synthesis – joining 2 smaller molecules by removing a
molecule of water
Acids, Bases, and Salts – ionic compounds
acids – dissolve to form hydrogen ions (H+); (proton donors)
bases – dissolve to form anions that can bind H+ (proton acceptors)
salts – do not affect pH of solution
pH – measurement of a solution’s acidity or alkalinity(basicity)
pH scale (Fig 2-9)
pH 7 = neutral
lower pH = more acidic = more hydrogen ions
higher pH = more basic = fewer hydrogen ions
body fluids maintain narrow pH ranges
buffers – chemicals that stabilize pH of a solution by accepting or
donating H+ when needed
ORGANIC COMPOUNDS – contain carbon and hydrogen (+ oxygen, nitrogen,
phosphorus, and other elements) joined almost entirely by covalent bonds; may be
very large and structurally complex
carbon skeleton – chain of carbon atoms; each can form 4 covalent bonds
functional groups – other atoms in specific arrangements attached to carbon
skeleton; confer characteristic chemical properties
CLASSES OF ORGANIC COMPOUNDS
Carbohydrates - sugars, starches, glycogen, cellulose
primarily an energy source in the body (some structural)
general chemical formula – 1 carbon:2 hydrogen:1 oxygen
monosaccharides – simple sugars(monomers); 3-7 carbons (eg. glucose)
disaccharides – 2 monosaccharides joined by dehydration (eg. sucrose)
polysaccharides – 10s to 100s of monosaccharides (eg. glycogen)
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Lipids – fats and oils, phospholipids, steroids, fatty acids
energy storage, insulation, main component of cell membranes
contain carbon, hydrogen, less oxygen than carbohydrates
mainly hydrophobic
fatty acids – carbon/hydrogen chains with carboxyl group
saturated fatty acids – only single covalent bonds
unsaturated fatty acids – at least 1 double covalent bond
triglycerides – energy storage, insulation, protection
glycerol – 3-carbon backbone
3 fatty acids
phospholipids – main component of cell membranes
glycerol + 2 fatty acids – nonpolar tail
phosphate linked polar head
amphipathic – has polar (charged) and nonpolar (uncharged) regions
steroids – cholesterol, sex hormones, cortisol
have 4 carbon rings
Proteins – major structural and functional molecules of body
contain carbon, hydrogen, oxygen, and nitrogen (some sulfur)
amino acids – 20 different protein monomers
central carbon with one H
amino group (-NH2)
carboxyl group (-COOH)
side chain (R group)
peptide bond – covalent dehydration reaction links amino acids
peptides – dipeptide (2), tripeptide (3), polypeptide (>10)
proteins – 1 or more polypeptide chains, may be very structurally
complex; function is related to shape
primary structure – sequence of amino acids
secondary structure – repeated twisting or folding due to hydrogen
bonds – alpha helix, beta pleated sheet
tertiary structure – 3-D folding due to hydrogen bonds,
hydrophobic interactions, and disulfide bridges
quaternary structure – some proteins are composed of more than 1
polypeptide chain held together like tertiary structures
enzymes – protein catalysts; most common catalysts in body
very specific – only catalyze specific reactions
substrate – reactant molecule enzyme acts on
active site – recognizes and binds specific substrate
very efficient – may increase reaction rate billions of times
enzyme is not altered or used up
enzyme regulation – cofactors, coenzymes, concentration
denatured enzyme – loses its functional structure
(eg. change in pH, temperature)
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Nucleic Acids – DNA, RNA
control heredity and cell function through protein synthesis
composed of carbon, hydrogen, oxygen, nitrogen, and phosphorus
nucleotides – monomers of nucleic acids
pentose sugar (5-carbon)
DNA – deoxyribose
RNA – ribose
phosphate group
nitrogenous base (5 types)
adenine (A) – DNA and RNA
guanine (G) – DNA and RNA
cytosine (C) – DNA and RNA
thymine (T) – DNA only
uracil (U) – RNA only
nucleic acids are strands of nucleotides joined by dehydration reactions
RNA is single-stranded
DNA is a double-stranded helix held together by hydrogen bonds
between bases of adjacent strands
ATP (adenosine triphosphate) – high energy organic compound
energy currency of body – temporarily stores energy released by catabolic
reactions so it can be released later, where it is needed
nucleotide – adenosine monophosphate
+ phosphate groups
phosphorylation (addition of phosphate groups by enzymes)
high-energy bonds formed by specific enzymes
ADP – 1 high-energy phosphate bond
ATP – 2 high-energy phosphate bonds
Breaking the high-energy bonds releases the energy for use in endergonic
reactions in the body.
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