Biology 55
Chemistry
CHEMICAL LEVEL OF ORGANIZATION
elements – building blocks of matter
chemical symbol – 1 or 2 letters representing an element
C = carbon
H = hydrogen
O = oxygen
N = nitrogen
Na = sodium
K = potassium
Cl = chloride
Ca = calcium
P = phosphorus
atom – smallest unit of an element
nucleus – dense core of an atom
protons – positively charged particles; number determines element
neutrons – uncharged particles; number can vary
electrons – negatively charged particles that surround nucleus
# of protons = # of electrons (electrically neutral)
molecule – 2 or more atoms held together by chemical bonds
macromolecule – very large molecule
CHEMICAL BONDS – forces that hold atoms of a molecule together; depends on the
arrangement of electrons
Ionic Bonds – one atom loses electrons to another; molecule is held together by
attraction of opposite charges
ion – charged particle due to loss or gain of electrons
anion – gains electrons (negatively charged)
cation – loses electrons (positively charged)
ionic compounds dissociate into ions when dissolved in water
Covalent Bonds – atoms share electrons; most common bonds in body
single bond (share 1 pair of electrons)
double bond (share 2 pairs of electrons)
nonpolar covalent bond – electrons shared equally
polar covalent bond – unequal electron sharing
molecule is polarized – has partial negative charge on one side and
partial positive charge on the other
Hydrogen Bonds – weak bonds between hydrogen atoms (partial positive charge)
and molecules with partial negative charges
too weak to form molecules - form attractions between molecules or parts
of molecules
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CHEMICAL REACTIONS – foundation of all life processes
reactants – starting substances
products – ending substances
Energy of Chemical Reactions
activation energy – energy investment needed to start a reaction
makes electrons unstable so they can react
catalysts – molecules that lower activation energy so reactions
are more likely to occur
enzymes – biological catalysts (proteins made by cells)
most body reactions would not occur without enzymes
forming new bonds requires energy, and some is stored in the bonds
breaking bonds releases stored energy
Metabolism – sum of all chemical reactions occurring in body
synthesis reactions – smaller reactants combine to form larger products
requires energy input
decomposition reactions – large reactants broken down into smaller
products; usually releases energy
MOLECULES FOUND IN THE BODY
inorganic molecules – found in environment and are usually fairly simple
organic molecules – synthesized by living things; all contain carbon and many
are large and structurally complex (macromolecules)
Water – most important inorganic molecule
biological solvent – dissolves biological molecules so they can react with
each other (solvent + solutes = solution)
water is polar covalent – partial charges attract water molecules to each
other and to other charges particles
hydrophilic (water-loving) – dissolves easily in water
charged particles (ions and polar covalent molecules)
hydrophobic (water-fearing) – dissolve poorly in water
uncharged particles (nonpolar covalent molecules)
water 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+) [increase H+ in solution]
bases – dissolve to form anions that bind H+ [remove H+ from solution]
salts – dissolve to form other ions
electrolytes – ions that can conduct electrical currents
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pH – measurement of a solution’s hydrogen ion concentration
pH scale – pH 7 is neutral
lower pH = more acidic = more hydrogen ions
higher pH = more basic = fewer hydrogen ions
buffers – chemicals that stabilize pH of a solution by binding or
releasing H+ when needed
cells only function properly within a narrow pH range
ORGANIC MOLECULES
contain carbon and hydrogen (+ oxygen, nitrogen, phosphorus, 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
4 CLASSES OF ORGANIC MOLECULES
1) CARBOHYDRATES - sugars, starches, glycogen, cellulose
primarily an energy source in the body
general chemical formula – 1 carbon:2 hydrogen:1 oxygen
types of carbohydrates:
monosaccharides – simple sugars; 3-7 carbons
glucose – main carbohydrate in blood
disaccharides – 2 monosaccharides joined by dehydration
synthesis (eg. lactose – milk sugar)
polysaccharides – composed of many monosaccharides
glycogen – carbohydrate storage in animals
starch – carbohydrate storage in plants
cellulose – structural carbohydrate in plants
2) LIPIDS – fats and oils, phospholipids, steroids, fatty acids, triglycerides
contain carbon, hydrogen, and less oxygen than carbohydrates
mainly hydrophobic molecules
types of lipids:
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 (fat) – energy storage, insulation
phospholipids – main component of cell membranes
nonpolar tail (hydrophobic)
polar head (hydrophilic)
steroids – cholesterol, sex hormones, cortisol
have 4 carbon rings
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3) PROTEINS – major structural and functional molecules of body
contain carbon, hydrogen, oxygen, and nitrogen (some sulfur)
amino acids – 20 different building blocks of proteins
central carbon with one H
amino group (-NH2)
carboxyl group (-COOH)
R group – unique group for each different amino acid
peptide bond – dehydration synthesis links amino acids
peptide – chain of amino acids
(2) dipeptide, (3) tripeptide, (>3) polypeptide
proteins – large polypeptides; may be very structurally complex
function is related to shape
primary structure – chain of amino acids
secondary structure – repeated twisting or folding due to hydrogen
bonds – alpha helix, beta pleated sheet
tertiary structure – 3-D twisting due to hydrophilic and
hydrophobic interactions, and various bonds
quaternary structure – some proteins are composed of more than
1 polypeptide chain held together by attractions and bonds
enzymes – protein catalysts
very specific – only catalyze specific reactions
substrate – reactant molecule(s) enzyme acts on
active site – site that binds specific substrate(s)
very efficient – may increase reaction rate millions of times
enzyme is not altered or used up
enzyme regulation
enzyme concentration
inorganic cofactors (eg. Ca)
organic coenzymes (eg. vitamins)
denatured enzyme – loses its functional structure
eg. pH, temperature outside of homeostatic range
4) NUCLEIC ACIDS – DNA, RNA
control heredity and cell function by controlling protein synthesis
composed of carbon, hydrogen, oxygen, nitrogen, and phosphorus
nucleotides – building blocks of nucleic acids
5-carbon sugar
DNA – deoxyribose
RNA – ribose
phosphate group
nitrogenous base (5 types)
adenine (A), guanine (G), cytosine (C)
thymine (T) – only in DNA
uracil (U) – only in RNA
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nucleic acid strands have backbones of sugars and phosphates joined by
dehydration reactions
RNA is single-stranded
DNA is a double-stranded helix held together by hydrogen bonds between
nitrogenous bases of adjacent strands
ATP (adenosine triphosphate) – stores energy released by catabolic reactions
nucleotide – adenosine monophosphate
addition of 2 high energy phosphates by specific enzymes
ADP (adenosine diphosphate) – 1 high-energy phosphate bond
ATP – 2 high-energy phosphate bonds
breaking the high-energy bonds releases energy to use in synthesis reactions
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