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CHAPTER 3 NOTES CHEMISTRY OF LIFE.
SECTION 1: MATTER AND SUBSTANCE
An atom is the smallest unit of matter that cannot be broken down by chemical means.
Atoms are made of three types of particles:
Protons positively charged
Electrons negatively charged
Neutrons have no charge
An Element is a substance made up of atoms that have the same number of protons.
An Isotope is an atom that has different number of protons.
Valence Electrons – electrons in the outermost level
Chemical bonds:
1. Covalent bonds – atoms share valence electrons. A molecule is a group of atoms held together by covalent
bonds. Water is a covalent compound.
2. Ionic bonds – atoms loose or gain electrons. An ion is an atom that has an electric charge because it lost or
gained electrons. Table salt NaCl is an ionic compound.
3. Hydrogen bonds – when bonded to Oxygen, Nitrogen, or Fluorine, Hydrogen has a partial charge which attracts
the negative pole of other molecules. Hydrogen bonding plays an important role in many of the molecules that
make up living things.
Polarity – molecules with partial charges on the opposite ends. Water is a polar substance. Water can dissolve other
polar molecules such as sugar, and ionic compounds such as salt. Nonpolar substances such as oil, grease, and wax do
not dissolve in water.
SECTION 2: WATER AND SOLUTIONS
Water is a unique substance. Most of the unique properties of water result because water molecules form hydrogen
bonds between them. Atoms inside the water molecule are joined together by covalent bonds, and each water molecule
is joined with another molecule by hydrogen bonds.
Properties of water:

Ice floats

Water absorbs and retains heat

Water molecules stick to each other. (Cohesion)

Water molecules stick to other polar substances (adhesion)
SOLUTIONS – a mixture in which ions or molecules of one or more substances are evenly distributed in another
substance.
Acids are compounds that form extra hydronium ions (H₃O⁺) when dissolved in water. E.g. lemon juice, vinegar.
Bases are compounds that form extra hydroxide ions (OH⁻) when dissolved in water. E.g. antacid, hand soap.
pH- is a measure of how acidic or basic a solution is. pH scale 0-14
<7 acidic, >7 basic, 7 –is neutral.
Buffer- is a substance that reacts to prevent pH changes in solution. An important buffer in living things is the
bicarbonate ion, HCO₃⁻.
Section 3 : Carbon Molecules
Monomers and Polymers
All biological molecules are very large and are built by assembling small molecules ( monomers or building blocks),
into long chains. The resulting molecules are called macromolecules, or polymers, or biomolecules. They can also be
called organic molecules because the all have H and C atoms. The most common element in all this molecules is
Carbon.
CARBOHYDRATES:
Like most classes of biological molecules, carbohydrates occur as both monomers and polymers. The smaller
molecules from which carbohydrates are built are called sugars, which commonly include monosaccharides (single
sugars) and some disaccharides (two sugars linked together). Larger carbohydrates are called polysaccharides (many
sugars linked together).
Examples of monosaccharides – Glucose, Fructose
Examples of disaccharides – Sucrose, Lactose.
Examples of polysaccharides – starch (produced by plants), chitin( used to make shells in lobsters and crabs),
cellulose ( a component in a cell wall), glycogen (produced in human body and other animals).
Mono- and Disaccharides are simple carbohydrates. Polysaccharides are complex carbohydrates.
Functions of carbohydrates include:
• storing short-term energy
• providing structural building materials
• serving as molecular ID "tags" to allow recognition of specific cells and molecules
LIPIDS:
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Lipids include various biomolecules whose common property is their
insolubility in water.
Lipids include a variety of molecular types, such as neutral fats, oils, steroids,
and waxes. Lipids are built from fatty acids and glycerol molecules (
monomers)
Lipids perform many important functions in biological systems, including:
• contributing to the structure of membranes that enclose cells and cell
compartments
• protecting against dessication (drying out)
• storing concentrated energy
• insulating against cold
• absorbing shocks
• regulating cell activities by hormone actions
PROTEINS:
The most abundant and diverse molecules found in living cells are
proteins.
Proteins are macromolecules, ranging from simply large to enormous. Proteins
typically make up about half the total weight of biomolecules in a cell
(excluding water). Proteins are built from amino acids molecules ( monomers).
We need 20 different amino acids to be able to build all the proteins our body
needs.
Proteins play a wide variety of functional roles, including:
• enzymes(types of proteins) as catalysts that accelerate specific chemical
reactions up to 10 billion times faster than they would spontaneously occur;
one cell may contain some thousand different types of enzymes at one time
• keratin (the protein found in hair and nails) and collagen (the protein found in
connective tissue)
• antibodies(proteins) that bind specifically to foreign substances to identify
them to the body's immune system
• membrane transport proteins that move substances across cell membranes,
and blood proteins, such as hemoglobin, that carry oxygen, iron, and other
substances through the body
• contraction of muscles such as actin(protein) and myosin(protein) fibers that
interact in muscle tissue
• signaling, including hormones such as insulin(protein) that regulate sugar
levels in blood
Nucleic Acids
Nucleic acids, built from nucleotides ( monomers), function primarily
as the storage and retrieval of hereditary information .
There are two types of nucleic acids:
• Deoxyribonucleic acid (DNA)
• Ribonucleic acid (RNA) which is needed to convert DNA information into
proteins .
Nucleic acids are built from subunits called nucleotides
Section 4 Energy and Metabolism
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The law of conservation of mass – Matter is neither created nor destroyed.
The law of conservation of energy – energy may change form , but the total amount of energy does not change.
Energy- the ability to move or change matter.
Physical change- when only the form or shape of the matter changes.
Chemical change – when a substance changes into another substance and the identity of the matter changes.
Chemical reactions- changing a substance by breaking bonds between atoms. Will occur only when the activation energy
is available and the correct atoms are aligned.
Reactant – a substance that is changed
Product- a new substance that is formed
The activation energy – the minimum amount of energy required to start a chemical reaction.
Biological reactions –chemical reactions carried out by living things, will not occur quickly and easily without the help of
enzymes.
ENZYMES- are molecules that increase the speed of biochemical reactions by 1) lowering the amount of activation
energy of a reaction and 2) holding molecules close together and in correct orientation.
LOCK AND KEY principle: enzymes fit reactants like a lock fits a key. Active site, the region on the enzyme, has a very
specific shape that will accommodate only specific molecules.
Many enzymes are proteins. Changes in temperature and pH can change a protein’s shape. If an enzyme changes
shape, it won’t work well.
Enzymes belong to a group of substances called catalysts . A catalyst is a substance which changes the rate of a
chemical reaction but is chemically unchanged at the end of the reaction.