Chemistry for Biology StudentsPresentation Transcript
• The Universe consists of
matter and energy.
o Matter is anything that
occupies space and has mass.
o Energy is the capacity to
produce change. For example,
energy is needed to move
• Matter is composed of elements. An element is a substance
that cannot be broken down into other substances by
ordinary chemical means. Each element has its own:
o Name and chemical symbol
o Characteristic physical properties, such as melting point and boiling
o Characteristic chemical properties, such as what elements it reacts
• An atom is the smallest part of an element that retains the
properties of that element. The three major sub-atomic
particles are protons, neutrons, and electrons.
Particle Location Relative mass Charge
Proton Nucleus 1 +1
Neutron Nucleus 1 0
Electron Electron shell 1/1840 −1
o All atoms of an element contain the same number of protons.
o Protons and neutrons are found in the centrally-located nucleus.
o A crude but still useful model says that electrons are found in
“electron shells” around the nucleus.
o An atom has the same number of protons and electrons, and
therefore has no net charge—that is, it is electrically neutral.
A “shell model” of the carbon
atom, with six protons, six
neutrons, and six electrons.
“The Importance of Being Electrons”
• Electrons are important for several reasons:
o Chemical bonds are formed when electrons are transferred or shared
between atoms. A chemical bond is the attraction between two
atoms that keeps them together.
o The arrangement of electrons in the atoms of an element
determines the chemical properties of that element.
o Electrons can carry and store energy. In every chemical reaction,
electrons are shared or transferred between atoms and hence
energy is shared or transferred. This is important to understanding
• Electrons occupy specific electron shells.
o Electrons in the same shell all have the same energy as one another.
o Electrons in higher shells have more energy than those in lower shells.
o Each electron shell has a maximum occupancy.
o Electrons fill in a regular pattern from the lowest shell outward.
o An electron can
move from one
shell to another
only if it absorbs
or releases a
• Only the electrons in the outermost occupied electron shell of
an atom are involved in chemical bonding.
o Most atoms are stable when their outermost electron-containing shell
has eight electrons (two in the case of hydrogen).
o Stability can be achieved by adding, losing, or sharing electrons.
• When an atom with an almost
empty outer shell reacts with
an atom with a nearly full
outer shell, the first atom may
lose an electron(s) to the
second, becoming positive and
negative ions respectively. The
attraction that holds two ions
together is therefore called an
• When two atoms with
partially full outer shells
react, they may share
electrons, forming a
o The shared electrons are
called bonding electrons.
o A covalent bond may consist
of two, four, or six electrons
being shared, called a single,
double, or triple bond
o A molecule consists of
two or more atoms
that are held together
by covalent bonds.
The atoms may be of
the same element or
of different elements.
o Like atoms, molecules
can also become ions.
Nonpolar and Polar Covalent Bonds
• A bond in which two atoms
share their electrons equally is
nonpolar covalent; a bond in
which two atoms share them
unequally is polar covalent,
because it has electrical poles.
o In a polar covalent bond, one
atom gets a partial negative
charge (δ−) and the other a
partial positive charge (δ+).
However, the atoms together
Nonpolar and Polar Molecules
• If a molecule has a partial positive charge at one end and a
partial negative charge at the other end, it is a polar molecule;
otherwise, it is a nonpolar molecule.
• A compound is a substance composed of two or more
elements in a specific, fixed ratio.
o For example, sodium chloride (table salt) is a compound made
of two elements, sodium and chlorine. For every sodium ion,
there is one chloride ion.
Types of Compounds and Elements
• A compound composed of ions, such as sodium chloride, is
called an ionic compound; one composed of molecules, such
as glucose or water, is called a molecular compound.
o NOTE: An element composed of molecules in nature (such as
hydrogen, oxygen, and nitrogen) is not a compound; it is called a
• Types of chemical
o Simplest formula: The
number ratio for the
used for ionic
o Molecular formula:
The number of atoms
of each element in a
o Structural formula:
Adds the bonding
pattern to the
Simplest Molecular Structural
Oxygen O O2
Water H2O H2O
Organic and Inorganic Compounds
• Compounds that contain
hydrogen and carbon, with the
carbon atoms covalently bonded
to each other (usually in long
chains), are called organic
compounds. They may also
contain other elements.
o Compounds that are not organic
are called inorganic compounds.
• A mixture contains different
compounds (and sometimes
elements) mixed together,
but they are not chemically
o The components are in no
o The properties of the mixture
are the same as those of the
o The components can be
separated by physical means,
such as filtration, evaporation,
• A solution is a uniform
mixture of two or more
o The dissolving medium is the
solvent, usually a liquid.
Solutions in living organisms are
aqueous solutions, meaning
that water is the solvent.
o The dissolved substance is the
solute. Solutions in living
organisms usually contain
• A hydrogen bond is the very weak attraction between a
slightly-positive hydrogen in one covalent bond and a slightly-
negative atom (usually oxygen or nitrogen) in another covalent
bond. This attraction is about 5% to 10% of the strength of one
(covalent) single bond.
o Hydrogen bonds form
within water and
o They easily form
molecules and other
polar molecules, such
o Also, hydrogen bonds
between atoms within
the same molecule, as
in DNA, RNA, and many
Nonpolar Covalent Bonds Polar Covalent Bonds
Ionic Bonds Hydrogen Bonds
Summary of Chemical Bonds
The (Almost) Universal Solvent
• Due to its polar nature, water is
an extremely effective solvent,
able to dissolve just about
anything. This also makes
water vital for life, because
most biochemical reactions
occur only within aqueous
o Water easily dissolves small polar molecules, like table sugar, and ionic
compounds, like table salt. That's because the charged ends of the
water molecules are attracted to the charges on these molecules and
ions, keeping the latter in solution.
Found in Living
Cl−, K+, Na+,
o However, large polar
molecules and all
nonpolar molecules do
not dissolve in water.
Oil does not dissolve in water.
o Since water molecules cannot form hydrogen bonds with nonpolar
molecules, they associate only with each other, leaving the nonpolar
molecules (purple) by themselves.
Water and pH
• In water, a very small percentage of the molecules break
apart (dissociate) into hydrogen ions (H+) and hydroxide
ions (OH−). pH is a measure of the concentration of H+ in
water and in aqueous solutions.
Acids and Bases
• Some compounds change the concentration of hydrogen ions
(H+) when dissolved in water.
o Acids are substances that increase the H+ concentration, thus causing
solutions to become more acidic and less basic.
o Bases are substances that decrease the H+ concentration, thus causing
solutions to become more basic (more alkaline) and less acidic.
The pH Scale
• The pH scale ranges from
0 (most acidic) to 14 (most
basic), with 7 as neutral.
Due to the way pH is
o As the H+ concentration
increases, the pH
decreases, and vice versa.
o Each number in the pH
scale represents a tenfold
change in the H+
14 Sodium hydroxide (NaOH)
13 Oven cleaner
12 Soda ash
11 Household ammonia
10 Great Salt Lake
9 Baking soda
7 Pure water
6 Urine; Saliva (6.5)
5 Black coffee
3 Vinegar; cola; beer
2 Lemon juice
1 Stomach acid
0 Hydrochloric acid (HCl)
• Organic molecules can be
very large and complex
because the carbon atom
has four electrons in its
electron shell and therefore
can bond with up to four
o Since carbon atoms can bond
to other carbon atoms, carbon
chains and rings that serve as
the backbones of organic
molecules are possible.
• Thus, many of the important molecules found in living things
are macromolecules—large molecules consisting of many
thousands of atoms. They are made by chemically linking
together smaller molecules called subunits.
factor. Each little
Polymers and Monomers
• Most biological macromolecules are polymers. A polymer is a
large molecule made by chemically linking together many
repeating subunits to make a long chain analogous to box cars
in a train. In this case, the subunits are called monomers.
• Carbohydrates contain atoms of
carbon, hydrogen, and oxygen in the
ratio 1:2:1 respectively. Their
subunits are single sugars, such as
glucose and fructose.
o Two single sugars joined together form a
double sugar. The names of all sugars
end in “ose.” They are sweet and
dissolve in water.
o Complex carbohydrates are chains
(polymers) of single sugars (monomers).
They are neither sweet nor soluble in
water. Polymers of glucose include
starch, cellulose, glycogen, and chitin.
A model of the glucose
molecule. Black =carbon
atoms, red=oxygen atoms, and
• Major functions of carbohydrates in plants and animals
include providing energy for cells, storing energy in the
organism, and physically supporting the organism.
• Proteins consist of one or more polypeptides. A polypeptide
is a chain (polymer) of amino acids (monomers).
o There are 20 different amino acids.
o The particular sequence of amino acids in a polypeptide determines
its three-dimensional shape.
o The shape of a protein determines its function.
• Proteins have many
o Enzymes catalyze
o Structural proteins (e.g.
o Transport (e.g.
o Antibodies of the
o Hormones (e.g. insulin)
Hemoglobin carries oxygen through the blood.
• Nucleic acids (DNA and RNA) function in heredity. A nucleic
acid molecule consists of one or two polymers called
polynucleotides (or strands), which are made up of
subunits (monomers) called nucleotides. Each nucleotide
consists of three parts:
o A phosphate (PO4
o A sugar: Deoxyribose in DNA or ribose in RNA.
o A base: Adenine (A), cytosine (C), or guanine (G) in both DNA and
RNA; thymine (T) only in DNA; uracil (U) only in RNA.
• DNA molecules consist of two polynucleotides held together
by many hydrogen bonds; RNA molecules consist of just one.
ATP (Adenosine Triphosphate)
related to one of the
nucleotides in RNA, is
the most common
molecule in the cell.
o Removing the terminal
phosphate group of ATP
diphosphate (ADP) and
also releases energy.
The ATP/ADP Cycle
• The ATP/ADP cycle can be described by two different analogies:
o ATP is the “energy currency” of the cell because it is used as a sort of
intracellular money to “pay” for nearly every energy-requiring activity
cells carry out.
I Cells use energy from organic
molecules like glucose to make ATP.
Most people work to earn money.
II Then cells use ATP to provide the
energy for most biological processes.
Then people spend their money to
buy the things they need or want.
o ATP is like a rechargeable battery. It releases stored energy that the
cell can use, becoming ADP in the process. ADP can then be
“recharged” to ATP with energy from food or light and saved for future
• Lipids dissolve in nonpolar solvents but not in water. They
are not polymers and do not have a common structure.
There are three major types:
o Triglycerides (fats) store energy, insulate, and waterproof;
o Steroids, such as testosterone and cholesterol, are hormones or
o Phospholipids perform an extremely important function—they form
• Each phospholipid molecule
has a phosphate (PO4
as its “head” and two long fatty
acids for “tails.” Because the
head is polar and the tails are
nonpolar, the head attracts
water molecules but the tails