Transcript CHEMISTRY-Text notes

Chapter 2: The Molecules of
Cells
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Basic Chemistry
Matter is anything that takes up space
and has weight.
All matter, living or nonliving, is made up
of elements.
Elements contain atoms.
An atom is the smallest unit of matter
that can enter chemical reactions.
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Atoms have a central nucleus made up of
protons and neutrons, and shells
around the nucleus in which electrons
orbit.
• inner energy shell holds two electrons
• outer energy shell holds eight electrons
The number of electrons in the outer
energy shell determines the chemical
properties of the atom.
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Model of an Atom
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The atomic number of an atom is its number
of protons.
• protons bear a positive electrical charge
The atomic weight of an atom is its number
of protons plus its number of neutrons.
• neutrons bear no electrical charge
• electrons bear a negative electrical
charge
An electrically neutral atom means:
number of protons = number of electrons
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Elements are arranged in a periodic
table:
• horizontally in order of increasing
atomic number
• vertically according to the number of
electrons in the outer shell
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Atoms have an atomic symbol, atomic
number, and atomic mass.
Some atoms differ in their number of
neutrons and are called isotopes.
Carbon has 3 isotopes:
• Carbon 12 (most abundant)
• Carbon 13
• Carbon 14 (radioactive - unstable)
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• Atoms form bonds to fill the outer
shell with electrons.
• When atoms bond with other atoms,
molecules are formed.
• When atoms of different elements
bond, a compound is formed.
• Two types of bonds are ionic bonds
and covalent bonds.
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In ionic bonding, atoms give up or
accept electrons, resulting in ions.
Ions with opposite charges (- or +) are
attracted to each other and form an
ionic bond.
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Ionic Bonds
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Ions can have important biological
functions.
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Covalent Bonds
In covalent reactions, atoms share
electrons, resulting in covalent
bonds.
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There are other ways of representing
covalent bonds.
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Aside from single covalent bonds,
double, or triple covalent bonds can
form.
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The three-dimensional shape of
molecules can be represented in two
ways:
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Water and Living Things
• Water is the most abundant molecule in
living things.
• Water has special traits that make it
important to life.
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• Because oxygen atoms are large and
hydrogen atoms are small, water is a
polar molecule.
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• Hydrogen bonds form when a
covalently-bonded H+ is attracted to
a negatively-charged atom in a
neighboring molecule.
• Because of its polarity and hydrogen
bonding, water has unique
characteristics that benefit living
things.
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Characteristics of water:
1.
2.
3.
4.
5.
6.
liquid at room temperature
universal solvent for polar molecules
water molecules are cohesive
temperature of water changes slowly
high heat of vaporization
frozen water is less dense so ice
floats
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• Water dissociates and releases
hydrogen ions (H+) and hydroxide
ions (OH-).
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• Acids are molecules that release
hydrogen ions in solution.
HCl  H+ + Cl-
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• Bases are molecules that either take
up hydrogen ions or give off
hydroxide ions in solution.
NaOH  Na+ + OH-
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• Concentrations of hydrogen ions or
hydroxide ions can be represented
using the pH scale.
moles/liter
1 x 10 –6 [H+] = pH 6
1 x 10 –7 [H+] = pH 7
1 x 10 –8 [H+] = pH 8
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• Buffers are substances that help to
resist change in pH.
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Organic Molecules
Organic molecules are found in
living things.
The chemistry of carbon accounts
for the chemistry of organic
molecules.
Organic molecules are
macromolecules.
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Hydrocarbon chains can have
functional groups that cause the
macromolecule to behave in a certain
way.
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Macromolecules (polymers) are formed
from smaller building blocks called
monomers.
Polymer
carbohydrate
protein
nucleic acid
Monomer
monosaccharides
amino acid
nucleotide
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Carbohydrates
Carbohydrates serve as quick energy
and short-term energy storage.
They play a structural role in plants,
bacteria, and insects.
Monomers of carbohydrates are the
monosaccharides:
glucose
fructose
galactose
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Structure of Glucose
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A disaccharide is made from linking
two monosaccharides together.
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Larger polysaccharides are made from linking many
glucose molecules together through condensation
synthesis.
Examples of polysaccharides:
Starch
glycogen
cellulose
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Lipids
Lipids serve as long-term energy stores
in cells, form membranes, and serve as
hormones and insulation.
Lipids do not dissolve in water.
Fats and oils are formed from a glycerol
molecule and three fatty acid
molecules.
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Structure of Triglycerides
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Fatty acids are long chains of
hydrocarbons ending in - COOH
Fatty acids may be saturated fatty acids
or unsaturated fatty acids.
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Some lipids are phospholipids that
form cell membranes.
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Other lipids are steroids.
Examples include cholesterol, and the
sex hormones estrogen and
testosterone.
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Proteins
Proteins perform many functions in cells.
Proteins:
Serve as structural proteins
Act as enzymes to speed reactions
Serve as transport carriers
Act as antibodies
Allow materials to cross cell membranes
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Proteins are polymers of amino acids.
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Peptide bonds join amino acids.
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Proteins have levels of organization.
Proteins can be denatured.
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Nucleic Acids
Nucleic acids are polymers of nucleotides.
Examples include Deoxyribonucleic Acid
(DNA) and Ribonucleic Acid (RNA).
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DNA is double-stranded, with
complementary base pairing.
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Some nucleotides also perform functions
in cells.
Adenosine triphosphate (ATP) is the
energy currency of cells.
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