Transcript Chapter 2: The Chemistry of Life

Chapter 2: The
Chemistry of Life
Mr. Grivensky/Mr. Rutkoski
Elements and Atoms
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A chemical element is a substance that
cannot be broken down into another
substance
The smallest unit of an element is an atom
1,000,000 atoms placed side by side would
only measure about 1 cm across
Parts of an Atom
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There are 3 main parts of an atom
Particle
Proton
Location
Nucleus
Charge
Positive (+)
Electron
Orbits the Nucleus
Negative (-)
Neutron
Nucleus
Neutral, No
charge
Atoms
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Most of the mass (99.9%) of an atom is found in
the nucleus
The mass of an electron is about 1/2000 that of a
Proton
The opposite charges of the electrons and
protons keep the electrons orbiting the nucleus
Atoms of different elements differ in the number of
protons, electrons, and neutrons
Bonds and Compounds
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There are 92 natural elements
About 20 more have been created in
laboratory settings
Atoms form chemical bonds with other
atoms to form compounds
They bond in such as way as to create
stable arrangements
Ionic Bonds
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An ion is an atom that has gained or lost an
electron
If an atom loses an electron, it has a
positive (+) charge
Atoms that gain an electron have negative
(-) charges
Two oppositely charged ions are attracted
to one another and may form a compound
Ionic Bond Example
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Sodium chloride (NaCl)
Na loses an electron and becomes Na+
Cl gains an electron and becomes ClThese two are attracted to one another and
form NaCl
Covalent Bonds
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Covalent bonds form when 2 or more
atoms share electrons
These compounds are called molecules
Molecules may contain few atoms (H2O) or
even millions (DNA)
The more electrons the atoms share, the
stronger the bonds between the atoms
Chemical Formulas
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A chemical formula indicates the elements
present in a compound and the proportions
in which they combine
Examples:
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H20 (water) 2 Hydrogen atoms and 1 Oxygen
C6H12O6 (glucose)
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6 Carbon, 12 Hydrogen, and 6 Oxygen
Water
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Liquid water is found inside every cell and most
cells are surrounded by water
Water is a polar molecule
In a polar molecule the electrons are shared, but
they spend more time around one atom than
another
Since the electrons in water spend more time
around the Oxygen atom, that end of the molecule
is slightly positive, while the Hydrogen side is
slightly negative
Solutions
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When water dissolves a substance it forms a solution
The compounds found in cells are often found in solutions
containing water and dissolved chemicals
This is one of the reasons water is so important to living
things
Parts of a solution
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Solute: The part that is in the smaller amount
Solvent: The part that is in the larger amount
Example: Salt water
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Water = greater amount = solvent
Salt = smaller amount = solute
H+ and OH- ions
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Water has the ability to break down into
ions of its own
This results in the formation of H+
(Hydrogen ions) and OH- (Hydroxide ions)
The H+ and OH- ions are two of the most
reactive ions found in nature
H 2O
H+ +
OH-
Acids and Bases
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Certain compounds dissociate in water to
form ions
Acids are compounds that produce H+ ions
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Example: Hydrochloric acid is formed in the
stomach when it dissociates
HCl
H+ + Cl-
Bases
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Bases are compounds that produce OHions
Example: Sodium hydroxide (NaOH)
NaOH
Na+ +
OH-
pH Scale
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The pH scale is used to indicate the
strength of an acid or base
Acids have a pH of 0 to 6
Bases have a pH of 8 to 14
A pH of 7 is considered neutral
pH Scale
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pH is actually a measurement of the H+
ions produced
A substance that produces 10-3 H+ ions
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10-3 = .0001 ions has a pH of 3 (acid)
A substance that produces 10-9 H+ ions
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10-9 = .0000000001 ions has a pH of 9 (base)
Carbon
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Carbon is an especially important element to all
living things
Organic compounds are compounds which
contain at least 2 Carbon atoms
Carbon typically forms 4 covalent bonds to
become stable
It has the ability to combine with many different
elements
It also has the ability to form chains of Carbon
atoms
Macromolecules
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Macromolecules are very large polymers
Polymers are large molecules which are
made up of many small molecules called
monomers
There are 4 main groups of
macromolecules which are important to
living things; carbohydrates, lipids, proteins,
and nucleic acids
Carbohydrates
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Sugars and starches are examples
Carbohydrates are made up of Carbon,
Hydrogen, and Oxygen
They usually contain 2x as many Hydrogen
atoms as Oxygen atoms
Example: Glucose: C6H12O6
Carbohydrates
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Simple sugars make up most of the smallest of
the carbohydrates
Examples include: Galactose (Milk), Fructose
(Fruits), and Glucose (in all cells)
Each simple sugar has the same formula:
C6H12O6; they only differ in the arrangement of the
atoms
Simple sugars are easy for the cells to produce
and break down; they serve as the way for cells to
store and release chemical energy
Carbohydrates
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Organisms can also use simple sugars to assemble larger
polymers
2 simple sugars joined together form a disaccharide
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Table sugar (sucrose is an example)
Simple sugars which contain only one sugar are called
monosaccharides
Polysaccharides contain many sugars which can be broken
down when the cell needs a simple sugar or energy
Plants store energy in the form of a polysaccharide known as
starch
Animals store energy in the form of a polysaccharide known
as glycogen
Lipids
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Examples of lipids are waxes, fats, and oils
Lipids are also a way to store energy but
they have other functions as well
Proteins
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Proteins are polymers that are made up of
monomers called amino acids
There are 20 common amino acids which
make up the majority of proteins
Amino acids share a common structure
In Glycine the R
group is a
Hydrogen atom
Amino acid Structure
H
N
Amino Group
(NH2)
-
C
-
H
O
-
H
-
C
R
In alanine the R
group is a
Methyl group
(CH3)
OH
R Group
Varies from one
amino acid to
another
Carboxyl Group
(COOH)
Amino Acids
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2 or more amino acids can be joined
together by the reaction of the amino group
(NH2) of one amino acid and the carboxyl
group (COOH) of another
The bond formed is a chain and is called a
peptide bond
A chain of amino acids is known as a
polypeptide
Proteins
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A complete protein is made up of many
polypeptides and may contain other
chemical groups
Proteins are the major components of
many structures including skin, muscles,
and feathers