Transcript Atom

Chapter 2
The Chemical Basis of Life
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Basic Chemistry
• Matter and Energy
–Matter, Mass, and Weight
• Matter: everything that occupies space
and has mass. You, your chair, your car,
the air.
• Mass: the amount of matter in an object.
• Weight: the gravitational force acting on
an object of a given mass (on earth, mass
= weight).
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Basic Chemistry
• Elements and Atoms
– Element:
• the simplest type of matter
with unique chemical
properties.
• composed of atoms of only
one kind (gold, helium, carbon,
oxygen).
– Atom:
• smallest particle of an element
that has chemical
characteristics of that element.
• Individual atoms are too small
to see, even with a
microscope.
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Atomic Structure
• Everything (all matter) is
made of Atoms.
• Atoms: composed of
subatomic particles
– Neutrons: no electrical charge
(0)
– Protons: one positive charge (+)
– Electrons: one negative charge
(-)
• Nucleus: formed by protons
and neutrons. Most of the
mass of atom.
• Most of the volume of an
atom occupied by electrons in
orbit.
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Atomic Number and Mass Number
• Atomic Number (P) :
number of protons in
each atom
– Determines element
and it characteristics.
– Usually equal to the
number of electrons.
– Atom is neutrally
charged.
– Periodic table shows
the atomic number of
each element.
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Electron orbits or shells
• Electrons are thought of as
circling the nucleus in orbits
or shells.
– The inner shell can hold 2
electrons.
– The next shell holds 8
electrons. The next 18, then
32.
– The inner shells fill up first.
– The outermost shell
containing electrons is called
the valence shell.
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Electrons and Chemical Bonding
• Intramolecular bonding
occurs when outermost
(valence) electrons are
either shared with or
transferred to another
atom.
– Ionic Bonding: atoms
exchange electrons.
– Covalent Bonding: two
or more atoms share
electron pairs.
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Ionic Bonding
• Ion: an atom that loses or
gains one or more
electrons and becomes
charged.
– Cation: positively charged
ion, Written as Na+, Ca2+
– Anion: negatively charged
ion, Written as Cl-
• In an ionic bond, cations
and anions are attracted to
each other and remain
close to each other.
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Play Video
Covalent Bonding
Atoms share one or more pairs of
electrons
– Single covalent: two atoms
share one pair of electrons.
– Double covalent: Two atoms
share 2 pairs of electrons.
– Nonpolar covalent: Electrons
shared equally because nuclei
attract the electrons equally.
– Polar covalent: Electrons not
shared equally because one
nucleus attracts the electrons
more than the other does.
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Molecules
• 2 or more atoms
bonded together form
a Molecule.
• Water= 2 hydrogens
bound to an oxygen
• Written as a formula:
H2O
• Some molecules (like
glucose) are very
complex and we
simplify with line
drawings.
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Hydrogen Bonds
• When an oxygen has polar covalent
bonds with 2 hydrogen atoms, the
oxygen pulls the electrons to itself.
• Oxygen side of the molecule is partly
negative.
• Hydrogen side is partly positive.
• Water is a polar molecule.
• The hydrogen of one molecule is
attracted to the oxygen of another
molecule
• This makes water sticky.
• Hydrogen bonds occur in other
molecules, too.
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Intermolecular Forces: Hydrogen Bonds
• Occur when the positively
charged H of one molecule is
attracted to the negatively
charged O, N or F of another
molecule.
– For example, in water the
positively charged hydrogen
atoms of one water molecule
bond with the negatively
charged oxygen atoms of
other water molecules.
– Hydrogen bonds play an
important role in
determining the shape of
complex molecules.
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Solubility and Dissociation
• Solubility: ability of one
substance to dissolve in
another.
– For example, sugar or salt
dissolves in water
• Dissociation or Separation:
– In ionic compounds,
• positive ions are attracted to
negative end of water
molecules.
• negative ions attracted to
positive end of water
molecules.
– The ions separate and each
becomes surrounded by
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water molecules.
Functional Groups
• Organic molecules may have one or more
functional groups.
• All functional groups are polar because their
oxygen or nitrogen atoms exert a strong pull on
shared electrons.
• Their polarity makes them hydrophilic (water
loving) and therefore soluble in water, the
solvent of life.
•
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Chemical Reactions
• Atoms, ions, molecules or
compounds interact to form
or break chemical bonds.
– Reactants: substances that
enter into a chemical reaction.
– Products: substances that result
from the reaction
– Synthesis = anabolism = making
chemical bonds
– Decomposition = catabolism =
breaking chemical bonds
• Metabolism: collective term
used for the sum of all of the
anabolic and catabolic
reactions in the body.
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Synthetic Reactions
• Two or more reactants chemically combine to form a new
and larger product. Anabolism.
–
–
–
–
When chemical bonds are made; energy is stored in the bonds.
Responsible for growth, maintenance and repair
Dehydration: synthetic reaction where water is a product.
Produce chemicals of life: carbohydrates, proteins, lipids, and
nucleic acids.
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Decomposition Reactions
• A large reactant is broken down to form smaller products.
Catabolism.
– When chemical bonds are broken, energy is released.
– Hydrolysis: water is split into two parts that contribute to the
formation of the products.
– Example: the breakdown of starch to sugars with a release of
energy that the body can use.
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Reversible Reactions
• Chemical reactions in which the reaction can
proceed either from reactants to products or
from products to reactants.
• Equilibrium: rate of product formation is
equal to rate of reactant formation.
• Equilibrium is like Substituting Players in a
Sports Game.
• H2O
H+ + OH20
Oxidation-Reduction Reactions
• Oxidation-Reduction Reactions:
the complete or partial loss of an
electron by one atom is
accompanied by the gain of that
electron by another atom
– Na + Cl  Na+ Cl-
• Oxidation: loss of an electron by
an atom
• Reduction: gain of an electron by
an atom
• Which atom is oxidized?
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Energy: the capacity to do work
• Potential Energy:
– stored energy
– energy that could do
work if it were
released.
• Kinetic Energy:
– does work and
moves matter
– energy of motion
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Energy: the capacity to do work
• Mechanical Energy: energy
resulting from the position
or movement of objects
• Heat Energy: energy that
flows between objects of
different temperatures
• Chemical Energy: form of
potential energy in the
chemical bonds of a
substance
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Heat Energy
• When a chemical bond is broken and energy is
released, only some of that energy is stored.
• Energy that is released but not captured is
released as heat.
• That heat is used by humans to maintain body
temperature.
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Speed of Chemical Reactions
• Temperature affects rate of reaction.
– Increase in temperature means increase of kinetic
energy.
– Molecules move faster, collide harder and more
frequently.
• Concentration of reactants affects rate of reaction.
– As concentration of reactants increases, rate of reaction
increases.
• Catalysts: substances that increase the rate of
chemical reactions without being permanently
changed or depleted
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Activation Energy and Enzymes
• Activation Energy:
minimum energy
reactants must have to
start a chemical reaction.
• Enzymes: protein
catalysts that increase the
rate of chemical reactions
by lowering the activation
energy necessary for
reaction to begin.
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Solutions and Concentration
• Solution: mixture of liquids, gasses, or solids that are
uniformly distributed
– Solvent: substance that dissolves the solute.
– Solute: substance that is dissolved by the solvent.
– Like dissolves like; polar substances dissolve in water, nonpolar substances dissolve in oils.
• Concentration: measure of number of particles of
solute per volume of solution (particles/ml).
– Unit used by physiologists is osmole.
– Concentration = osmolality.
– Concentration of body fluids influences movement of fluid into
and out of cells.
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Chemistry
• Inorganic Chemistry: generally, substances
that do not contain carbon
– Water, oxygen
– Exceptions: CO, CO2, and HCO3-
• Organic Chemistry: study of carboncontaining substances.
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Oxygen and Carbon Dioxide: Important
Inorganic Compounds
•
Oxygen (O2):
– Two oxygen molecules with double covalent
bond (O=O)
– Important reactant in metabolism.
•
Carbon dioxide (CO2):
– produced during the catabolism of organic
compounds.
– Metabolic waste product.
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Organic Chemistry: Macromolecules
• Carbohydrates:
cellulose, starches,
sugars
– Strings of sugar molecules
– Example: sucrose
– Energy sources and
structure
• Proteins: muscle
– Example: insulin
– Functions: regulate
processes, aid transport,
protection, muscle
contraction, structure,
energy
• Lipids: fats, oils, waxes
– Relatively insoluble in
water.
– Example: anabolic
steroids
– Functions: protection,
insulation, physiological
regulation, component of
cell membranes, energy
source
• Nucleic Acids:
– Examples: ATP, DNA, RNA
– Functions: store energy,
genetic information
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Carbohydrates: Monosaccharides
• Simple sugars.
• Six-carbon sugars like
glucose, fructose, and
galactose are important
in the diet as energy
sources.
• Five-carbon sugars are
components of ATP,
DNA and RNA
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Carbohydrates: Disaccharides
• Two simple sugars bound together by dehydration
• Examples: sucrose, lactose, maltose
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Carbohydrates: Polysaccharides
• Long chains of many
monosaccharides.
• Storage molecules for
monosaccharides and form
part of cell surface markers
• Glycogen formed by
animals.
• Starch and cellulose
formed by plants
– Starch in food is used as a
source of monosaccharides
– Cellulose in food acts as
fiber (bulk) in the diet
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Lipids: Fats
•
•
•
•
•
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95% triglycerides composed of glycerol and
fatty acids
Glycerol linked by
dehydration synthesis to
3 fatty acids
Saturated = contains only
single covalent bonds
(lard)
Unsaturated =  1 double
covalent bonds
(vegetable oils)
Trans fats – artificially
saturated (hydrogenated)
Functions: protection,
insulation, energy source
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Lipids: Phospholipids
• Polar (hydrophilic) at
one end
• Nonpolar
(hydrophobic) at the
other.
• Function: important
structural
component of cell
membranes
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Lipids: Steroids
•
•
•
•
Cholesterol, bile salts,
hormones
Carbon atoms arranged
in four rings
Functions:
physiological regulators
and component of cell
membranes
Anabolic-androgenic
steroids are derivatives
of the male hormone,
testosterone
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Proteins
• Large polar
compounds
• Amino acids:
– monomer
– building blocks of
protein
• Peptide bonds:
covalent bonds
formed between
amino acids during
protein synthesis
ProteinVideo
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Protein Structure
• Primary: sequence
of amino acids in the
polypeptide chain
• Secondary:
formation of helices
or of pleated sheets;
caused in part by H
bonds between
amino acids
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Protein Structure
• Tertiary: folding and
bending of chain
caused by hydrogen
bonding
• Quaternary: two or
more proteins
associate as a
functional unit
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Denaturation of proteins
• Denaturation - the alteration
of a protein shape through
some form of external stress
(for example, heat, acid or
alkali), so that it will no
longer be able to carry out its
cellular function.
• Extreme changes in body
temperature or blood pH can
cause inactivation of
proteins.
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Enzymes: Protein Catalysts
• Lower the activation energy
necessary for a reaction to occur
• bring reactants into close
proximity
• Three-dimensional shape
contains an active site where
reactants attach.
• Enzyme names usually end in –
ase and often have the same
word stem as the reactant,
example: lipase.
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Nucleic Acids
• Include the nucleic
acids: DNA and RNA
and ATP.
• Nucleotides
– monomer
– Composed of a fivecarbon sugar, a
nitrogenous base,
and a phosphate
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DNA and RNA
DNA
• deoxyribonucleic acid
• Genetic material of cells
copied from one generation
to next
• Composed of 2 strands of
nucleotides in a double helix
RNA
• ribonucleic acid
• Similar to a single strand of
DNA
• Responsible for interpreting
the code within DNA into
the primary structure of
proteins
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Adenosine Triphosphate (ATP)
•
•
•
•
Energy currency of the body
Provides energy for other chemical reactions as anabolism
or drive cell processes as muscle contraction
All energy-requiring chemical reactions stop when there is
inadequate ATP
3 phosphate bonds (PO4) with energy stored in last PO4
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bond
ATP and Potential Energy
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