Download Chapter 2: Chemical Foundations

By: Debbie Schwagerman
January 31, 2005
Atomic Bonds and Molecular Interactions
Each atom has a defined
number and geometry of
covalent bonds.
Atomic Bonds and Molecular Interactions
Electrons are shared unequally
in polar covalent bonds.
Atoms with higher
electronegativity values have
a greater attraction for
electrons.
Atomic Bonds and Molecular Interactions
Covalent bonds are much
stronger and more stable
than noncovalent bonds.
Atomic Bonds and Molecular Interactions
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Ionic bonds result from the attraction of a positively charged ion
(cation) for a negatively charged ion (anion).
The atoms that form the bond have very different electronegativity
values and the electron is completely transferred to the more
electronegative atom.
Ions in aqueous solutions are surrounded by water molecules, which
interact via the end of the water dipole carrying the opposite charge of
the ion.
Atomic Bonds and Molecular Interactions
Van der waals interactions are caused by transient dipoles.
Atomic Bonds and Molecular Interactions
The hydrophobic effect causes
nonpolar molecules to adhere
to one another.
Atomic Bonds and Molecular Interactions
Molecular complementarity
permits tight, highly specific
binding of biomolecules.
Chemical Building Blocks of Cells
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Proteins
 Amino Acids
Nucleic Acids
 Nucleotides
Polysaccharides
 Monosaccharides
Chemical Building Blocks of Cells
Common structure of
amino acids.
Chemical Building Blocks of Cells
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20 amino acids.
All amino acids in nature are L form.
Structure consists of Ca, to which an amino group, a carboxyl
group, a hydrogen atom, and a variable group.
Amino acids are classed according to their R group.
Chemical Building Blocks of Cells
Common
structure of
nucleotides.
Chemical Building Blocks of Cells
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Common structure: phosphate group,
base, and a five-carbon sugar.
Sugar is either DNA or RNA.
Bases are adenine, guanine, cytosine,
thymine (DNA), and uracil (RNA).
Nucleotides link together to build
nucleic acids.
Chemical Building Blocks of Cells
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Monosaccharides are carbohydrates
of combinations of carbon and water
in a one-to-one ratio.
Except for fructose, all sugars are in
nature are D form.
D-Glucose (C6H12O6) is primary
energy source.
Chemical Building Blocks of Cells
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Polysaccharides:
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Disaccharides are simplest
polysaccharides.
Anomeric carbon of one sugar molecule
is linked to hydroxyl oxygen of another
sugar molecule.
Polysaccharides can contain dozens to
hundreds of monosaccharides.
Chemical Equilibrium
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The extent to which a reaction can proceed and the rate at which the
reaction takes place determines which reactions occur in a cell.
Reactions in which the rates of the forward and backward reactions
are equal, so that the concentrations of reactants and products stop
changing, are said to be in chemical equilibrium.
At equilibrium, the ratio of products to reactants is a fixed value
termed the equilibrium constant (Keq) and is independent of reaction
rate.
Chemical Equilibrium
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Keq depends on the nature of the reactants and products, the
temperature, and the pressure.
The Keq is always the same for a reaction, whether a catalyst is present
or not.
Keq equals the ratio of the forward and reverse rate constants (Keq =
kf/kr).
The concentrations of complexes can be estimated from equilibrium
constants for binding reactions.
Biochemical Energetics
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The change in free energy ∆G is the most useful measure for predicting the
direction of chemical reactions in biological systems. Chemical reactions tend to
proceed in the direction for which ∆G is negative.
A chemical reaction having a positive ∆G can proceed if it is coupled with a
reaction having a negative ∆G of larger magnitude.
The chemical free energy change ∆G equals -2.3RT log keq. Thus the value of ∆G
can be calculated from the experimentally determined concentrations of reactants
and products at equilibrium.