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Vanders
Human Physiology
The Mechanisms of Body FunctionTenth Editionby
Widmaier Raff Strang The McGraw-Hill Companies, Inc.
Figures and tables from the book, with additional comments by:
John J. Lepri, Ph. D.,
The University of North Carolina at Greensboro
Chapter 2
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Molecules you need to know Carbohydrates
Lipids Proteins
Nucleic acids
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Introduction forChapter 2
Chemical composition of the body
The three-dimensional shape of a molecule determines
its function.
Atoms interact and bond by various means and with
varying strength of association.
Ions are the result of a mismatch between the numbers
of protons and electrons.
Carbohydrates, proteins, lipids, and nucleic acids have
essential roles in cell physiology.
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Atoms are made up of subatomic particles:
an atomic nucleus with neutrons and protons
and a surrounding cloud of electrons.
Humans are large collections of
tissues and organ systems.
Organ systems are large collections of
extracellular matrixes and cells.
Cells are large collections of
organelles and molecules.
Molecules are small to large collections of
elements whose atoms are held together
by chemical bonds.
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In a methane molecule, each of 4 hydrogen atoms is
covalently bonded (sharing electrons with) to a carbon atom.
Figure 2-1
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There are several ways to express the structure of molecules.
Structure helps us understand function.
Two dimensions:
Three dimensions:
Space-filling models:
Figure 2-2
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Table 2-3:
Most frequently encounteredionic forms of elements.
An ion results when a molecule
gains or loses one or more electrons.Ions are mismatched in the number
of protons and electrons, and are
therefore electrically charged.
What is an ion?
The origin of an ions proton-electron mismatch is indicatedby the sign (plus or minus) and number of signs:
Cl- represents a chlorine atom that has gained an electron.
Ca++ represents a calcium atom that has lost two
electrons.
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Rotations of
bonds can
result in major
rearrangementsof a molecules
three-dimensional
shape, and,
therefore, its
molecular function.
becoming a ring
linear chain
Figure 2-3
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Table 2-4:
Examples of non-polar and polar
bonds, and ionized chemical groups.
Like dissolves like applies here:
polar compounds, including water molecules, readilyassociate with each other, whereas
non-polar compounds readily associate with each
other, including such compounds in cell membranes.
Hydrophilic, or water-loving, compounds, e.g., NaCl,dissolve readily in water.
Hydrophobic, or water-fearing, compounds, e.g., fats, do
not dissolve readily in water, but will dissolve readily
into non-polar solvents, even cell membranes.
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In each water molecule,
the shared electronsspend more time
close to the larger oxygen
atom, making that area
slightly electronegative
compared to the areanear the hydrogen atoms.
The dotted lines betweenwater molecules represent the
hydrogen bonds, resulting
from the weak electrical
attractions.
Figure 2-4
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Solvent + Solute(s) = A Chemical Solution
To describe the number of dissolved solutes ina solution, we refer to the chemical concentration
of the solute, which is the amount of solute present
in a given volume of solvent.
The molecular weight (MW) of a solute reveals
the number of grams of that solute you would
need to add to one liter (L) of solvent to produce
a 1-molar solution, e.g.:
C6H12O6 (glucose) has a MW of 180, so
to make a 1M glucose solution,
add 180 g of glucose to 1 L of water.
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Positive sodium ions (Na+)
are attracted to negative
chloride ions (Cl-) to form
ionic bonds.
Water, because of its regions of
polarity, is a solvent that readily
dissolves Na+Cl- .
Figure 2-5
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In a collection of
amphipathic molecules,e.g., phospholipids,
similar regions
will spontaneously
arrange themselves
with other similar regions.
Here, the non-polar regions
associate with each other
and the polar regions form
hydrogen bonds with the
surrounding (polar) water
molecules.
Figure 2-6
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Covalent bonds (share electrons)
e.g., methane, CH4 (Figure 2-1)
Ionic bonds (opposite charges attract)
e.g., sodium chloride, Na+Cl- (Figure 2-5)
Hydrogen bonds (attraction of H to O or N)
e.g., between H2O molecules (Figure 2-4)
van der Waals forces (like dissolves like)
e.g., between lipid molecules (Figure 2-6)
STRONG
WEAK
Strength and type of chemical bonds and interactions:
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The pH value indicates the acidity of a solution.
The concentration of free hydrogen ions in a solution isthe primary determinant of that solutions acidity:
pH= -log[H+]remember that the representation [x]
is a quick way to state the chemicalconcentration of solute x
When the number in [H+] is high, the value of pH is low,
owing to the way the math works.
Thus,
an acidic solution has a pH < 7.
pH 7 is considered neutral,
and pH > 7 is considered alkaline (basic).
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Both representations of glucose show the many covalent
bonds that make this monosaccharide an energy-rich
molecule.
Figure 2-7
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A difference in the position of the indicated OH group is
the structural difference between the monosaccharides
glucose and galactose.
Figure 2-8
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The disaccharide sucrose and a water molecule result from
the linkage of the monosaccharides glucose and fructose
(energy input is required and intermediate stages are not
shown here).
Figure 2-9
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Glycogen is a polysaccharide that serves as a high-energy
storage polymer made up of glucose units. When needed,
these glucose units are released into the blood for energy-
transfer reactions.
Figure 2-10
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Glycerol and fatty acids are subunits for the formation of:
triglycerides (among the bodys fats), and phospholipids
(membrane components).Figure 2-11
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Cholesterol molecules promote membrane fluidity and serve
as starting materials for the synthesis of steroid hormones.
Figure 2-12
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Side chains can be:
non-polar groups
or
polar groups
or
ionized groups
All amino acids have:
an amino group,
a carboxyl group, and a
varying side chain [R]
Figure 2-13
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Peptide bonds are covalent bonds that connect
neighboring amino-acids together to form a polypeptide.
[Intermediate stages are not shown].
Figure 2-14
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This necklace cartoonindicates the linear
sequence of neighboring
amino-acid components
in a protein and also shows
that the side-chains caninteract (see also Figure 2-17).
Each colored bead
represents one of the
component amino acids.
Figure 2-15
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A space-filling cartoon
of the protein myoglobins
3-D shape or conformation.
Each dot represents the
location of a single aminoacid.
Figure 2-16
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Chemical interactions between non-adjacent amino acids
in a protein range from strong (covalent bonds, 4) to
weak (van der Waals, 3), but all of these interactions play
essential roles in determining protein conformation.
Figure 2-17
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Many proteins include regions where helical structure is
apparent: these result from hydrogen bonding between
regularly spaced peptide bonds.
Figure 2-18
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Many proteins also include regions where structures called
beta sheets are apparent: these result from H-bonding
between certain non-adjacent amino acids.
Figure 2-19
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Table 2-6:
Bonding forces between atoms
and molecules.
Covalent bonds (share electrons)
e.g., methane, CH4 (Figure 2-1)
Ionic bonds (opposite charges attract)
e.g., sodium chloride, Na+Cl- (Figure 2-5)
Hydrogen bonds (attraction of H to O or N)
e.g., between H2O molecules (Figure 2-4)
van der Waals forces (like dissolves like)
e.g., between lipid molecules (Figure 2-6)
Strength and type of chemical bonds and interactions:
STRONG
WEAK
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Some proteins include regions with covalent bonds
between sulfhydryl groups of non-adjacent cysteines.
Figure 2-20
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Figure 2-21
A three-dimensional, space-filling cartoon (partial) depiction
of hemoglobin, a protein that plays a key role in gas transport.
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DNA is made up of a chain of deoxyribonucleotides
and RNA is made up of a chain of ribonucleotides.
or:
adenine,
guanine,
thymine
or:
adenine,
guanine,
uracil
Figure 2-22
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The sequence of
bases in DNA and in
RNA is held together
by phosphate-sugarbonds.
You will learn later
how this sequence
is an information code.
Figure 2-23
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A T
G C
Hydrogen bonds between
complementary bases hold
together the DNA double helix.
Figure 2-25
Figure 2-24
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ATP serves as the energy currency of the cell since the
hydrolysis that removes one phosphate group is
accompanied by a discrete and controllable energy release.
Figure 2-26
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T
he End.
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