Transcript File

Chapter 02
*Lecture Outline
*See separate Image PowerPoint slides for
all figures and tables pre-inserted into
PowerPoint without notes.
PowerPoints prepared by
Melanie Waite-Altringer
Biology Faculty Member of
Anoka-Ramsey Community College
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Chapter 2
Chemical Basis of Life
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Introduction:
A.
B.
Chemistry deals with the composition of
matter and how it changes.
A knowledge of chemistry is necessary for
the understanding of physiology because
of the importance of chemicals in body
processes.
3
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Structure of Matter:
A.
Elements and Atoms:
1.
Matter is anything that has weight and
takes up space.
2.
All matter is composed of elements.
4
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3.
4.
5.
Living organisms require about 20
elements, of which oxygen, carbon,
hydrogen, and nitrogen are most
abundant.
Elements are composed of atoms;
atoms of different elements vary in
size, weight, and interaction with other
atoms.
Attractions between two or more atoms are
called chemical bonds.
5
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B.
Atomic Structure:
1.
An atom consists of a nucleus
containing protons and neutrons, with
electrons in orbit around the nucleus in
shells.
2.
Protons, with a positive charge, are
about equal in size to neutrons, which
have no charge.
6
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3.
4.
5.
6.
Electrons are much smaller and bear
a negative charge.
An electrically neutral atom has
equal numbers of protons and electrons.
The number of protons denotes the atomic
number of an element; the number of
protons plus the number of neutrons equals
the atomic weight.
Atoms with the same atomic number, but
different weights are isotopes of an
element.
7
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C.
Bonding of Atoms:
1.
Atoms form bonds by gaining, losing,
or sharing electrons.
2.
Electrons are found in shells around
the nucleus.
a.
The first energy shell holds a
maximum of two electrons; the
other energy shells each hold a
maximum of eight electrons when
on the outside. Elements that have
their outermost shells filled, are
stable structures that are chemically
inert.
8
Fig02.02
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-
+
Hydrogen (H)
0
-
-
+
+ 0
+
0
0
+ 0
+
0
-
-
Helium (He)
Lithium (Li)
-
9
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3.
Atoms with incompletely filled outer
shells tend to be reactive to form
stable outer shells of 8.
4.
When atoms gain or lose electrons,
they become ions with a charge. Whether
they gain or lose will depend on how
many electrons they have in the outer
shell to start with.
5.
Oppositely-charged ions attract each
other and form an ionic bond.
10
Fig02.04
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-
-
-
11p+
-
-
-
-
12n0
-
-
-
17p+
-
-
18n0
-
-
-
-
-
-
-
-
Sodium atom (Na)
-
Chlorine atom (Cl)
(a) Separate atoms
If a sodium atom loses an electron to a chlorine atom, the sodium
atom becomes a sodium ion (Na+), and the chlorine atom becomes
a chloride ion (Cl–)
-
-
+
-
11p+
12n0
-
-
-
-
-
-
-
17p+
18n0
-
-
-
-
-
-
-
-
-
-
-
Chloride ion (Cl–)
Sodium ion (Na+)
Sodium chloride
(b) Bonded ions
These oppositely charged particles attract electrically and join by
an ionic bond
Na+
Cl–
(c) Salt crystal
Ionically bonded substances form arrays such as a crystal of NaCl.
11
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6.
Covalent bonds are formed when atoms
share electrons to become stable with
filled outer shells.
a.
7.
8.
Two pairs of electrons shared
between atoms form a double
covalent bond.
A polar molecule has a covalent bond in
which the electrons are not shared
equally.
A hydrogen bond forms from a positive H
end of a polar molecule to the negative N
12
or O end of another polar molecule.
Fig02.05
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H
-
H2
-
+
+
+
+
-
Hydrogen atom
+
Hydrogen atom
Hydrogen molecule
13
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D.
Molecules and Compounds:
1.
2.
A molecule is formed when two or
more atoms combine.
If atoms of different elements
combine, the molecule can also be
called a compound.
a.
Compounds always have a
definite kind and number of
atoms.
14
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E.
Formulas:
1.
2.
A molecular formula represents the
numbers and types of atoms in a molecule.
Ex: Glucose = C6H12O6
Various representations, called structural
formulas, can be used to illustrate
molecules.
15
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F.
Chemical Reactions:
1.
A chemical reaction occurs as bonds are
formed or broken between atoms, ions, or
molecules.
2.
Those changed by the reaction are the
reactants; those formed are the products.
3.
Two or more atoms or molecules can be
joined during synthesis.
16
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4.
Larger molecules can be broken into
smaller ones in decomposition reactions.
5.
Exchange reactions occur as parts of
molecules trade places.
6.
Reversible reactions are symbolized by
using two arrows.
7.
Catalysts influence the speed of
chemical reactions.
17
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G.
Acids and Bases:
1.
Substances that release ions in water
are called electrolytes.
2.
Electrolytes that release hydrogen
ions in water are called acids.
3.
Electrolytes that release ions that
combine with hydrogen ions in water
are called bases.
18
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4.
The concentrations of H+ and OH- in
the body is very important to
physiology.
5.
pH represents the concentration of
hydrogen ions [H+] in solution.
19
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6.
A pH of 7 indicates a neutral solution
with equal numbers of hydrogen ions and
hydroxyl (OH-) ions.
a.
A pH of zero to less than 7
indicates the presence of more
hydrogen ions, and thus the
solution is more acidic; a pH
greater than 7 to 14 indicates
more hydroxyl ions, or a basic
solution.
b.
Between each whole number of
the pH scale there is a tenfold
difference in hydrogen ion
concentration.
20
Fig02.11
7.
Buffers are chemicals that combine
with excess acids or bases to help
minimize pH changes in body fluids.
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Relative
amounts
of H+ (red)
and OH(blue)
Acidic
H+
pH 0
Acidic
3.0
apple
juice
2.0
gastric
juice
1
4.2
tomato
juice
6.6
cow’s
milk
5.3
cabbage
6.0
corn
2
3
H+
4
5
concentration increases
6
8.4
sodium
bicarbonate
7.4
human
blood
8.0
egg
white
7.0
distilled
water
7
Neutral
10.5
milk of
magnesia
11.5
household
ammonia
Basic
OH8
9
OH-
10
11
concentration increases
12
13
14
Basic (alkaline)
21
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Chemical Constituents of Cells:
A.
B.
Organic compounds contain both hydrogen and
carbon.
All other compounds are considered inorganic
and they usually dissolve in water and release
ions, making them electrolytes.
1.
Water
a.
Water is the most abundant
compound in living things and
makes up two-thirds of the
weight of adults.
22
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b.
c.
d.
Water is an important solvent so
most metabolic reactions occur
in water.
Water is important in transporting
materials in the body since it is a
major component of blood.
Water carries waste materials and
can absorb and transport heat.
23
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2.
3.
Oxygen
a.
Oxygen is needed to release energy
from nutrients and is used to drive
the cell's metabolism.
Carbon Dioxide
a.
Carbon dioxide is released as a waste
product during energy-releasing
metabolic reactions.
24
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4.
Salts
a.
Salts provide necessary
ions including sodium, chloride,
potassium, calcium, magnesium,
phosphate, carbonate, bicarbonate,
and sulfate.
b.
These electrolytes play important
roles in many of the body's metabolic
processes.
25
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C.
Organic Substances:
1.
Carbohydrates
a.
Carbohydrates provide energy for
cellular activities and are composed
of carbon, hydrogen, and oxygen.
b.
Carbohydrates are made from
monosaccharides (simple sugars);
disaccharides are two
monosaccharides joined together;
complex carbohydrates
(polysaccharides), such as starch,
are built of many sugars.
c.
Humans synthesize the
polysaccharide glycogen.
26
Fig02.13
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O
O
O
O
(a) Monosaccharide
(b) Disaccharide
O
O
O
O
(c) Polysaccharide
O
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2.
Lipids:
a.
Lipids are organic substances that
are insoluble in water and include
fats, phospholipids, and steroids.
b.
Fats supply energy for cellular
function, and are built from
glycerol and three fatty acids. Fats
have a smaller proportion of
oxygen atoms than carbohydrates.
Fatty acids with hydrogen at every
position along the carbon chain are
saturated; those with one or more
double bonds are called
unsaturated fats.
28
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c.
Phospholipids contain glycerol, two fatty
acids, and a phosphate group, and are
important in cell structures.
d.
Steroids are complex ring structures, and
include cholesterol, which is used to
synthesize the sex hormones.
29
Fig02.14
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H
H
H
H
C
C
C
H
Glycerol
portion
O
O
O
O
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
O
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
O
H
H
H
H
H
H
C
C
C
C
C
C
H
H
H
H
H
Fatty acid
portions
H
H
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3.
Proteins:
a.
Proteins have a great variety of
functions in the body--as structural
materials, as energy sources, as
certain hormones, as receptors on
cell membranes, as antibodies, and
as enzymes to catalyze metabolic
reactions.
31
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b.
c.
Proteins contain C, O, H, and
nitrogen atoms; some also contain
sulfur.
Building blocks of proteins are the
amino acids, each of which has a
carboxyl group, an amino group
and a side chain called the R
group.
32
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d.
Proteins have complex shapes held
together by hydrogen bonds.
e.
Protein shapes (conformations),
which determine how proteins
function, can be altered
(denatured) by pH, temperature,
radiation, or chemicals.
33
Fig02.18
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Amino acids
(a) Primary structure—Each
oblong shape in this
polypeptide chain represents
an amino acid molecule. The
whole chain represents a
portion of a protein molecule.
C
H
C
H
N
C
(b) Secondary structure—The
polypeptide chain of a protein
molecule is often either pleated
or twisted to form a coil. Dotted
lines represent hydrogen bonds.
R groups (see fig. 2.17)
are indicated in bold.
O
C
R
N
O
C
H
H
H
H
H
R
H
N
O
C
H H
H
R
Pleated
structure
Three-dimensional
folding
(d) Quaternary structure—Two or more
polypeptide chains may be connected
to form a single protein molecule.
O
O
C
H
H
H
C
N
R
C
O
N
H
C
HO
R
H
C
O
O
Coiled
structure
H
N C
C
C
R
C
N
H
H
R
C
R
R
C
H
O
H
C
O
C
C
(c) Tertiary structure—
The pleated and coiled
polypeptide chain of a
protein molecule folds
into a unique threedimensional structure.
C
N
C
H O
C
N
R
H
N
C
H
H
C
O
R
H
R
C
R
N
H
C
H
H
R
C
H
O
C
R
N
C
C
H
C
H
C
R
H
N
O
N
O
C
R
C
C
O
H
H
C
H
O
N
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4.
Nucleic Acids:
a.
b.
c.
Nucleic acids form genes and take
part in protein synthesis.
They contain carbon, hydrogen,
oxygen, nitrogen, and phosphorus,
which are bound into building
blocks called nucleotides.
Each nucleotide consists of a 5carbon sugar, a phosphate group,
and one of many nitrogenous
bases.
35
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d.
e.
Nucleic acids are of two major
types: DNA (with deoxyribose) and
RNA (with ribose).
RNA (ribonucleic acid) functions in
protein synthesis; DNA
(deoxyribonucleic acid) stores the
molecular code in genes.
36
Fig02.21
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P
B
S
P
S
P
B
B
B
B
P
S
B
S
P
S
P
S
S
P
B
P
S
P
B
B
B
B
B
B
P
S
B
S
P
S
P
S
B
S
P
S
(a) RNA
P
S
P
S
P
B
S
B
P
B
S
P
(b) DNA
37