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Chapter 2
The Chemistry of Life
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Objective: You will be able to differentiate between
the different types of bonds
Do Now:
• Read “Atoms” on page 35
• Describe the three particles that make up an
atom
Representations of the Atom
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An element is a pure substance that consists of only
one type of atom
The periodic table of the elements
Hydrogen
1H
Atomic mass
First
shell
2
He
4.00
Atomic number Helium
2He
Element symbol
Electron-shell
diagram
Lithium
3Li
Beryllium
4Be
Boron
3B
Carbon
6C
Nitrogen
7N
Oxygen Fluorine
8O
9F
Neon
10Ne
Second
shell
Sodium Magnesium Aluminum Silicon Phosphorus Sulfur
13Al
16S
11Na
12Mg
14Si
15P
Third
shell
Figure 2.8
Chlorine
17Cl
Argon
18Ar
• Valence electrons
– Are those in the outermost, or valence shell
– Determine the chemical behavior of an atom
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• Formation of a covalent bond
Hydrogen atoms (2 H)
1
2
3
In each hydrogen
atom, the single electron
is held in its orbital by
its attraction to the
proton in the nucleus.
When two hydrogen
atoms approach each
other, the electron of
each atom is also
attracted to the proton
in the other nucleus.
The two electrons
become shared in a
covalent bond,
forming an H2
molecule.
Figure 2.10
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+
+
+
+
+
+
Hydrogen
molecule (H2)
• Covalent bonding in compounds
Name
(molecular
formula)
Electronshell
diagram
(c) Water (H2O).
Two hydrogen
atoms and one
oxygen atom are
joined by covalent
bonds to produce a
molecule of water.
(d) Methane (CH4).
Four hydrogen
atoms can satisfy
the valence of
one carbon
atom, forming
methane.
Structural
formula
O
H
H
H
H
C
H
Figure 2.11 C, D
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H
Spacefilling
model
• Single and double covalent bonds
Name
(molecular
formula)
Electronshell
diagram
(a) Hydrogen (H2).
Two hydrogen
atoms can form a
single bond.
(b) Oxygen (O2).
Two oxygen atoms
share two pairs of
electrons to form
a double bond.
Figure 2.11 A, B
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Structural
formula
H
H
O
O
Spacefilling
model
• Electronegativity
– Is the attraction of a particular kind of atom for
the electrons in a covalent bond
• The more electronegative an atom
– The more strongly it pulls shared electrons
toward itself
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• In a nonpolar covalent bond
– The atoms have similar electronegativities
– Share the electron equally
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• In a polar covalent bond
– The atoms have differing electronegativities
– Share the electrons unequally
Because oxygen (O) is more electronegative than hydrogen (H),
shared electrons are pulled more toward oxygen.
d–
This results in a
partial negative
charge on the
oxygen and a
partial positive
charge on
the hydrogens.
O
Figure 2.12
d+
H
H
H2O
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d+
Ionic Bonds
• In some cases, atoms strip electrons away
from their bonding partners
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• Electron transfer between two atoms
creates ions
• Ions
– Are atoms with more or fewer electrons
than usual
– Are charged atoms
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2
1
The lone valence electron of a sodium
atom is transferred to join the 7 valence
electrons of a chlorine atom.
Each resulting ion has a completed
valence shell. An ionic bond can form
between the oppositely charged ions.
–
+
Na
Na
Sodium atom
(an uncharged
atom)
Cl
Cl
Chlorine atom
(an uncharged
atom)
Figure 2.13
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Cl
Na
Na+
Sodium on
(a cation)
Cl–
Chloride ion
(an anion)
Sodium chloride (NaCl)
• Ionic compounds
– Are often called salts, which may form crystals
Na+
Cl–
Figure 2.14
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Triose sugars
(C3H6O3)
H
O
Pentose sugars
(C5H10O5)
H
Aldoses
C
O
Hexose sugars
(C6H12O6)
H
C
H
O
C
C
H
C
OH
H
C
OH
H
C
OH
H
C
OH
H
C
OH
HO
C
H
C
OH
H
H
C
OH
H
O
H
C
OH
H
HO
C
H
C
OH
HO
C
H
H
C
OH
H
C
OH
H
C
OH
H
C
OH
Glyceraldehyde
H
Ribose
H
H
Ketoses
H
Glucose
Galactose
H
C OH
C
H
H
C OH
C
O
H
H
C OH
C
O
O
C OH
H
C OH
HO
H
H
C OH
H
C OH
Dihydroxyacetone
H
C OH
H
C OH
H
H
C OH
H
Ribulose
Figure 5.3
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C H
H
Fructose
Objective: You will be able to discus how the
properties of water affect living things.
Do Now:
• Read “The water molecule” on page 40
• Describe the polarity of the water molecule
Hydrogen Bonds
• A hydrogen bond
– Forms when a hydrogen atom covalently
bonded to one electronegative atom is also
attracted to another electronegative atom
d–
d+
H
Water
(H2O)
O
H
d+
d–
Ammonia
(NH3)
N
H
d+
Figure 2.15
H
H
d+
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d+
A hydrogen
bond results
from the
attraction
between the
partial positive
charge on the
hydrogen atom
of water and
the partial
negative charge
on the nitrogen
atom of
ammonia.
The polarity of water molecules results in
hydrogen bonding
The polarity of water molecules
d–
+
Hydrogen
bonds
H
+
d–
H
d–
+
Figure 3.2
+
d–
• Cohesion
– Helps pull water up through the microscopic
vessels of plants
Water conducting cells
Figure 3.3
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100 µm
• Surface tension
– Is a measure of how hard it is to break the
surface of a liquid
– Is related to cohesion
Figure 3.4
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Insulation of Bodies of Water by Floating Ice
• Solid water, or ice
– Is less dense than liquid water
– Floats in liquid water
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• The hydrogen bonds in ice
– Are more “ordered” than in liquid water, making
ice less dense
Hydrogen
bond
Figure 3.5
Ice
Liquid water
Hydrogen bonds are stable
Hydrogen bonds
constantly break and re-form
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• Water has a high specific heat, which allows it
to minimize temperature fluctuations to within
limits that permit life
– Heat is absorbed when hydrogen bonds break
– Heat is released when hydrogen bonds form
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Evaporative Cooling
• Evaporation
– Is the transformation of a substance from a
liquid to a gas
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• Evaporative cooling
– Is due to water’s high heat of vaporization
– Allows water to cool a surface
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Objective: You will be able to list the ways carbon-based molecules
display a huge array of diversity.
Docan
Now:
• Read, “Carbon Compounds” on p. 52 only
• How are organic and inorganic compounds
different?
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Figure 4.3 Valences for the major elements of organic molecules
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Figure 4.2 The shapes of three simple organic molecules
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Figure 4.4 Variations in carbon skeletons
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Table 4.1 Functional Groups of Organic Compounds
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Objective: You will be able to list the four types of organic
compounds and describe how they are formed and broken
down.
Do Now:
• Read, “Macromolecules” on p. 45
• Differentiate between monomers and
polymers
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Inorganic versus Organic
• Living things are made of both types of
substances
• Inorganic does not contain both carbon and
hydrogen.
– Ex. Water and Salt
• Organic contains both carbon and hydrogen
– There are 4 categories
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Four categories of organic compounds
– Carbohydrates
– Lipids
– Proteins
– Nucleic acids
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Figure 5.2 The synthesis and breakdown of polymers
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Objective: You will be able to describe the
structure and function of carbohydrates.
Do Now:
• Read, “Carbohydrates” on p. 45-46
• Differentiate between monosaccharides and
polysaccharides
Carbohydrates
• Functions
– Readily available source of energy
– Energy storage
– Strong building materials
• Structure
– Consists of carbon, hydrogen and oxygen
– Hydrogen and oxygen are always in a 2:1 ratio
– Each carbon is connected to a hydroxyl group
except one which is connected to a carbonyl
group
Carbohydrate Classes
• Carbohydrates are classified into three categories
– Monosaccharides
– Ex. Glucose
– Disaccharides
– Ex. Sucrose
– Polysaccharides
– Ex. Starch
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Figure 5.3 The structure and classification of some monosaccharides
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Figure 5.4 Linear and ring forms of glucose
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Figure 5.5 Examples of disaccharide synthesis
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Polysaccharides
• Consist of many repeating units of
monosaccharides
• Have two main purposes:
– Energy storage
– Structural component
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Energy Storage
• Plants store their excess carbohydrates as a
polysaccharide called starch
• Animals store theirs as glycogen
Structural Component
• Plants make their cell walls out of cellulose
• The exoskeletons of some animals is made of
a polysaccharide called chitin
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Figure 5.6 Storage polysaccharides
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Figure 5.9 Chitin, a structural polysaccharide: exoskeleton and surgical thread
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Objective: You will be able to describe the
structure and function of lipids.
Do Now:
Read “Lipids” on p. 46-47
What monomers are used to make a lipid?
Lipids
• Lipids have several functions
– Long term energy storage
– Make up cell membranes
– Work as steroids
• Structure
– Most consist of glycerol and fatty acids which are
long chains of carbon and hydrogen
– Greater than 2:1 ratio of hydrogen to oxygen
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Categories of lipids
• Fats
• Phospholipids
• Steroid
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Figure 5.10 The synthesis and structure of a fat, or triacylglycerol
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Figure 5.11x Saturated and unsaturated fats and fatty acids: butter and oil
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Figure 5.11 Examples of saturated and unsaturated fats and fatty acids
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Figure 5.12 The structure of a phospholipid
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• The structure of phospholipids
– Results in a bilayer arrangement found in cell
membranes
WATER
Hydrophilic
head
WATER
Hydrophobic
tail
Figure 5.14
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Figure 5.14 Cholesterol, a steroid
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Objective:
You will be able to describe the structure and
function of proteins.
Do Now:
• Read “Proteins” on p. 47-48
• List the parts of an amino acid
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Proteins
• Functions
– Control chemical reactions by acting as enzymes
– Used for building materials
– Transport material
– Send signals by acting as hormones
• Structure
– Consist of C, H, O, N
– Proteins are huge polymers made from small
monomers
– Monomers called amino acids
Figure 5.15 The 20 amino acids of proteins: polar and electrically charged
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Objective: You will be able discuss how proteins
are made.
Do Now:
• Answer questions 1-3 on p. 48
Figure 5.16 Making a polypeptide chain
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Figure 5.18 The primary structure of a protein
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Figure 5.19 A single amino acid substitution in a protein causes sickle-cell disease
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Figure 5.20 The secondary structure of a protein
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Figure 5.22 Examples of interactions contributing to the tertiary structure of a protein
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Figure 5.23 The quaternary structure of proteins
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Figure 5.25 Denaturation and renaturation of a protein
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The Roles of Nucleic Acids
• There are two types of nucleic acids
– Deoxyribonucleic acid (DNA)
– Ribonucleic acid (RNA)
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DNA
1
Synthesis of
mRNA in the nucleus
mRNA
NUCLEUS
CYTOPLASM
mRNA
2
Movement of
mRNA into cytoplasm
via nuclear pore
3
Figure 5.25
Ribosome
Synthesis
of protein
Polypeptide
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Amino
acids
The Roles of Nucleic Acids
Deoxyribonucleic acid (DNA)
Contains the information to make the different
proteins in your body
Ribonucleic acid (RNA)
Carries the information in the DNA to a ribosome
to actually make the protein
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Nucleic acids are made up of nucleotides linked
together
Nucleotide
The Structure of Nucleic Acids
• Nucleic acids
– Exist as polymers called polynucleotides
5’ end
5’C
O
3’C
O
O
5’C
O
3’C
OH
Figure 5.26
3’ end
(a) Polynucleotide,
or nucleic acid
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