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Chapter 2
Atoms, Molecules,
and Life
Lectures by
Gregory Ahearn
University of North Florida
Copyright © 2009 Pearson Education, Inc..
2.1 What Are Atoms?
 Elements: substances that can neither be
broken down nor converted to other
substances (e.g., carbon)
Copyright © 2009 Pearson Education Inc.
2.1 What Are Atoms?
 Atoms: basic structural unit of matter; made
up of subatomic particles
• Atomic nucleus (central part of the atom)
• Protons (positive charge)
• Neutrons (neutral charge)
• Electrons (negative charge)
 Atomic number: the number of protons in
the nucleus
• Is unique for each element
• 92 different elements have been described.
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2.1 What Are Atoms?
 Hydrogen and helium have the simplest
atomic structure.
• Hydrogen has one proton and one electron.
• Helium has two protons, two neutrons, and
two electrons.
e
e-
p+
p+
p+
(a) Hydrogen (H)
Copyright © 2009 Pearson Education Inc.
n
n
atomic
nucleus
e(b) Helium (He)
Fig. 2-1
2.1 What Are Atoms?
 Atoms of the same element with different
numbers of neutrons are called isotopes of
the element.
 Some isotopes spontaneously break apart,
forming different kinds of atoms and
releasing energy in the process.
 Such isotopes are radioactive.
 Example: radioactive uranium isotopes
decay and form lead in the process
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2.1 What Are Atoms?
PLAY
Animation—Atomic Structure
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2.1 What Are Atoms?
 Electron shells: electrons orbit around
atomic nuclei at specific distances, called
electron shells.
 Different atoms have different electron
shells:
• The inner shell only has two electrons.
• The second shell holds up to eight electrons.
• Additional shells hold up to eight electrons.
Copyright © 2009 Pearson Education Inc.
2.1 What Are Atoms?
 The first four atomic electron shells
•
•
•
•
Carbon (C)
Oxygen (O)
Phosphorus (P)
Calcium (Ca)
2e8e-
4e-
6e-
5e8e-
2e-
2e-
2e-
2e-
6p+
6n
8p+
8n
15p+
16n
20p+
20n
Carbon (C)
C
Oxygen (O)
O
Phosphorus (P)
P
8e-
Calcium (Ca)
Ca
Fig. 2-2
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2.1 What Are Atoms?
 Electrons can move
from electron shell
to electron shell.
• Electrons move
from an inner to an
outer shell when
absorbing energy.
• Electrons move
from an outer shell
to an inner shell
when releasing
energy.
Copyright © 2009 Pearson Education Inc.
2
1 An electron absorbs energy
The energy boosts the electron
to a higher-energy shell
energy
–
–
+
+
3 The electron drops back
into lower-energy shell,
releasing energy as light
light
–
+
Fig. 2-3
2.2 How Do Atoms Form Molecules?
 Molecules: two or more atoms of one or
more elements held together by interactions
among their outermost electron shells
• Atoms interact with one another according to
two basic principles:
• An inert atom will not react with other atoms
when its outermost electron shell is
completely full or empty.
• A reactive atom will react with other atoms
when its outermost electron shell is only
partially full.
Copyright © 2009 Pearson Education Inc.
2.2 How Do Atoms Form Molecules?
 Atoms combine with each other to fill outer
electron shells (e.g. hydrogen and oxygen
have unfilled outer electron shells, and thus,
can combine to form the water molecule).
 The water molecule, with a filled outer
electron shell, is more stable than either the
hydrogen or oxygen atoms that gave rise
to it.
 The results of losing, gaining, or sharing
electrons are chemical bonds—attractive
forces that hold atoms together in
molecules.
Copyright © 2009 Pearson Education Inc.
2.2 How Do Atoms Form Molecules?
PLAY
Animation—Biologically Important Atoms
Copyright © 2009 Pearson Education Inc.
2.2 How Do Atoms Form Molecules?
 A molecule may be
depicted in different
ways.
H
H
H
H
H
C
C
C
C
H
H
H
H
O
H
(a) All bonds shown
CH3
CH2
CH2
CH2
OH
(b) Bonds within common groups omitted
OH
(c) Carbons and their attached hydrogens omitted
(d) Overall shape depicted
Copyright © 2009 Pearson Education Inc.
Fig. 2-4
2.2 How Do Atoms Form Molecules?
 Types of bonds
• Ionic bonds: formed by passing an electron
from one atom to another
• One partner becomes positive, the other
negative, and they attract one another.
• Na+ + Cl– becomes NaCl (sodium chloride)
• Positively or negatively charged atoms are
called ions.
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2.2 How Do Atoms Form Molecules?
Sodium atom (neutral)
Chlorine atom (neutral)
–
 Charged atoms
interact to form ionic
bonds.
• Positively charged
atoms
• Negatively charged
atoms
–
–
–
–
–
–
–
–
–
11p+
11n
–
–
–
–
–
–
–
–
–
–
–
–
17p+
18n
–
–
–
–
–
Electron transferred
(a) Neutral atoms
Sodium ion (+)
Chloride ion (–)
–
–
–
–
–
–
–
–
–
–
11p+
11n
–
–
–
–
–
(b) Ions
–
–
–
–
–
–
–
–
17p+
18n
–
Copyright © 2009 Pearson Education Inc.
–
–
–
–
–
Attraction between
opposite charges
(c) An ionic compound: NaCl
Cl-
Na+
Cl-
Na+
Cl-
Na+
Cl-
Na+
Cl-
Fig. 2-5
2.2 How Do Atoms Form Molecules?
PLAY
Animation—Ionic Bonds
Copyright © 2009 Pearson Education Inc.
2.2 How Do Atoms Form Molecules?
 Types of bonds (continued)
• Covalent bonds: bond between two atoms that
share electrons in their outer electron shell
• For example, an H atom can become stable
by sharing its electron with another H atom,
forming H2 gas.
Copyright © 2009 Pearson Education Inc.
2.2 How Do Atoms Form Molecules?
 Covalent bonds produce either nonpolar or
polar molecules.
• Nonpolar molecule: atoms in a molecule
equally share electrons that spend equal time
around each atom, producing a nonpolar
covalent bond
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2.2 How Do Atoms Form Molecules?
 Nonpolar covalent bonding in hydrogen
Same charge on
both nuclei
+
–
–
(uncharged)
+
Electrons spend
equal time near
each nucleus
(a) Nonpolar covalent bonding in hydrogen
Fig. 2-6a
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2.2 How Do Atoms Form Molecules?
 Covalent bonds produce either nonpolar or
polar molecules (continued).
• Polar molecules: atoms in a bond unequally
share electrons, producing a polar covalent
bond
• One atom in the bond has a more positive
charge in the nucleus, and so attracts
electrons more strongly, becoming the
negative pole of the molecule.
• The atom in the bond that has a less
positive charge in the nucleus gives up
electrons, becoming the positive pole of
the molecule.
Copyright © 2009 Pearson Education Inc.
2.2 How Do Atoms Form Molecules?
 Polar covalent bonding in water
(oxygen: slightly negative)
(–)
–
–
–
–
–
–
Larger positive
charge
–
8p+
8n
–
Electrons spend
more time near
the larger nucleus
–
–
+
+
Smaller positive
charge
(hydrogens:
slightly positive)
(+)
(+)
(b) Polar covalent bonding in water
Fig. 2-6b
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2.2 How Do Atoms Form Molecules?
PLAY
Animation—Covalent Bonds
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2.2 How Do Atoms Form Molecules?
 Types of bonds (continued)
• Hydrogen bonds: weak electrical attraction
between positive and negative parts of polar
molecules
• Example: the negative charge of oxygen
atoms in water molecules attract the positive
charge of hydrogen atoms in other water
molecules
Copyright © 2009 Pearson Education Inc.
2.2 How Do Atoms Form Molecules?
 Hydrogen bonds
H
(+)
O
(–)
H
(+)
H
(+)
O
(–)
H
(+)
hydrogen
bonds
Fig. 2-7
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2.2 How Do Atoms Form Molecules?
PLAY
Animation—Introducing Water’s Properties
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2.2 How Do Atoms Form Molecules?
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2.3 Why Is Water So Important To Life?
 Water interacts with many other molecules.
• Oxygen released by plants during
photosynthesis comes from water.
• Water is used by animals to digest food.
• Water is produced in chemical reactions that
produce proteins, fats, and sugars.
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2.3 Why Is Water So Important To Life?
 Many molecules dissolve easily in water.
• Water is an excellent solvent, capable of
dissolving a wide range of substances
because of its positive and negative poles.
 NaCl dropped into H2O
• The positive end of H2O is attracted to Cl–.
• The negative end of H2O is attracted to Na+.
• These attractions tend to push apart the
components of the original salt.
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2.3 Why Is Water So Important To Life?
 Water as a solvent
Cl–
Na+
H
Na+
Cl–
H
O
Cl–
Na+
Fig. 2-8
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2.3 Why Is Water So Important To Life?
PLAY
Animation—Solvent
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2.3 Why Is Water So Important To Life?
 Water molecules tend to stick together.
• Surface tension: water tends to resist being
broken
• Cohesion: water molecules stick together
Fig. 2-9
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2.3 Why Is Water So Important To Life?
PLAY
Animation—High Cohesion
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2.3 Why Is Water So Important To Life?
 Water can form ions.
• Water spontaneously becomes H+ and OH–.
• Acid solutions have a lot of H+ (protons).
• Alkaline solutions have a lot of OH– (hydroxyl
ions).
• A base is a substance that combines with H+,
reducing their numbers.
• pH measures the relative amount of H+ and
OH– in a solution.
Copyright © 2009 Pearson Education Inc.
2.3 Why Is Water So Important To Life?
 A water molecule is ionized.
(–)
O
H
O
H
water
(H2O)
(+)
+
H
H
hydroxide ion
(OH–)
hydrogen ion
(H+)
Fig. 2-10
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2.3 Why Is Water So Important To Life?
 pH measures acidity.
•
•
•
•
Acids have a pH below 7.
Bases have a pH above 7.
Neutral solutions have a pH of 7.
Buffers are substances that maintain a
constant pH in a solution.
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0
100
1
10–1
2
10–2
3
pH
value
10–3
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10–4
5
10–5
H+
6
10–6
7
10–7
8
10–8
(H+ > OH–)
10–9
increasingly acidic
10
10–10
11
10–11
12
10–12
13
10–13
drain cleaner (14.0)
1 molar sodium
hydroxide (NaOH)
oven cleaner (13.0)
household ammonia (11.9)
washing soda (12)
phosphate detergents
chlorine bleach (12.6)
toothpaste (9.9)
seawater (7.8–8.3)
baking soda (8.4)
water from faucet
milk (6.4)
pure water (7.0)
blood, sweat (7.4)
normal rain (5.6)
urine (5.7)
black coffee (5.0)
orange (3.5)
tomatoes
beer (4.1)
vinegar, cola (3.0)
stomach acid (2)
lemon juice (2.3)
1 molar
hydrochloric
acid (HCl)
2.3 Why Is Water So Important To Life?
 The pH scale
4
9
14
neutral
(H+ = OH–)
(H+ < OH–)
10–14
increasingly basic
concentration in moles/liter
Fig. 2-11
2.3 Why Is Water So Important To Life?
PLAY
Animation—pH Scale
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2.4 Why Is Carbon So Important To Life?
 Carbon can combine with other atoms in
many ways to form a huge number of
different molecules.
 This is possible because carbon has four
electrons in its outermost shell, leaving
room for four more electrons from other
atoms.
 Therefore, carbon can form many bonds
with other atoms.
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2.4 Why Is Carbon So Important To Life?
 The great variety of substances found in
nature is therefore constructed from a
limited pool of atoms.
 Organic molecules have a carbon skeleton
and some hydrogen atoms.
 Much of the diversity of organic molecules is
due to the presence of functional groups.
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2.4 Why Is Carbon So Important To Life?
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2.4 Why Is Carbon So Important To Life?
PLAY
Animation—Functional Groups
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2.5 How Are Biological Molecules Joined
Together Or Broken Apart?
 Dehydration synthesis
• The construction of large molecules yields
water.
• Small molecules are joined together to form
large molecules.
• During the joining of small molecules, water is
released.
• This water-releasing reaction is called
dehydration synthesis.
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2.5 How Are Biological Molecules Joined
Together Or Broken Apart?
 Dehydration synthesis
dehydration
synthesis
+
HO
OH
HO
OH
O
HO
H
O
OH
H
(a) Dehydration synthesis
Fig. 2-12a
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2.5 How Are Biological Molecules Joined
Together Or Broken Apart?
 Hydrolysis reactions
• During the breakdown of large molecules,
covalent bonds are broken, separating the
subunits
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2.5 How Are Biological Molecules Joined
Together Or Broken Apart?
 Hydrolysis
hydrolysis
+
O
HO
H
O
OH
HO
OH
HO
OH
H
(b) Hydrolysis
Fig. 2-12b
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2.5 How Are Biological Molecules Joined
Together Or Broken Apart?
PLAY
Animation—Dehydration Synthesis and Hydrolysis
Copyright © 2009 Pearson Education Inc.
2.6 What Are Carbohydrates?
 Carbohydrates are molecules composed of
carbon, hydrogen, and oxygen in the ratio of
1:2:1.
 They can be small single sugar molecules
or long chains of single sugar molecules
strung together.
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2.6 What Are Carbohydrates?
 A simple sugar
CH2OH
H
O
H
6
H
H
5
C
H
4
C
O
O
H
3
C
2
C
O
H
H
O
H
H
(a) Glucose, linear form
H
1
C
C
O
O
H
H
H
H
HO
OH
H
H
OH
OH
(b) Glucose, ring form
Fig. 2-13
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2.6 What Are Carbohydrates?
 Monosaccharide: a carbohydrate consisting
of one sugar molecule
 Disaccharide: two sugars linked together
 Polysaccharide: three or more sugars linked
together
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2.6 What Are Carbohydrates?
 Simple sugars, such as glucose, provide
important energy sources for organisms.
 Sucrose, such as table sugar, is a
disaccharide containing one glucose
molecule attached to a fructose molecule.
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2.6 What Are Carbohydrates?
 Manufacture of a disaccharide
glucose
fructose
CH2OH
O
H H
HOCH2
CH2OH
O
O
H
H
+
HO
OH
H
H
OH
OH
sucrose
HO
H
OH
HO
H
dehydration
CH2OH synthesis
H H
HO
HOCH2
H
OH
H
H
OH
O
H
OH
O
H
HO
CH2OH
H
O
H
H
Fig. 2-14
Copyright © 2009 Pearson Education Inc.
2.6 What Are Carbohydrates?
PLAY
Animation—Carbohydrates
Copyright © 2009 Pearson Education Inc.
2.6 What Are Carbohydrates?
 Some complex sugars, such as cellulose,
provide support for cells or even the entire
bodies of organisms.
 Complex sugars are made by the
dehydration synthesis of simple sugars.
 Cellulose is the most abundant organic
molecule on Earth because it provides
support for plants in fields and forests.
 Cellulose is made of long chains of glucose
subunits.
Copyright © 2009 Pearson Education Inc.
2.6 What Are Carbohydrates?
 Cellulose structure
wood is mostly cellulose
plant cell with cell wall
close-up of cell wall
Hydrogen bonds
cross-linking
cellulose molecules
CH2OH
H
O
H
O
H
OH
OH
O
H
H
H
CH2OH
OH
H
H
H
H
O
OH
CH2OH
Copyright © 2009 Pearson Education Inc.
OH
OH
H H
O
H
OH
O
H
H
O
H
H
H
H
O
O
H
OH
CH2OH
individual
cellulose
molecules
bundle of
cellulose
molecules
cellulose
fiber
Fig. 2-15
2.6 What Are Carbohydrates?
PLAY
Animation—Carbohydrate Functions
PLAY
Animation—Structure Determines Function
Copyright © 2009 Pearson Education Inc.
2.7 What Are Lipids?
 Molecular characteristics of lipids
• Lipids are molecules with long regions
composed almost entirely of carbon and
hydrogen.
• The nonpolar regions of carbon and hydrogen
bonds make lipids hydrophobic and insoluble
in water.
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2.7 What Are Lipids?
 Lipid classification
• Group 1: Oils, fats, and waxes
• Group 2: Phospholipids
• Group 3: Steroids
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2.7 What Are Lipids?
 Group 1: Oils, fats, and waxes
• Contain only carbon, hydrogen, and oxygen
• Contain one or more fatty acid subunits—long
chains of C and H with a carboxyl group
(–COOH)
• They usually do not have a ring structure.
Copyright © 2009 Pearson Education Inc.
2.7 What Are Lipids?
 Group 1: Oils, fats, and waxes (continued)
• Fats and oils form by dehydration synthesis
from three fatty acid subunits and one
molecule of glycerol.
etc.
CH2
CH2
CH2
H
H C OH
O
CH
HO C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH
H C OH
O
HO C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 etc.
+
H C OH
H
glycerol
O
HO C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 etc.
fatty acids
Fig. 2-16
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2.7 What Are Lipids?
 Group 1: Oils, fats, and waxes (continued)
• Fats and oils formed by dehydration synthesis
are called triglycerides.
• Triglycerides are used for long-term energy
storage in both plants and animals.
etc.
CH2
CH2
CH2
H
O
CH
H C O C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH
+
O
H
O
O
H C O C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 etc.
+
H
O
H C O C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 etc.
H
+
H
triglyceride
H
H
O
H
3 water
molecules
Fig. 2-16
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2.7 What Are Lipids?
PLAY
Animation—Lipids
Copyright © 2009 Pearson Education Inc.
2.7 What Are Lipids?
 Group 1: Oils, fats, and waxes (continued)
• Characteristics of fats
• Fats are solid at room temperature.
• Fats have all carbons joined by single
covalent bonds.
• The remaining bond positions on the
carbons are occupied by hydrogen atoms.
Copyright © 2009 Pearson Education Inc.
2.7 What Are Lipids?
 Group 1: Oils, fats, and waxes (continued)
• Fatty acids of fats are said to be saturated and
are straight molecules that can be stacked.
(a) Beef fat (saturated)
Fig. 2-18a
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2.7 What Are Lipids?
 Group 1: Oils, fats, and waxes (continued)
• Characteristics of oils
• Oils are liquid at room temperature.
• Some of the carbons in fatty acids have
double covalent bonds.
• There are fewer attached hydrogen atoms,
and the fatty acid is said to be unsaturated.
Copyright © 2009 Pearson Education Inc.
2.7 What Are Lipids?
 Group 1: Oils, fats, and waxes (continued)
• Unsaturated fatty acids have bends and kinks
in fatty acid chains and can’t be stacked.
(b) Peanut oil (unsaturated)
Fig. 2-18b
Copyright © 2009 Pearson Education Inc.
2.7 What Are Lipids?
 Group 1: Oils, fats, and waxes (continued)
• Characteristics of waxes
• Waxes are solid at room temperature.
• Waxes are highly saturated.
• Waxes are not a food source.
• Waxes form waterproof coatings over plant
leaves and stems.
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2.7 What Are Lipids?
 Group 1: Oils, fats, and waxes (continued)
• Bees use waxes to store food and honey.
Fig. 2-17b
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2.7 What Are Lipids?
PLAY
Animation—Lipid Function
Copyright © 2009 Pearson Education Inc.
2.7 What Are Lipids?
 Group 2: Phospholipids
• Phospholipids have water-soluble heads and
water-insoluble tails.
• They are found in cell membranes in a double
layer.
• They are like oils except one fatty acid is
replaced by a phosphate group attached to
glycerol.
Copyright © 2009 Pearson Education Inc.
2.7 What Are Lipids?
 Group 2: Phospholipids (continued)
• The phosphate end of the molecule is water
soluble; the fatty acid end of the molecule is
water insoluble.
CH3
O–
H3C - N+- CH2 - CH2 -O-P- O -CH2 O
CH3
O HC-O-C- CH2 -CH2 - CH2 - CH2 - CH2 - CH2 - CH2 -CH
O
CH
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH3
H2C-O-C- CH2 -CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 -CH3
polar head
glycerol
(hydrophilic)
fatty acid tails
(hydrophobic)
Fig. 2-19
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2.7 What Are Lipids?
 Group 3: Steroids
• Steroids contain four carbon rings fused
together.
• Various functional groups protrude from the
basic steroid “skeleton”.
• Cholesterol is a steroid found in cell
membranes.
Copyright © 2009 Pearson Education Inc.
2.7 What Are Lipids?
 Group 3: Steroids
• Testosterone and estrogen are male and
female reproductive hormones, respectively,
and are steroids.
OH
CH3
CH3
HC
CH3
CH2
CH2
HO
(b) Estrogen
CH2
HC CH3
CH3
OH
CH3
CH3
CH3
HO
O
(a) Cholesterol
(c) Testosterone
Fig. 2-20
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2.8 What Are Proteins?
 Functions of proteins
• Proteins act as enzymes to catalyze many
biochemical reactions.
• They can act as energy stores.
• They are involved in carrying oxygen around
the body.
• They are involved in muscle movement.
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2.8 What Are Proteins?
 Some proteins are structural and provide
support in hair, horns, spider webs, etc.
Fig. 2-21
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2.8 What Are Proteins?
 Proteins are formed from chains of amino
acids.
• All amino acids have the same basic structure:
• A central carbon
• An attached amino group
• An attached carboxyl group
• An attached variable side group
Copyright © 2009 Pearson Education Inc.
2.8 What Are Proteins?
 Amino acid structure
variable
group
R
H
amino
group
O
N
H
C
carboxylic
acid group
C
H
O
H
hydrogen
Fig. 2-22
Copyright © 2009 Pearson Education Inc.
2.8 What Are Proteins?
 Amino acids join to form chains by
dehydration synthesis.
• Proteins are formed by dehydration reactions
between individual amino acids.
• The –NH2 group of one amino acid is joined to
the –COOH group of another, with the release
of H2O and the formation of a new peptide
(two or more amino acids).
Copyright © 2009 Pearson Education Inc.
2.8 What Are Proteins?
 More and more individual amino acids are
added to the peptide until a polypeptide
(protein) is formed.
amino acid
R
H
N
H
amino
group
C
H
amino acid
O
C
N
+
O
R
H
H
H
carboxylic amino
acid
group
group
C
H
water
peptide
O
H
C
N
O
H
H
R
O
H
R
C
C
N
C
H
H
O
C
+
O
H
O
H
H
peptide
bond
Fig. 2-23
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2.8 What Are Proteins?
PLAY
Animation—Proteins
Copyright © 2009 Pearson Education Inc.
2.8 What Are Proteins?
 Three-dimensional shapes give proteins
their functions.
• Long chains of amino acids fold into threedimensional shapes in cells, which allows the
protein to perform its specific functions.
• When a protein is denatured, its shape has
been disrupted and it may not be able to
perform its function.
Copyright © 2009 Pearson Education Inc.
2.8 What Are Proteins?
H
C
H O C
C
N
N
O C
C
lys
helix
pro
O C
N
O C
N
O C
H
N
val
O C
C
lys
N
H
N
O C
H
C
O C
H
hydrogen
bond
(b) Secondary structure:
Folding usually maintained
by hydrogen bonds
C
ala
H
his
H
O C
C
gly
N
N
H
lys
C
lys
N H O C
O C
val
C
N
H
leu
H C R
(a) Primary structure: The
sequence of amino acids linked
by peptide bonds
(c) Tertiary structure: Folding
results from bonds with
surrounding water molecules
and between amino acids
(d) Quaternary structure:
Individual polypeptides are linked
to one another
Fig. 2-24
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2.8 What Are Proteins?
PLAY
Animation—Protein Function
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2.9 What Are Nucleic Acids?
 Structure of nucleic acids
• Nucleic acids are long chains of similar, but
not identical, subunits called nucleotides.
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2.9 What Are Nucleic Acids?
 Structure of nucleic acids (continued)
• All nucleotides have three parts.
• A five-carbon sugar (ribose or deoxyribose)
• A phosphate group
• A nitrogen-containing molecule called a
base
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2.9 What Are Nucleic Acids?
 Deoxyribose nucleotide
base
NH2
phosphate
N C C
N
OH
HO
P
HC
O
CH2
O
H
N C N CH
O
sugar
H
H
OH
H
H
Fig. 2-25
Copyright © 2009 Pearson Education Inc.
2.9 What Are Nucleic Acids?
 Types of nucleotides
• Those that contain the sugar ribose.
• Those that contain the sugar deoxyribose.
• Nucleotides string together in long chains as
nucleic acids with the phosphate group of one
nucleotide bonded to the sugar group of
another.
Copyright © 2009 Pearson Education Inc.
2.9 What Are Nucleic Acids?
 Nucleotide chain
base
sugar
phosphate
Fig. 2-26
Copyright © 2009 Pearson Education Inc.
2.9 What Are Nucleic Acids?
 DNA and RNA, the molecules of heredity,
are nucleic acids.
• There are two types of nucleic acids.
• Deoxyribonucleic acid (DNA): contains the
genetic code of cell
• Ribonucleic acid (RNA): is used in the
synthesis of proteins
Copyright © 2009 Pearson Education Inc.
2.9 What Are Nucleic Acids?
PLAY
Animation—Nucleic Acids
PLAY
Animation—Nucleic Acids
Copyright © 2009 Pearson Education Inc.
2.9 What Are Nucleic Acids?
 Other nucleotides perform other functions.
• Adenosine monophosphate: acts as a
messenger in the cell, carrying information to
other molecules
• Adenosine triphosphate: carries energy from
place to place in the cell
Copyright © 2009 Pearson Education Inc.