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Chapter 3
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1
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
3.1 Polymers Are Built of
Monomers
• Organic molecules are formed by living
organisms
– have a carbon-based core
– the core has attached groups of atoms
called functional groups
•the functional groups confer specific
chemical properties on the organic
molecules
2
Figure 3.2 Five principal functional groups
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Group
Structural
Formula
Hydroxyl
Ball-andStick Model
OH
Carbonyl
C
O
O
Amino
O
H
Carbohydrates
C
O
Lipids
O
C
C
Carboxyl
Proteins
OH
O
H
H
N
Proteins
H
O–
O–
O
H
N
H
Phosphate
Found In
P
O
O–
O
P
O
O–
DNA,
ATP
3
• The building materials of the body are known as
macromolecules because they can be very large
• There are four types of macromolecules:
1. Proteins
2. Nucleic acids
3. Carbohydrates
4. Lipids
• Large macromolecules are actually assembled
from many similar small components, called
monomers
– the assembled chain of monomers is known as
a polymer
4
• All polymers are assembled the same way
– a covalent bond is formed by removing
a hydroxyl group (OH) from one subunit
and a hydrogen (H) from another
subunit
– because this amounts to the removal of
a molecule of water (H2O), this process
of linking together two subunits to form a
polymer is called dehydration
synthesis
5
Figure 3.3(a) Dehydration synthesis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
H2
O
HO
H
H HO
Energy
HO
(a) Dehydration synthesis
H
6
• The process of disassembling polymers
into component monomers is essentially
the reverse of dehydration synthesis
– a molecule of water is added to break
the covalent bond between the
monomers
– this process is known as hydrolysis
7
Figure 3.3(b) Hydrolysis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
H2
O
H
HO
Energy
HO
(b) Hydrolysis
H HO
H
8
3.2 Proteins
• Proteins are complex macromolecules that
are polymers of many subunits called
amino acids
– the covalent bond linking two amino
acids together is called a peptide bond
– the assembled polymer is called a
polypeptide
9
Figure 3.5 The formation of a peptide bond
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Amino acid
H
Amino acid
H
R
N
C
C
H
O
H
OH
H
R
N
C
C
H
O
OH
H2O
Polypeptide chain
H
H
R
N
C
C
H
O
H
R
N
C
C
H
O
OH
10
3.2 Proteins
• Amino acids are small molecules with a
simple basic structure, a carbon atom to
which three groups are added
– an amino group (—NH2)
– a carboxyl group (—COOH)
– a functional group (R)
• The functional group gives amino acids
their chemical identity
– there are 20 different types of amino acids
11
• Protein structure is complex
– the order of the amino acids that form the
polypeptide is important
• the sequence of the amino acids affects
how the protein folds together
– the way that a polypeptide folds to form the
protein determines the protein’s function
• some proteins are comprised of more than
one polypeptide
12
3.2 Proteins
•
There are four general levels of protein
structure
1. Primary
2. Secondary
3. Tertiary
4. Quaternary
13
3.2 Proteins
• Primary structure—the sequence of amino
acids in the polypeptide chain
– Determines all other levels of protein structure
• Secondary structure forms because
regions of the polypeptide that are nonpolar
are forced together; hydrogen bonds can
form between different parts of the chain
– The folded structure may resemble coils,
helices, or sheets
14
3.2 Proteins
• Tertiary structure—the final 3-D shape
of the protein
– The final twists and folds that lead to this
shape are the result of polarity differences in
regions of the polypeptide
• Quaternary structure—the spatial
arrangement of proteins comprised of
more than one polypeptide chain
15
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Primary
structure
Amino acids
H
N
Secondary
structure
C
C
N
N
C C
C
O
H O
C
N
H
C
C
O
H
H
N
O
C
C
N
C
C
H
β-pleated sheet
C N
O
O
H
C
N
C
O
C
N
O
α-helix
C
C
O
Tertiary
structure
Quaternary
structure
16
3.2 Proteins
• The shape of a protein affects its function
– changes to the environment of the protein
may cause it to unfold or denature
•increased temperature or lower pH
affects hydrogen bonding, which is
involved in the folding process
– a denatured protein is inactive
17
3.2 Proteins
• Enzymes are globular proteins that have a
special 3-D shape that fits precisely with
another chemical
– they cause the chemical that they fit with
to undergo a reaction
– this process of enhancing a chemical
reaction is called catalysis
18
• Proteins fold specifically
– the folding process is helped by special
proteins called chaperone proteins
•these proteins somehow correct a
misfolded protein
•defective chaperone proteins may
play a role in certain genetic disorders
that involve defective proteins
–Cystic fibrosis
–Alzheimer’s
19
Figure 3.8 How one type of chaperone protein works
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Misfolded
protein
Chaperone
protein
Correctly folded
protein
Cap
Isolated
protein
Chance for protein to refold
20
3.3 Nucleic Acids
•
Nucleic acids are very long polymers that
store information
– comprised of monomers called nucleotides
• Each nucleotide has 3 parts
1. a five-carbon sugar
2. a phosphate group
3. an organic nitrogen-containing base
• There are five different types of nucleotides
– information is encoded in the nucleic acid by
different sequences of these nucleotides
21
Figure 3.9 The structure of a nucleotide
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structure of nucleotide
7N
Phosphate group
O
P
N
9
O
4
O
NH2
N
1
H
N C C
N
N C
C H
C
2
N
3
H
N
C
H
CH
5′ 2
4′
1′
3′
2′
OH
H C
OH in RNA
H C
R
Sugar
C
N
N C
NH2
N
C
O
N
C O
H
H in DNA
H
Guanine
NH2
O
N C C N
H
Adenine
O–
(a)
5
NH2
6
8
O
–
Nitrogenous bases
Nitrogenous base
Cytosine
H3C
C
H C
C
N
O
N H
H
C
C
H
C
H
Thymine (DNA only)
O
C
N
N
H
C O
H
Uracil (RNA only)
(b)
22
3.3 Nucleic Acids
• There are two types of nucleic acids
– Deoxyribonucleic acid (DNA)
– Ribonucleic acid (RNA)
• RNA is similar to DNA except that
– it uses uracil instead of thymine
– it is comprised of just one strand
– it has a ribose sugar
23
3.3 Nucleic Acids
• The structure of DNA is a double helix
because
– there are only two base pairs possible
•Adenine (A) pairs with thymine (T)
•Cytosine (C) pairs with Guanine (G)
– properly aligned hydrogen bonds hold
each base pair together
– a sugar-phosphate backbone comprised
of phosphodiester bonds gives support
24
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 3.11 The
DNA double helix
O
P
Sugar-phosphate
“backbone”
O
O
C
P
P
G
O
P
O
G
P
O
C
O
Hydrogen bonds
between nitrogenous
bases
P
T
A
P
O
Phosphodiester bond
P
C
O
G
O
P
P
O
A
T
O
P
OH
25
3.3 Nucleic Acids
• The structure of DNA helps it to function
– the hydrogen bonds of the base pairs can be
broken to unzip the DNA so that information
can be copied
• each strand of DNA is a mirror image so
that the DNA contains two copies of the
information
– having two copies means that the information
can be accurately copied and passed to the
next generation
26
3.4 Carbohydrates
• Carbohydrates are monomers that make up the
structural framework of cells and play a critical
role in energy storage
• A carbohydrate is any molecule that contains the
elements C, H, and O in a 1:2:1 ratio
• The sizes of carbohydrates varies
– simple carbohydrates—consist of one or two
monomers
– complex carbohydrates—are long polymers
27
3.4 Carbohydrates
• Simple carbohydrates are small
– monosaccharides consist of only one
monomer subunit
• an example is the sugar glucose (C6H12O6)
– disaccharides consist of two monosaccharides
• an example is the sugar sucrose, which is
formed by joining together glucose and
fructose
28
Figure 3.13 Formation of sucrose
29
3.4 Carbohydrates
• Complex carbohydrates are long
polymer chains
– because they contain many C-H bonds, these
carbohydrates are good for storing energy
• these bond types are the ones most often
broken by organisms to obtain energy
– the long chains are called polysaccharides
30
3.4 Carbohydrates
• Plants and animals store energy in
polysaccharide chains formed from glucose
– plants form starch
– animals form glycogen
• Some polysaccharides are structural and
resistant to digestion by enzymes
– plants form cellulose cell walls
– some animals form chitin for exoskeletons
31
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 3.14 A polysaccharide: Cellulose
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
H
Plant
cell wall
H
H
O
OH
O
H
H
H
OH
H
H
OH
H
H
H
O
O
H
CH 2O
© J.D. Litvay/Visuals Unlimited
H
H
2
O
H
H
O
H
H
O
O
O
CH
H
CH2OH
H
OH
H
H
OH
CH 2
O
O
H
OH
H
OH
32
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
TABLE 3.1
CARBOHYDRATES AND THEIR FUNCTIONS
Carbohydrate
Example
Description
Transport Disaccharides
Glucose is transported with in some organisms as a
disaccharide. In this form, it is less readily metabolized
because the normal glucose-utilizing enzymes of the
organism cannot break the bond linking the two
monosaccharide subunits. One type of disaccharide is
called lactose. Many mammals supply energy to their
young in the form of lactose, which is found in milk.
Lactose
O
O
O
Another transport disaccharide is sucrose. Many plants
transport glucose throughout the plant in the form of
sucrose, which is harvested from sugarcane to make
sugar.
Sucrose
CH2OH
CH2OH
O
O
O
CH2OH
Storage Polysaccharides
Starch
O
O
O
O
O
O
Organisms store energy in long chains of glucose
molecules called polysaccharides. The chains tend
to coil up in water, making them insoluble and ideal
for storage. The storage polysaccharides found in
plants are called starches, which can be branched or
unbranched. Starch is found in potatoes and in grains,
such as corn and wheat.
O
Glycogen
In animals, glucose is stored as glycogen. Glycogen
is similar to starch in that it consists of long chains of
glucose that coil up in water and are insoluble. But
glycogen chains are much longer and highly branched.
glycogen can be stored in muscles and the liver.
O
O
O
O
O
O
O
(cow, potatoes, leaves): © Corbis RF; (sugarcane): © PhotoLink/Getty RF; (arm): © Getty RF
33
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural Polysaccharides
Cellulose
O
O
O
O
O
O
O
Chitin
O C
O C
N
N
O
O C
N
O
O
O
O
O
O
O
Cellulose is a structural polysaccharide found in the cell
walls of plants; its glucose sub units are joined in away
that cannot be broken down readily. Cleavage of the
links between the glucose sub units in cellulose requires
an enzyme most organisms lack. Some animals, such as
cows, are able to digest cellulose by means of bacteria
and protists they harbor in their digestive tract, which
provide the necessary enzymes.
O
O
O
N
N
N
O C
O C
O C
Chitin is a type of structural polysaccharide found in
the external skeletons of many invertebrates, including
insects and crustaceans ,and in the cell walls of fungi.
Chitin is a modified form of cellulose with a nitrogen
group added to the glucose units. When cross-linked by
proteins, it forms a tough, resistant surface material.
)leaves): © Corbis RF; (lobster): © image100/PunchStock RF
34
3.5 Lipids
• Lipids—fats and other molecules that are
not soluble in water
– lipids are nonpolar molecules
– there are many different types of lipids
• fats
• oils
• steroids
• rubber
• waxes
• pigments
35
3.5 Lipids
• Fats are converted from glucose for longterm energy storage
• Fats have two subunits
– 1. fatty acids
– 2. glycerol
– Fatty acids are chains of C and H atoms,
known as hydrocarbons
• the chain ends in a carboxyl (—COOH)
group
36
Figure 3.15 Saturated and unsaturated fats
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
H
Because there
are 3 fatty acids
attached to a
glycerol, another
name for a fat is
triglyceride
H
H
H
O
H
H
H
H
H
H
H
H
C O
C
C
C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
O
H
H
H
H
H
H
H
H
C
C
C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
O
H
H
H
H
H
H
H
H
C
C
C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
C O
C O
H
Glycerol
backbone
H
H
H
Fatty acids
(a) Fat molecule (triacylglycerol)
37
3.5 Lipids
• Fatty acids have different chemical
properties due to the number of hydrogens
that are attached to the non-carboxyl
carbons
– if the maximum number of hydrogens are
attached, then the fat is said to be
saturated
– if there are fewer than the maximum
attached, then the fat is said to be
unsaturated
38
Figure 3.15 Saturated and unsaturated fats
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
H
H
H
H
C
C
C
C
H
H
(b) Hard fat (saturated): Fatty
acids with single
bonds
between all carbon
(c) Oil (unsaturated): Fatty acids
that contain double bonds
between one or more
pairs
39
• Biological membranes involve lipids
– phospholipids make up the two layers of the
membrane
– cholesterol is embedded within the membrane
Figure 3.17 Lipids are a key component of biological membranes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Outside of cell
Carbohydrate chains
Cell
membrane
Membrane proteins
Phospholipid
Cholesterol
40
Inside of cell
Inquiry & Analysis
How Does pH Affect a Protein’s
Function?
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Which of the three pH values
represents the highest
concentration of hydrogen
ions?
• How does pH affect the
release of oxygen from
hemoglobin?
Effects of pH on Hemoglobin O2Binding
100
pH 7.60
pH 7.40
pH 7.20
90
Percent hemoglobin bound to O2
• In the graph, what is the
dependent variable?
80
70
60
50
40
30
20
10
0
0
20
40
60
80
100
120
Oxygen levels (measured in mm
Hg)
140
41