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Molecules of Life
Chapter 3
3.1 Organic Compounds
Hydrogen and other elements
covalently bonded to carbon
Carbohydrates
Lipids
Proteins
Nucleic Acids
Carbon’s Bonding Behavior
• Outer shell of
carbon has 4
electrons; can
hold 8
• Each carbon atom
can form covalent
bonds with up to 4
atoms
Methane: Simplest Organic
Compound
H
H
C
H
Ball-and-stick
model
H
Structural formula
Space-filling
model
Figure 3.2
Page 36
Bonding Arrangements
• Carbon atoms can
form chains or rings
• Other atoms project
from the carbon
backbone
Glucose
(ball-and-stick model)
In-text figure
Page 36
Hemoglobin Molecular Models
Ball-and-stick model
Space-filling model
Ribbon model
Figure 3.3
Page 37
3.2 Functional Groups
• Atoms or clusters of atoms that are
covalently bonded to carbon backbone
• Give organic compounds their different
properties
Examples of Functional
Groups
Methyl group
- CH3
Hydroxyl group
- OH
Amino group
- NH3+
Carboxyl group
- COOH
Phosphate group
- PO3-
Sulfhydryl group
- SH
3.3 Types of Reactions
Functional group transfer
Electron transfer
Rearrangement
Condensation
Cleavage
Condensation Reactions
• Form polymers from subunits
• Enzymes remove -OH from one
molecule, H from another, form bond
between two molecules
• Discarded atoms can join to form water
Condensation
enzyme action at functional groups
enzyme action at functional groups
Figure 3.7a
Page 39
Hydrolysis
• A type of cleavage reaction
• Breaks polymers into smaller units
• Enzymes split molecules into two or
more parts
• An -OH group and an H atom derived
from water are attached at exposed
sites
Hydrolysis
enzyme action at functional groups
Figure 3.7b
Page 39
3.4 Carbohydrates
Monosaccharides
(simple sugars)
Oligosaccharides
(short-chain carbohydrates)
Polysaccharides
(complex carbohydrates)
Monosaccharides
• Simplest
carbohydrates
• Most are sweet
tasting, water
soluble
• Most have 5- or 6carbon backbone
Structure of glucose
Disaccharides
• Type of
oligosaccharide
• Two
monosaccharides
covalently bonded
• Formed by
condensation reaction
glucose
fructose
+ H2O
sucrose
Figure 3.8b
Page 40
Polysaccharides
• Straight or
branched chains
of many sugar
monomers
• Most common are
composed entirely
of glucose
Figure 3.9
Page 40
Starch chain
Cellulose & Starch
• Differences in bonding patterns between
monomers yield different properties
cellulose
Figure 3.10
Page 41
amylose (a starch)
Glycogen
• Sugar storage form in animals
• Large stores in muscle and liver cells
Figure 3.10
Page 41
Chitin
• Polysaccharide
• Nitrogen-containing groups attached to
glucose monomers
• Structural material for hard parts of
invertebrates, cell walls of many fungi
3.5 Lipids
• Most include fatty acids
– Fats
– Phospholipids
– Waxes
• Sterols and their derivatives have no
fatty acids
• Tend to be insoluble in water
Fatty Acids
• Carboxyl group at
one end
• Carbon backbone
• Saturated or
unsaturated
Figure 3.12
Page 42
stearic acid oleic acid
linolenic
acid
Fats
• Fatty acid(s)
attached to glycerol
• Triglycerides are
most common
Figure 3.13
Page 42
Phospholipids
• Main component of
cell membranes
• Hydrophilic head
• Hydrophobic tails
Fig. 3.14a,b
Page 43
Sterols and Derivatives
• No fatty acids
• Rigid backbone of
four fused-together
carbon rings
Cholesterol
• Cholesterol - most
common type in
animals
Figure 3.15a
In-text p43
Waxes
• Long-chain fatty acids linked to
long-chain alcohols or carbon
rings
• Firm consistency, repel water
• Important in water-proofing
3.6 Amino Acid Structure
Carboxyl
group
Amino
group
Figure 3.16
Page 44
R group
tryptophan
(trp)
Figure 3.17
Page 44
Protein Synthesis
• Peptide bond
– Condensation reaction links amino group of
one amino acid with carboxyl group of next
Water forms as a by-product
Fig. 3.18a
Page 45
Primary Structure
• Sequence of amino acids
• Unique for each protein
• Two linked amino acids = dipeptide
• Three or more = polypeptide
• Backbone of polypeptide has N atoms:
-N-C-C-N-C-C-N-C-C-N-
3.7 Second and Third
Levels
• Hydrogen bonding
produces helix or
sheet
• Domain formation
Tertiary structure
Secondary
structure
Figure 3.19a
Page 46
Fourth Level Structure
Some proteins
are made up of
more than one
polypeptide
chain
Figure 3.20
Page 47
HLA-A2 quaternary structure
Hemoglobin
alpha chain
beta chain
beta chain
alpha chain
3.8 One Wrong Amino Acid
• Single amino acid change in beta chain
can cause sickle-cell anemia
HbS
valine
histidine
leucine
proline
threonine
valine
glutamate
Fig. 3.21c,d
Page 48
Sickle Cell Anemia
• Caused by two mutated copies (HbS) of
Hb gene
• Low oxygen causes red blood cells to
clump
• Clumping prevents normal blood flow
• Over time, may damage tissues and
organs throughout the body
3.9 Nucleotide Structure
• Sugar
• At least one
ATP
phosphate group
• Nitrogen-
containing base
Figure 3.23a
Page 50
Nucleotide Functions
• Energy carriers
• Coenzymes
• Chemical messengers
• Building blocks for
nucleic acids
DNA
• Double-stranded
• Sugar-phosphate
backbone
• Covalent bonds in
backbone
• H bonds between
bases
Figure 3.25
Page 51
RNA
• Usually single strands
• Four types of nucleotides
• Unlike DNA, contains the base uracil in
place of thymine
• Three types are key players in protein
synthesis