Molecules of Life
Chapter 3
3.1 Molecules of Life
 Molecules of life are synthesized by living cells
•
•
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Carbohydrates
Lipids
Proteins
Nucleic acids
Structure to Function
 Molecules of life differ in three-dimensional
structure and function
• Carbon backbone
• Attached functional groups
 Structures give clues to how they function
Organic Compounds
 Consist primarily of carbon and hydrogen atoms
• Carbon atoms bond covalently with up to four
other atoms, often in long chains or rings
 Functional groups attach to a carbon backbone
• Influence organic compound’s properties
An Organic Compound: Glucose
 Four models
Functional Groups
In alcohols (e.g.,
sugars, amino acids);
water soluble
hydroxyl
methyl
In fatty acid chains;
insoluble in water
carbonyl
(aldehyde)
(ketone)
In sugars, amino acids,
nucleotides; water
soluble. An aldehyde
if at end of a carbon
backbone; a ketone if
attached to an interior
carbon of backbone
carboxyl
(non-ionized)
(ionized)
In amino acids, fatty
acids, carbohydrates;
water soluble. Highly
polar; acts as an acid
(releases H+)
Fig. 3.3, p. 36
amino
In amino acids and
certain nucleotide
bases; water soluble,
acts as a weak base
(accepts H+)
(non-ionized)
(ionized)
phosphate
icon
In nucleotides (e.g.,
ATP), also in DNA,
RNA, many proteins,
phospholipids; water
soluble, acidic
Fig. 3.3, p. 36
Functional Groups:
The Importance of Position
one of the estrogens
testosterone
Fig. 3.4, p. 37
Animation: Functional group
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Processes of Metabolism
 Cells use energy to grow and maintain
themselves
 Enzyme-driven reactions build, rearrange, and
split organic molecules
Building Organic Compounds
 Cells form complex organic molecules
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•
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Simple sugars → carbohydrates
Fatty acids → lipids
Amino acids → proteins
Nucleotides → nucleic acids
 Condensation combines monomers to form
polymers
What Cells Do to Organic Compounds
Condensation and Hydrolysis
enzyme action at functional groups
enzyme action at functional groups
Condensation
Hydrolysis
Fig. 3.5, p. 37
Animation: Condensation and hydrolysis
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Key Concepts:
STRUCTURE DICTATES FUNCTION
 We define cells partly by their capacity to build
complex carbohydrates and lipids, proteins, and
nucleic acids
 The main building blocks are simple sugars, fatty
acids, amino acids, and nucleotides
 These organic compounds have a backbone of
carbon atoms with functional groups attached
3.2 Carbohydrates –
The Most Abundant Ones
 Three main types of carbohydrates
• Monosaccharides (simple sugars)
• Oligosaccharides (short chains)
• Polysaccharides (complex carbohydrates)
 Carbohydrate functions
• Instant energy sources
• Transportable or storable forms of energy
• Structural materials
Simple Sugars: Glucose and Fructose
Oligosaccharides: Sucrose
glucose
fructose
sucrose
c Formation of a sucrose molecule
Fig. 3.6, p. 38
Complex Carbohydrates:
Bonding Patterns
Complex Carbohydrates:
Starch, Cellulose, and Glycogen
Complex Carbohydrates:
Starch, Cellulose, and Glycogen
Structure of
cellulose
c Glycogen. In animals, this
polysaccharide is a storage form
for excess glucose. It is
especially abundant in the liver
and muscles of highly active
animals, including fishes and
people.
Fig. 3.8, p. 39
Animation: Structure of starch and
cellulose
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Complex Carbohydrates:
Chitin
Key Concepts:
CARBOHYDRATES
 Carbohydrates are the most abundant biological
molecules
 Simple sugars function as transportable forms of
energy or as quick energy sources
 Complex carbohydrates are structural materials
or energy reservoirs
3.3 Greasy, Oily – Must Be Lipids
 Lipids
• Fats, phospholipids, waxes, and sterols
• Don’t dissolve in water
• Dissolve in nonpolar substances (other lipids)
 Lipid functions
• Major sources of energy
• Structural materials
• Used in cell membranes
Fats
 Lipids with one, two, or three fatty acid tails
• Saturated
• Unsaturated (cis and trans)
 Triglycerides (neutral fats )
• Three fatty acid tails
• Most abundant animal fat (body fat)
• Major energy reserves
Fatty Acids
Animation: Fatty acids
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Trans and Cis Fatty Acids
Triglyceride Formation
glycerol
three fatty acid tails
Triglyceride, a neutral fat
Fig. 3.11, p. 40
Animation: Triglyceride formation
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Phospholipids
 Main component of
cell membranes
• Hydrophilic head,
hydrophobic tails
hydrophilic head
two hydrophilic tails
b
Fig. 3.13, p. 41
c Cell membrane section
Fig. 3.13, p. 41
Animation: Phospholipid structure
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Waxes
 Firm, pliable, water repelling, lubricating
Sterols: Cholesterol
 Membrane components; precursors of other
molecules (steroid hormones)
Animation: Cholesterol
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Key Concepts:
LIPIDS
 Complex lipids function as energy reservoirs,
structural materials of cell membranes, signaling
molecules, and waterproofing or lubricating
substances
3.4 Proteins –
Diversity in Structure and Function
 Proteins have many functions
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•
•
•
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Structures
Nutrition
Enzymes
Transportation
Communication
Defense
Protein Structure
 Built from 20 kinds of amino acids
Fig. 3.15, p. 42
amino
group
carboxyl
group
Fig. 3.15, p. 42
Fig. 3.15, p. 42
valine
Fig. 3.15, p. 42
Protein Synthesis
Protein Synthesis
Protein Synthesis
Four Levels of Protein Structure
1. Primary structure
• Amino acids joined by peptide bonds form a
linear polypeptide chain
2. Secondary structure
• Polypeptide chains form sheets and coils
3. Tertiary structure
• Sheets and coils pack into functional domains
Four Levels of Protein Structure
4. Quaternary structure
• Many proteins (e.g. enzymes) consist of two or
more chains
 Other protein structures
• Glycoproteins
• Lipoproteins
• Fibrous proteins
Levels of Protein Structure
a Protein primary
structure: Amino
acids bonded in a
polypeptide chain.
Fig. 3.17, p. 43
Levels of Protein Structure
b Protein secondary
structure: A coiled
(helical) or sheetlike
array, held in place
by hydrogen bonds
( dotted lines) between
different parts of the
polypeptide chain.
helical coil
sheet
Fig. 3.17, p. 43
Levels of Protein Structure
barrel
c Protein tertiary structure: A
chain’s coiled parts, sheetlike
arrays, or both have folded and
twisted into stable, functional
domains, including clusters,
pockets, and barrels.
Fig. 3.17, p. 43
Levels of Protein Structure
d Protein quaternary
structure: Many weak
interactions hold two
or more polypeptide
chains together as
a single molecule.
Fig. 3.17, p. 43
Animation: Structure of an amino acid
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Animation: Peptide bond formation
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Animation: Secondary and tertiary
structure
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Animation: Globin and hemoglobin
structure
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3.5 Why is Protein Structure
So Important?
 Protein structure dictates function
 Sometimes a mutation in DNA results in an
amino acid substitution that alters a protein’s
structure and compromises its function
• Example: Hemoglobin and sickle-cell anemia
Normal Hemoglobin Structure
alpha globin
heme
a Globin. The secondary
structure of this polypeptide
includes several helixes. The
coils fold up to form a pocket
that cradles heme, a functional
group with an iron atom at its
center. The kind of molecular
representation shown here is
called a ribbon model, after its
appearance. Appendix V has
more details about such models.
Fig. 3.18, p. 44
Normal Hemoglobin Structure
alpha globin
beta globin
alpha globin
beta globin
b Hemoglobin is one of the proteins with quaternary structure. It
consists of four globin molecules held together by hydrogen bonds.
To help you distinguish among them, the two alpha globin chains
are shown here in green, and the two beta globins are in brown.
Fig. 3.18, p. 44
Sickle-Cell Mutation
VALINE
HISTIDINE
LEUCINE THREONINE PROLINE GLUTAMATE GLUTAMATE
a Normal amino acid sequence at the
start of a beta chain for hemoglobin.
Fig. 3.19, p. 45
Sickle-Cell Mutation
VALINE
HISTIDINE
LEUCINE THREONINE PROLINE
b One amino acid substitution results in the
abnormal beta chain in HbS molecules. Instead
of glutamate, valine was added at the sixth
position of the polypeptide chain.
c Glutamate has an overall negative charge; valine
has no net charge. At low oxygen levels, this
difference gives rise to a water-repellent, sticky
patch on HbS molecules. They stick together
because of that patch, forming rodshaped clumps
that distort normally rounded red blood cells into
sickle shapes. (A sickle is a farm tool that has a
crescent-shaped blade.)
VALINE
GLUTAMATE
sickle cell
normal cell
Fig. 3.19, p. 45
Sickle-Cell Mutation
Clumping of cells in bloodstream
Circulatory problems, damage to brain,
lungs, heart, skeletal muscles, gut, and
kidneys
Heart failure, paralysis, pneumonia,
rheumatism, gut pain, kidney failure
Spleen concentrates sickle cells
Spleen enlargement
Immune system compromised
Rapid destruction of sickle cells
d Melba Moore, celebrity spokesperson for sickle-cell anemia
organizations. Right, range of
symptoms for a person with two
mutated genes for hemoglobin’s
beta chain.
Anemia, causing weakness,fatigue,
impaired development,heart chamber
dilation
Impaired brain function, heart failure
Fig. 3.19, p. 45
Clumping of cells in bloodstream
Circulatory problems, damage to brain,
lungs, heart, skeletal muscles, gut, and
kidneys
Heart failure, paralysis, pneumonia,
rheumatism, gut pain, kidney failure
Spleen concentrates sickle cells
Spleen enlargement
Immune system compromised
Rapid destruction of sickle cells
d Melba Moore, celebrity spokesperson for sickle-cell anemia
organizations. Right, range of
symptoms for a person with two
mutated genes for hemoglobin’s
beta chain.
Anemia, causing weakness,fatigue,
impaired development,heart chamber
dilation
Stepped Art
Impaired brain function, heart failure
Fig. 3-19, p. 45
Animation: Sickle-cell anemia
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Denatured Proteins
 If a protein unfolds and loses its threedimensional shape (denatures), it also loses its
function
 Caused by shifts in pH or temperature, or
exposure to detergent or salts
• Disrupts hydrogen bonds and other molecular
interactions responsible for protein’s shape
Key Concepts:
PROTEINS
 Structurally and functionally, proteins are the
most diverse molecules of life
 They include enzymes, structural materials,
signaling molecules, and transporters
Animation: Molecular models of the
protein hemoglobin
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3.6 Nucleotides, DNA, and RNAs
Nucleotide structure, 3 parts:
• Sugar
• Phosphate group
• Nitrogen-containing base
base (blue)
sugar (orange)
three phosphate groups
Fig. 3.20, p. 46
Nucleotide Functions:
Reproduction, Metabolism, and Survival
 DNA and RNAs are nucleic acids, each
composed of four kinds of nucleotide subunits
 ATP energizes many kinds of molecules by
phosphate-group transfers
 Other nucleotides function as coenzymes or as
chemical messengers
Nucleotides of DNA
phosphate
group
sugar
(deoxyribose)
adenine
(A)
base with a
double-ring
structure
Fig. 3.21, p. 46
THYMINE
(T)
base with a
single-ring
structure
Fig. 3.21, p. 46
GUANINE
(C)
base with a
double-ring
structure
Fig. 3.21, p. 46
CYTOSINE
(C)
base with a
single-ring
structure
Fig. 3.21, p. 46
DNA, RNAs, and Protein Synthesis
 DNA (double-stranded)
• Encodes information about the primary structure
of all cell proteins in its nucleotide sequence
 RNA molecules (usually single stranded)
• Different kinds interact with DNA and one another
during protein synthesis
The DNA Double-Helix
covalent
bonding in
carbon
backbone
hydrogen bonding
between bases
Fig. 3.22, p. 47
Key Concepts:
NUCLEOTIDES AND NUCLEIC ACIDS
 Nucleotides have major metabolic roles and are
building blocks of nucleic acids
 Two kinds of nucleic acids, DNA and RNA,
interact as the cell’s system of storing, retrieving,
and translating information about building
proteins
Animation: Nucleotide subunits of DNA
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Animation: Structure of ATP
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