Biological Molecules:
The Carbon Compounds
of Life
Why It Matters
 Mars

landing
Life?
Fig. 3-1, p. 42
Carbon Bonding
 Organic


molecules based on carbon
Each carbon atoms forms 4 bonds
Allows for a great variety of molecular shapes
p. 43
Hydrocarbons
 Hydrocarbons



Molecules of carbon linked only to hydrogen
Methane is the simplest hydrocarbon
CH4 = 1 carbon + 4 hydrogens
Hydrocarbons
 Hydrocarbon



linear chains
Ethane = C2H6
Propane = C3H8
Butane = C4H10
 Hydrocarbon
branched chain
Hydrocarbons
 Hydrocarbon

rings.
Cyclohexane = C6H12
Hydrocarbons
 Hydrocarbons
can also have double or
triple bonds between the carbons
Hydrocarbons
 Other
organic molecules in living
organisms contain elements in addition to
C and H




Carbohydrates
Lipids
Proteins
Nucleic Acids
Functional Groups
 Small,
reactive groups of atoms attached
to organic molecules
 Their
covalent bonds are more easily
broken or rearranged than other parts of
the molecules
Functional Groups
Table 3-1a, p. 44
Functional Groups
Table 3-1b, p. 44
Functional groups
Dehydration
 In
a dehydration synthesis or
condensation reaction, an —OH and —
H group are removed from two subunits to
join them together
Fig. 3-2a, p. 44
a. Dehydration synthesis reactions
The components of a water molecule are removed
as subunits join into a larger molecule.
Fig. 3-2a, p. 44
Hydrolysis
a hydrolysis reaction, an —OH and —
H group are added to two subunits when
they are broken apart
 In
Fig. 3-2b, p. 44
Hydrolysis
The components of a water molecule are added
as molecules are split into smaller subunits.
Stepped Art
Fig. 3-2b, p. 44
Reaction types
Carbohydrates
 Most
abundant biological molecules
 Contain

carbon, hydrogen, and oxygen
Usually 1 carbon:2 hydrogens:1 oxygen
Carbohydrates
 Important
as fuel sources and for energy
storage

Glucose, sucrose, starch, glycogen
 Important

as structural molecules
Cellulose, chitin
Monosaccharides
 Monosaccharides

(“one sugar”)
Usually three to seven carbons
Fig. 3-3, p. 46
Monosaccharides
 The
position of the side groups determine
the characteristics of different
monosaccharides
Fig. 3-4, p. 46
Monosaccharide Isomers
 Asymmetric
carbons can lead to two
molecules with different structures but the
same formula

Enantiomers or optical isomers
Dextrorotatory
Levorotatory
Monosaccharide Isomers
 Monosaccharides
with five or more
carbons can change from the linear form
to a ring form
Fig. 3-5, p. 47
a. Glucose
(linear form)
α-Glucose
b. Formation of
glucose rings
or
β-Glucose
Stepped Art
Fig. 3-5ab, p. 47
Monosaccharide Isomers
 Asymmetric
carbons in 5and 6-carbon
monosaccharides can form
α- and β-ring isomers
 Polysaccharides
with
α- or β-ring subunits
can have vastly different
chemical properties
Isomers
 Carvone
isomers
Disaccharides
 Disaccharides

(“two sugars”)
Two monosaccharides linked by a
dehydration reaction to form a glycosidic
bond
Fig. 3-6, p. 48
Polysaccharides
 Polysaccharides


(“many sugars”)
Macromolecules formed by the polymerization of
many monosaccharide subunits (monomers)
Two common energy storage polysaccharides:
• Starch and glycogen

Two common structural polysaccharides:
• Cellulose and chitin
Storage Polysaccharides
 Starch


is made by plants to store energy
Amylose = linear, unbranched
Amylopectin = branched
Fig. 3-7a, p. 49
Storage Polysaccharides
 Glycogen
is made by animals to store
energy, usually in liver and muscle tissues

Highly branched
Fig. 3-7b, p. 49
Structural Polysaccharides
 Cellulose
is made by plants as a
structural fiber in cell walls


Unbranched chain of glucoses connected by
β-linkages
Extremely strong
Fig. 3-7c, p. 49
Structural Polysaccharides
 Cellulose


is called fiber in human nutrition
Indigestible by most animals
Termites and ruminant mammals have microorganisms in their digestive tract that can
break down cellulose into glucose subunits
Structural Polysaccharides
 Chitin
is tough and resilient, used for cell
walls of fungi and exoskeletons of
arthropods

Similar structure to cellulose, but glucose subunits modified with nitrogen-containing groups
Fig. 3-7d, p. 49
Structure of starch and cellulose
The building blocks of
carbohydrates are
1.
2.
3.
4.
Amino acids
Monosaccharides
Nucleotides
Fatty acids
25%
1
25%
25%
2
3
25%
4
The bond that joins monosaccharides into
polysachharides are
1.
2.
3.
Glycosidic bonds
Peptide bonds
Phosphodiester
bonds
33%
1
33%
2
33%
3
Cellulose, glycogen and starch are all
composed entirely of glucose monomers.
1.
2.
True
False
50%
1
50%
2
Lipids
 Lipids
are mostly nonpolar, waterinsoluble molecules because they contain
many hydrocarbon parts



Neutral lipids are important energy-storage
molecules
Phospholipids help form membranes
Steroids contribute to membrane structure or
function as hormones
Neutral Lipids
 Neutral
lipids are nonpolar, with no
charged groups at cellular pH


Triglycerides are used for energy storage.
Glycerol (3-carbon alcohol) + fatty acids
Fig. 3-9, p. 51
a. Formation of a triglyceride
Glycerol
Fatty acids
Triglyceride
Fig. 3-9a, p. 51
b. Glyceryl palmitate
Fig. 3-9b, p. 51
c. Triglyceride model
Fig. 3-9c, p. 51
Neutral Lipids
 Fats
are semisolid at biological
temperatures
 Saturated fatty acid chains:
• Usually 14 to 22 carbons long
• Contain only single bonds between the carbons
• Maximum number of hydrogen atoms (“saturated”)
Neutral Lipids
 Oils

are liquid at biological temperatures
Unsaturated fatty acid chains:
• Contain one or more double bonds
• Fewer hydrogen atoms (“unsaturated”)
• Fatty acid chains bend or “kink” at double bond
Neutral Lipids
 Triglycerides
store twice as much energy
per weight as carbohydrates



Excellent energy
source in the diet
Animals store fat
rather than glycogen
to carry less weight
Triglycerides are used
by some birds to make
their feathers water
repellent
Molecular Modeling
 3-D
structures of Biomolecules
Phospholipids
 Phospholipids
provide the framework of
biological membranes

Glycerol + 2 fatty acids + polar phosphate
group
Fig. 3-12, p. 53
Phospholipid structure
a. Structural plan of
a phospholipid
b. Phosphatidyl
ethanolamine
c. Phospholipid
model
d. Phospholipid
symbol
Polar
unit
Phosphate
group
Glycerol
Fatty
acid
chains
Polar
Nonpolar
Fig. 3-12, p. 53
Steroids
 Steroids
have a common framework of
four carbon rings with various side groups
attached
Fig. 3-13a, p. 54
Steroids
 Cholesterol
(animals) and phytosterols
(plants) alter characteristics in membranes
Fig. 3-13b,c, p. 54
Steroids
 Steroid
hormones: important regulatory
molecules
Fig. 3-14, p. 54
Which lipids are found in
biological membranes?
1.
2.
3.
4.
Neutral lipids
Cholesterol
Phospholipids
Both 2 and 3
25%
1
25%
25%
2
3
25%
4
Compared to tropical fish, arctic
fish oils have
more unsaturated
fatty acids.
2. More cholesterol
3. Less saturated fatty
acids
4. More transunsaturated fatty
acids
1.
25%
1
25%
25%
2
3
25%
4
Proteins
 Cells
assemble 20 kinds of amino acids
into proteins by forming peptide bonds
 Proteins
structure
have as many as four levels of
Amino Acids
 Amino


acids: building blocks of proteins
All amino acids contain an amino group (—
NH2), a carboxyl group (—COOH), and a
hydrogen around the central carbon
The fourth “R” group represents the variety of
side groups in different amino acids
R
|
H2N—C—COOH
|
H
Amino Acids
 Nonpolar
amino acids:
Fig. 3-15a, p. 56
Amino Acids
 Uncharged
polar amino acids:
Fig. 3-15b, p. 56
Amino Acids
 Negatively
and positively charged amino
acids:
Fig. 3-15c, p. 56
Amino Acids

Methionine and
cysteine contain
sulfur side groups
 —SH groups in
two cysteines can
bond together to
produce a disulfide
bridge (—S—S—)
that helps stabilize
the structure of
proteins
Fig. 3-16, p. 57
Amino acids
Amino acid
backbone
chains
Disulfide
linkage
Cysteine side
groups
Fig. 3-16, p. 57
Amino Acids
 Peptide
bonds are covalent bonds that
join amino acids to form polypeptides
Fig. 3-17, p. 58
Side
group
Amino
group
Carboxyl
group
Amino acid 1
N-terminal
end
C-terminal
end
Peptide bond
Amino acid 2
Peptide
Fig. 3-17, p. 58
Primary Protein Structure
 Primary
structure: Sequence of amino
acids that characterizes a specific protein
Fig. 3-19, p. 59
Secondary Protein Structure
 Secondary
structure: Amino acids
interact with their neighbors to bend and
twist protein chain
 Some secondary structures have
distinctive shapes and have been named
Secondary Protein Structure
 Alpha
helix
(α-helix)
 Stabilized with
hydrogen
bonds
Fig. 3-20, p. 59
Secondary Protein Structure
 Beta
strand (β-strand) zigzags in flat
plane
Fig. 3-21a, p. 60
Secondary Protein Structure
 Beta
sheet (β-sheet) stabilized with H
bonds
Fig. 3-21b, p. 60
Secondary Protein Structure
 Random
 Irregular


coil
folded arrangement
Fold-back loops
“Hinges”
Tertiary Protein Structure
 Tertiary
structure is the overall
conformation or three-dimensional shape
of a protein
Tertiary Protein Structure
 Stabilized


to maintain the protein’s shape
Disulfide linkages • Positive/negative attractions
Hydrogen bonds • Polar/nonpolar associations
Fig. 3-22, p. 60
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
NH3+
O
CH2
C
O–
+
NH3
CH2
CH2
CH2
CH2
HC
CH3
CH2
CH3
CH2 OH
CH2
O
NH2 C CH2
CH2
CH2
S
S
CH2
73
COO–
5 factors promoting protein folding
and stability
1.
2.
3.
4.
5.
Hydrogen bonds
Ionic bonds and other polar interactions
Hydrophobic effects
Van der Waals forces
Disulfide bridges
74
Tertiary Protein Structure
 Chaperone
proteins (chaperonins) help
some new proteins fold into their correct
conformation
Fig. 3-24, p. 62
Quaternary Protein Structure
 Quaternary
structure: Two or more
proteins joined together into a larger
complex protein
Fig. 3-18, p. 58
Proteins Contain Functional
Domains Within Their Structures
 Module
or domains in proteins have
distinct structures and function
 Signal transducer and activator of
transcription (STAT) protein example
 Each domain of this protein is involved in a
distinct biological function
 Proteins that share one of these domains
also share that function
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
STAT
protein
HN3+
COO–
Protein Data Bank
 PDB
Secondary structure of protein
is dependent on
1.
2.
3.
The R groups
The polypeptide
backbone
Neither
33%
1
33%
2
33%
3
Secondary structure of proteins
requires what type of bonds?
1.
2.
3.
Covalent bonds
Hydrogen bonds
Ionic bonds
33%
1
33%
2
33%
3
One amino acid change in a protein can
affect its structure and therefore the function
of the protein.
1. True
50%
50%
2. False
1
2
Sickle cell anemia is caused by a mutation in the betahemoglobin gene that changes a charged amino acid,
glutamic acid, to valine, a hydrophobic amino acid. Where
in the protein would you expect to find glutamic acid?
1.
2.
3.
On the exterior
surface of the
protein
In the interior of
the protein, away
from water
At the hemebinding site
33%
1
33%
2
33%
3
The sickle cell hemoglobin mutation alters what
level(s) of protein structure?
1.
2.
3.
4.
Primary
Tertiary
Quantenary
All
25%
1
25%
25%
2
3
25%
4
Nucleic Acids
 Nucleic
acids are long polymers of
nucleotide building blocks


DNA (deoxyribonucleic acid) stores hereditary
information
RNA (ribonucleic acid) is used in various
forms to help assemble proteins
Nucleotides
 Nucleotides:
Fig. 3-26, p. 64
Nucleotides
 Nucleotides
vary in sugar (ribose or
deoxyribose) and in nitrogenous base:
Fig. 3-27, p. 65
Nucleic Acids

DNA and RNA
polynucleotide
chains are formed
by linking the
phosphate group
of one nucleotide
to the sugar of the
next one
 Phosphodiester
bond
Fig. 3-28, p. 65
DNA
 DNA
forms a double helix when two
strands are twisted together
Fig. 3-29, p. 66
DNA
 Two
strands of DNA are joined by
hydrogen bonds between the nitrogenous
bases following base-pairing rules: A–T
and C–G
Fig. 3-30, p. 66
DNA
 Because
of the base-pairing rules, the
nucleotide sequence of one DNA chain is
complementary to the other chain
Fig. 3-31, p. 67
RNA
 RNA
usually exists as single strands
 Ribose
instead of deoxyribose sugar
 RNA
nucleotide sequences are distinctive
because Uracil replaces Thymine
 Follows
the same base-pairing rules:
• A–U instead of A–T
• G–C
If you want to selectively label nucleic acids being
synthesized by cells, what radioactive compound
would you add to the medium?
1. 35S-labeled
sulfate
25%
25%
25%
2
3
25%
2. 32P-labeled
phosphate
3. 14C-labeled leucine
4. 14C-labeled guanine
1
4