Chapter 5: The Structure and Function of Macromolecules
Macromolecule: Giant molecules of living matter
I. Polymers: A large molecule consisting of many identical or
similar subunits strung together
A. Monomers: Subunits that serve as the building blocks of
a polymer
B. Making and Breaking Polymers
1. Condensation reactions or dehydration reactions:
Process by which monomers become covalently bonded
to each other, through the loss of a water molecule
2. Hydrolysis: Process by which bonds between
monomers are broken by the addition of water
II. A limitless variety of polymers can be built from a small set of
monomers
A. All macromolecules are constructed from 40 –50
monomers
1. Proteins: 20 arranged in chains more than 100 aa
long
III. Carbohydrates: Include sugars and their polymers
A. Monosaccharides : Single or simple sugars
1. Glucose C6H12O6: Most common monosaccharide
a. 1 carbonyl group
b. Multiple hydroxyl groups
c. Major nutrients for cells
1. Cellular respiration extracts energy from it
2. If not used immediately incorporated as
monomers into disaccharides or
polysaccharides
1
2. Aldose: Aldehyde sugar
3. Ketose: Ketone sugar
4. Size of C skeleton 3-7 C long
a. Numerous shapes and behaviors
5. In aqueous solutions monosaccharides form rings
B. Disaccharides: Double sugar, two monosaccharides
joined by a glycosidic linkage
1. Glycosidic linkage: Covalent bond formed between
two monosaccharides
a. Maltose:
b. Lactose:
c. Sucrose:
C. Polysaccharides: Macromolecules in which a few
hundred to a few thousand monosaccharides are joined by
glycosidic linkages
1. Storage Polysaccharides
a. Starch: Storage polysaccharides of plants
1. Helical shape is a result of bond angles
2. Two forms of starch
a. Amylose: unbranched
b. Amylopectin: branched
3. Plants store starch as granules in plastids,
including chloroplasts
4. Withdrawn by hydrolysis
5. Animals: Enzymes that hydrolyze plant
starch
a. Makes glucose available as a nutrient
for cells
b. Potatoes (tubers), grains, fruits of
wheat, corn, rice
2
b. Glycogen: A polymer of glucose stored by
animals
1. More extensively branched
2. Stored in liver and muscle cells
3. Hydrolyzed to release glucose when the demand
for sugar increases
4. Depleted in a day, unless replenished by food
2. Structural Polysaccharides: Organisms build strong
materials
1. Cellulose: Major component of the tough walls
that enclose plant cells
a. Glycosidic linkages of starch and cellulose
differ
b. Microfibrils: Parallel cellulose molecules
held together in plant cell walls
1. wood
c. Enzymes that digest starch by hydrolyzing
the alpha bonds are unable to hydrolyze the
beta linkages of cellulose
d. Microbes can digest cellulose
2. Chitin: Structural polysaccharide, used by
arthropods to build their exoskeletons
a. Leathery, hardens when encrusted with
CaCO3
b. Fungi cell walls
c. Similar to cellulose except glucose
monomer has a N-containing appendage
III. Lipids: Class of large biological molecules that have little or
no affinity for water
A. Fat: Large molecule constructed from 2 kinds of smaller
molecules
3
1. Glycerol: An alcohol with 3 C each bearing a OH
group
2. Fatty acid: Long C skeleton (16 -18 C) even #
a. One end: Head consisting of a COOH
b. Tail: Non polar C-H bonds
c. Joined to glycerol by an ester linkage
1. Ester linkage: Bond between a hydroxyl
group and a carboxyl group
3. Triacylglycerol (fat): 3 fatty acids joined to one
glycerol
4. Saturated fatty acid: No double bonds between C
atoms, as many H as possible are bonded to the C
skeleton
a. Animal fats: Bacon grease, lard, butter
b. Solidify at room temp.
c. Can contribute to atherosclerosis:
5. Unsaturated fatty acid: One or more double bonds,
formed by the removal of H atoms from the C skeleton
a. Kink wherever double bond occurs
b. Plant and fish fats: Corn, olive, and cod liver oil
c. Liquid at room temp
6. “Hydrogenated vegetable oils”
a. Unsaturated fats synthetically converted to
saturated fats by adding H
7. Energy storage
a. Similar to gasoline molecules, energy rich
b. Twice as much energy as a gram of
polysaccharide (starch)
c. Plants: Immobile can function with bulky
energy storage in the form of starch
d. Animals carry energy storage (fuel) with them
4
1. Adipose cells: Swell and shrink as fat is
deposited and withdrawn
a. Cushions vital organs
b. Insulation:
B. Phospholipids: Similar to fats, 2 fatty acids rather than 3
1. 3rd OH of glycerol is joined to a phosphate group (-)
2. Tails: Hydrophobic
3. Head: Hydrophilic
C. Steroids: Lipids characterized by a C skeleton consisting
of 4 interconnected rings
1. Vary in attachment of functional groups
2. Cholesterol: Common component of animal cell
membranes
a. Precursor from which other steroids are
synthesized
b. Hormones, (sex hormones)
c. High concentration in blood: Atherosclerosis
IV. Proteins; Many Structures, many functions
A. Account for 50% of dry weight of most cells
1. Instrumental in almost everything organisms do
a. Structural support
2. Storage
3. Transport of other substances (Hemoglobin)
4. Signaling from one part of the organism to another
5. Movement (actin and myosin)
6. Defense against foreign substances (antibodies)
7. Enzymes: Proteins that selectively accelerate
chemical reactions in a cell
8. Humans: 10s of thousands of different kinds of
proteins
B. Most structurally sophisticated molecules known
5
1. Vary extensively in structure
2. Conformation: A unique 3-dimensional shape
3. All polymers constructed from the same set of 20
amino acids
4. Polypeptide: Polymers of amino acids
5. Protein: One or more polypeptides folded and coiled
into a specific conformation
C. Amino Acids: Organic molecules possessing both COOH
and NH2
1. Consists of an asymmetric C (alpha) bonded to 4
different covalent partners
a. OH
b. H
c. NH2
d. R (variable group)
2. R Group: side chain (20 aa differ only in this)
a. Nonpolar side chains: Hydrophobic
b. Polar side chains: Hydrophylic
c. Acidic: Neg side chains
d. Basic: pos groups in side chains
D. Polypeptide Chains
1. Peptide bond: Covalent linkage between amino
acids
2. Polypeptide: A polymer of many aa linked by
peptide bonds
a. One end: Free amino group (N-terminus)
b. One end: Free carboxyl group (C-terminus)
c. Chain has polarity
D. Protein Conformation: Shape of a 3 dimensional shape
formed by polypeptide chains twisted, wound and folded on
themselves to form a macromolecule
6
1. Globular: roughly spherical
2. Function of protein depends ability to recognize and
bind to some other molecule
a. Hormonal proteins bind to a cell receptor
b. Antibodies bind to foreign substances
c. Enzyme binds to a substrate
E. Four levels of Protein Structure
Functional protein: One or more polypeptides
precisely twisted, folded, and coiled into a molecule of
unique shape
1. Primary Structure: Protein’s unique sequence of aa
a. Lysozyme: Antibacterial enzyme, 129 aa long
b. Slight change in structure can affect
conformation and ability to function
1. Sickle-cell anemia: One aa is substituted
for another in a single position in the primary
structure of hemoglobin
a. Substitution at #6; 146 aa long
c. Biochemists ascertained the primary structures
of hundreds of proteins
1. Frederick Sanger 1940-1950s
2. AA sequence of insulin
3. Chromatography
2. Secondary Structure: Coils and folds as a result of
H bonds at regular intervals along polypeptide
backbone
a. Pos H attached to N has affinity for \
b. Alpha helix: A delicate coil held together by H
bonding between every 4th peptide bond
1. Linus Pauling and Robert Corey (1951)
7
2. alpha-keratin (hair): Fibrous protein, alpha
helix for entire length
c. Beta pleated sheet: Two or more regions of the
polypeptide chain lie parallel to each other
1. Held together by H bonds
2. fibroin: structural protein of silk (spider)
3. Tertiary Structure: Results from irregular
contortions from bonding between side chains of
various aa
a. Superimposed on secondary structure
b. Many weak bonds give protein stable shape
1. H
2. Ionic: Between + and - charged side chains
3. Hydrophobic interactions
c. Strong bonds
4. Disulfide bridges: Covalent bonds
between the side chains of cysteine pairs
4. Quaternary Structure: Protein structure that results from
aggregation of polypeptide subunits
1. Subunits: Each pp chain
2. Some proteins consist of 2 or more pp chains
aggregated into 1 macromolecule
3. Collagen
a. 3 helical subunits supercoiled into a larger triple
helix
1. Gives rope like structure of great strength
2. Girders of connective tissue;
4. Globular protein: Hemoglobin
a. 4 subunits
1. 2 alpha chains
2. 2 beta chains
8
b. Heme: Fe atom that binds to O
c. Hemoglobin: Oxygen binding protein of red
blood cells
E. Factors Determining Conformation
1. Occurs when protein is being synthesized
2. Physical & chemical conditions of environment
a. Denaturation: Unraveling, losing its native
conformation and becoming inactive in response to
its environment being altered
a. pH, salt concentration, temp
b. Transferred from aqueous environment to
an organic solvent
3. Sequence of amino acids determines conformation
F. The Protein folding problem
1. Chaperonins (Chaperone proteins): Protein
molecules that assist the proper folding of other
proteins
2. Accumulation of misfolded proteins can lead to
a. Alzheimer’s, Parkinson’s, and mad cow disease
3. X-ray crystallography: Method used to determine
3-D structure of many proteins
IV. Nucleic Acids: Class of compounds that include the polymers
DNA and RNA
A. Gene: Unit of inheritance that programs the aa sequence
B. Deoxyribonucleic acid (DNA)
1. Provides direction for its own replication
2. Hundreds of thousands of genes
3. Instructions that program cells activities
4. Stores coded instructions for the synthesis of a
specific protein
C. Ribonucleic acid (RNA)
9
1. DNA directs the synthesis of mRNA
2. DNA-->RNA-->protein
D. Nucleotides: Monomers of polymers of nucleic acids
1. 3 parts
a. Phosphate group
b. Pentose (sugar)
c. Nitrogenous base
2. Families of Nitrogenous bases
a. Pyrimidine: Characterized by a 6-membered
ring made up of C and N (smaller)
1. Cytosine, Thiamine, Uricil
2. Differ only in groups attached to rings
b. Purine: 5 membered ring is fused to the
pyrimidine type of ring
1. Adenine, guanine
2. Differ only in groups attached to rings
3. Nitrogenous bases in RNA
a. Ribose: Pentose
C. Polynucleotides: A nucleic acid (a term that emphasizes
the way macromolecules are constructed)
1. Phosphodiester linkages: Covalent bonds that join
nucleotides in a DNA polymer
2. Order of bases encoded in gene specifies aa sequence
a. Specifies protein’s 3 dimensional conformation
b. Specifies function of cell
D. Double Helix; James Watson, Francis Crick 1953
1. Double helix: 2 polynucleotide chains that spiral
around an imaginary axis
2. 2 strands are held together by H bonds
3. Vanderwaal forces between stacked bases
10
V. Genes (DNA) and their products (proteins) document the
hereditary background of an organism
A. Linear sequences are passed on from parents to offspring
1. Determine aa sequences of proteins
B. Species that appear to be closely related based on fossil
and anatomical evidence
1. Share a greater proportion of their DNA and proteins
11
12