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Chapter 5: Structure & Function of
Macromolecules
• Most macromolecules are polymers.
which is not?
• Polymer: large molecule consisting of many
identical or similar subunits connected
together in repeating fashion
• Monomer: the building block molecule of a
polymer
Macromolecule: a large organic
polymer
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There are four classes of macromolecules:
Carbohydrates
Lipids
Proteins
Nucleic acids
• macromolecules are synthesized by
polymerization reactions.
 A type of synthesis reaction
 Also called a condensation rxn or dehydration
rxn
Condensation reactions reactions during
which monomers are covalently linked,
producing a net removal of one water
molecule per covalent linkage.
 One monomer loses a hydroxyl (-OH) and the
other loses a hydrogen (-H)
 REQUIRES ENERGY!!!
 Requires biological catalysts (enzymes)
How are macromolecules broken?
• Hydrolysis is a reaction process that breaks
covalent bonds between monomers by the
addition of water.
 Also called a decomposition reaction.
 A hydrogen from the water bonds to one
monomer, and the hydroxyl bonds to the other
monomer.
 Digestive enzymes are hydrolytic
• Structural variation
only 40-50 common monomers are used to
form biological macromolecules.
I. Carbohydrates – organic molecules
made of sugars and their polymers
 Consists of the elements C, H, O
 The monomers =monosaccharides. (C H2 O)
 Are classified based on the number of simple
sugars
mono- , di- , poly-
A. Monosaccharides – Simple sugars in which C,
H, and O occur in the ratio of: CH2O (glucose
– C6H12O6)
 Are the major nutrients for cells [Glucose )
• Can be produced by photosynthesis
Characteristics of a sugar:
1. A hydroxyl is attached to each carbon except one,
which is double bonded to an oxygen (carbonyl)
• 2. Size of the carbon skeleton varies from 3 to 7
carbons. The most common monosaccharides are:
•
• Classification
# of carbons
example
• Triose
3
Glyceraldehyde
• Pentose
5
Ribose
• Hexose
6
Glucose
•
3. Spatial arrangment around asymmetric
carbons may vary. For example, glucose and
galactose
4. In aqueous solutions, many
monosaccharides from rings.
B. Disaccharides – a double sugar that consists
of two monosaccharides joined by a glycosidic
linkage.
 A glycosidic linkage is a covalent bond(5.5]
• Common examples of disaccharides:
Maltose – Glucose + Glucose (brewing)
Lactose – Glucose + Galactose (present in milk)
Sucrose – Glucose + Fructose (table sugar)
C. Polysaccharides – polymers of a few
hundred or thousand monosaccharides
 Formed by condensation reactions
 Have two important biological functions.
Energy storage (starch and glycogen)
Structural support (cellulose and chitin)
Storage polysaccharides:
Cells hydrolyze storage polysaccharides into
sugars as needed.
 Starch is a storage polysaccharide in
plants. Major sources are potato and grains
(wheat, corn, rice, etc.)
 Glycogen is a storage polysaccharide in
animals. stored in the muscle and liver
• Structural polysaccharides:
 Cellulose is a major component of plant
cell walls.
- reinforces plant cell walls using H-bonds.
-can’t be digested by most organisms
 Chitin forms exoskeletons of arthropods
and the cell walls of some fungi.
LIPIDS
insoluble in H2O, but will dissolve in nonpolar
solvents.
 fats, phospholipids, and steroids
A. Fats – macromolecules that consist of:
- Glycerol, a three-carbon alcohol
- Fatty acids, a carboxylic acid
A fatty acid- carboxyl group at one end and an
attached hydrocarbon chain (“tail”) [Fig. 5.10]
 The carboxyl functional group (“head”) has
acidic properties.
 The hydrocarbon chain has a long carbon
skeleton usually with an even number of
carbon atoms (most 16 – 18)
 The nonpolar C-H bonds make the chain
hydrophobic and water insoluble.
condensation reactions link glycerol to fatty
acids by an ester linkage.
 An ester linkage is a bond between a
hydroxyl group and a carboxyl group.
Each of glycerol’s three hydroxyl groups can
bond to a fatty acid by an ester linkage
producing a fat.
T Y P E S of FATS
A)Triacylglycerol is a fat composed of
three fatty acids bonded to one glycerol by
ester linkages (triglyceride)
Fatty acids may vary in the number and
location of carbon-to-carbon double bonds:
SATURATED FAT
No double bonds between carbons in FA tail
Carbon skeleton of FA is“saturated” w/
hydrogens)
Usually solid at room temp.
Most animal fats- Bacon grease, lard, butter
Unsaturated fats
Tail kinks at each C=C, so molecules do not pack
close enough to solidify at room temp.
Usually liquid at room temp.
Most plant fats- Corn, peanut, and olive oil
Are there any unsaturated fats that are solid at
room temp?
Hydrogenated or trans-fats
Triglyceride FUNCTIONS
Energy storage (1g of fat stores twice as much
energy as 1g of polysaccharide)
Animals store more energy with less weight
than plants which use starch. Oxygen is
heavy!!
Cushions vital organs in mammals (e.g.
kidney)
Insulates against heat loss
B. Phospholipids – compounds with
molecular building blocks of glycerol, two
fatty acids, and a phosphate group (usually
w/ a polar molecule attached) [Fig 5.12]
 third carbon of glycerol is joined to a
negatively charged phosphate group.
 Are amphipathic (have hydrophobic and
hydrophilic ends).
Phospholipids are…..
 The major constituents of cell membranes.
form a bilayer held together by hydrophobic
interactions among the hydrocarbon tails.
If placed in water, a “micelle” can form. [Fig
5.13
C. Steroids – lipids which have four fused
carbon rings with various functional groups.
example: Cholesterol
1) precursor to sex hormones,
2) component in animal cell membranes
3) contributes to atherosclerosis
PROTEIN
III. Protein–
polymer (chain) of amino acids
Functions
Structural support
Storage (of amino acids)
Transport (e.g. hemoglobin)
Signaling (chemical messengers)
Movement (contractile proteins)
Cellular response (receptor proteins)
Defense (antibodies)
Catalysis of biochemical reactions (enzymes)
What’s an amino acid?
consist of a carbon (alpha carbon) bonded to:
a) Hydrogen atom
b) Carboxyl group
c) Amino group
d) R group (a side chain that makes each
amino acid unique)
The twenty amino acids can be grouped by
properties of the side chain (Fig 5.15)
Nonpolar side groups (hydrophobic).
Polar side groups (hydrophilic)
- uncharged polar
- charged polar
How are polypeptide chains
formed?
amino acid monomers are covalently linked by
peptide bonds. [Fig 5.16]
 Formed by a condensation reaction that
links the carboxyl group of one amino acid to
the amino group of another.
How are polypeptide chains broken?
A protein’s function depends upon
its unique structure.
Primary structure
Secondary structure
Tertiary structure
Quaternary structure
These four levels of protein structure are
responsible for the correlation between form
and function in proteins.
Primary Structure – unique sequence of amino
acids in a protein
 Determined by genes
 Slight change can affect a protein’s
conformation and function (e.g. sickle-cell
hemoglobin; Fig 5.19)
 Can be sequenced in a laboratory; Fredrick
Sanger (insulin sequence in late 1940’s, early
1950’s)
Secondary Structure – regular, repeated coiling
and folding of a protein’s polypeptide
backbone.
 Contributes to protein’s overall
conformation
 Stabilized by hydrogen bonds between
peptide linkages in the protein’s backbone
(carbonyl & amino groups).
Two major types of secondary
structure:
Alpha Helix – secondary structure of a
polypeptide that is a helical coil stabilized by
hydrogen bonding
Beta sheet – secondary protein structure
which is a sheet of antiparallel chains folded
like an accordian.
 Parallel regions are held together by
hydrogen bonds
Tertiary Structure – irregular foldings of a
protein due to bonding between side chains
(R groups)
1-H-bonding between polar side chains
2-Ionic bonds between charged side groups
3-Hydrophobic interactions between
nonpolar side chains in protein’s interior
4-Covalent linkages
5-Disulfide bridges between cystine
monomers
Quaternary Structure – results from the
interaction among several polypeptide
(subunits) in a single protein
Examples: collagen, hemoglobin
If a protein’s environment is
altered, it may become denatured.
Denaturation is a process that alters a protein’s
native conformation and biological activity.
Proteins can be denatured by:
1-Chemical agents that disrupt H-bonds, ionic
bonds, and disulfide bonds
2-Excessive heat
3-Transfer to an organic solvent. The
hydrophobic chains that were originally
inside, turn outward
Predicting 3-dimensional shape of
proteins is difficult!!
 Chaperone proteins have been discovered
that temporarily brace a folding protein
Nucleic Acids – polymer of nucleotides liked
together by condensation reactions
I.Deoxyribonucleic Acid (DNA)
-Contains coded information that programs
all cell activity(genes)
-Contains directions for its own replication
-Is copied and passed from one generation of
cell to another
-Found in the nucleus of eukaryotes
II. Ribonucleic Acid (RNA)
Functions in the actual synthesis of proteins
coded for by DNA
-Sites of protein synthesis are on ribosomes in
the cytoplasm
-Messenger RNA (mRNA) carries encoded
genetic message from the nucleus to the
cytoplasm
A nucleotide is a building block molecule of
nucleic acid, made up of 1) a five carbon
sugar covalently bonded to 2) a phosphate
group and 3) a nitrogenous base
 The 5-carbon sugar can be either ribose or
deoxyribose.
There are two families of nitrogenous bases:
Pyrimidine
Cytosine (C)
Thymine (T) – found only in DNA
Uracil (U) – found only in RNA
Purine
Adenine (A)
Guanine (G)
A nucleic acid is a polymer of nucleotides joined by
phosphodiester linkages between the phosphate of
one nucleotide and the sugar of the next.
 Each gene on DNA contains a unique linear sequence of
nitrogenous bases which ultimately codes for a unique
linear sequence of amino acids in a protein.
In 1953, James Watson and Francis Crick proposed the double
helix as the three dimensional structure of DNA
 the sugar-phosphate backbones are on the outside of
the helix
 nitrogenous bases are paired in the interior of the
helix and are held together by hydrogen bonds.
 A always pairs with T; G always pairs with C
 The two strands of DNA are complimentary, thus can
serve as templates to make new complimentary stands.
DNA  RNA  polypeptide