Chapter 1
Macromolecules
Macromolecules: Giant Polymers
•
There are four major types of biological
macromolecules:

Proteins

Carbohydrates

Lipids

Nucleic Acids
•
These macromolecules are made the same way in all living things, and are present in all
organisms in roughly the same proportions.
•
An advantage of this biochemical unity is that organisms acquire needed biochemicals by
eating other organisms.
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Macromolecules are giant polymers. 6
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Polymers are formed by covalent linkages of smaller units called monomers.
Condensation and Hydrolysis Reactions
•
Macromolecules are made from smaller monomers by
means of a condensation (or dehydration) reaction in
which an OH from one monomer is linked to an H
from another monomer.
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The reverse reaction, in which polymers are broken
back into monomers, is a called a hydrolysis
reaction.
•
Energy must be added to make a polymer; and,
released when breaking one.
Proteins: Polymers of Amino Acids
•
Proteins are polymers of amino acids. They are molecules with diverse structures and
functions.
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Each different type of protein has a characteristic amino acid composition and order.
•
Proteins range in size from a few amino acids to thousands
of them.
•
Folding is crucial to the function of a protein and is
influenced largely by the sequence of amino acids.
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An amino acid has four groups attached to a central carbon
atom.
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Amino acids can be classified based on the characteristics of their R groups.
•
5 have charged
hydrophilic side
chains.
•
5 have uncharged
hydrophilic
(polar) side
chains.
•
7 have
hydrophobic
(nonpolar) side
chains.
•
Cysteine has a
terminal disulfide
(—S—S—).
•
Glycine has a
hydrogen atom
as the R group.
•
Proline has a
modified amino
group that forms
a covalent bond
with the R group,
forming a ring.
•
Proteins are synthesized by condensation
reactions between the amino group of one amino
acid and the carboxyl group of another. This
forms a peptide linkage.
•
Thus, proteins are also called polypeptides.
•
A dipeptide is two amino acids long; a
tripeptide, three; etc. A polypeptide is multiple
amino acids long.
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There are four levels of protein structure:
•
primary, secondary, tertiary, and
quaternary.
•
The precise sequence (i.e., order) of amino acids
is called its primary structure.
•
The peptide backbone consists of repeating units
of atoms: N—C—C-----N—C—C------N—C—C...
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Enormous numbers of different proteins are possible.
•
A protein’s secondary structure consists of regular, repeated patterns in different
regions in the polypeptide chain.
•
This shape is influenced primarily by hydrogen bonds arising from the amino acid
sequence (the primary structure).
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The two common secondary structures are:
•
the a-helix, and;
•
the b-pleated sheet.
The a-helix:
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Is a right-handed coil.
•
Ex: Fibrous proteins such as the keratins found in hair, feathers, and hooves.
The b-pleated sheets:
•
Are formed from peptide regions of a single strand that lie parallel to each other.
•
Ex: Spider silk.
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Tertiary structure: Bending and folding results in a macromolecule with specific threedimensional shape.
•
The primary determinant of the tertiary structure is the interaction between R groups:

Disulfide bonds (see slide)

Aggregation of hydrophobic side
chains

van der Waals forces

Ionic bonds

Hydrogen bonds
•
Quaternary structure results from the ways in which multiple (2 or more) polypeptide
subunits bind together and interact.
•
This level of structure adds to the three-dimensional shape of the finished protein.
•
Hemoglobin is an example of such a protein; it has four subunits.
•
Shape is crucial to the functioning of some proteins: enzymes need certain surface shapes
in order to bind substrates correctly.
•
Changes in temperature, pH, salt
concentrations, and oxidation or
reduction conditions can change the
shape of proteins.
•
This loss of a protein’s normal 3D
structure (and therefore loss of
function) is called denaturation.
•
Chaperonins are specialized proteins that help keep other proteins from interacting
inappropriately with one another.
•
When a protein fails to fold correctly, serious complications can occur.
•
Some chaperonins help folding; some prevent folding until the appropriate time.
Carbohydrates: Sugars and Sugar Polymers
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Carbohydrates are carbon molecules with hydrogen groups and hydroxyl groups
H—C—OH
•
They act as energy storage and transport molecules.
•
They also serve as “carbon skeletons” for other molecules.
•
There are four major categories of carbohydrates:
•
•
Monosaccharides are the monomers of carbohydrates; simple sugars.
•
Disaccharides, which consist of two monosaccharides linked by one covalent
bond.
•
Oligosaccharides, which consist of between 3 and 20 monosaccharides
•
Polysaccharides, which are composed of hundreds to hundreds of thousands of
monosaccharides---starch, glycogen, cellulose.
There are four major categories of carbohydrates:
•
Monosaccharides are the monomers of carbohydrates; simple sugars.
•
Disaccharides, which consist of two monosaccharides linked by one covalent
bond.
•
Oligosaccharides, which consist of between 3 and 20 monosaccharides
•
Polysaccharides, which are composed of hundreds to hundreds of thousands of
monosaccharides---starch, glycogen, cellulose.
•
The general formula for a carbohydrate monomer is Cn(H2O)n , maintaining a ratio of 1
carbon to 2 hydrogens to 1 oxygen.
•
During the polymerization, which is a condensation reaction, water is removed.
•
Therefore, carbohydrate polymers have ratios of carbon, hydrogen, and oxygen that differ
somewhat from the 1:2:1 ratios of the monomers.
•
Different monosaccharides have different numbers or different arrangements of carbons.
Most monosaccharides are isomers.
•
Triose (3-carbon sugars) include glyceraldehyde.
•
Tetrose (4-carbon sugars) include erythrose.
•
Pentoses (5-carbon sugars) include ribose, deoxyribose.
•
Hexoses (6-carbon sugars) include the structural isomers glucose, fructose,
mannose, and galactose.
•
All cells use glucose (monosaccharide) as their preferred energy source.
•
Exists as a straight chain or ring form.
•
Ring is more common—it is more stable.
•
Monosaccharides bind together in condensation reactions to form glycosidic linkages.
Glycosidic linkages can be α or β.
•
Disaccharides have just one glycosidic linkage: sucrose, lactose, maltose, cellobiose.
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Oligosaccharides contain more than two monosaccharides.
•
•

Often covalently bonded to proteins and lipids on cell surfaces and act as
recognition signals.

The human ABO blood types owe their specificity to oligosaccharide chains.
Polysaccharides are giant polymers of monosaccharides connected by glycosidic
linkages.

Starch: storage of glucose in plants

Glycogen: storage of glucose in animals

Cellulose (i.e., fiber): very stable, good for structural components in plants.
Animals have enzymes that can hydrolyze α-glycosidic links, but not β-links. Therefore,
fiber is not digestible.
•
Carbohydrates can be modified by the addition of functional groups:

Phosphate added to one or more hydroxyl (—OH) sites creates a sugar
phosphate, such as fructose 1,6-bisphosphate.

Amino groups can be substituted for —OH groups, making amino sugars, such
as glucosamine and galactosamine.
Lipids: Water Insoluble Molecules
•
Lipids are insoluble in water.
•
This insolubility results from the many nonpolar covalent bonds of hydrogen and carbon
in lipids.
•
Lipids aggregate away from water, which is polar, and are attracted to each other via
weak, but additive, van der Waals forces.
•
Lipids are the only group of macromolecules that does not consist of polymers.
•
Lipids are, thus, not made up of a particular monomer, but smaller “fatty” molecules such
as fatty acids and glycerol.
Fats and oils
•
Fats and oils store energy.
•
Chemically, fats and oils are triglycerides, composed of three fatty acid molecules and
one glycerol molecule.

Glycerol is a three-carbon molecule with three hydroxyl (—OH) groups, one for
each carbon.

Fatty acids are long chains of hydrocarbons with a carboxyl group (—COOH) at
one end.
•
Saturated fatty acids have only single
carbon-to-carbon bonds (i.e., no double
bonds) and are said to be saturated with
hydrogens.
•
Saturated fatty acids are rigid and straight,
and solid at room temperature (i.e., fat).
Animal fats are saturated.
•
Unsaturated fatty acids have at least one
double-bonded carbon in one of the chains —
the chain is not completely saturated with
hydrogen atoms.
•
monounsaturated: one double bond
•
polyunsaturated: more than one double
bond
•
The double bonds cause “kinks” that prevent
easy packing.
•
Thus, they are liquid at room temperature (i.e., oil). Plants commonly have unsaturated
fatty acids.
Phospholipids
•
Phospholipids have two hydrophobic fatty acid tails and one hydrophilic phosphate
group attached to the glycerol.
•
As a result, phospholipids orient themselves so that the phosphate group faces water and
the tail faces away.
•
Phospholipids are amphipathic: they have a hydrophilic and a hydrophobic end
•
In aqueous environments, these lipids form bilayers, with heads facing outward, tails
facing inward. Cell membranes are structured this way.
Carotenoids & Chlorophylls
•
These are light-absorbing pigments found
mostly in plants.
•
The carotenoid b-carotene is a plant
pigment used to trap light in
photosynthesis.
•
In animals, b-carotene can be broken into
two molecules of vitamin A.
Steroids
•
Steroids are signaling molecules/hormones.
•
Steroids are organic compounds with a series
of fused rings.
•
The steroid cholesterol is a common part of
cell membranes, especially in animals.
•
Cholesterol also is an initial substrate for
synthesis of the hormones’ testosterone and
estrogen.
Fat-soluble vitamins
•
Some lipids are vitamins: small organic molecules essential to health, not synthesized by
the body, so must be acquired from diet.
•
The lipid-soluble vitamins are: A, D, E, and K.
•
All others (B’s and C) are water-soluble.
Waxes
•
Waxes are highly nonpolar molecules consisting of saturated long fatty acids bonded to
long fatty alcohols via an ester linkage.
•
A fatty alcohol is similar to a
fatty acid, except for the last
carbon, which has an —OH
group instead of a —COOH
group.
•
Waxy coatings repel water and prevent water loss from structures such as hair/fur,
feathers, and leaves.