Download Chapter 5-The Structure and Function of Macromolecules

Chapter 5
The Structure and Function of
Macromolecules
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Macromolecules
• There are many molecules that comprise
living organisms and many of them are quite
large.
• As such, they are called macromolecules.
• There are 4 main macromolecules that
comprise living organisms:
– 1. Proteins.
– 2. Lipids.
– 3. Carbohydrates.
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– 4. Nucleic acids.
Macromolecules
• Three of the four classes
(carbohydrates, protein, and nucleic
acids) are comprised of polymers which
are long molecules made up of the
same or similar subunits covalently
linked together.
• The subunits that are linked together
are called monomers.
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Macromolecules
• The synthesis and breakdown of
macromolecules is governed by a
series of condensation/dehydration or
hydrolysis reactions.
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Condensation Reactions
• In a condensation reaction (aka a
dehydration reaction) monomers are
added to a growing polymer and a
water molecule is given off--hence the
name dehydration reaction.
• These reactions require energy and the
action is carried out by enzymes.
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Hydrolysis
• Hydrolysis is the process that adds a water
molecule to a polymer giving one of the
monomers.
• This occurs during digestion and it makes the
large molecules useable by our bodies by
producing smaller subunits that our cells can
uptake.
• The four main types of macromolecules can
be broken down further and analyzed.
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Polymers
• Polymers
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Carbohydrates
• Carbohydrates are molecules
consisting of carbon, hydrogen, and
oxygen.
• The three classifications are
monosaccharides or simple sugars,
disaccharides or double sugars, and
polysaccharides which are 3 or more
sugars linked together forming a sugar
polymer.
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Monosaccharides
• Monosaccharides generally have the
formula CnH2nOn and depending on the
location of the carbonyl group, the
sugar is either an aldose or a keytone.
• When the carbonyl group is the last
carbon on the chain, it is an aldose,
when it is not, it is a keytone.
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Monosaccharides
• Glucose C6H12O6 is an aldehyde that is
a common monosaccharide used as
energy by our body.
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Monosaccharides
• Not only is it used as an energy energy
source (as are other monosaccharides),
but their carbon skeletons serve as
building blocks for other major
macromolecules within the organism-amino acids and fatty acids.
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Disaccharides
• A disaccharide, such as sucrose,
lactose, and maltose are joined
together by a glycosidic linkage--a
covalent bond between 2
monosaccharides by a dehydration
reactions.
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Disaccharides
• The fruit of a plant is often a great
source of sucrose--glucose and
fructose (the most common
disaccharide) because as the plants
form it during photosynthesis, this is
where it gets stored.
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Disaccharides
• Disaccharides
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Polysaccharides
• When monosaccharides are
glycosidically linked together thousands
of times, polysaccharides are formed.
• There are 2 main types of
polysaccharides, structural and storage.
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Structural or Storage?
• There are actually 2 forms of glucose, 
and , and the form is determined by
the placement of a hydroxyl group.
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Structural or Storage?
• In  -glucose, the -OH group is below
the ring structure and in -glucose, it is
above the ring structure.
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Structural Polysaccharides
• In structural
polysaccharides,
strong materials
are built to provide
strength and
support for the
organism.
• A good example of
this is cellulose.
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Structural Polysaccharides
• Plant cell walls are comprised of
cellulose which gives them strength.
Some animals such as cows can digest
cellulose, but humans can’t.
• For us, it is called “insoluble fiber” and
is found in many fruits and vegetables.
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Structural Polysaccharide
• Another important structural polysaccharide
is chitin.
• Chitin makes up the hard exoskeleton of
arthropods, and the cell walls of fungi.
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Storage Polysaccharides
• Although the starch and cellulose
molecules are comprised of glucose
molecules, the different types of
glucose give them vastly different uses.
• For example starch can be used by
humans for food, cellulose can’t.
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Storage Polysaccharides
• There are two main
types of storage
polysaccharides:
That which is found
in plants (starch),
and that which is
found in animals
(glycogen).
• Glycogen is
branched, and
starch is helical.
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Proteins
• Proteins are another
class of
macromolecules
consisting of many
monomers linked
together by peptide
bonds forming
polymers.
• Enzymes are protein
polymers that act as
catalysts within cells.
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Proteins
• Polymers of amino acids are called
polypeptides and the same 20 amino acids
form all polypeptides.
• Proteins consist of one or more of the
polypeptides coiled into a specific
conformation.
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Proteins
• Amino acids are
organic molecules
containing a
carboxyl group and
an amino group.
• These are each
bounded to a
central carbon
atom which also
has an amino acid
attached to it.
 carbon
Amino
Group
Carboxyl
Group
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Proteins
• There are 2 groups that are linked
together to form a peptide bond.
• A peptide bond is a dehydration
reaction which links the amino group of
one amino acid to the carboxyl group of
a different amino acid yielding water in
the process.
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Proteins
• Once amino acids are added to the
polypeptide, they begin to interact with
the other amino acids on the growing
polypeptide.
• The sequence then determines the 3D
conformation the protein will take.
• The conformation of the protein
determines how it will function.
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Proteins
• An enzyme is an example and the
conformation it takes determines how it
functions when it interacts with a
substrate.
• There are 4 different types of protein
structure: 1°, 2°, 3°, and 4°.
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Proteins--Primary Structure
• The primary structure
is the specific
sequence of amino
acids.
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Proteins--Primary Structure
• Primary Structure
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Proteins--Primary Structure
• Primary Structure
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Proteins--Secondary
Structure
• The secondary structure of the polypeptide is the
coiled and/or folded patterns that emerges as the
amino acids begin to interact with one another (Hbonds) not from the R-groups, but from the
backbones of the amino acids.
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Proteins--Secondary
Structure
• Secondary Structure
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Proteins--Secondary
Structure
• There are two main types of secondary
protein structure, the  -helix and the pleated sheet.
• The  -helix is a delicate coil held
together by H-bonds.
• The -pleated sheet forms when 2
polypeptides are aligned side by side
and hydrogen bond along their lengths.
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Proteins--Tertiary Structure
• The tertiary
structure of the
protein is due to
the interactions of
the R-groups on
the amino acids.
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Proteins--Tertiary Structure
• Tertiary Structure
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Proteins--Quaternary
Structure
• The quaternary structure of a protein occurs
when 2 or more polypeptide chains interact
with each other to form a large, functional
protein.
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Proteins--Quaternary
Structure
• Quaternary Structure
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Small Change = Big
Problem
• Sickle cell anemia
example: glutamic
acid out, valine in,
causes changes in
quarternary structure.
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Malarial Zones
• On the left, the brown regions indicate areas
with endemic falciparium malaria.
• On the right, the colored regions represent
percentages of the sickle cell allele.
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Areas with endemic falciparium
malaria
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14+
12-14
10-12
6-8
4-6
2-4
8-10
0-2
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Nucleic Acids
• Nucleic acids store and
transmit information about a
protein’s primary structure.
• There are 2 types of nucleic
acids: RNA and DNA.
• DNA provides the necessary
information for guiding its
own replication.
• It also guides RNA synthesis
and using RNA controls
protein synthesis.
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GIF decompressor
are needed to see this picture.
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Nucleic Acids
• DNA is the information that controls the
cell. This information is used to create
messenger RNA that interacts with the
cells protein synthesizing machinery
(ribosomes) to create the proteins that
run the cell.
• DNA--> RNA --> Protein
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Nucleic Acids
• Nucleic acids are
polymers called
polynucleotides which
consist of monomers
called nucleotides.
• The nucleotides are
composed of a
pentose (a 5-carbon
sugar), a nitrogenous
base, and a
phosphate group.
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Nucleic Acids
• The nucleotide
monomers are built
from sugar atoms
(ribose and
deoxyribose) attached
to a nitrogenous base
(C,T, U, A G). This
forms a nucleoside
which becomes a
nucleotide once the
phosphate group has
been added.
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Nucleic Acids
• Nucleotides are linked together by covalent
(phosphodiester) bonds between a hydroxyl
group on the 3’ carbon of one nucleotide and
the phosphate on the 5’ carbon on the next.
• This bond starts the repeating sugarphosphate bond. This gives rise to the 3’ and
5’ ends of the DNA molecule. The sequence
of each of the bases in the polynucleotide is
unique to each gene.
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Nucleic Acids
• RNA consists of a single strand of
nucleic acids in a polynucleotide chain.
• DNA, on the other hand, consists of 2
polynucleotide chains that run in
opposite directions to one another.
• This gives rise to the term “antiparallel.”
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Nucleic Acids
• The 2 anti-parallel strands of DNA
appear like a divided highway and are
joined together by hydrogen bonds and
Van der Waals interactions.
• H-bonds are between paired bases
• Van der Waals interactions are between
stacked bases.
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Nucleic Acids
• There are certain bases that you find in
DNA and RNA.
• DNA has A,T,C,G
• RNA has A,U,C,G
• When the bases pair together, they only
pair one way: A & T, C & G in DNA, and
in RNA A pairs with U, C pairs with G.
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Nucleic Acids
• The two strands are always said to be
complementary. That is, if you know
the order of one strand of DNA, you can
deduce the other.
• 5’ --------> 3’
• AGGTCCG
• TCCAGGC
• 3’<-------- 5’
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Nucleic Acids
• This feature of DNA is what makes
precise copying possible.
• When cells divide, the DNA serves as a
template and the new DNA that is
formed is copied from it.
• When finished, there are 2 identical
copies (ideally) of DNA within the cell
and identical daughter cells can now
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form upon division.
Nucleic Acids
• The parts of the DNA molecule that
make up the polynucleotides that
encode for the amino acids can be used
to show how closely organisms are
related from an evolutionary standpoint.
• Molecular biologists can sequence
genes and determine how much
difference there is between organisms
and this helps them form their tree of
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life.
Nucleic Acids
• For example, upon examination of the
polypeptide chain of human hemoglobin
with that of a gorilla, we only find one
amino acid different out of 146.
• In gibbons, which are a tree monkey
found in SE Asia, there is only a
difference of 2 amino acids.
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Lipids
•
•
•
•
There are three classes of lipids:
Fats (Fatty acids)
Phospholipids
Steroids
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Lipids
• Lipids are not
polymers, they are
long chain fatty
acids attached via
a dehydration
reaction to a
glycerol head.
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Lipids
• Lipids
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Lipids
• The glycerol molecule is a 3 carbon
alcohol with a hydroxyl group attached
to each carbon. During the reaction,
the carboxyl group at the end of the
fatty acid loses its hydroxyl (-OH) and
attaches to the oxygen on the glycerol
molecule. The -H lost from the glycerol
combines with the -OH forming water.
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Lipids
• The fatty acid portion is a long
hydrocarbon usually 16 to 18 carbons in
length.
• These portions are hydrophobic and
this makes fats hydrophobic.
• Fatty acids can be classified as
saturated on unsaturated as we often
hear about in nutrition.
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Lipids
• When they are saturated, all
of the carbon atoms contain
a maximum number of H
atoms n the chain. Thus
they are allowed to group
tightly together as we see in
butter and animal fat. Most
animal fat is saturated.
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Lipids
• Unsaturated fats contain carbon atoms
that are double bonded to other carbon
atoms in the fatty acid chain. This
creates a kink in the chain and prevents
the molecules from packing closely
together.
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Lipids
• Such examples are
olive oil and
vegetable oil.
• The oils of fish and
vegetables
generally are
unsaturated.
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Phospholipids
• Phospholipids are a very important
molecule that are similar to fact except
that they only have 2 fatty acids
attached to the glycerol head.
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Phospholipids
• The 3rd carbon is
attached to a
phosphate group.
The phosphate
group has a
negative charge
and allows the
phospholipid to be
both hydrophobic
and hydrophilic.
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Phospholipids
• The head region of the phospholipid is hydrophilic
and the tail region of the phospholipid is
hydrophobic.
• Thus, when phospholipids are added to water they
form a bilayer with the heads orienting out, in contact
with the water and the tail regions are pointing
inward away from the water.
• This forms the basis of the phospholipid bilayer that
is the cell membrane.
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Steroids
• Steroids are a final class of lipids that
we’ll discuss. They are comprised of 4
fused rings and have various functional
groups attached to them.
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Steroids
• Cholesterol is an important sterol found
in animal cell membranes and is the
precursor of many hormones found
within the body.
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Steroids
Testosterone
Estrogen
Cortisol
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