Macromolecules
AP Biology
2012-2013
Big Ideas 2
• Biological systems utilize free energy
and molecular building blocks to grow,
to reproduce, and to maintain
homeostasis.
Molecules of Life
• 4 main classes of large biological molecules
– Carbohydrates
– Lipids
– Proteins
– Nucleic Acids
• Very large molecules called macromolecules
– macro = giant
– Ex. Some proteins are over 100,000 daltons
Polymers are built from Monomers
• 3 classes of
molecules are
polymers
– Carbohydrates,
nucleic acids, and
proteins
– They are made of
many similar or
identical components
called monomer.
Synthesis of polymers
• Covalent bonds are formed between two
molecules by a dehydration reaction-removal
of water
– When the bonds form there is a loss of a water
molecule
– The cell must expend energy to carry out
dehydration synthesis
– Occurs only with the help of enzymes
LE 5-2a
Short polymer
Unlinked monomer
Dehydration removes a water
molecule, forming a new bond
Longer polymer
Dehydration reaction in the synthesis of a polymer
Breakdown of Polymers
• Polymers are broken down by hydrolysis
– Addition of water
– food, which is in the form of macromolecules, is
digested with the aid of hydrolysis
• Monomers are absorbed in the bloodstream
– Hydrolysis of polymers is catalyzed by enzymes
LE 5-2b
Hydrolysis adds a water
molecule, breaking a bond
Hydrolysis of a polymer
Diversity of Polymers
• Diversity of
macromolecules is vast
– Variation exists between
siblings
• Greater variation
between unrelated
individuals
– Even greater between
species
Carbohydrates
• Simple or single sugarsmonosaccharides
• Double sugars –
disaccharides
• Macromolecules are
polysaccharides
Sugars
• Chemical formula is a multiple of – CH20
• Contains a carbonyl group and a hydroxyl
group
• Sugar can be an aldose (aldehyde sugar) or a
ketose (ketone sugar)
• Can be categorized by the size of the carbon
skeleton.
LE 5-3
Triose sugars
(C3H6O3)
Pentose sugars
(C5H10O5)
Hexose sugars
(C5H12O6)
Glyceraldehyde
Ribose
Galactose
Glucose
Dihydroxyacetone
Ribulose
Fructose
• Glucose is the most common monosaccharide
• Forms rings in aqueous solutions
• Cell extract energy stored in glucose through
cellular respiration.
• Fructose is structural isomer of glucose
• Sugars and their carbon skeletons provide raw
materials for other organic molecules.
LE 5-4
Linear and
ring forms
Abbreviated ring
structure
Disaccharides
• Two monosaccharides joined by glycosidic
linkgage (covalent bond through dehydration
reaction)
• Maltose = two glucose molecules
• Sucrose= glucose + fructose
• Plants use sucrose for carbohydrate transport
from roots to leaves
• Lactose = glucose + galactose
LE 5-5
Dehydration
reaction in the
synthesis of maltose
1–4
glycosidic
linkage
Glucose
Glucose
Dehydration
reaction in the
synthesis of sucrose
Maltose
1–2
glycosidic
linkage
Glucose
Fructose
Sucrose
Polysaccharides
• Polymers with a few hundred to a few
thousand monosaccharides joined by
glycosidic linkages.
• Function is determined by sugar monomers
and the position of its glycosidic linkages.
Storage Polysaccharides
• Starch – consist of all glucose monomers
–
–
–
–
–
Joined by 1-4 linkage (#1 C to #4 C)
The bond’s angles make the polymer helical
Plants can store surplus glucose in starch
Starch represents energy
Animals have enzymes that can hydrolyze plant starch
• Glycogen – animals store this polymer if glucose
– Humans store glycogen in the liver and muscle cells.
– Hydrolysis release glucose when sugar is in demand
– Glycogen stores are depleted in about a day.
LE 5-6
Chloroplast
Starch
Mitochondria Glycogen granules
0.5 µm
1 µm
Amylose
Starch: a plant polysaccharide
Amylopectin
Glycogen
Glycogen: an animal polysaccharide
Structural polysaccharides
• Cellulose- polymer of glucose
– Component of cell walls
– Most abundant organic compound
– Two different ring structures for glucose
•
•
•
•
Alpha ring
Beta ring
Starch uses alpha configuration
Cellulose use beta configuration
– Straight, never branched
LE 5-7a
a Glucose
a and b glucose ring structures
b Glucose
LE 5-7b
Starch: 1–4 linkage of a glucose monomers.
LE 5-7c
Cellulose: 1–4 linkage of b glucose monomers.
LE 5-8
Cellulose microfibrils
in a plant cell wall
Cell walls
Microfibril
0.5 µm
Plant cells
Cellulose
molecules
b Glucose
monomer
• Enzymes in animals that hydrolyze alpha
linkages in starch and unable to hydrolyze beta
linkages.
• Cellulose in our food passes through the
digestive system and is eliminated.
• Cellulose scrapes the wall of the digestive
tract stimulates the lining to secrete mucushelps the passage of food.
Figure 5-09
Chitin
• Used by arthropods to build exoskeletons
• leathery becomes hard when encrusted with
Calcium carbonate
• Also found in fungi
• Similar to cellulose except the glucose has a
nitrogen-containing arm.
LE 5-10
The structure of chitin.
Chitin forms the exoskeleton of arthropods.
This cicada is molting, shedding its old
exoskeleton and emerging in adult form.
Chitin is used to make a strong and
flexible surgical thread that decomposes
after the wound or incision heals.
Lipids
• Not polymers
• Include fats, phospholipids, and steroids.
• Consists of glycerol and fatty acids
– 3 fatty acid molecules joined to glycerol by ester
linkage ( bond between hydroxyl group and
carboxyl group)
– Also called a triaclglycerol or triglceride
LE 5-11
Fatty acid
(palmitic acid)
Dehydration reaction in the synthesis of a fat
Ester linkage
Fat molecule (triacylglycerol)
Saturated vs. unsaturated
• Fatty acids vary in length and the number and
location of double bonds
• Saturated fat contains the maximum of
hydrogen atoms with no double bonds
• Unsaturated fat – contains one or more
double bonds
LE 5-12
Stearic acid
Saturated fat and fatty acid.
Oleic acid
cis double bond
causes bending
Unsaturated fat and fatty acid.
• Animal fats are saturated fats and are solid at
room temperature.
• Plant fats are generally unsaturated usually liquid
at room temperature.
• Hydrogenated vegetable oils means that fat has
been converted to saturated fat
• Diets high in saturated fats is a key factor in
cardiovascular disease- atherosclerosis- deposits
of plaque within the walls of blood vessels
Function of fats
• Storage of energy
• Stores 2X as much energy polysaccharide
• Provides animals with compact reservoir of
fuel
– Adipose cells
• stock long-term reserves for mammals and humans.
• Provides cushions for organs
• Insulation in the body
Phospholipids
• Two fatty acids and phosphate group attached
to a glycerol
• Hydrophobic tail and hydrophilic head
• Self-assemble into a double-layered
aggregates or bilayer.
LE 5-13b
Hydrophilic
head
Hydrophobic
tails
Phospholipid symbol
LE 5-14
Hydrophilic
head
Hydrophobic
tails
WATER
WATER
Steroids
• Consist of 4 fused rings
• Vary by functional groups
• Cholesterol –component of animal
membranes
• Many hormones are steroids
Figure 5-15
Proteins
• 50% of the dry mass of most cells
• Functions
– Speed chemical reactions
– Roles in structural support
– Storage
– Transport
– Cellular communications
– Movement and
– Defense against foreign substances
Polypeptides
• Polymers of amino acids
are called polypeptides
• Amino acids contain
carboxyl and amino
groups
• R group or the side
chains varies
• R group determines the
characteristic of the
amino acid
Nonpolar
polar
Electrically
charged
Amino Acid Polymers
• Amino acids are join covalently by a
dehydration reaction
• The bond is called a peptide bond
• Polypeptide is a polymer of many amino acids
linked by peptide bonds.
Protein Conformation and Function
• A functioning protein is not just a polypeptide
chain but one or more polypeptides twisted,
folded and coiled into a molecule of unique
shape.
• The amino acid sequence determines what
the 3-D conformation will take.
LE 5-19
Groove
A ribbon model
Groove
A space-filling model
• A proteins
conformation
determines how it
works
• The function often
depends on the ability
to recognize and bind to
some other molecule
Levels of Protein Structure
• Primary Structure – unique sequence of amino
acids
• Secondary Structure- alpha helix or beta
pleated sheet
• Tertiary Structure- overall shape resulting
from the interactions between the side (R
groups) chains
• Quaternary Structure- the number of
polypeptide subunits
Levels of Protein Structure
Primary Structure
• The unique sequence of amino acids
• Like the order of letters in a very long word
• Not random it is determined by inherited
genetic information
LE 5-20a
Amino end
Amino acid
subunits
Carboxyl end
Secondary Structure
• Segments of polypeptide chains that have
repeated coiled or folded sections
• Coils and folds are the result of hydrogen
bonds of repeating constituents of the
polypeptide backbone
• Alpha helix coil held together by H bonds
• Beta pleated sheet bonds between parallel
polypeptide backbones
LE 5-20b
b pleated sheet
Amino acid
subunits
a helix
Tertiary Structure
• Overall shape of a polypeptide resulting from
the interactions between the side chains (R
groups) of the amino acids
• Nonpolar side chains end up in a cluster at the
proteins core.
• van der Waal forces hold them together
• Ionic bonds stabilize the structure
• Disulfide bridges reinforce the conformation
LE 5-20d
Hydrophobic
interactions and
van der Waals
interactions
Polypeptide
backbone
Hydrogen
bond
Disulfide bridge
Ionic bond
Quaternary Structure
• Some proteins consist of two or more
polypeptide chains aggregated together
LE 5-20e
Polypeptide
chain
b Chains
Iron
Heme
Polypeptide chain
Collagen
a Chains
Hemoglobin
Sickle- Cell Disease
• Change in the primary sequence of the
hemoglobin protein
• Abnormal hemoglobin crystallizes, deforming
the shape of the red blood cell.
• Abnormal shaped red blood cells clog tiny
blood vessels- stopping blood flow.
LE 5-21a
10 µm
Red blood Normal cells are
cell shape full of individual
hemoglobin
molecules, each
carrying oxygen.
10 µm
Red blood
cell shape
Fibers of abnormal
hemoglobin deform
cell into sickle
shape.
LE 5-21b
Sickle-cell hemoglobin
Normal hemoglobin
Primary
structure
Val
His
1
2
Leu
Thr
3
4
Pro
Glu
5
6
Secondary
and tertiary
structures
7
b subunit
Quaternary Normal
hemoglobin
structure
(top view)
Primary
structure
Secondary
and tertiary
structures
Molecules do
not associate
with one
another; each
carries oxygen.
His
Leu
Thr
Pro
Val
Glu
1
2
3
4
5
6
7
Exposed
hydrophobic
region
b subunit
a
Quaternary
structure
b
Val
b
a
Function
Glu
Sickle-cell
hemoglobin
b
a
Function
Molecules
interact with
one another to
crystallize into
a fiber; capacity
to carry oxygen
is greatly reduced.
b
a
Protein Environment
• Conformation dependent on physical and
chemical environment
• Alteration of pH, salt concentration,
temperature, or other aspects can cause a
protein to lose its native conformation
• The change is called denaturation
Chaperonins
• Chaperone proteins that help in the proper
folding of other proteins
• Keep new polypeptides segregated in the
cytoplasmic environment.
LE 5-23b
Polypeptide
Steps of Chaperonin
Action:
An unfolded polypeptide enters the
cylinder from one
end.
Correctly
folded
protein
The cap attaches, causing
the cylinder to change
shape in such a way that
it creates a hydrophilic
environment for the
folding of the polypeptide.
The cap comes
off, and the
properly folded
protein is released.
Nucleic Acids
• The amino acid sequence of a polypeptide is
determined by a unit of inheritance called a
gene
• Genes consists of DNA
• Two types of Nucleic Acids- DNA & RNA.
DNA
•
•
•
•
Provides direction for its own replication
Directs RNA synthesis
And with RNA directs protein synthesis
Genetic material inherit from parents
RNA
• Messenger RNA carries the genetic
instructions
• Ribosomes (RNA) the sites of protein
synthesis.
LE 5-25
DNA
Synthesis of
mRNA in the nucleus
mRNA
NUCLEUS
CYTOPLASM
mRNA
Movement of
mRNA into cytoplasm
via nuclear pore
Ribosome
Synthesis
of protein
Polypeptide
Amino
acids
Structure of Nucleic Acids
• Nucleic Acids are polymers of monomers
called nucleotides
• Nucleotide consist of 3 parts
– 5- carbon sugar
– Nitrogenous base
– Phosphate group
LE 5-26a
5 end
Nucleoside
Nitrogenous
base
Phosphate
group
Nucleotide
3 end
Polynucleotide, or
nucleic acid
Pentose
sugar
Nucleotides
• Two classes of nitrogen bases
– Pyrimidines
• Single six ring carbon skeleton with a nitrogen atom
• Include cytosine, thymine, and uracil.
– Purines
• Six ring fused to a five ring carbon skeleton
• Larger than pyrimidines
• Include adenine and guanine.
• Five carbon sugar
– Ribose in RNA
– Deoxyribose in DNA
LE 5-26b
Nitrogenous bases
Pyrimidines
Cytosine
C
Thymine (in DNA) Uracil (in RNA)
U
T
Purines
Adenine
A
Guanine
G
Pentose sugars
Deoxyribose (in DNA)
Nucleoside components
Ribose (in RNA)
Polymerization of Nucleotides
• Nucleotides are linked together covalently
through phosphodiester linkages between the
–OH group on the 3’ carbon of one nucleotide
to the phosphate on the 5’ carbon of the next.
• DNA strand has directionality from 5’ to 3’
The Double Helix
• DNA consists of two polynucleotides that
spiral around each other forming a double
helix.
• The two strands run in opposite directions are
antiparallel.
• The two strands are held together by
hydrogen bonds and by van der Waals
interactions between stacked bases.
Base Pairing
• A (adenine) always pairs with T (thymine)
• G (guanine) always pairs with C (cytosine)
• 5’- AGGTCCG-3’ is complementary to
3’-TCCAGGC-5’
LE 5-27
5 end
3 end
Sugar-phosphate
backbone
Base pair (joined by
hydrogen bonding)
Old strands
Nucleotide
about to be
added to a
new strand
5 end
New
strands
5 end
3 end
5 end
3 end
Molecular comparisons of DNA and
Proteins
• DNA carries heritable information in the form
of genes
• Genes and proteins document the hereditary
background of an organism
• Siblings have similarity in DNA and proteins
• Molecular comparisons DNA between species
show evolutionary relationships