Tertiary Structure
• A result of interactions between side (R) chains
that are widely separated within the peptide
chain
Covalent disulfide bonds - between 2 cysteine AA
Salt bridges - between AA w/ charged side chains
(acid & base AA)
Hydrogen bonds - between AA with polar R groups
Hydrophobic attractions - between NP side chains
• Spatial relationship of 2˚ structures
• Level responsible for 3-D orientation of proteins.
• Thermodynamically most stable conformation
protein.
• May have intra-chain and inter-chain linkages
of a
Tertiary protein structure bonding
Human insulin, a small two-chain protein:
Tertiary structure has both
intra-chain & inter-chain disulfide linkages.
3o protein structure - Non-covalent R group interactions:
(a) electrostatic interaction
(b) hydrogen bonding
(c) hydrophobic interaction
Tertiary structure of the single-chain
protein: myoglobin.
found mainly in
muscle tissue
where it serves
as an intracellular
storage site
for oxygen
Quaternary structure:
Shape or structure from joining more than one
protein molecule (protein subunits) together to
make a larger protein complex.
Same non-covalent bonds as tertiary form:
•Electrostatic interactions (Van der Waals)
•Hydrophobic interactions
•Hydrogen bonding
Quaternary structure is easily disrupted
Tertiary and quaternary structure of the
oxygen-carrying protein hemoglobin.
When O2 binds to
Fe of Heme group,
tension on the
molecule pulls
an amino acid,
which alters the
3o structure –
This in turn affects the 4o structure bonds
Exposes more heme sites creates greater affinity for O2
Protein
Structure
R eview
Review part 1: can you…
•List the characteristics of proteins
•Draw the basic structure of amino acids (a.a.)
•Compare & contrast structural differences
between the 4 main classes of a.a.
•Draw a peptide formation between a.a.
•List characteristics of four levels of protein
structure (1o, 2o, 3o, and 4o)
Types of Proteins
• Two major types - based on structural
levels
– Fibrous - peptide chains are arranged in
long strands/sheets
– Globular - peptide chains are folded into
spherical/globular shapes
Fibrous versus Globular protein
Fibrous Proteins
Have fiber-like structures – good structural material.
Relatively insoluble in water.
Unaffected by moderate
in temp and pH.
Subgroups within this category include:
Collagens & Elastins: the proteins of connective
tissues. tendons and ligaments.
Keratins: proteins that are major components of
skin, hair, feathers and horn.
Fibrin: a protein formed when blood clots.
Myosin: a protein that makes up muscle tissue
Globular Proteins
In living organisms:
Serve regulatory, maintenance and catalytic roles.
Include hormones, antibodies, and enzymes.
Either dissolve or form colloidal suspensions in water.
Generally more sensitive to temperature & pH change
than fibrous protein counterparts.
Examples within this category include:
Insulin
Regulatory – controls glucose levels
Hemoglobin
Transport – moves O2 around body
Myoglobin
Storage – stores O2 near muscles
Transferrin
Transport – moves Fe in blood
Immunoglobulins Defense – attacks invading pathogens
Fibrous structural protein: Keratin
Nails
Horn & Hoof
feathers
Hair
Keratin structural molecules are normally long and thin,
insoluble in water, very high tensile strength,and
arranged to form fibers.
Composed of long rods,
twisted together,
laid down in criss-cross matrix
form.
Keratinized stratified squamous epithelial layer:
found only in skin!
Dead cell layers at surface. Keratin effectively
waterproofs cells. Blocks diffusion of nutrients & wastes.
Provides protection against friction, microbial invasion,
and desiccation.
Many cross-links create very little flexibility: horns,
claws, hooves, or nails.
Fewer cross-links allows some stretching but returns
to normal: wool, skin, and muscle proteins.
Fibrous structural protein: Collagen
•Collagen most abundant protein in human body
•Structural protein
•Major component of the connective tissue:
•sheaths muscles & attaches them to bone through tendons
•or attaches skeletal elements together through cartilage
Collagen exists as a
molecule that is tightly
coiled about itself
forming a secondary
triple coil.
The molecules bunch together in groups of three,
forming a larger coil (superhelical coil)
that gives collagen fibers their strength in living tissue.
Tendons
Collagen structure can be disrupted
in diseases such as scurvy,
which is a lack of ascorbic acid, a cofactor
in the hydroxylation of proline (Hydroxyproline)
In addition, collagen structure is disrupted
in rheumatoid arthritis.
Myosin & Actin
• Muscle proteins which allow for
contraction of the muscle.
• Myosin
– Fibrous tail - two coiled -helices
– Globular head - one at the end of each tail
• Actin
– A multimeric protein
– Long fiber of connected globular proteins
Muscle tissue contracts
and relaxes when
triggered by electrical
stimuli from brain.
Muscle fibers bundled
together make up a
single muscle. Many
myofibrils make up
each fiber.
Myofibrils have
striations, formed by
arrangements of
protein molecules.
The protein forms filaments. 2 types of filament: thick & thin.
Thick filaments contain myosin; thin filaments contain
actin, troponin and tropomyosin.