4-8 PROTEIN EXAMPLES
Collagen

The major protein component of the _______________ tissue
of vertebrates.

Structure deduced by G. N. Ramachandran.

Consists of three left-handed helical chains coiled around each
other to form a right-handed _______________, stabilized by
_______________ bonds.
o Contains __________ residues, which makes the structure
somewhat __________.
o Stabilized by _______________ cross-links which occurs
during the maturation of tissues, but the chemistry of these
cross-link conversions is unknown.

Contains hydroxylated residues that require ascorbic acid (_______________ _____) to
assemble the protein properly.
o Without ascorbic acid, humans develop __________, which causes skin lesions,
fragile blood vessels, loose teeth and bleeding gums. Humans cannot synthesize
ascorbic acid because one of the genes required to do this is _______________.
Myoglobin and Hemoglobin

Both bind molecular _______________ (_____).

Both have a heme prosthetic group shown below:
-
A prosethetic group is a protein-bound organic molecule
essential for the _______________ of the protein.
-
This heme prosethetic group is called Fe(II)–protoporphyrin
IX, and is responsible for the __________ color of oxygenated
forms of myoglobin and hemoglobin.
-
The __________ is the site of oxygen binding, which for both
myoglobin and hemoglobin is a reversible process because no
_______________ are exchanged at the binding site.

Myoglobin – relatively small _______________ protein – facilitates the
______________ of O2 in vertebrates.
o Member of the family of proteins called ______________.
o Structure is a bundle of eight  helices, putting it in the _____
category.
o Heme prosthetic group occupies a __________ formed by three
 helices and two loops.

Hemoglobin – larger _______________ protein – carries O2 in the __________.
o Hemoglobin binds oxygen in _____ blood cells, or
erythrocytes.
o A typical human erythrocyte contains ~__________
hemoglobin molecules!
o Contains two different globin units called ___–globin
and ___–globin, which are both similar to myoglobin.
o The tertiary structure of each of the four chains is
almost _______________ to that of myoglobin. Hemoglobin isn’t a tetramer of
myoglobin, though, but a dimer of  subunits.
o Hemoglobin is an _______________ protein – one whos activity is modulated by
the binding of another molecule. For hemoglobin, this molecule is 2,3Bisphospho-D-glycerate (2,3BPG), which is classified as an allosteric effector (or
modulator) and it binds to a different site than O2.

When 2,3BPG binds to the allosteric binding site of hemoglobin it is
known as _______________, and is said to be in the T state (the
__________ state), which inhibits the ability of oxygen to bind to the
__________ group.

When O2 binds to hemoglobin it is known as _______________, and is
said to be in the R state (the __________ state), which causes the allosteric
binding site to be too __________ for 2,3BPG to bind.
o Without 2,3BPG, hemoglobin would not unload its oxygen in tissues!
o The CO2 + H2O
H2CO3
H+ + HCO3– equilibrium can affect the
pH inside red blood cells, causing hemoglobin to bind or release O2.
Antibodies

The immune system synthesizes defense proteins know as _______________ that recognize and
bind _______________.

Antibodies are synthesized by __________ blood cells called _______________. Each of these
synthesizes the same antibody.

Despite repeated exposure, the _______________ of the immune system is the reason certain
infections do not recur, and the reason why _______________ administered to children are
effective (immunity established in childhood lasts through adulthood).

When an antigen binds to the surface of lymphocytes, the lymphocytes are stimulated to produce
antibodies. The antibodies bind to the antigen, causing antibody-antigen complexes that
_______________ and mark the antigen for _______________ (by interacting proteases) or
_______________ (by engulfing it).

The most abundant antibodies are of the immunoglobulin G class (IgG), which are Y-shaped
oligomers composed of two identical light chains and two identical heavy chains connected by
disulfide bonds.
o
They are _______________ - they contain covalently
bound carbohydrates.
o
The characteristic feature is a  of two
antiparallel sheets.
o
The N-termini of pairs of light and heavy chains are
close together, and they determine the _______________
of antigen binding.
o
Human Antibody Structure
The loops from a light chain and a heavy chain
combine to form a __________, which is
complementary to the shape and polarity
of a specific antigen! The match between the antigen
and antibody is so close that there is no space for
water molecules between the two!

Antigen-binding specificity is used in the lab during
_______________ for diagnostic tests. Fluid containing an unknown
amount of _______________ is mixed with a solution of labeled
_______________, and the amount of antibody-antigen complex
formed is measured.
Human Antibody Diagram