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Fundamentals Transcript 8/20/08
Part II 11:00-12:00
Protein Dynamics – Hemoglobin power point lecture
Slide 16
 BPG promotes the deoxy state of Hemoglobin (Hb)
 It occupies the central cavity
 2,3-bisphosphoglycerate when bound to the cavity of Hb stays there and then
oxygen is delievered more efficiently to the tissues
 When in high altitudes, such as in Colorado, it takes a few weeks to build up the
concentration of BPG to perform like normal
 Hb of adults (HbA) has 2 alpha chains and 2 beta chains
 Hb of fetuses (HbF) do not have beta chains, instead they have 2 alpha chains
and 2 gamma chains.
o It takes a few weeks for the transformation of the gamma chains to beta
chains.
o The gamma chains and beta chains can be substituted, only if necessary.
Such as if a person was unable to make the beta chains, they then could
“hold” on to their gamma chains.
o 2,3-bisphosphoglygerate does not have a big effect on HbF because of the
absence of His residues that bind the BPG. The mother is able to readily
pass of oxygen to the fetus.
Slide 17
 Slide of a graph of HbA and HbF
 HbF, which in the graph is similar to myoglobin, is not so easily deoxygenated.
 HbA has a high affinity for oxygen, but HbF has a greater affinity for oxygen.
Slide 18
 This graph is not related to what is happening in a person, but what is done in a
laboratory setting, such as in a test tube.
 Stripped Hb, which you never have, it already has a great affinity for oxygen by
itself.
 When you add CO2 with the Hb, which makes a few protons, the affinity for
oxygen is decreased and this drop in affinity continues as you add in BPG by
itself with Hb and you see an even a larger decrease with all 3, Hb+BPG+CO2.
 Whole blood (the dotted line) is not far below the Hb+BPG+CO2 line, because
these are molecules are all found in the blood.
o So hemoglobin on its own is somewhat similar to myoglobin, in that it has
a great affinity for oxygen, but when found in a physiological system it
has less affinity due to CO2 and BPG and protons.
Slide 19 – Summary of Hemoglobin Function
 In the lungs: oxygen is up, pH is up (~7.4), and CO2 is down. This is known as
the relaxed state. The relaxed state (R) can also represent the oxy state.
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In tissues: oxygen is down, pH is down, and CO2 is up. This is the tense state.
The tense state (T) can also represent the deoxy state.
In the first box, representing lungs: oxygen is being taken up by the hemoglobin
molecule; H+ (protons) are released, along with CO2 is released. The His and
Asp amino acids are changed, which were close together, are now spread apart.
In the second box, representing tissues: oxygen is leaving as the BPG enters the
cavity; the H+ (protons) with protonate the His side chain giving it a positive
charge which will promote the shift closer to Asp; the CO2 will bind to the
hemoglobin.
These reactions can go both ways. The oxygen will come in and force the BPG
out when moving from the tissues to the lungs. Also, the protonation will be
eliminated at high pH and there will no longer be any charge and the His and Asp
will spread apart.
Nitric acid/oxide is another factor. It has an unpaired set of electrons and its
function is to dilate vessels, a vasodilator. This is beneficial. It attaches to oxy
Hb and is delivered to tissues to help dilate the vessels of the small vessels.
Slide 20 – The polymerization of Hb S
 A mutation in Hb beta chains, for instance the 6th amino acid in normal
hemoglobin is glutamic acid, which is negatively charged at neutral pH. In a
mutated hemoglobin if you put a valine in that position, it has now changed from
a negatively charged hydrophilic group to a non-polar hydrophobic group. If this
happens normal oxy Hb has a normal configuration, deoxy Hb will have a cleft in
the beta chain (as seen in picture). Now in Hb S, instead of carboxyl group we
have a hydrophobic cleft. The molecules will then polymerize to make fibers.
 When both beta chains have the projection you get the total sickle cell formation.
 This mutation has some advantage. Hb S mutation has some protection against
malaria. When they are heterozygous it is not as damaging as if you were
homozygous.
 As long as the molecules are in the oxy state the cleft does not appear. The cleft
appears in the deoxy state, when the vessels are so small you get the greatest
tendency of the clumping of the cells. The cells become sickle in the tissues, not
in the lungs, and this is where the major damage is done.
Slide 21 – Other Hemoglobinopathies
 Another mutation in the cavity where the heme group is suppose to sit, and the
cavity becomes more hydrophilic, the heme group, which is very hydrophobic,
will float out of the cavity and will attach to the hydrophobic cell membrane and
will lyse the red blood cell membrane. = hemolytic anemia!
 You can have mutations at the alpha-beta contact points. You have no ability to
transport or transfer from the hemoglobin to myoglobin. Metabolic system is
starved of oxygen.
 If the His in F or E helix has been modified or if Tyr has been placed there, you
have a big oxygen molecule, which is electronegative, and it will pull electrons
away from the iron atom, giving you ferric iron instead of ferrous iron. Leaving
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you with poor affinity for oxygen. When this occurs the blood will look
brownish!
Thalassemias is when an individual cannot make one or another of the chains in
the hemoglobin molecule. Usually it is individuals that don’t have the beta chains
or they don’t work properly; it is here that the gamma chains can come in and
work. Alpha chains, however, are a necessity, if you cannot make the alpha
chains then you cannot live.
Muscle Proteins – new power point lecture
Slide 1 – Muscle Proteins
 Q: How do we go from chemical energy, structures to movements?
Slide 2 – Skeletal Muscle Anatomy
 A fiber bundle is really a number of many myofibrils
 Each myofibril is a linear array of sarcomeres, which is the basic unit of a
myofibril
 Each sarcomere is capped on its ends by a transverse tubule
 The surfaces of the sarcomeres are covered by this reticulum containing calcium
o And calcium is an absolute requirement for muscle activity and if there is
too much or too little available it can lead to problems, such as problems
contracting muscles.
Slide 3 – Electron micrograph of a skeletal muscle myofibril.
 This is a picture of a muscle myofibril.
 One sarcomere is noted and it’s divided into 6 parts, but each part is there twice.
 The first part is composed of thin filaments, which are actin polymers.
 The second part is composed of both thin and thick filaments, has a mixture.
 And the third section is composed of thick filaments, which are myosin polymers.
 The sarcomere has a mirror image, and the sections noted above are mirrored
across the M disc
 The M disc separates the 2 parts of the sarcomere and is where the myosin
molecules are clumped together and branch out on both sides.
Slide 4 – actin monomer
 The thin filaments are the actin molecules.
 Actin has 4 different domains
 The alpha helices and beta sheets are mixed together to form the interior of this
globular protein
 Actin molecules proliferate and make fibers, which is crucial to muscle function
Slide 5 – F-actin
 Each “blue” ball is an actin molecule
 Actin molecules proliferate and make strands which are coiled around each other
forming a coiled-coil.
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The rows of globules are wrapped around each other making a coiled-coil
This is what an actin fiber looks like from an electron microscope.
This kind of actin is F-actin, fibrous actin. It is now formed in fibers.
o They have a pitch (the distance along a helix that is traversed around the
axis of a helix before it comes around to a full turn) of 72nm and a repeat
distance of 36 nm.
Slide 6
 This is another view of an actin fiber, found in picture (a).
 Picture (b) is a reconstruction image, what an artist would make
 Picture (c) : F-actin fiber is really covered by other molecules, troponin and
tropomyosin. These molecules are wrapped around the coiled-coil.
 All you need to know is that you have an actin fiber that is covered by troponin
and tropomyosin. Those molecules are there to be uncovered or to allow the
myosin heads to grab a hold of the actin fiber. Myosin heads should only grab
hold only when calcium is present. When calcium is present these molecules will
fall away so the myosin heads can grab the fiber. Then you can have muscle
contraction!
Slide 7 – The Composition and Structure of Thick Filaments
 Now myosin has 2 heavy chains and 4 light chains, so it has 6 subunits.
 The heads of the heavy chains have ATPase activity. The energy resides in the
heads of the myosin.
 The light chains are homologous to calmodulin, which is a calcium binding
protein, and Troponin C.
Slide 8 – myosin molecule
 You can see (in the top picture) that myosin has a coiled-coil tail formed from the
alpha helices and made possible by the heptad repeat.
 It involves about 400 amino acids in each of these chains of the coiled-coil
structure.
 Then you have 2 light chains on each globular head, there are 2 heads, which
controls ATP and the cleavage of ATP.
 This is a good illustration of quaternary structure, based upon a large element of
super secondary structure, and of different domains, the globular regions (heads)
and the coiled-coil region (tail).