Protein Function 1 v4

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1. Induced fit labeling. Fill in the blanks.
a. Substrate-enzyme complex
b. Products
c. Substrates
d. Substrate-product complex
e. Enzyme
__
2. Protein A has a Ka = 6.0 M–1 for binding ligand L, and protein B has a Kd = 4.0 M for binding of
L.
a. What is the Kd for Protein A?
b. Which protein has a higher affinity for L?
Hemoglobin is a protein in red blood cells (RBCs) that carries oxygen. Almost 30%, percent of the mass of
RBCs is made up by hemoglobin. This allows RBCs to carry much more oxygen than could otherwise be
dissolved into blood.
A researcher studies the oxygen dissociation curves of normal adult hemoglobin (HbA), fetal hemoglobin
(HbF), and myoglobin (Mb), a related compound. He dissolves samples of each protein in a cup of water, and
places each cup in a sealed canister in contact with a gas. He changes the partial pressure of oxygen pO2 the
gas. For each measured pO2, he measures the saturation of oxygen in the proteins in the fluid. The saturation
is the percentage of total binding sites on the HbA, HbF, or Mb, which are bound to oxygen. The results are
shown below.
3. Based on the previous graph, which protein has the highest affinity for O2?
a. Myoglobin
b. Fetal hemoglobin (HbF)
c. Adult hemoglobin (HbA)
d. Can’t tell
4. Short Answer: Why would a lower Kd (or P50) for O2 compared to the mother be important for a
fetus?
5. Using the curves on the previous page, determine the partial pressure of oxygen at 50% (p50)
saturation for
a. Myoglobin_______________________________
b. Adult Hemoglobin_________________________
c. Fetal Hemoglobin _________________________
6. Using your resources, find the partial pressure of O2 in the lungs and tissues in mm Hg.
a. pO2 lungs _____________________
b. pO2 tissues ____________________
7. Using the graph above, determine the fraction of adult hemoglobin (Y) bound to O2 in the lungs
and in the tissues.
a. Y for Adult hemoglobin in the lungs_____________________________
b. Y for Adult hemoglobin in the tissues____________________________
8. Hemoglobin made a round trip from the lungs to the tissues and back to the lungs again. Before
picking up more oxygen in the lungs, what percentage of binding sites are occupied by oxygen
(hint look at problem 7)?
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