CH 460

Dr. Muccio

Myoglobin is primarily (helicies/sheets) with a _____ heme in the center coordinated by the amino acid _____. Myoglobin is biologically relevant in _____.

Helicies, Fe2+, His, muscle tissues

Myoglobin has a (hydrophobic/philic) exterior and a (hydrophobic/philic) interior. It has _____ heme group(s).

Phobic interior, philic exterior, 1

Fill in the blanks for the following Mb Oxygen Binding Curve

Hyperbolic shape with P50=2 torr

When [O2] > P50, then Mb becomes saturated (fraction bound is basically 1.00, or 100%)

When [O2] < P50, increasing O2 means increasing fractions of oxygen bound to Mb

Hb has _____ subunits with _____ heme binding sites.

4 (tetramer…they are Mb-like with 2 alpha subunits and 2 beta subunits. They are held by ionic and hydrophobic forces), 4

Hb binds oxygen cooperatively. What does “cooperativity” mean? What is the Hill coefficient?

Unlike Mb, each oxygen that binds to Hb, is held more tightly than the previous. The Hill coefficient quantifies cooperativity. The larger the Hill coefficient, the more cooperative the binding.

Fill in the blanks for the following Hb Oxygen Binding Curve

Sigmoidal curve with P50 =26 torr and a Hill coefficient (nH) of 3.3

When [O2] > P50, then Hb becomes saturated (there are more sites that are bound…i.e. we are getting closer to the max of 4 sites)

When [O2] < P50, the amount of oxygen bound to Hb is low…increasing oxygen does not increase the number of bound sites linearly (like Mb)

Here are four states of Hb. Which is the T-state? Which is the R-state? Describe the difference between the two states.

The second one is the T-state, or “Tense” state. It occurs when there is no oxygen bound to the Hb molecule. As a result, there are strong interactions among the subunits.

The fourth one is the R-state (I remember this because it’s the final “r”esulting state and the subunits are “r”elaxed). It occurs when all sites are occupied by oxygen molecules and thus the subunits only weakly interact.

The partial pressure of oxygen to saturate 50% of Hb with oxygen is _____ than the pressure needed to saturate 50% of Mb. This means that Hb has a ______affinity for oxygen than Mb.

Smaller; lower

Larger; higher

Smaller; higher

Larger; lower

None

In the Bohr shift, the Hb binding curve shifts _____ as the pH decreases from 7.6 to 7.2.

  1. Left
  2. Right
  3. Up
  4. Down

Rapidly metabolizing tissues, such as active muscle, have a high need for oxygen and generate large amounts of carbon dioxide. Increasing levels of CO2 = more acidic blood (Due to the equilibrium between CO2 and carbonic acid). The oxygen affinity of hemoglobin decreases as pH decreases from the value of 7.4 found in the lungs. So, as hemoglobin moves into a region of low pH, its tendency to release oxygen increases (i.e. hemoglobin responds to the CO2 increase with a decrease in oxygen affinity so it can release the oxygen to the tissues that need it.