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43 Cards in this Set
- Front
- Back
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Describe basic features of Myoglobin
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globular protein
smaller than hemoglobin oxygen binding protein found in muscle cells Stores oxygen to be used during respiration |
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Structure of Myoglobin:
What is the backbone? |
Backbone is 8 airly straigh segments of alpha helix interrupted by bends
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What is the main component of the myoglobin structure
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Single polypeptide with 153 aa long.
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What is the prosthetic group of Myoglobin?
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Contains a heme group - iron porphyrin
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Describe the level of compactedness of Myoglobin
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It is such a compact molecule that in its interior it only has room for 4 water molecules
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Hemoglobin:
Where is it found? What is it responsible for? |
Found in erythrocytes
Responsible for binding oxygen in the lung and transporting the bound oxygen throughout the body where it is used in aerobic metabolic pathways. |
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What sort of structure does it have?
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Quaternary structure of proteins
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What does Hb Consists of??
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4 polypeptide chains (subunits)
(2xAlpha globins & 2xBeta globins) and 4 heme prosthetic groups |
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What type of protein is it??
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Hb is an oligomeric protein
(it is made up of more than 1 subunit) |
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How are the Heme groups situated with in the molecule?
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Heme groups are separated and filled at different angles and partially buried in a pocket lined with hydrophobic amino acid side chains.
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How is the Heme group bonded to the protein?
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bonded to the polypeptide chain via the Fe atom to the R group of a histidine residue.
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Oxygen Transport:
How much oxygen is transported / 100mL |
20mL
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RBC — or Erythrocytes
Describe |
• 6 to 9μm in diameter
• Consist of biconcave disks • No nucleus or organelles. • Unable to reproduce they have a life span of 120 days. • Hb content is about 34% |
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What is the venous reserve
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Hb is 64% saturated with oxygen in venous return blood returning to the heart.
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How much oxygen is released at resting tissue?
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1/3 of the oxygen it carries.
Therefore each 100m1 of blood unloads 6.5 ml of oxygen. |
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What is the driving force for Oxygen binding to Hb?
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Oxygen tension in the capillaries (partial pressure).
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When is Hb said to be 100 % saturated?
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When all four binding sites are occupied
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At what pressure does myoglobin have 50% saturation?
Why?? |
It is already 50% saturated with oxygen at very low partial pressures of oxygen 1 to 2 mmHg
Myoglobin has a very high affinity for oxygen. |
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What type of curve does myoglobin have?
When Does it have 95% saturation |
simple hyperbolic curve
20mmHg |
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What type of curve does a Hb have?
Why? |
sigmoidal shaped curve
Hemoglobin has a much lower affinity for oxygen compared to Myoglobin |
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Explain the Loding zone of Hb
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Is where association of Oxygen with Hb occurs. This is illustrated by a plateau that occurs at tensions or pressures above 60mmHg
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Explain the unloading zone
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< 60mmHg and means that oxygen is easily removed from the blood at these pressures — ie. tissues where there is a low pO2.
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What happens at the lungs?
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In the lungs partial pressure of oxygen (p02) is 100mmHg. At this pressure Hb is 96 % saturated.
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What happens at working tissue?
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pO2 = 26mmHg and Hb releases about a 1/3 of its bound oxygen
Myoglobin in the muscle at pO2 around 26 mmHg is saturated with over 95 % Oxygen. |
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Oxygen binding:
What happens to Hb after the first oxygen binds |
the affinity for oxygen rises some 500 times. There is a cooperative interaction between the subunits; positive cooperativity is seen.
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Why is cooperative interaction not seen in myoglobin?
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because there is only one polypeptide chain.
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What does cooperative binding of oxygen do?
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enhances the efficiency of Hb as an oxygen carrier
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How do the subunits increase their oxygen affinity?
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involves a change in the conformation (3D shape) of Hb.
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Three Dimensional Changes:
What happens when the 1st oxygen binds to the Fe atom? |
It pulles the Fe atom into the plane of the heme.
The residue histidine (which Fe is bound to) is also pulled toward the plane of the heme ring |
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What does the conformational change of the distidine mean for the rest of the Hb?
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the change is transmitted to the peptide backbone which significantly changes the 3D structure of the entire subunit
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Conformational changes at the subunit surface lead to.....?
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a new set of binding interactions — formation of new H bonds and new hydrophobic interactions all contribute to the new quaternary structure.
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The conformational changes also involve the following:
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Salt links rupture (electrostatic interactions)
Energy is required to break salt links, therefore binding of first 02 is energetically less favorable than for the other 3 |
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What is the result of the overall conformational changes
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results in easier access of oxygen to the iron atom of the second heme and thus a greater affinity for the Hb molecule for a second oxygen molecule
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Factors which affect the affinity of Hb for Oxygen:
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Shift to the Right
1. p02 2. Increased [CO2] 3. Increased [H+ ion] 4. Temperature 5. 2,3 diphosphoglycerate (2,3-DPG) |
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What does a shift to the right mean?
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helps delivery of 02 from Hb to the tissues
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What is the equation for the formation of carbonic acid when CO2 dissolves in tissues?
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H2O + CO2 —> H2CO3 —> H+ + HCO3
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Why does the formation of Carbonic acid occur quickly?
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RBC have carbonic anhydrase therefore this reaction occurs relatively quickly
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What else is Hb used to transport?
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end products of tissue respiration
H+ and CO2 (20% of total CO2 and H+ transported this way). H+ to the kidneys and CO2 to the lungs. |
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What is a carbaminohemoglobin.
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CO2 bound to alpha amino groups at the amino terminal end of each of the 4 polypeptide chains of a Hb
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What is the Bohr effect?
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Increased delivery of 02 to the tissues occurs when CO2 and H+ are in increased amounts
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2, 3-DPG: how does it affect the Hb molecules
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Reduces the affinity of Hb for O2 by becoming bound to deoxyhaemoglobin.
Increased [DPG] decreased the amount of O2 bound to Hb at any given oxygen concentration |
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Fetal Hb and 2, 3- DPG
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fetal form of Hb binds 2,3 DPG much less than adult Hb, with the result that Hb fetal binds O2 with a greater affinity than the mothers own Hb
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Effect of Exercise on Curve
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shift the curve to the right
Exercising muscles release large quantities of CO2 Muscle temperature can rise which increases the p02 level for the release of oxygen into the muscle. |
