Hemoglobin- Structure and Function Flashcards
How many pairs of polypeptide chains are contained in a single hemoglobin?
2 Pairs
What polypeptide chains make up Hemoglobin A1?
2 alpha chains and 2 beta chains
What polypeptide chains make up Hemoglobin A2?
2 alpha chains and 2 delta chains
What polypeptide chains make up Hemoglobin F?
2 alpha chains and 2 gamma chains
True or False: A total lack of alpha-globin chains is compatible with life.
False. There is no substitute for alpha-chains so the a total lack of alpha chains is incompatible with life
What three amino acids make the surface of hemoglobin hydrophilic (preventing it from precipitation)?
Lysine
Arginine
Glutamic Acid
Define: Allosteric regulation.
Binding to substrate, oxygen, the hemoglobin molecule changes its conformation, altering the binding affinity for additional oxygen molecules.
Describe: Configuration T (Taut) of hemoglobin
No sites are occupied by oxygen
Descrbie: R form (relaxed) of hemoglobin
All sites are occupied by oxygen
What is positive coopertivity?
Binding of a substrate leading to increased affinity for additional substrates
What has a higher oxygen affinity myoglobin or hemoglobin?
Myoglobin
What is the interpretation of a left shift on a dissociation curve?
Left shift means the hemoglobin has an increased oxygen affinity and a lower P50
What is the interpretation of a right shit on a dissociation curve?
Decreased oxygen affinity and higher P50
Name three factors that shift the oxygen dissociation curve.
- pH
- Temperature
- 2,3-BPG concentration
What is the Bohr Effect?
Oxygen held more tightly in higher pHs and released more easily in acidic environments
How does carbon dioxide effect the dissociation of oxygen from hemoglobin?
Right shift.
Carbonic anhydrase converts carbon dioxide to carbonic acid which decomposes into bicarbonate and hydrogen ions leading to a drop in pH.
How does higher temperature effect the dissociation curve?
Higher temperature shifts the curve to the right
What is 2,3-Bisphosphoglycerate?
-It is a byproduct of anaerobic glycolytic pathway
How does 2,3-BPG effect the dissociation curve?
High 2,3-BPG: Oxygen affinity of hemoglobin decreases and shifts to the right
Mechanism- Stabilizes deoxyhemoglobin in T configuration leading to decreased affinity
Define P50.
The partial pressure of oxygen at which the oxygen carrying protein is 50% saturated
Why is the oxygen dissociation curve sigmoidal in shape?
Because of COOPERATIVITY, when the percent saturation of hemoglobin by oxygen is plotted as a function of the partial pressure of oxygen
Compare oxygen dissociation curves for myoglobin and hemoglobin and explain the reasons for the difference
Myoglobin- is a protein which stores oxygen in muscle cells and is very similar to hemoblobin except that it is a monomer rather than a tetramer and therefore does not undergo allosteric regulation or cooperativity.
The myoblobin curve is shaped more like a hyperbola, giving the myoglobin molecule very high oxygen affinity at very low oxygen concentrations
On what chromosome is alpha globin found?
Chromosome 16
On what chromosome is beta globin found?
Chromosome 11
What three distinct hemoglobins are found in embryos between week 4 and week 14?
What is a common characteristic of all three?
- Hemoglobin Gower I
- Hemoglobin Gower II
- Hemoglobin Portland
-They all have a higher affinity for oxygen (left shift) than adult hemoglobin
What hemoglobin predominates after 8 weeks of gestation?
Fetal hemoglobin
Name one unique feature of fetal hemoglobin.
It binds 2,3-BPG poorly giving it a higher oxygen affinity
What hemoglobin predominates at eh time of birth?
65-95% Hemoglobin F
20% Hemoglobin A1
What two conditions results in hemoglobin F remaining elevated after birth?
Premature infants
Mom with diabetes
Name some unique characteristics of Hemoglobin A2.
- More heat setable
- Slightly higher oxygen affinity
- Can become elevated in certain diseases
What are Heinz bodies?
They are precipitated denatured hemoglobin. They are a result of variants producing a physically unstable molecule
What is high affinity hemoglobin variants?
Hemoglobin variant that holds onto oxygen more tightly (left shift).
What is a common symptom of people with high affinity hemoglobin variants?
Erythrocytosis due to oxygen delivery being reduced leading to erythropoietin being produced leading to increased red blood cell production.
Give one example of a high affinity hemoglobin variant
Hemoglobin Chesapeak
What is low affinity hemoglobin variants?
Hemoglobin releases oxygen too easily (right shift)
What is a common symptom of people with low affinity hemoglobin variants?
Cyanosis and physiological anemia
True or False: Hemoglobin Zurich is a low affinity hemoglobin variant.
False. The mutation does not affect oxygen binding but does increase binding to carbon monoxide
What are some characteristics of Hemoglobin Koln?
- Most commonly recognized unstable Hgb
- Mild Anemia
- Reticulocytosis
- Splenoomegaly
What is methemoglobin?
It is hemoglobin with ferric (3+) instead of ferrous (2+)
What maintains iron in the ferrous form of iron in the erythrocyte?
NADPH methemoglobin reductase pathway
How can you get acquired methemoglobinemia?
Exposure to drugs such as benzocaine or nitrates in well water
What causes genetic methemoglobinemia?
Homozygous deficiency of cytochrome b5 reductase which is responsible for the transfer of electrons from NADH to cytochrome b5
May also be mutation in hemoglobin that leads to methemoglobin
What would an oxygen dissociation curve look like for someone with methemoglobinemia?
Left shift
What are they symptoms of methemoglobinemia?
Cyanotic, but arterial partial pressure is normal
Blood looks chocolate, brown-blue
What is the treatment for patients with methemoglobinemia?
Cosmetic with methylene blue
Remove inciting drug for acquired
What binds heme better CO or O2
CO2!!!! About 240X better
A 15 yo boy comes into the ER. In the ambulance he had a seizure and then became unresponsive. His friend reported that an hour prior he was nauseated and dizzy. The friend seemed disoriented and disconnected and was shielding his eyes from the bright light of the emergency room. What should be on the differential diagnosis?
Carbon monoxide poisoning. possibly from sniffing pain remover
What is the treatment for carbon monoxide poisoning?
100% oxygen to competitively compete
Can you diagnose carbon monoxide poisoning with pulse oximetry?
No. Pulse oximetry only measures two wavelengths and cannot differentiate between carboxyhemoglobin and oxyhemoglobin.
Co-oximetry measures four wavelengths and can accurately measures carboxyhemoglobin and methemoglobin
