Respiratory Pigments & Gas Diffusion Quiz

Respiratory Pigments & Gas Diffusion

• Gases combined chemically with other molecules do not contribute to partial pressure
• Impacts diffusion
• Example of a chemical combination: CO2 + H2O  H2CO3  H+ + HCO3-
• Example of another chemical combination: Hb H + O2 ՞ Hb O2 + H+

Oxygen Transport: Respiratory Pigments

• Heme: porphyrin ring complexed with one iron atom
• Myoglobin (Mb): monomeric protein (globin) plus one heme molecule with one oxygen binding site
• Typically found in muscle tissue

Pigment Diversity

• Chlorocruorins: use iron and a different porphyrin ring from Mb, Hb
• Bind oxygen and turn green
• Found in four marine annelid worm families including feather duster worms

Pigment Diversity

• Hemerythrins: non-porphyrin, iron-containing proteins found within muscle and blood cells with two oxygen binding sites
• Found in some types of worms and brachiopods including sipunculid worms and brachiopod molluscs

Pigment Diversity

• Hemocyanins: copper containing, non-porphyrin proteins with up to 160 oxygen binding sites
• Bind oxygen and turn blue
• Found extracellularly in some molluscs and arthropods including decapod crustaceans (lobster) and cephalopod molluscs (squid)

Pigment Diversity: Plants

• Leghemoglobin: monomeric (like Mb), porphyrin ring, globin protein
• In legumes supplies O2 for symbiotic bacteria, which fix N2 for the plant
• Found in soybean root nodules

Hemoglobin (Hb)

• Found in the blood cells of most vertebrates
• Up to four heme-globin subunits
• Mammals have 2 α, 2 β subunits

Oxygen – Hb Binding: Key Points

• Equilibrium reaction:
  • Higher PO2, more binding
  • Low PO2, O2 unbinds from Hb
• O2 – binding non-linear (sigmoidal)
• O2 only available to tissue if unbound
• Binding/unbinding affected by internal environment – acute effects: Temp., pH, CO2

1: Equilibrium Binding

• Higher PO2, more binding
• Low PO2, O2 unbinds from Hb
• PO2 falls in blood due to a decrease in pressure or oxygen depletion
• Very little O2 dissolved in blood plasma

2: Binding Sigmoidal

• Cooperativity: binding O2 at one Hb subunit of multimeric facilitates binding at other subunits (slope increases)
• At high PO2 most subunits “saturated” (slope decreases)

3: O2 Must Unbind

• To access tissues
• At lungs high PO2 so O2 can diffuse into blood, bind to Hb
• At exercising muscle, blood PO2 low so O2 more likely to unbind from Hb

Hb vs.Mb

• Mb monomeric, so no cooperativity
• When blood passes through Mb-containing muscle, O2 binds to Mb as PO2 decreases but does not unbind until conditions are right. It is a store of O2 for the muscle

Describing Hb – O2 Binding

• P50: PO2 at which Hb reaches 50% saturation
• Measure of affinity of Hb for O2
• Can change acutely, with acclimation and adaptation

“Shifting” Hb – O2 Binding

• Changes in PO2, pH, CO2, and temperature impact the affinity of Hb for oxygen
• A higher P50 means the affinity of Hb for oxygen is lower

Hb Adaptations:

• Changing amino acid sequence of globin molecule can change P50

Hb Adaptations:

• Water vs. Air breathers have different P50s
• Water breathers have a lower P50

Hb Adaptations:

• Water vs. Air breathers…why?
• Water breathers need a higher affinity for oxygen as there is less oxygen available in water
• Water breathers have a lower P50 so they maintain a higher saturation of oxygen in their blood

Hb Adaptations: O2 Availability

• Animals living in low O2 environments have a lower P50, higher affinity for oxygen
• Examples: Deep-sea fish, animals at high altitude, or burrowers

Hb Adaptations: High Altitude

• Animals at high altitudes have a lower P50, indicating a higher affinity for oxygen

Hb Adaptations: Burrowers

• Many burrowers have a lower P50, indicating a higher affinity for oxygen

Hb Adaptations: Body Size

• Smaller mammals have a lower P50, indicating a higher affinity for oxygen

Hb Acclimation:

• Express different globin isoforms in response to changing O2 availability
• Change in P50 (blue line)

4: Hb – Acute Binding Effects

• Bohr effect/shift: pH and/or CO2
• Low pH or high CO2 decreases Hb’s affinity for O2 (right shift)

4: Hb – Acute Binding Effects

• Temperature:
• Higher temperature decreases Hb’s affinity for O2 (right shift)

4: Hb – Acute Binding Effects

• Organic phosphates in blood cells bind to Hb and reduce affinity for O2
• Examples of organic phosphates and the animals they are found in:
  • Fish: ATP, GTP, Inositol pentaphosphate (IPP)
  • Amphibians: ATP, 2,3-diphosphoglycerate (DPG) some GTP
  • Reptiles: ATP, GTP
  • Birds: DPG (embryo), IPP (adult)
  • Mammals: DPG

Organophosphate Modulators

• Increase the P50 value and decrease Hb's affinity for O2
• Facilitates oxygen delivery to tissues under low oxygen conditions

Compare Hb at Lung vs. Working Muscle

• Factor | Lung | Muscle | Favours? ------- | -------- | ------- | -------- PO2? | High | Low | Hb binding or unbinding Temperature?| Low | High | Hb binding or unbinding CO2/pH | Low | High | Hb binding or unbinding

Hb Quantity

• Increase expression, synthesis of Hb, red blood cells (red line)

Hb Quantity

• Hematocrit: % blood volume comprised of red blood cells

Hematocrit: Adaptation

• Diving animals have higher hematocrit

Hematocrit: Adaptation

• Diving animals have a higher hematocrit
• Higher total O2 carrying capacity

Hematocrit: Acclimation

• Acclimation to high altitude can increase hematocrit (if enough dietary iron)

Mammalian Fetal Hemoglobin

• Fetus expresses γ globin, incorporates four into Hb
  • γ globin has a higher affinity for oxygen
  • γ globin is less sensitive to organophosphates
  • Allows the fetus to extract oxygen from the maternal blood

Test your knowledge on respiratory pigments and gas diffusion processes in organisms. This quiz covers the chemical combinations of gases, the types of respiratory pigments like hemoglobin and myoglobin, and the diversity of these pigments in various species. Challenge yourself and deepen your understanding of oxygen transport mechanisms.