http:www'bw'uaf'educoursesbiol310

1
http//www.bw.uaf.edu/courses/biol310

• Syllabus and all powerpoints used in lecture
  (including Class 1)
• Note typo on syllabus My office phone is
  474-5762!

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Thought questions

• What happens when you hold your breath?
• CO2 levels increase
• You breathe or you pass out (and then you
  breathe)
• If you take several deep breaths in rapid
  succession, what do you think should happen to
  your ventilation rate?
• CO2 levels drop
• Ventilation rate drops
• What should breathing into a paper bag do to your
  ventilation rate?
• CO2 should be increased
• Ventilation rate increases

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Blood and Circulation (1)O2 and CO2
TransportBlood pH
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Alveolar cells
Red blood cell
O2
Air in Lungs
Hemoglobin pigment inside RBC
Endothelial cell of capillary
distance 0.01 mm
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Why Respiratory Pigments?

• Enhance carrying capacity of blood for O2!
• Oxygen is not very soluble in water
• High temperature decreases that solubility even
  further
• Pigments allow oxygen to be sequestered in blood
  at higher than would go naturally into
  solution
• Reduce circulatory costs
• Circulation costs about 10 of total energy
  expenditure in a resting human
• Without Hb this would be 10-fold higher!

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Respiratory Pigments

• A.k.a. metalloproteins All have a metal group
  to bind O2
• All absorb light at specific wavelengths

Haemocyanin Molluscs Arthropods
Haemoglobin Found in every major animal phylum!
(including some plants)
Chlorocruorin polychaetes
Hemerythrin Minor worms (Sipunculids,
Priapulids) Brachiopods
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Arthropods
Molluscs
Annelids
Chordates
Nematodes
Platyhelminthes
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Hemoglobin (Hb)

• What is it?
• In vertebrates protein made of four peptide
  chains (tetramer)
• 2 alpha (a), 2 beta (b)
• Animal hemoglobins vary in size among taxa from
  16-2000 kD!!!
• Some are dimers, some are octamers
• Where is it?
• In vertebrates, packed inside red blood cells (
  RBCs, erythrocytes)
• Not so in all animals some have it loose in
  blood!
• Why RBCs?
• Maybe allows Hb buildup without affecting blood
  viscosity?
• Generally it is the smaller Hbs in RBCs

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Hemoglobin Heme Globin
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HEME

• HEME
• Flat ring structure like a plate
• Fe at the middle

• Function binding oxygen
• Fe molecule binds 1 O2
• By itself, does not hold onto O2 very well
• Tends to get oxidized to Fe3
• Binds very well with carbon monoxide (20,000X
  higher affinity!)

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Globin

• Sandwich structure
• 3 a-helixes form top bread
• 3 a-helixes form bottom bread

• Heme is held in place between Helix F and E
• Prevents it reacting with other Heme,
• Lowers affinity for inappropriate substrates (CO)
• Allows O2 binding to be temporary and reversible

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Hemoglobin
2 a-subunit 2 b-subunit
a - chain
Total carrying capacity 4 O2
b - chain
b - chain
a - chain
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Red Blood Cells

• In mammals these have no nucleus
• In all other vertebrates they are nucleated!
• Size is consistently between 5 and 10 mm
• ( microns)

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Properties of Hemoglobin

• Binding of oxygen is sigmoidal
• Affinity for oxygen is affected by
• CO2
• pH
• Temperature
• Affinity Willingness to bind oxygen at a given
  PO2

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Oxygen binding pattern
Why this shape? At low PO2, low chance of Hb/O2
collision At high PO2, Hb saturates (all binding
sites are bound) Interaction among
subunits cooperative binding Binding of 1st O2
molecule facilitates 2nd, etc.
Hemoglobin
Saturation of with Oxygen
PO2 (torr)
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Formation of Oxyhemoglobin
Hb O2
HbO2
In equilibrium
hemoglobin
oxyhemoglobin
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Shifting the curve
1 PO2 needed for 50 saturation
Affinity
Saturation of with Oxygen
Affinity 1/25 0.04
Affinity 1/17 0.06
Affinity 1/37 0.03
PO2 (torr)
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CO2 and pH ions affect Hb affinity
Saturation of with Oxygen
Bohr Effect/Root Effect tendency of Hb to
drop O2 in presence of CO2 and low pH
PO2 (torr)
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Bohr/Root Effect example
100
binding of O2 to Hemoglobin
50
0
50
100
150
0
PO2 oxygen (mm Hg)
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Allosteric protein modification

• When other factors influence protein-substrate
  binding
• Bohr / Root effect is an example
• CO2 binds directly to Hemoglobin allosteric
  modification
• CO2 ? carbonic acid pH (not allosteric)
• Very general concept in physiology
• Allows physiological functions to be adjusted to
  local conditions!

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Temperature affects Hb Binding
100
10º C
20º C
30º C
binding of O2 to Hemoglobin
50
0
50
100
150
0
PO2 oxygen (mm Hg)
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Comparing hemoglobin affinity
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O2 binding and Altitude
100
binding of O2 to Hemoglobin
50
0
50
100
150
0
PO2 oxygen (mm Hg)
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Antarctic Icefish

• Family Chaenichthyidade
• (some members)
• Lack RBCs
• Lack Hemoglobin
• Blood is clear
• Gills are white

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Myoglobin

• Small Heme protein
• Very similar structure to Hb subunit
• Found in cytoplasm of muscle cells
• Local reservoir for O2 storage
• Very abundant in diving mammals
• Steepens the O2 gradient between blood and muscle

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What does myoglobin do?

• Gary et al 1998 Nature 395 905-908
• Myoglobin knockout mice do fine!
• Survive and reproduce
• Exercise capacity unchanged!
• Goedecke et al 1999 PNAS 9610495
• Myoglobin knockout mice compensate
• Higher blood flow rates
• Higher capillary densities

Is myoglobin UNNECESSARY in non-diving mammals?
This suggests it plays a role in oxygen delivery!
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Alveolar cells
Red blood cell
O2
Air in Lungs
Hemoglobin pigment inside RBC
Endothelial cell of capillary
distance 0.01 mm
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What about CO2?

• Transport is not as big a deal as for O2
• Because CO2 solubility is much higher in water
• Blood plasma has a higher capacity for CO2 than
  O2
• However, tends to dissociate in water to form a
  weak acid

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Carbon Dioxide and Bicarbonate
fast
slow
Hydrogen ion Bicarbonate ion
Carbonic acid
CA speeds up the hydration of carbon dioxide CA
is found in high concentrations inside RBCs!
At physiological pH (7.4), ratio of CO2HCO3
120! Most CO2 is present as bicarbonate
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Carbon dioxide and bicarbonate

• Carbon dioxide and water react slowly to form
  carbonic acid
• Carbonic acid rapidly dissociates to H and HCO3-
• Therefore, high dissolved CO2 lower pH (higher
  acidity)
• Carbonic anhydrase speeds this process up
• Added CO2 shifts balance toward bicarbonate
• Added bicarbonate or H ions shifts balance
  toward CO2

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CO2 transport in blood
In tissues
Red blood cell
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CO2 transport in blood
In Lungs
carbonic anhydrase
Red blood cell
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Carbon dioxide and bicarbonate

• Carbon dioxide and water react slowly to form
  carbonic acid
• Carbonic acid rapidly dissociates to H and HCO3-
• Therefore, high dissolved CO2 lower pH (higher
  acidity)
• Carbonic anhydrase speeds this process up
• Added CO2 shifts balance toward bicarbonate
• Added bicarbonate or H ions shifts balance
  toward CO2
• Carbonic anhydrase is present inside the RBC
• Hemoglobin buffers the H, leaving bicarbonate
  ions
• RBCs important in carbon dioxide transport!

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Blood pH in vertebrates

• Tends to be 0.6 pH units more basic (higher) than
  neutrality
• Neutrality pH changes with temperature
• Animals that live at higher temperatures have
  lower blood pH
• Data include all classes of vertebrates
• Mammals, birds, fish, reptiles, amphibians

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General concepts (1)

• Enzyme / protein affinity
• Defined as the inverse of how much substrate it
  takes to reach 50 of saturation
• Allosteric modification
• Molecules other than the reactants (substrates)
  can influence enzyme function
• Equilibrium reactions
• Adding either end products will drive reaction
  the other way

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General concepts (2)

• Proteins can serve as buffers of H
• Because of basic amino acid side chains
• Blood CO2 makes bicarbonate (HCO3-)
• Serves as an important physiological buffer
• Many physiologically important proteins are OLD!
• Can find them in very remote ancestors
• Sometimes performing slightly different functions

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http//www.bw.uaf.edu/courses/biol310

• Syllabus and all powerpoints used in lecture
  (including Class 1)
• Note typo on syllabus My office phone is
  474-5762!