3.4.1 Mass transport in animals-Haemoglobin Flashcards
(27 cards)
Describe the role of red blood cells & haemoglobin (Hb) in oxygen transport (6)
● Red blood cells contain lots of Hb
○ No nucleus & biconcave → more space for Hb, high SA:V & short diffusion distance
● Hb associates with / binds / loads oxygen at gas exchange surfaces (lungs) where partial pressure of oxygen (pO2) is high
● This forms oxyhaemoglobin which transports oxygen
○ Each can carry four oxygen molecule, one at each Haem group
● Hb dissociates from / unloads oxygen near cells / tissues where pO2 is low
Describe the structure of haemoglobin (3)
● Protein with a quaternary structure
● Made of 4 polypeptide chains
● Each chain contains a Haem group containing an iron ion (Fe2+)
In terms of protein structure,describe the structure of haemoglobin +more about ions (6)
- Primary structure, sequence of amino acids in the four polypeptide chains
- Secondary structure, each of these polypeptide chains is coiled into alpha helix (held by h bonds)
- Tertiary structure, each polypeptide chain is folded into a precise shape to allow it to carry oxygen
- Two polypeptide chains from alpha chains (a chains) and another 2 polypeptide chains form a beta chain.
- Quaternary structure, in which all four polypeptides are linked together to form an almost spherical molecule.
- Each polypeptide is associated with a haem group – which contains a ferrous (Fe²⁺) ion.
- Each Fe²⁺ ion can combine with a single oxygen molecule (O₂), making a total of four O₂ molecules that can be carried by a single haemoglobin molecule in humans.
Describe the loading, transport and unloading of oxygen in relation to the oxyhaemoglobin dissociation curve (6)
- Areas with low pO2- respiring tissues:
● Hb has a low affinity for oxygen
● So oxygen readily unloads / dissociates with Hb
● So % saturation is low - Areas with high pO2 - gas exchange surfaces
● Hb has a high affinity for oxygen
● So oxygen readily loads / associates with Hb
● So % saturation is high
Draw the graph of %saturation of Hb with oxygen against partial pressure of oxyegn-Oxygen dissociation curve also define it
- The graph of the relationship between the saturation of haemoglobin with oxygen and the partial pressure of oxygen
-At 25% is the respiring tissues
-At 100% is the gas exchange surface
Explain the shape of the oxygen dissociation curve (6)
- The shape of the haemoglobin molecule makes it difficult for the first oxygen molecule to bind to one of the sites on its four polypeptide subunits because they are closely united.
- Therefore at low oxygen concentrations, little oxygen binds to haemoglobin.
- The gradient of the curve is shallow initially.
- However, the binding of this first oxygen molecule changes the quaternary structure of the haemoglobin molecule, causing it to change shape.
- This change makes it easier for the other subunits to bind to an oxygen molecule. In other words, the binding of the first oxygen molecule induces the other subunits to bind to an
oxygen molecule. - It therefore takes a smaller increase in the partial pressure of oxygen to bind the second oxygen molecule than it did to bind the
first one.
Explain why it is harder for the 4th oxygen molecule to bind to haemoglobin (3)
-While in theory it is easier for haemoglobin to bind the fourth oxygen molecule, in practice it is harder.
-This is simply due to probability. With the majority of the binding sites occupied, it is less
likely that a single oxygen molecule will find an empty site to bind to.
-The gradient of the curve reduces and the graph flattens off.
What is positive cooperativity
When the binding of the first molecule makes binding of the second easier and so on.
The gradient of the curve steepens.
What does it mean if the cure of the oxygen dissociation curve is slightly more to the left or to the right
- The further to the left the curve, the greater is the affinity of haemoglobin for oxygen (so it loads oxygen readily but unloads it less easily).
- The further to the right the curve, the lower is the affinity of haemoglobin for oxygen (so it loads oxygen less readily but unloads
it more easily).
Explain how the cooperative nature of oxygen binding results in an S-shaped (sigmoid) oxyhaemoglobin dissociation curve ()2
- Binding of first oxygen changes tertiary / quaternary structure of haemoglobin
- This uncovers Haem group binding sites, making further binding of oxygens easier
Describe evidence for the cooperative nature of oxygen binding (4)
● A low pO2, as oxygen increases there is little / slow increase in % saturation of Hb with oxygen
○ When first oxygen is binding
● At higher pO2, as oxygen increases there is a big / rapid increase in % saturation of Hb with oxygen
○ Showing it has got easier for oxygens to bind
What is the Bohr effect?
Effect of CO2 concentration on dissociation of oxyhaemoglobin → curve shifts to right
Explain effect of CO2 concentration on the dissociation of oxyhaemoglobin (4)
- Increasing blood CO2 eg. due to increased rate of respiration
- Lowers blood pH (more acidic)
- Reducing Hb’s affinity for oxygen as shape / tertiary / quaternary structure changes slightly
- So more / faster unloading of oxygen to respiring cells at a given pO2
Draw the graph of % saturation of Hb with oxygen against partial pressure of oxygen/kPa for the Bohr effect
Weird S shape
-Lower pH is on the right side
-Higher pH is on the left and takes longer
Describe evidence for the Bohr effect
At a given pO2 %, the saturation of Hb with oxygen is lower
Explain the advantage of the Bohr effect (eg. during exercise)
More dissociation of oxygen → faster aerobic respiration / less anaerobic respiration → more ATP produced
Explain why different types of haemoglobin can have different oxygen transport properties (3)
● Different types of Hb are made of polypeptide chains with slightly different amino acid sequences
● Resulting in different tertiary / quaternary structures / shape
● So they have different affinities for oxygen
Explain how organisms can be adapted to their environment by having
different types of haemoglobin with different oxygen transport properties
Curve shift left
Hb has higher affinity for O2
● More O2 associates with Hb more readily
● At gas exchange surfaces where pO2
is lower
● Eg. organisms in low O2 environments - high
altitudes, underground, or foetuses
Curve shift right
Hb has lower affinity for O2
● More O2 dissociates from Hb more readily
● At respiring tissues where more O2
is needed
● Eg. organisms with high rates of respiration /
metabolic rate (may be small or active)
Define Affinity of haemoglobin for oxygen
The ability of haemoglobin to attract, or bind, oxygen
Define Saturation of haemoglobin with oxygen
When haemoglobin is holding the maximum amount of oxygen it can bind
Define Loading / association of haemoglobin
The binding of oxygen to haemoglobin
Define Unloading/ dissociation of haemoglobin
When oxygen detaches, or unbinds, from haemoglobin
The role of haemoglobin
-To transport oxygen
-Readily associates with oxygen at the surface where gas exchange takes place
-Readily dissociates from oxygen at those tissues requiring it
Why do different haemoglobins have different affinities for oxygen?
. Depending on its structure haemoglobin
molecules range from those that have a high affinity for oxygen to
those that have a low affinity for oxygen.
- Each species produces a haemoglobin with a slightly different amino acid sequence.
- The haemoglobin of each species therefore has a slightly different tertiary and quaternary structure and hence different oxygen binding properties
