Mass transport

Haemoglobin

Allows red blood cells to pass through capillaries

Increases surface area to volume ratio so it increases the area in which oxygen can diffuse

Allows red blood cells to be flexible so can squeeze through capillaries

Contains only haemoglobin so increases oxygen carrying capacity

Red blood cells contain enzymes the cant be released as they have no nucleus so can’t pass on the code to form those enzymes

Structure of haemoglobin

Primary, secondary and tertiary same as protein

quaternary - four polypeptides linked together to form haemoglobin, each is associated with a haem group and holds 1 02 molecule so a total of 402 molecules per haemoglobin

3 bases form 1 amino acid so to find out how many amino acids you have you divide by 3

Function

Transport 02 from the lungs to the respiring tissues

Has a high affinity (an attraction between molecules that results in the formation of a new molecule)

→ needs the be able to readily load oxygen at the site of gas exchange - at gas exchange surface oxygen concentration is high, co2 concentration is low and the affinity of haemoglobin for oxygen is high so oxygen is associated

At the respiring tissues 02 concentration is low, co2 concentration is high so affinity of haemoglobin for oxygen is low so oxygen is dissociated

To unload the oxygen affinity must be low

Partial pressure

Is the pressure that would be exerted by one of the gases in a mixture if it occupied the same volume on its own

Partial pressure of oxygen is highest in the alveoli where haemoglobin dissociates oxygen

Transport of oxygen in the blood

Hb + 4O2 → Hb(O2)4, over 95% of oxygen is carried this way in erythrocyte

Has a biconcave shape, is flexible, has large SA, short diffusion pathway, no nucleus so there’s more space for more Hb

Cooperativity → when one O2 bonds the Hb changes shape to allow for me O2 to bind more readily

Haemoglobin dissociation curve

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Haemoglobin is therefore high effective in the loading of large amounts of ozygen from environments but unloads it easily at the respiring tissues

Affinity

At high partial pressure there’s a higher affinity between Hb and oxygen and a change in the quaternary structure of the Hb molecule which allows the first Hb to bind, the Hb shows cooperativity so once an oxygen molecule has loaded it makes it easier for subsequent molecules to bind. This allows for sufficient loading in the lungs the pO2 is high

→ At respiring tissues CO2 is increased so affinity of Hb and O2 is decreased so PH is decreased so it’s easy to unload so more pressure is needed to have some Hb% in increasing amounts of CO2, is difficult to load more O2 so CO2 increases and is right shifted

→ At locations where CO2 is decreased the affinity for O2 is increased so the PH is increased so it’s difficult to unload CO2 and is easy to load so needs less Kpa to load the same % of Hb so is left shifted

Affinity in respiring tissues

In actively respiring tissues, CO2 concentration increased which dissolves in the blood plasma, the CO2 forms carbonic acid so there’s an increase in hydrogen ion concentration causing a reduction in the PH of blood plasma

More O2 is more easily unloaded because of the lower affinity of haemoglobin for O2 bought about by the reduction in Ph that means more O2 is available for respiration at the same partial pressure

In the alveolus the concentration of CO2 is low so the Bohr effect is reversed so the loading of O2 is easier because of the higher affinity of haemoglobin for oxygen bought about by the higher PH

circulatory system of a mammal