dissociation curves

haemoglobin structure

4 pp chains

iron ion haem grp

prosthetic grp attached to each chain via ionic disulphide bridges

why is haemoglobin able to bind w/ oxygen so well

it has a high affinity for oxygen

affinity

strength of binding of haemoglobin to oxygen

what do oxygen and hemoglobin join when formed and how ?

form oxyhaemoglobin in a reversible reaction so it can also unload and disassociate oxygen able to diffuse into body cells for respiration

what happens when haemoglobin binds to its first oxygen ?

its tertiary structure shape alters uncovering another haem binding state making it easier for other molecules to join

shown by the steep middle in the curve

how is a more rapid intake of oxygen ensured in the lungs (refer to the graph)?

a small change in pO2 can cause a big change in the vol of O2 carried by the Hb

why does the graph begin to flatten towards the end ?

as the Hb becomes more saturated it becomes harder for the O2 to join onto it as most of the binding sites are taken

however Hb will still always load O2 even at high concs

partial pressure of oxygen

the conc of dissolved oxygen in cells

how is Hbs affinity for oxygen affected by the partial pressure of oxygen increasing ?

affinity incs

Hb loads more readily than unloads and dissociates so becomes more saturated

how is Hbs affinity for oxygen affected by the partial pressure of oxygen decreasing ?

affinity decs

Hb unloads and dissociates more readily than loads so becomes less saturated

effect of partial pressure in the lungs

alveoli have a high pO2

Hbs affinity incs readily loads than unloads

higher saturation

effect of partial pressure at the body cells

rbcs deliver the oxyhaemoglobin to the respiring tissues which have used the O2 up (low pO2 )

affinity decs

Hb readily unloads and dissociates

lower saturation

curve for an active animal

curve to the right

lower affinity + saturation

Hb unloads and dissociates more readily than loads and is less saturated at any given partial pressure

more O2 to cells so more respiration

what happens as the partial pressure of CO2 increases ?

the Bohr effect

Hbs affinity decs

unloads and dissociates more readily than loads

O2 saturation of Hb decs

more O2 is released to allow for aerobic resp and prevent anaerobic resp

less chance of lactic acid build up

curve shifts right

what causes the Bohr effect

CO2 diffuses into rbcs

CO2 reacts w/ water to form carbonic acid catalysed by carbonic anhydrase

carbonic acid dissociates into H+ and HCO3-

H+ causes O2 to unload from Hb - affinity decs - saturation decs at any given pO2

H+ binds w/ Hb to produce haemoglobonic acid -decs blood pH

HCO3- diffuses out of rbcs

chloride shift - Cl- ions enter rbcs to balance charge

how is CO2 made for exhalation ?

in the lungs :

pO2 is much higher causing haemoglobonic acid to dissociate - H+

H+ binds to HCO3- ions that diffuse back into the rbcs making carbonic acid

carbonic anhydrase catalyses this reversible reaction back to water and CO2

CO2 is exhaled

Hb is now free to bind w/ O2

how does fetal haemoglobin differ from adult haemoglobin

fetal Hb has a higher affinity for oxygen at any given partial pressure bcs :

adult Hb unloads and dissociates at the placenta due to low pO2

Hb saturation decs

O2 diffuses frm adult to fetal Hb

fetal Hb loads and becomes more saturated at this given pO2

O2 is then delivered to cells of fetus for resp

energy released for cell division - growth

myoglobin

dark red muscle pigment found in muscle cells

no role in O2 transport

used as an O2 store

what is the role of myoglobin?

high affinity for O2

readily picks up O2 but will only give it up when O2 conc dips to vv low lvls

in vv active muscles the O2 delivered by the blood may not be enough and the O2 conc drops below 0.5kPa

myoglobin releases its O2 providing a reserve supply to keep the muscle going

eventually the myoglobin will have no more O2 to give and the muscle has to respire anaerobically

how does size affect the curve

smaller mammals have a a higher sa:v ratio

they lose heat vv quickly

so they have a high metabolic rate to keep warm

high O2 demand so lower affinity to O2

curve shifts to the right