Topic 7 : Mass Transport Flashcards
mass transport
large multicellular organisms, mass transport systems needed to carry substances between exchange surfaces and rest of body
why is mass transport needed?
most cells far away from exchange substances/each other for diffusion to maintain composition of tissue fluid within suitable metabolic range
maintains final diffusion gradients to and fro cells
maintains relatively stable immediate environments of cells that is tissue fluid
haemoglobins
group of chemically similar molecules
protein molecules with 4th structure has evolved to make it efficient at loading o2 in one set of conditions but unloading it in another set
structure of haemoglobins
primary structure = sequence of amino acids in 4 polypeptide chains
2nd structure = each of these polypeptide chains coiled into helix
3rd structure = each polypeptide chain folded into precise shape ( affects ability to carry O2)
4th structure = all 4 polypeptide chains linked to form globular shape
- each chain associated with haem group - Fe++
- ferrous ion combine with single O2 molecule
- single haemoglobin can carry 4 molecules
role of haemoglobin
to transport oxygen
to be efficient:
- readily associate with O2 at surface where gas exchange occurs
- readily dissociate from O2 at tissues requiring it
affinity of O2 under conditions
gas exchange surface = high O2 conc = low CO2 conc= high affinity = O2 associated
respiring tissues = low O2 conc = high CO2 conc - low affinity = O2 dissociated
why are there different haemoglobins?
many organisms have haemoglobin
different organisms have different properties dependent on affinity for O2
why do different haemoglobins have different affinities?
each species - slight difference in sequence of amino acids - thus different tertiary and quaternary structures so diff oxygen binding properties so different affinities for O2
description of oxygen dissociation curves
haemoglobin exposed to different partial pressures of O2 , doesn’t bind to O2 evenly
graph of saturation of haem with O2 and pp of O2 = oxygen dissociation curve - usually S shape
explanation of O2 dissocation curve S shape - 1
shape of Hbr mol makes it diff for 1st O2 to bind to 1 of 4 sites b/c they’re closely united
low O2 conc = little O2 binds to Hbr
gradient initially shallow
explanation of O2 dissocation curve S shape - 2
h/w binding of 1st mol changes 4th structure of Hbr - changes shape
makes it easier for other ( induces others to bind)
explanation of O2 dissocation curve S shape - 3
so takes small increase in pO2 to bind to 2nd O2 molecule than needed for 1st
positive cooperativity: binding of 1st makes binding of 2nd easier and etc
gradient steepens
explanation of O2 dissocation curve S shape - 4
theory reverses : becomes harder for Hbr to bind to 4th O2 due to probabilty
with maj of binding sites occupied - less likely O2 mol finds empty site to bind
gradient reduces and graph flattens over
affinities and O2 curves
further to left the curve = greater affinity of Hbr to O2 - loads O2 readily but unloads it less easily)
further to right curve = lower affinity of Hbr to O2 - loads O2 less readily / unloads more easily
effects of CO2 conc – 1
Hbr low affinity for O2 in presence of CO2
greater conc of CO2 - Hbr more readily releases O2 ( Bohr effect)
