Mass transport in animals - Haemoglobin Flashcards
What is haemoglobin (structure)
A protein with a quaternary structure
Why would haemoglobin readily associate with O2? (Bohrs effect)
-At gas exchange surface O2 constantly removed.
-Partial pressure CO2 increased
-CO2 slightly acidic
-PH lowered slightly
-Higher PH changes shape/tertiary structure of haemoglobin into one that has a:
-higher affinity for O2 so O2 loads/ associates more readily
What are the haemoglobins?
A group of chemically similar molecules found in many different organisms.
Why would haemoglobin readily dissociate with O2? (Bohrs effect)
-In the tissues, CO2 produced by respiring cells
-Partisl pressure CO2 increases
-CO2 is slightly acidic in solution, so pH within tissues lowered
-Lower pH changes shape of haemoglobin into one which has:
-a has lower affinity for O2
so O2 dissociates/ unloads more readily
What effect does increased CO2 conc. have on the oxygen dissociation curve ?
⬆️ CO2 = oxygen dissociation curve shifts right
What effect does decreased CO2 have on oxygen dissociation curve?
⬇️CO2 = O2 dissociation curve shifts left
What is the benefit of having a higher affinity for O2?
So it is not released in blood when transported to tissues
What two things must haemoglobin do to efficiently transport O2?
-Readily associate w/ O2 at gas exchange surface
-readily dissociate w/ O2 at tissues requiring it
How could change in DNA lead to different haemoglobin molecules having different affinities for O2?
Different base sequence in DNA ➡️ different a/a sequence ➡️ different tertiary/ quaternary structure and shape ➡️ different affinities for O2
Primary, secondary, tertiary, quartenary structure haemoglobin ?
-Sequence of a/a in the four polypeptide chains.
-Each polypeptide chain coiled into a helix
-Each polypeptide chain folded into precise shape
-All 4 polypeptides linked to form almost spherical molecule, each polypeptide associated with a haem group ( containing an Fe 2+ ion)
How much O2 can a single haemoglobin molecule carry in humans, and why?
4 - in quartenary structure, 4 polypeptides linked, each associated with a haem group.
-Each haem group contains one Fe 2+ ion which can combine with single O2 molecule
How does O2 concentration effect haemoglobin loading/ unloading ?
-O2 loads onto haemoglobin to form oxyhaemoglobin where there is a high partial pressure of O2
-Oxyhaemoglobin unloads its oxygen where theres a low partial pressure of O2
What two facts need to be kept in mind to understand an oxygen dissociation curve?
-The further to the left the curve, the greater the affinity of Haemoglobin to O2 ( so it loads O2 readily, but unloads less easily )
-The further to the right the curve, the lower the affinity of haemoglobin for O2 ( so it loads less readily, but unloads more easily )
Describe positive cooperativity of O2 binding to haemoglobin molecules (5)
-shape of haemoglobin makes it hard for first O2 to bond to one of the sites on its four polypeptide sub-units as they are closely united, so at low partial pressure of O2, little O2 binds to haemoglobin
-Oxygen dissociation curve shallow initially
-Addition of first O2 changes quaternary structure of haemoglobin, making it easier for other for O2 to bond to other subunits
-Therefore, it took a smaller increase in partial pressure to bind second O2 to haemoglobin than it did the first.
-However, gradient of oxygen dissociation curve flattens off after third polypeptide subunit bound 2, as it is less likely that an O2 will bind to the 4th, when all the rest are taken up, due to probability.
Describe and explain the oxygen dissociation curve of the haemoglobin of an organism which lives in an environment with a low conc. of O2
-Further left, as they have a higher affinity for O2
