Lecture 8 - proteins in action Flashcards
how is oxygen binding weakened in haemoglobin
it is weakened allosterically by BPG, CO2 and low pH
weakening oxygen binding allosterically is described as …
shifting the tetramer to the T state
what is the shape of haem in deoxyhaemoglobin
dished shape
what happens ti the haem in oxyhaemoglobin
the oxygen flattens the haem, pulls histidine F8 and helix F toward the binding site
what will weaken oxygen binding
anything that keeps helix F away from the binding site
how does BPG inhibit O2 binding to haemoglobin
- BPG binds to deoxyhaemoglobin by electrostatic interactions
- BPG stabilises haemoglobin in the tense state, reducing oxygen affinity
what does cooperativity allow for
efficient unloading
why does haemoglobin show little cooperativity in the absence of inhibitors
because “stripped haemoglobin” is predominantly in the R state
why does haemoglobin show cooperativity in the presence of inhibitors
allosteric inhibitors BPG, CO2 and H+ stabilise the T state which unmasks cooperativity
what is the Bohr effect
elevated CO2 and low pH in metabolising tissues both reduce the affinity of haemoglobin for O2
how does CO2 reduce the affinity for oxygen
like BPG, CO2 can bind (allosteric binding) to the amino acid terminal amino group, stabilising deoxyhaemoglobin in the T state
what occurs at increased altitude
pO2 in the lungs is lower so haemoglobin can not uptake as much oxygen
what is the adaptation to help when increased altitude
increased BPG, reduces haemoglobins oxygen binding, can deliver more oxygen to tissues
what is methaemoglobin
oxidation of haem Fe2= to Fe3+, shifts 1 subunit to the R state confirmation, without oxygen bound
how does methaemoglobin have impaired function
- doesn’t bind oxygen despite being in the R state due to Fe3+
- three other subunits of tetramer shifted to R state, so do not release oxygen
= therefore whole tetramer doesn’t release as much oxygen as it should
