Lecture 7 - proteins in action Flashcards
explain the structure of myoglobin at all levels
- primary structure = 150 amino acids
- secondary structure = 8 a-helices A-H and connecting loops (AB, BC etc)
- tertiary structure = globin fold with a hydrophobic pocket
- quaternary structure = monomeric (a single polypeptide chain)
where does haem bind to in myoglobin
haem binds to His F8 (the 8th amino acid in helix F, which is histadine) in a globin protein
what does haem include
four pyrrole rings linked together in a plane
how many coordinate bonds does iron have and what do they bind to
6
- 4 to nitrogen atoms of the haem
- one to a nitrogen atom of histidine F8
- one to O2
what gives haem the red colour
the electronic orbitals
is the binding of oxygen to the Fe2+ a reversible interaction
yes
what does lactate do to myoglobins affinity for oxygen
decreases myoglobins affinity for oxygen, but does not bind where oxygen does
what does lactate build up in muscles do
promotes the release of myoglobin, increasing O2 availability for respiration
what does the concept of “allosteric” build on
builds on ‘steric hinderance’, the impossibility of two atoms occupying the same space
what has haemoglobin evolved to be
a tetramer
what is a tetramer
four globin proteins associate together non covalently (4 structural sub-units)
how many O2 can bind to one haemoglobin tetramer
maximum of four
- because each globin protein contains one haem that can bind to one oxygen
is myoglobin saturated or unsaturated at low pO2
saturated
when will myoglobin release O2 to muscle cells
only when the cellular pO2 is very low
what is the partial pressure of oxygen in the lungs
pO2 is ~100 Torr
what is the partial pressure of oxygen in resting muscle
pO2 is ~20 Torr
does haemoglobin have a stronger or weaker binding affinity for oxygen and why is it important
much weaker than myoglobin, this is important as its function is to transport oxygen
what is the function of myoglobin
back up store of O2 in muscle cells
what is the function of haemoglobin
O2 transporter
what is the structure of haemoglobin
tetramer
what is the structure of myoglobin
monomer
in both myoglobin and haemoglobin the affinity for oxygen is altered by …
by molecules (e.g lactate to myoglobin) binding elsewhere (allosteric control)
what type of curve does myoglobin show on the degree of saturation vs O2 pressure graph
tighter, hyperbolic
what type of curve does haemoglobin show on the degree of saturation vs O2 pressure graph
weaker, sigmoidal binding curve
what is cooperative interaction in terms of haemoglobin
- when an oxygen atom binds to one of hemoglobin’s four binding sites, the affinity to oxygen of the three remaining available binding sites increases
- this gives the sigmoidal binding curve
what does the MWC model say about subunits states
all subunits will be in the same state
- either low affinity, tense (T) or high affinity, relaxed (R) confirmation
what does the binding of each successive substate shift the equilibrium in favour of
the R form
what form do inhibitors stabilise
the T form
what form do activators stabilse
the R form