Lecture 4 Flashcards
How many helices and turns doe myoglobin have? How are they labeled?
8 helices (labeled A-H), 7 turns (labeled based on which helix is turning into which, except for the first which is NA and the last which is HC).
What are the key points about myoglobin?
It is a globin protein plus a haem group within the hydrophobic cleft, it is a monomer (single protein subunit), with eight alpha helices, it has reversible high affinity oxygen binding and is used in muscle tissue to store oxygen.
How are individual amino acids labeled in myoglobin?
They are numbered based on which helix they are in.
What is a haem group?
Four pyrrole rings linked by methene bridges, it is an isomer of protoporphyrin IX (Fe 2+ in centre, binded to nitrogens)
What is a pyrrole ring?
A five carbon ring with one nitrogen atom.
What part of the haem group attaches to the myoglobin? At what amino acid? Which amino acid helps prevent bad gases joining and how? Why does this not affect carbon monoxide?
The Fe2+ bonds to the His F8 amino acid. Found on the other side His E7 influences binding of gas molecules by imposing steric hindrange, this prevents larger gases from binding, because carbon monoxide is a two atom gas it is not hindered anymore than oxygen and as such can still bind.
What is haemoglobin? What is it made up of?
A tetramer made up of four globin proteins which acts to transport oxygen in the blood. It is made up of two alpha globin proteins at the top and two beta globin proteins at the bottom, with a haem group in the centre of each.
What is the difference in oxygen saturation degree between myoglobin and haemoglobin? Why is haemoglobin the way it is?
Myoglobin rapidly reaches its peak in saturation at relatively low partial pressures of oxygen (meaning it absorbs lots at low partial pressures of oxygen and releases it at slightly lower partial pressures).
Haemoglobin is much more gradual in its release and absorption of oxygen based on partial pressure of oxygen, this is due to the interacting subunits influencing each other (causing a conformation change which makes the binding of oxygen easier for affected subunits).
What is the major overall change between oxy and deoxy-haemoglobin?
The centre hole is larger in deoxy-haemoglobin.
What are the two models of oxygen binding to haemoglobin? How do they work?
The sequential: the subunits can be relaxed or tense, relaxed has oxygen bound. When one becomes relaxed it causes a shape change in the two neighbouring which makes taking up oxygen easier, the same occurs backwards, one becoming tense causes a shape change which makes the others more able to lose oxygen.
Concerted: All subunits exist in an equilibrium of two states, as more oxygens bind the relaxed state becomes more favored, causing oxygen to become easier to bind. This is the model that haemoglobin is considered to follow.
