chapter 5 Flashcards
what three things can a ligand be?
regulators of protein function, antigens, important substances that need to be transported or stored.
what molecules are bound to a protein and do not chemically modify the protein?
ligands
What two things can a substrate be?
precursors, fuel
what molecules are used in catalysis
substrates
molecules that are bound to a protein and are chemically modified (the protein is not modified just the thing bound to it).
substrate
magnitude of strong binding versus weak binding
strong= Kd less than 10 micrometers
weak= Kd greater than 10 micrometers
two important functions of globins
oxygen transport and oxygen storage
in order for globins to bind oxygen, they require what?
a heme prosthetic group
heme and hemoglobin composition
heme is composed of a complex organic ring. iron is coordinated by heme and two amino acid residues from the globin.
what does the globin prevent from happening to the iron atom
it prevents the oxidation of the iron to move from Fe2+ to Fe3+
myoglobin structure (5 things)
- a single polypeptide chain folding into 8 alpha helixes.
- Globular
-one heme prosthetic group - oxygen storage
-can bind CO, NO, H, S
P50
the partial pressure of oxygen at which half of the binding sites are occupied by the ligand (O2). It is also a measure of affinity for the ligand.
P50 for myoglobin
1.95 or 0.26 kPa
Kd value and affinity relationship
low Kd= high affinity
globins require what in order to bind oxygen
a prosthetic group (heme)
proximal histidine names
His 93, His F8 in myoglobin
distal histidine names
His 64, His E7 in myoglobin
reversible binding of a protein to a ligand
P+Lāā> PL
Ka
association constant, describes relationship between the complex and unbound components of the complex
Ka and Kd relationship
Kd= 1/Ka
when [L]=Kd
half of the binding sites are occupied
how to find Kd on a graph
x value for when fractional saturation is 0.5
low affinity state of hemoglobin
T state
why does the first O2 molecule to bind to hemoglobin bind weakly
because the first one to bind binds to hemoglobin as it is in the T state, where affinity is lower. However, the binding of this first O2 molecule triggers the conformational change from T state to R state.
