Chapter 7: Protein Function Flashcards
The functions of proteins are determined by the reversible binding of molecules called?
ligands
Ligands
can be any molecule including another protein that binds to another molecule
*binds to the binding site on a protein
Bind and chemically transform other molecules-they catalyze reactions
Enzyme
Induced Fit
Protein structure typically changes upon binding to a ligand
What do enzymes bind to?
Substrates in a catalytic site or active site.
Why can’t oxygen travel through the body without a protein?
Doesn’t dissolve in aqueous solutions easily and cannot diffuse through tissues easily.
Fe and O2 alone would damage our DNA, so it is sequestered in a protein to make it less reactive…the protein-bound prosthetic group heme is born!
Fax
Heme consists of?
a.) complex organic ring structure
b.) protoporphyrin IX (porphoryin)
c.) bound iron atom in its ferrous (Fe+2) state
Which iron state can bind O2?
Fe+2 binds O2 reversibly, Fe+3 cannot bind O2
Myoglobin is made up of -
a.) 1 polypeptide chain
b.) 1 heme group
c.) capacity to bind and release their ligands
PRIMARILY FOUND IN MUSCLE TISSUE
How does Ka play a role in protein-ligand interactions?
Provides a measure of the affinity of the ligand L for the protein.
HIgher Ka = stronger affinity for L and. protein
What does a small Kd value mean?
The protein binds TIGHTER to its ligand.
What is Kd representing?
The state of the protein when half of the ligand binding sites are occupied. Used to describe strength of protein’s ability to bind its ligand.
Theta θ means…
a.) fraction of binding sites occupied by ligand
Kd = θ = 0.5
What does x represent?
Greator affinity for ligand, binds tighter than protein Y
t/f
Carbon monoxide will outcompete Oxygen all the time
TRUE
What else effects how ligands bind?
The protein function, and its steric effects
Erythrocytes
Red blood cells, does not contain nucleus
Hemoglobin
a.) Contained within erythrocytes
b.) Transports oxygen throughout our blood supply
c.) Takes O2 from lungs and carries it to all the extremities
d.) 4 subunits (2 alpha and 2 beta)
e.) Beta subunit is very similar to structure of myoglobin
What bonds play a role in the quarternary structure of hemoglobin?
Hydrophobic interactions
Hydrogen Bonds
Salt bridges
What are the 2 conformations of hemoglobin?
R and T states
Talk about R state (relaxed) of Hemoglobin
a.) Binds oxygen more easily than T state
b.) Binding of oxygen causes heme to assume a more planar conformation
Talk about T state (tense) of Hemoglobin.
a.) More stable than R state
b.) Called deoxyhemoglobin, stabilized by the greater number of ion pairs
c.) When bound to O2, conformation is changed to R state
What is the high affinity state of hemoglobin (sigmodial)?
When multiple O2 molecules are bound
*only occurs with multi-subunit proteins
A sigmodial curve represents:
proteins binds to multiple ligand
t/f
affinity of hemoglobin should drop as it travels through peripheral tissue
true
Allosteric proteins
binding of one ligand affects the binding properties of another site on the same protein
Can interconvert more-active and less-active forms of the protein
Modulator
When the ligand and modulator are the same, it is called
homotropic
ex. O2
When the ligand the modulator are different, it is called
heterotrophic
concerted model (interconversion of inactive and active forms of a protein during cooperative ligand binding)
This model is based on the assumption that the subunits of a cooperatively binding protein are functionally identical, that each subunit can exist in two confirmations and the all subunits undergo the transition from one conformation to the other simultaneously.
Structure of Immunoglobulin G
- 2x anti-binding site
- Papain cleavage sites (Fc) (links it all together)
Process of IgG and macrophage phagocytosis?
Fc region binf to Fc receptors on macrophage surface, truggering macrophage to eat and destroy virus.
