Chapter 5 Flashcards
For myoglobin and hemoglobin, which ones the storage of oxygen and which ones the delivery?
Hemoglobin= delivery Myoglobin= storage
What is a protein ligand?
What is oxygen a ligand for?
The molecule which is reversible bound by the protein
Can be any kind of molecule
In enzymes the ligand is called the substrate
Oxygen is a ligand for myoglobin and hemoglobin
Where does a ligand bond on a protein?
The binding site
This is complimentary in size and shape to the ligand
What other ligand does hemoglobin have besides oxygen?
2,3 bisphosphoglycerate
2,3 BPG
What effects of an induced fit of a ligand to a protein cause?
Can change the properties of the protein and therefore a new function
Change in structure->change in function
What is myoglobin?
Monomeric protein that facilitates oxygen storage in peripheral tissue Binary event Can take oxygen from hemoglobin Has high affinity for oxygen Example of tertiary structure
What is hemoglobin?
Tetrametric protein found in erythrocytes that transports oxygen from lungs to the periphery
4 subunits that oxygen can bind to (subunits structurally similar to myoglobin)
Example of quaternary structure
What limits the size of organisms?
The amount of available (or usable) oxygen
Insects grown in the presence of elevated oxygen often achieve greater sizes
BUT as you get bigger, it’s harder to maintain oxygen transport system
What are heme oxygen-binding groups?
A protoporphyrin ring system bound to a single (Fe2+) iron atom
Fe2+ binds oxygen reversible while Fe3+ does not
Provides four coordinating interactions with the iron atom
What proteins use the heme oxygen-binding group?
Myoglobin and hemoglobin
Hemoglobin is essentially 4 myoglobin stuck together (essentially)
How many coordinating interactions does Fe2+ seek?
What are they?
Seeks 6 coordinating interactions
- 4 come from interactions with four groups of heme ring
- 5th comes from imidazole group of proximal histidine
- 6th is for O2 binding
Why is carbon monoxide dangerous?
It has similar molecular structures as oxygen
Competes with oxygen for binding to heme
CO bonds with 200 times greater affinity than O2
What was the first protein structure to be determined through x Ray crystallography?
Sperm whale myoglobin was the first since it is a rich source of myoglobin that can hold for long periods of time
What is the structure of myoglobin?
A single polypeptide of 153 residues arranges in eight α-helices
And a heme prosthetic group
Picture in lecture 5 just under halfway
What an oxygen-saturation curve?
A graph of the decimal percent saturation with oxygen (Y) over the partial pressure of oxygen (pO2) in torr
Look at myoglobin and hemoglobin saturation curves in lecture 5 at halfway point
What is the P50 mark on a oxygen saturation curve?
The amount of O2 required to half saturate the protein
P50 of myoglobin is 3 torr
What is the equation used to calculate the fraction of myoglobin saturated with oxygen at a given partial pressure of oxygen?
θ= [pO2] / ([PO2] + [P50])
Examples on lecture 5 mid way point
What does myoglobins high affinity for oxygen mean for its saturation with oxygen everywhere in the body?
High affinity for oxygen= nearly completely saturated with oxygen everywhere within the body under normal circumstances
What does allosteric mean?
What is an allosteric protein?
Greek word for other shape
Allosteric proteins have Active (R state) and inactive (T state) forms that are in rapid equilibrium
What are allosteric effectors?
Modulators
They bind to allosteric proteins at sites separate from the functional binding site
Can be activators or inhibitors
What do allosteric activators do compares to allosteric inhibitors?
Activators- stabilize R state
Inhibitors- stabilize T state
What is a homotropic interaction compared to a heterotropic?
Homotropic- when normal ligand and modulator are the same
Heterotropic- when the modulator is different from the normal ligand
What’s the difference in tissue and lung saturation with a protein that binds O2 with high and constant affinity compared to a protein that binds O2 with a lower affinity?
How does hemoglobin fix this?
High O2 affinity- saturate effectively with O2 in lungs but not release it to the tissue
Low O2 affinity- would be able to release O2 to the tissues but not have sufficient affinity to saturate the lungs
Hemoglobin fixes by undergoing transition from a low affinity state to a high affinity state
Look at graph just over halfway of lecture 5
What is the homotropic allosteric activator of hemoglobin?
How does it work?
O2 is
Example:
The four subunits of hemoglobin are in the T state then when one O2 binds to a T is changes it to R state and eventually all four subunits have O2’s on them and are all turned into R state
Diagram on lecture 5 just over half
