Ch. 6 Flashcards
What are the structural differences between myoglobin & hemoglobin?
- Myoglobin: single polypeptide chain with 1 heme group
- Hemoglobin: 4 polypeptides with 2 alpha and 2 beta subunits
What is fractional saturation?
The fraction of protein binding sites that are occupied
What is the formula for fractional saturation?
[protein-ligand complex]/[protein-ligand complex]+[protein]
What is the Bohr effect?
pH and CO2 dependence of oxygen binding
Where is 2,3-bisphosphoglycerate?
RBCs
What does 2,3-bisphosphoglycerate do?
Traps hemoglobin the the T state and acts as a negative effector
Where are positive regulators graphed?
To the left
How does 2,3-BPG affect oxygen binding?
Binding of 2,3-BPG to a secondary site inhibits binding of O2 to the primary sites
Where does 2,3-bisphosphoglycerate bind?
Between the 2 beta subunits
Why does 2,3-BPG prefer to bind to the T state of Hb?
R state of Hb has a smaller central cavity
What stabilizes the binding of 2,3-BPG to the beta subunits?
Ionic interactions between 2,3-BPG and 3 positively charges residues on each beta subunit
What is the effect of amino acid differences between adult and fetal hemoglobin?
- Reduces the affinity of 2,3-BPG for the α2γ2 complex (fetus) compared to its affinity for the normal adult α2β2 complex
- Decrease in 2,3-BPG affinity facilitates transfer of O2 from the mom’s Hb to the fetal Hb because fetal Hb can get more O2 if more Hb molecules are in the R-state (high-affinity)
List membrane proteins.
- Membrane receptor proteins
- Membrane-bound metabolic enzymes
- Membrane transport proteins
What do membrane receptor proteins do?
Signal transduction
What do membrane-bound metabolic enzymes do?
Involved in redox reactions and ATP synthesis
Whta do membrane transport proteins do?
Facilitate the movement of polar molecules across the hydrophobic membrane
What are the types of transport/transporters?
Passive and active
What are the shapes of transport graphs?
- Linear (simple diffusion and facilitated diffusion through a CHANNEL)
- Hyperbolic (facilitated diffusion through a CARRIER and active transport through a carrier)
How do you calculate free energy of transport?
What is the structure and function of aquaporins?
- Tetrameric protein complexes
- Transport water molecules across a hydrophobic membrane
What is primary active transport?
Uses the hydrolysis of ATP to drive molecules across membranes against their concentration gradient
What is secondary active transport?
Uses the energy available from a downhill electrochemical gradient for one molecule to co-transport a second molecule against an uphill electrochemical gradient
What is an ATP pump?
- Na+/K+ pump
- Exports Na+
- Imports K+
- Energy from ATP hydrolysis causes a conformational change in the protein that allows it to mediate Na+ and K+ transport against their concentration gradients
What is an ATP binding cassette?
An active membrane transport protein that uses energy from ATP hydrolysis to drive large conformational changes and pump molecules across the membrane
How do you use hydropathy plots to predict which portions of a protein cross a membrane?
- Plot delta G against residue number
- Positive delta G: hydrophobic
- Negative delta G: hydrophilic
Practice question: The heme group attached for myoglobin and hemoglobin provides 4 nitrogen atoms that are bond to iron. What are the other 2 atoms that bind to iron?
Proximal histidine and oxygen
Practice question: What 2 molecules are involved in the Bohr effect and hemoglobin?
CO2 and protons
Practice question: What describes the structure of hemoglobin?
All alpha helices with quaternary level of structure
Practice question: What is moved into the plane of the heme ring when oxygen binds?
Fe
Practice question: The fetal hemoglobin saturation curve would be ___.
In between the myoglobin binding curve and the adult hemoglobin curve
