Ch. 6

Question 1

What are the structural differences between myoglobin & hemoglobin?

Answer 1

• Myoglobin: single polypeptide chain with 1 heme group
• Hemoglobin: 4 polypeptides with 2 alpha and 2 beta subunits

Question 2

What is fractional saturation?

Answer 2

The fraction of protein binding sites that are occupied

Question 3

What is the formula for fractional saturation?

Answer 3

[protein-ligand complex]/[protein-ligand complex]+[protein]

Question 4

What is the Bohr effect?

Answer 4

pH and CO2 dependence of oxygen binding

Question 5

Where is 2,3-bisphosphoglycerate?

Answer 5

RBCs

Question 6

What does 2,3-bisphosphoglycerate do?

Answer 6

Traps hemoglobin the the T state and acts as a negative effector

Question 7

Where are positive regulators graphed?

Answer 7

To the left

Question 8

How does 2,3-BPG affect oxygen binding?

Answer 8

Binding of 2,3-BPG to a secondary site inhibits binding of O2 to the primary sites

Question 9

Where does 2,3-bisphosphoglycerate bind?

Answer 9

Between the 2 beta subunits

Question 10

Why does 2,3-BPG prefer to bind to the T state of Hb?

Answer 10

R state of Hb has a smaller central cavity

Question 11

What stabilizes the binding of 2,3-BPG to the beta subunits?

Answer 11

Ionic interactions between 2,3-BPG and 3 positively charges residues on each beta subunit

Question 12

What is the effect of amino acid differences between adult and fetal hemoglobin?

Answer 12

• 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)

Question 13

List membrane proteins.

Answer 13

• Membrane receptor proteins
• Membrane-bound metabolic enzymes
• Membrane transport proteins

Question 14

What do membrane receptor proteins do?

Answer 14

Signal transduction

Question 15

What do membrane-bound metabolic enzymes do?

Answer 15

Involved in redox reactions and ATP synthesis

Question 16

Whta do membrane transport proteins do?

Answer 16

Facilitate the movement of polar molecules across the hydrophobic membrane

Question 17

What are the types of transport/transporters?

Answer 17

Passive and active

Question 18

What are the shapes of transport graphs?

Answer 18

• Linear (simple diffusion and facilitated diffusion through a CHANNEL)
• Hyperbolic (facilitated diffusion through a CARRIER and active transport through a carrier)

Question 19

How do you calculate free energy of transport?

Answer 19

Question 20

What is the structure and function of aquaporins?

Answer 20

• Tetrameric protein complexes
• Transport water molecules across a hydrophobic membrane

Question 21

What is primary active transport?

Answer 21

Uses the hydrolysis of ATP to drive molecules across membranes against their concentration gradient

Question 22

What is secondary active transport?

Answer 22

Uses the energy available from a downhill electrochemical gradient for one molecule to co-transport a second molecule against an uphill electrochemical gradient

Question 23

What is an ATP pump?

Answer 23

• 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

Question 24

What is an ATP binding cassette?

Answer 24

An active membrane transport protein that uses energy from ATP hydrolysis to drive large conformational changes and pump molecules across the membrane

Question 25

How do you use hydropathy plots to predict which portions of a protein cross a membrane?

Answer 25

- Plot delta G against residue number - Positive delta G: hydrophobic - Negative delta G: hydrophilic

Question 26

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?

Answer 26

Proximal histidine and oxygen

Question 27

Practice question: What 2 molecules are involved in the Bohr effect and hemoglobin?

Answer 27

CO2 and protons

Question 28

Practice question: What describes the structure of hemoglobin?

Answer 28

All alpha helices with quaternary level of structure

Question 29

Practice question: What is moved into the plane of the heme ring when oxygen binds?

Answer 29

Fe

Question 30

Practice question: The fetal hemoglobin saturation curve would be ___.

Answer 30

In between the myoglobin binding curve and the adult hemoglobin curve