Protein Function

Question 1

How many subunits in hemoglobin

Answer 1

four (oligomer)

Question 2

Function of myoglobin?

Answer 2

Reserve of O2 during intense exercise

Question 3

Where does the proximal histidine (His 93) bind to the heme group

Answer 3

5th coordinate position

Question 4

How is the porphyrin ring held in place (with myoglobin)

Answer 4

Hydrophobic interactions AND coordination bond between Fe and proximal histidine (His F8)

Question 5

Where does O2 bind to the heme group

Answer 5

6th coordinate position of Fe

Question 6

Which histidine assists in O2 binding to heme

Answer 6

Distal histidine (His E7/64)

Question 7

What is the point of heme being attached to globin

Answer 7

Increases specificity and affinity for O2, CO binds with less affinity

Question 8

What kind of plot is used to represent O2 binding to myoglobin

Answer 8

Hyperbolic plot

Question 9

What kind of subunits does Hemoglobin have

Answer 9

Two alpha and two beta chains

Question 10

How are myoglobin, beta-globin and alpha-globin similar?

Answer 10

Each have 8 alpha helices with heme binding pockets, they bind O2 in the same manner as myoglobin

Question 11

What kind of affinity is indicated by a hyperbolic curve

Answer 11

Constant (monomers)

Question 12

Function of myoglobin vs hemoglobin

Answer 12

Mb: transport/store O2 within tissue
Hb: transport O2 from lungs to tissue

Question 13

What is hemoglobin tense state?

Answer 13

Low affinity for O2 (deoxy Hb, large central cavity)

Question 14

What is homoallostery

Answer 14

Binding of effector affects further binding of same compound (usually ligand increases its own affinity; sigmoidal curve)

Question 15

What is heteroallostery

Answer 15

Binding of effector affects further binding of different compound (either activators or inhibitors)

Question 16

When is the iron atom lowered from the heme groups plane?

Answer 16

In the T state (with no O2 bound)

Question 17

What happens when O2 binds

Answer 17

Fe moves into plane, His F8 moves with it. O2 binding site becomes high affinity (O2 binds more readily to R state)

Question 18

Which Hb effectors are negative effects on O2 binding

Answer 18

H+, CO2 and BPG favour the T state (O2 favours R state)

Question 19

What does 2,3-bisphosphoglycerate do in Hb

Answer 19

Stabilizes the T state

Question 20

What does CO2 do as an allosteric effector

Answer 20

Acts directly and indirectly to stabilize the T state (favours T state)

Question 21

What does H+ do in Hb

Answer 21

Lowers pH therefore protonates side chains (His–>His+, NH2–> NH3+). Once His is protonated this enhances BPG binding and reduces O2 binding
BOHR EFFECT

Question 22

When is the R state favoured

Answer 22

At high pp O2 and relatively high pH

Question 23

When is the T state favoured

Answer 23

At high [H+] and high CO2 and low pp O2

Question 24

What are the roles of His residues in Hb

Answer 24

His F8 (prox) = attachment of heme
His E7 (distal) = assist O2 binding, decrease affinity of CO
4 His in central cavity = BPG binding