Quiz 7

Question 1

myoglobin

Answer 1

with its single heme prosthetic group, exhibits a hyperbolic O2 binding curve

Question 2

hemoglobin can adopt

Answer 2

the deoxyribose (T) or oxy (R) conformation, which differ in O2 binding ability

Question 3

Hemoglobin (Hb) and myoglobin (Mb)

Answer 3

are oxygen-transport and oxygen-storage proteins

Question 4

Mb is

Answer 4

monomeric

Question 5

Hb is

Answer 5

tetrameric
- it is formed by a dimer of a B dimers

Question 6

Hb has

Answer 6

2 alpha chains of 141 residues, 2 Beta chains of 146 residues

Question 7

iron interacts with

Answer 7

six ligans in Hb and Mb

Question 8

four of these are the

Answer 8

N atoms of the heme porphyrin

Question 9

a fifth ligand

Answer 9

is donated by the imidazole side chain of amino acid residue His F8

Question 10

His F8

Answer 10

this residue is on the sixth or “F” helix, and it is the 8th residue in the helix

Question 11

When Mb or Hb bind oxygen,

Answer 11

the O2 molecule, itself, binds to the heme iron, as the sixth ligand.

Question 12

bound O2 molecule is

Answer 12

tilted relative to a perpendicular line to the heme plane

Question 13

Fe in Mb is

Answer 13

Fe2+, Fe(II)- ferrous iron- the form that binds oxygen

Question 14

mb with ferric iron Fe2+ is called

Answer 14

metmyoglobin and does not bind to oxygen

Question 15

when oxygen bind to Fe2+ in heme of mb,

Answer 15

the heme fe2+ is drawn toward the plane of the porphyrin ring

Question 16

for Mb, this small change has a little consequence

Answer 16

but a similar change in Hb initiates a series of conformational changes that are transmitted to adjacent subunits: very consequential

Question 17

Mb, an

Answer 17

oxygen-storage protein, has a greater affinity for oxygen at all oxygen pressures

Question 18

Hb becomes saturated with

Answer 18

O2 in the lungs, where the partial pressure of pO2 is high about 100 torr

Question 19

in capillaries pO2 is

Answer 19

low, about 40 torr, and oxygen is released from Hb

Question 20

the binding of O2 to Hb

Answer 20

is cooperative, binding of oxygen to the first subunit is tough, but it makes binding to the other subunits more favorable: cooperatively

Question 21

oxygen binding pulls the

Answer 21

Fe2+ into the heme plane

Question 22

as fe2+ moves,

Answer 22

it drags His F8 and the F helix with it

Question 23

this change is transmitted to the subunit interfaces, where the conformation changes leads to the

Answer 23

rupture of salt bridges between polypeptide subunits

Question 24

changes occur at the

Answer 24

4th level, leading to conformational change

Question 25

Hb must be able to

Answer 25

release oxygen in capillaries

Question 26

bohr effect

Answer 26

explains the connection between CO2, H+ and conversion oxy-Hb(R) to deoxy-Hb(T)

Question 27

thus as pH decreases

Answer 27

dissociation of O2 from hemoglobin is enhanced

Question 28

binding of protons,

Answer 28

H+ diminishes oxygen binding on Hb

Question 29

as the tissue-capillary interface, CO2 hydration

Answer 29

and glycolysis produces extra H+, promoting addition disassociation of O2 where it is needed most [tissues]

Question 30

at the lung-artery interface, the reverse reaction,

Answer 30

bicarbonate dehydration [required for CO2 exhalation] consumes extra H+, promoting CO2 release and O2 binding

Question 31

2,3 -BPG

Answer 31

an allosteric effector of hemoglobin

Question 32

the sigmoid binding curve, which reflects high sensitivity for O2 binding and release,

Answer 32

is only observed in the presence of 2,3 BPG

Question 33

since 2,3 BPG binds at a site distant from the F2+ where oxygen binds, it is called an

Answer 33

allosteric effector

Question 34

in the absence of 2,3 BPG

Answer 34

oxygen binding to Hb would have a hyperbolic curve like Mb

Question 35

where does 2,3-BPG bind?

Answer 35

• “inside”
• one molecule binds, in the central cavity formed by the four subunits

Question 36

what is special about 2,3 BPG?

Answer 36

negative charges interact with 8 positive charges in the cavity

Question 37

fetal Hb(Hb F)

Answer 37

has lower affinity for 2,3-BPG and higher affinity for oxygen, so it can take oxygen from mothers Adult Hb (Hb A)

Question 38

the ionic binding 2,3 BPG to the two

Answer 38

B subunits of Hb

Question 39

gas exchange takes place across the

Answer 39

placenta

Question 40

fetal Hb(Hb F) differs from adult Hb

Answer 40

• with y chains in place of B chains and this an a2y2 structure

Question 41

Why does fetal Hb (Hb F) bind O2 more tightly than Adult Hb (Hb A)?

Answer 41

1. Fetal γ-chains have Ser instead of His at position 143 and thus lack two of the positive charges that stabilize BPG binding.
2. As a result, Hb F has a higher affinity for O2

Question 42

sickle-cell anemia patients

Answer 42

have abnormally shaped red blood cells

Question 43

the cause is a single amino acid substitution in the

Answer 43

B chains of hb Glucoses at position 6 of the B-chains is replaced by val

Question 44

as a result, Hb S molecules

Answer 44

aggregate into long, chainlike polymeric structures that poke the erythrocyte membrane into a sickle shape

Question 45

the polymerization of Hb S molecules arises because

Answer 45

val replaces glu on the surface of B chains

Question 46

these can insert into

Answer 46

hydrophobic pockets in neighboring deoxy Hb S molecules