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BMSC 200 > Chapter 5 + Quiz Question > Flashcards

Chapter 5 + Quiz Question Flashcards

1
Q

Many proteins undergo ____ interactions with other molecules

A

reversible

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2
Q

What is a ligand?

A

A molecule reversibly bound by the protein. It can be any kind of molecule, even another protein

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3
Q

What is a binding site?

A

A specific site on the protein that a ligand bonds to

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4
Q

The binding site is usually complimentary to the ligand in terms of ?

A

Shape, charge, hydrophobicity, hydrogen bonding potential

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5
Q

True or False: a given protein can only have one binding site?

A

False, they may have multiple binding sites for multiple ligands

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6
Q

What are the ligands for hemoglobin?

A

Oxygen and 2,3-biphosphoglycerate (2,3 BPG)

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7
Q

The binding of a ligand may cause a conformation change in the protein, what is this called?

A

Induced fit

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8
Q

Can an induced fit cause a change in the properties/structure of a protein?

A

Yes

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9
Q

What is myoglobin (Mb)?

A

Monomeric protein that facilitates oxygen storage in peripheral tissue

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10
Q

What is hemoglobin (Hb)?

A

Tetrameric protein found in red blood cells that transports oxygen from lungs to the periphery

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11
Q

True or False: oxygen is poorly soluble in aqueous situations?

A

True

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12
Q

The emergence of larger, multi-cellular organisms depended on what?

A

The evolution of proteins that could transport and store oxygen

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13
Q

How is oxygen a limiting factor for life?

A

The amount of available oxygen which can be delivered within the organism can limit its size

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14
Q

Cellular iron is bound in forms that..?

A

Make it less reactive/sequester it

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15
Q

What is Heme?

A

Consists of a protoporphyrin ring system bound to a single iron (Fe 2+) atom

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16
Q

The ring system provides ___ coordinating interactions with the iron atom

A

4

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17
Q

Why is nitrogen so crucial to this ring system surrounding the iron atom?

A

The electron-donating characteristic of nitrogen prevents the conversion of Fe^2+ to Fe^3+

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18
Q

True or False: only myoglobin uses heme

A

False, both myoglobin and hemoglobin

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19
Q

How is heme bound?

A

With discrete pockets of myoglobin and hemoglobin

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20
Q

Fe^2+ seeks six coordinating interactions, what are they?

A

The first four come from heme
The fifth comes from an imidazole group of a proximal histidine residue
The sixth is for O2 binding

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21
Q

What does distal histidine provide stability for?

A

Provides a stabilizing interaction for bound O2

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22
Q

Carbon monoxide has a similar molecular structure as oxygen. Why is this so dangerous?

A

CO exerts its deadly effects by competing with O2 for binding to heme. CO binds to heme with x200 greater affinity than O2

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23
Q

Compare and Contrast Myoglobin to Hemoglobin

A

Myoglobin: single sub-unit, tertiary, single heme group, bind one oxygen molecule
Hemoglobin: four sub-units, quaternary, each sub-unit resembles myoglobin

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24
Q

Which has a higher affinity for oxygen, myoglobin or hemoglobin?

A

Myoglobin

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25
Q

Describe the appearance of myoglobin and hemoglobin on a graph

A

Myoglobin has a hyperbolic curve of oxygen binding
Binding of O2 by hemoglobin is a sigmoidal curve (S curve)

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26
Q

What does the hyperbolic curve indicate?

A

Indicates a single O2 binding constant

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27
Q

What does the sigmoidal behavior imply about the bonding of oxygen by hemoglobin?

A

It indicates cooperativity of oxygen binding, meaning that the more oxygen is bound, the easier it becomes to bind more

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28
Q

What consists a myoglobin?

A
  1. A single polypeptide of 153 residues arranged in eight α-helices
  2. A heme (iron porphyrin) prosthetic group
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29
Q

The amount of O2 required to half saturate the protein is quantified by ___

A

P50

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30
Q

What is the P50 of myoglobin?

A

3 torr

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31
Q

What is the P50 of hemoglobin?

A

30 torr

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32
Q

The fraction of myoglobin saturated with oxygen at a given partial pressure of oxygen is calculated by?

A

θ= [pO2] / ([pO2] + [P50])

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33
Q

Example: in peripheral tissues, the partial pressure of O2 is around 20 torr, what is the fraction saturation?

A

θ = 20 / (20 + 3) = 87% saturation

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34
Q

True or False: myoglobin has a very high affinity for oxygen and is normally nearly saturated with oxygen everywhere in the body?

A

True

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35
Q

Where is hemoglobin contained?

A

In erythrocytes (red blood cells)

36
Q

Hemoglobin is an ____ ____ whose oxygen affinity is regulated through various physiological signals

A

allosteric protein

37
Q

Allosteric proteins have two forms, what are they?

A

T (inactive) and R (active)

38
Q

These T and R forms are in rapid ____

A

equilibrium

39
Q

What is the T form for hemoglobin?

A

Deoxyhemoglobin

40
Q

What is the R form for hemoglobin?

A

Oxyhemoglobin

41
Q

A protein that binds O2 with high and constant affinity would..?

A

Saturate effectively with O2 in the lungs but not release it to tissues

42
Q

A protein with a lower O2 affinity would be able to..?

A

Release O2 to tissues would not have sufficient affinity to saturate in the lungs

43
Q

True or False: hemoglobin can undergo transitions from high and low transition states?

A

True

44
Q

Can proteins with a single ligand-binding site like myoglobin achieve this cooperate effect by going to and from transition states?

A

No

45
Q

What is an allosteric effector (modulator)?

A

They bond allosteric proteins at specific sites

46
Q

Are allosteric effectors activators or inhibitors?

A

They can be one or the other.

47
Q

Allosteric activators stabilize the __ state; allosteric inhibitors stabilize the __ state

A

R, T

48
Q

What is homotropic?

A

When the normal ligand and modulator are the same

49
Q

What is heterotropic?

A

When the modulator is different from the normal ligand

50
Q

The binding and release of O2 from Hb are _____ regulated

A

allosterically

51
Q

O2 is a ____ _____ ____ of hemoglobin

A

homotropic allosteric activator

52
Q

O2 binding promotes and stabilizes the __ state of hemoglobin which has a higher O2 affinity than the __ state

A

R, T

53
Q

With T state hemoglobin, the iron atom is where?

A

Just outside the plane of the heme ring

54
Q

With transition to the R state, the iron moves where? What does the movement cause?

A

Into the plane of the ring. This movement causes structural changes that are translated to the quaternary structure

55
Q

The P50 of hemoglobin closely matches the ___ ___of O2 found in periphery.

A

partial pressures

56
Q

Hb is most sensitive for O2 release at the partial pressures of O2 found in the periphery. What does this allow for Hb?

A

To sense and respond to changes in O2 levels in regions at greatest risk for hypoxia

57
Q

2,3 Bisphosphoglycerate is a ____ ____ ____ of hemoglobin

A

heterotropic allosteric inhibitor

58
Q

Initial investigations with highly purified hemoglobin indicated an extremely ___ for oxygen. What does this limit?

A

High. Limit the ability of the protein to release oxygen to the periphery

59
Q

By replacing various components of blood revealed that 2, 3 biphosphoglycerate ____ hemoglobin’s affinity for oxygen

A

decreased

60
Q

How many units of negative charge does 2,3 BPG carry?

A

5

61
Q

The pocket formed at the interface between the subunits of deoxyhemoglobin contains how many positively charged residues?

A

6

62
Q

How does a fetus “breathe?”

A

It strips O2 away from the maternal blood.

63
Q

Which Hb has the higher oxygen affinity, fetal or adult?

A

Fetal

64
Q

How does the fetal Hb have a higher O2 affinity?

A

Adult Hb has six (+) residues at the 2,3BPG binding site, fetal Hb has four, so the Decreased affinity for 2,3 BPG translates into
higher O2 affinity for fetal Hb

65
Q

Adaptation to high altitude can rapidly occur through ____ production of 2,3 BPG

A

increased

66
Q

___ 2,3 BPG ____ Hb’s O2
affinity to ensure sufficient O2 delivery to
the periphery

A

Increased, decreases

67
Q

What is the Bohr effect?

A

Describes the pH dependence of hemoglobin’s affinity of O2

68
Q

At ___ pH hemoglobin has a lower affinity for O2

A

decreased

69
Q

Active tissues have lower pH due to..?

A

Increased production of CO2. And CO2 eventually decreases pH

70
Q

What is the point of the Bohr effect?

A

Coordinate an increased release of oxygen to active tissues

71
Q

There are two primary challenges to cellular respiration and metabolism:

A
  1. Delivering sufficient O2 to tissues
  2. Removing CO2 from the periphery
72
Q

What is the first of the mechanisms for coordination of O2 delivery and CO2 removal?

A

CO2 is taken into the red blood cells and converted to bicarbonate and a proton by the enzyme carbonic anhydrase. Through this reaction:
1. CO2 is converted into a soluble form for transport to the lungs
2. The decreased pH decreases hemoglobin’s O2 affinity to promote O2 release to active tissues

73
Q

What is the second of the mechanisms for coordination of O2 delivery and CO2 removal?

A

CO2 can form a covalent carbamate linkage to the N terminus of each chain of hemoglobin chain to form carbaminohemoglobin. This reaction has three important outcomes.

74
Q

What are the three important outcomes when it comes to the second of the mechanisms for coordination of O2 delivery and CO2 removal?

A
  1. Converts CO2 into a more soluble form to assist in its transport to the lungs
  2. Carbamino hemoglobin has a lower O2 affinity than hemoglobin to promote O2 release
  3. The released proton promotes O2 release through the Bohr effect
75
Q

How does sickle cell anemia develop?

A

Results from a single amino acid change. The formation of fibers from the deoxy forms of HbS.

76
Q

Where do the fibers form in sickle cell anemia and how is this disastrous?

A

The fibers tend to form in the capillaries where the O2 concentration is the lowest, which blocked blood flow to the extremities of the body

77
Q

True or False: do people with sickle cell anemia also have a resistance/immunity to malaria? How is this possible?

A

True, because it changes the shape of the cell, causing the body to destroy the cell, with the disease inside.

78
Q

What is an alternative to hemoglobin in nature?

A

Hemocyanin

79
Q

How is hemocyanin distinct from hemoglobin?

A

It uses copper, which makes blood blue and not red.
The copper atoms bind a single oxygen molecule.
There is no heme ring group
Hemocyanin is not localized within specialized oxygen-transport cells

80
Q

Lists the following proteins from highest to lowest oxygen affinity: adult hemoglobin, fetal hemoglobin, myoglobin

A

Myoglobin, fetal hemoglobin, adult hemoglobin

81
Q

The oxygen saturation curves of hemoglobin and myoglobin differ in that..?

A

hemoglobin’s curve is sigmoidal and further from the y axis

82
Q

Calculate the fraction saturation of myoglobin when the partial pressure of oxygen is 50 torr. Assume the p50 of myoglobin is 3 torr

A

94.3%

83
Q

Relative to adult hemoglobin, fetal hemoglobin has a ______ affinity for oxygen because it has a ______ affinity for 2,3 bisphosphoglycerate

A

Higher, lower

84
Q

Oxygen serves as a _____ of hemoglobin

A

homotropic allosteric activator

85
Q

True or False: sickle cell fibers form from R state hemoglobin?

A

False

86
Q

Calculate the fraction saturation of myoglobin when the partial pressure of oxygen is 25 torr. Assume the p50 of myoglobin is 3 torr

A

89%

87
Q

2,3 Bis phosphoglycerate serves as a ____ of hemoglobin

A

hetrotropic allosteric inhibitor

BMSC 200 (11 decks)

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