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BMSC 200 > Chapter 5 + Quiz Question > Flashcards

Chapter 5 + Quiz Question Flashcards

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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
Describe the appearance of myoglobin and hemoglobin on a graph
Myoglobin has a hyperbolic curve of oxygen binding Binding of O2 by hemoglobin is a sigmoidal curve (S curve)
26
What does the hyperbolic curve indicate?
Indicates a single O2 binding constant
27
What does the sigmoidal behavior imply about the bonding of oxygen by hemoglobin?
It indicates cooperativity of oxygen binding, meaning that the more oxygen is bound, the easier it becomes to bind more
28
What consists a myoglobin?
1. A single polypeptide of 153 residues arranged in eight α-helices 2. A heme (iron porphyrin) prosthetic group
29
The amount of O2 required to half saturate the protein is quantified by ___
P50
30
What is the P50 of myoglobin?
3 torr
31
What is the P50 of hemoglobin?
30 torr
32
The fraction of myoglobin saturated with oxygen at a given partial pressure of oxygen is calculated by?
θ= [pO2] / ([pO2] + [P50])
33
Example: in peripheral tissues, the partial pressure of O2 is around 20 torr, what is the fraction saturation?
θ = 20 / (20 + 3) = 87% saturation
34
True or False: myoglobin has a very high affinity for oxygen and is normally nearly saturated with oxygen everywhere in the body?
True
35
Where is hemoglobin contained?
In erythrocytes (red blood cells)
36
Hemoglobin is an ____ ____ whose oxygen affinity is regulated through various physiological signals
allosteric protein
37
Allosteric proteins have two forms, what are they?
T (inactive) and R (active)
38
These T and R forms are in rapid ____
equilibrium
39
What is the T form for hemoglobin?
Deoxyhemoglobin
40
What is the R form for hemoglobin?
Oxyhemoglobin
41
A protein that binds O2 with high and constant affinity would..?
Saturate effectively with O2 in the lungs but not release it to tissues
42
A protein with a lower O2 affinity would be able to..?
Release O2 to tissues would not have sufficient affinity to saturate in the lungs
43
True or False: hemoglobin can undergo transitions from high and low transition states?
True
44
Can proteins with a single ligand-binding site like myoglobin achieve this cooperate effect by going to and from transition states?
No
45
What is an allosteric effector (modulator)?
They bond allosteric proteins at specific sites
46
Are allosteric effectors activators or inhibitors?
They can be one or the other.
47
Allosteric activators stabilize the __ state; allosteric inhibitors stabilize the __ state
R, T
48
What is homotropic?
When the normal ligand and modulator are the same
49
What is heterotropic?
When the modulator is different from the normal ligand
50
The binding and release of O2 from Hb are _____ regulated
allosterically
51
O2 is a ____ _____ ____ of hemoglobin
homotropic allosteric activator
52
O2 binding promotes and stabilizes the __ state of hemoglobin which has a higher O2 affinity than the __ state
R, T
53
With T state hemoglobin, the iron atom is where?
Just outside the plane of the heme ring
54
With transition to the R state, the iron moves where? What does the movement cause?
Into the plane of the ring. This movement causes structural changes that are translated to the quaternary structure
55
The P50 of hemoglobin closely matches the ___ ___of O2 found in periphery.
partial pressures
56
Hb is most sensitive for O2 release at the partial pressures of O2 found in the periphery. What does this allow for Hb?
To sense and respond to changes in O2 levels in regions at greatest risk for hypoxia
57
2,3 Bisphosphoglycerate is a ____ ____ ____ of hemoglobin
heterotropic allosteric inhibitor
58
Initial investigations with highly purified hemoglobin indicated an extremely ___ for oxygen. What does this limit?
High. Limit the ability of the protein to release oxygen to the periphery
59
By replacing various components of blood revealed that 2, 3 biphosphoglycerate ____ hemoglobin's affinity for oxygen
decreased
60
How many units of negative charge does 2,3 BPG carry?
5
61
The pocket formed at the interface between the subunits of deoxyhemoglobin contains how many positively charged residues?
6
62
How does a fetus "breathe?"
It strips O2 away from the maternal blood.
63
Which Hb has the higher oxygen affinity, fetal or adult?
Fetal
64
How does the fetal Hb have a higher O2 affinity?
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
Adaptation to high altitude can rapidly occur through ____ production of 2,3 BPG
increased
66
___ 2,3 BPG ____ Hb’s O2 affinity to ensure sufficient O2 delivery to the periphery
Increased, decreases
67
What is the Bohr effect?
Describes the pH dependence of hemoglobin's affinity of O2
68
At ___ pH hemoglobin has a lower affinity for O2
decreased
69
Active tissues have lower pH due to..?
Increased production of CO2. And CO2 eventually decreases pH
70
What is the point of the Bohr effect?
Coordinate an increased release of oxygen to active tissues
71
There are two primary challenges to cellular respiration and metabolism:
1. Delivering sufficient O2 to tissues 2. Removing CO2 from the periphery
72
What is the first of the mechanisms for coordination of O2 delivery and CO2 removal?
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
What is the second of the mechanisms for coordination of O2 delivery and CO2 removal?
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
What are the three important outcomes when it comes to the second of the mechanisms for coordination of O2 delivery and CO2 removal?
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
How does sickle cell anemia develop?
Results from a single amino acid change. The formation of fibers from the deoxy forms of HbS.
76
Where do the fibers form in sickle cell anemia and how is this disastrous?
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
True or False: do people with sickle cell anemia also have a resistance/immunity to malaria? How is this possible?
True, because it changes the shape of the cell, causing the body to destroy the cell, with the disease inside.
78
What is an alternative to hemoglobin in nature?
Hemocyanin
79
How is hemocyanin distinct from hemoglobin?
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
Lists the following proteins from highest to lowest oxygen affinity: adult hemoglobin, fetal hemoglobin, myoglobin
Myoglobin, fetal hemoglobin, adult hemoglobin
81
The oxygen saturation curves of hemoglobin and myoglobin differ in that..?
hemoglobin’s curve is sigmoidal and further from the y axis
82
Calculate the fraction saturation of myoglobin when the partial pressure of oxygen is 50 torr. Assume the p50 of myoglobin is 3 torr
94.3%
83
Relative to adult hemoglobin, fetal hemoglobin has a ______ affinity for oxygen because it has a ______ affinity for 2,3 bisphosphoglycerate
Higher, lower
84
Oxygen serves as a _____ of hemoglobin
homotropic allosteric activator
85
True or False: sickle cell fibers form from R state hemoglobin?
False
86
Calculate the fraction saturation of myoglobin when the partial pressure of oxygen is 25 torr. Assume the p50 of myoglobin is 3 torr
89%
87
2,3 Bis phosphoglycerate serves as a ____ of hemoglobin
hetrotropic allosteric inhibitor

BMSC 200 (11 decks)

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