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Biochemistry > Biochem Protein Lecture 11 > Flashcards

Biochem Protein Lecture 11 Flashcards

1
Q

Changes in the positions of key ________ chains surrounding heme may cause the change from T to R

A

Amino Acid Side Chains

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2
Q

When in the T state, the ______ ring of heme is slightly puckered.

The heme iron protrudes to some extent on the DISTAL/PROXIMAL His side

A

Porphyrin

Proximal His side

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3
Q

When O2 binds to heme initially in the T state, it pulls the ____ a short distance down into the heme resulting in a more planar heme

A

Fe2+ (Ferrous Iron)

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4
Q

What occurs to relieve the strain caused by oxygen binding to heme in the T state caused by the more planar state

A

Rearrangment

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5
Q

What shifts its position to perpendicular to relieve strain caused by O2 binding heme in the T-state?

What else does it shift?

What does it result in?

A

Proximal His

The F helix and FG corner

R state

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6
Q

After the proximal His moves, _______ is pushed to the right and its H bond with ______ is broken.

H bonds and salt bonds that connect FG corners of one unit with C helices of another subunit are STRENGHTENED/WEAKEND?

A

Val FG5, Tyr HC2

Weakened

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7
Q

In sum, binding of O2 pulls the ferrous iron a fraction of a nanometer into the heme, causing a larger shift in the surrounding structure, particularly at the ______.

The result is increased

A

α-β interfaces

Oxygen binding

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8
Q

As stated in the previous lecture, Mb with its hyperbolic binding curve, it would bind with HIGH/LOW affinity in the lungs, but it WOULD/WOULD NOT release much of it in the tissues

A

High affinity, would not release

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9
Q

Could a protein with a hyperbolic curve bind O2 at a low enough affinity to release it in the tissue, but it wouldn’t pick up enough O2 in the lungs?

A

Yes, the opposite of Mb

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10
Q

How does Hb deal with the pressure difference posed in the lung and the hyperbolic curve?

A

Going from a transition state from the low affinity (T state) to the high affinity (R state)

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11
Q

The binding curve for Hb is _____ because O2 binding is coopoerative.

A

Sigmoidal (S-curve) look at graph

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12
Q

This term means that the binding of O2 to the heme Fe in one subunit increases the Ka (binding affinity) of oxygen in the other subunits

A

Cooperative

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13
Q

The first O2 molecule interacting with deoxy Hb binds strongly or weakly?

By the time the last (4th) O2 molecule binds, it binds to a heme subunit already in the

A

Weakly (T-state)

R-state

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14
Q

Because of cooperative binding, Hb will be almost fully ____ at the pO2 of the lungs but only partially ____ (same word) at the pO2 in the tissues

A

Saturated.

Most of the O2 bound by Hb is released into the tissues

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15
Q

A protein where the binding of a small molecule (ligand) to one site on a protein affects the binding at another site on the same protein

A

Allosteric Protein

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16
Q

These are ligands which induce different conformation of allosteric proteins when the bind to the protein

A

Modulators

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17
Q

This type of interaction occurs when the normal ligand and modulator are identical

This type of interaction occurs when the modulator is a molecule other than the normal ligand

A

Homotropic Interaction

Heterotropic Interaction

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18
Q

An example of allosteric bind is the cooperative binding of O2 to ____

A

Hb

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19
Q

O2 is both a ___ and an activating _______ modulator

A

Ligand; homotropic modulator

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20
Q

The binding sites of an allosteric protein contain stable segments in close proximity to

A

Unstable segments (allows small shifts in conformation)

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21
Q

Note: just [P] means the concentration of the free protein in the Ka equation

A

!

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22
Q

What is the Hill equation to the binding of oxygen in Hb?

A

log [θ/(1-θ)] = n log pO2–n log P(50)

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23
Q

What does Kd = in the Hill equation?

A

K= [L]n (0.5)

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24
Q

A plot of Log (θ/ (1-θ)) vs log [L] is a

A

Hill plot

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25
Q

What is P(50)

A

The pressure at which half the subunit sites are occupied.

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26
Q

What is theta?

A

The fraction of oxygen that is bound

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27
Q

For Mb, what is the Hill plot like?

What is it for Hb?

A

A straight line with a slope of 1

Not linear, the maximum slop is a measure of the cooperativity of binding

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28
Q

For the Hill plot of Hb, the greater the slope, the LESS/MORE cooperative the binding?

A

More cooperative

29
Q

The slope of the hill plot variable is ____, a degree of the measure of cooperativity

A

n(H), the Hill coeffictient

30
Q

If n(H) =1, ligand binding is

If n(H)> 1, there is ____ cooperativty

If n(H)<1 there is ___ cooperativity

A

Not cooperative

Positive cooperativity

Negative cooperativity

31
Q

Hb is an example of ___ cooperativity

In this type of cooperativity, the binding of one ligand impedes the binding of others. It’s pretty rare

A

Positive cooperative n(H)>1

Negative cooperativity

32
Q

What are the two models that attempt to explain the cooperative binding of ligands to multisubunit proteins?

A

MWC model (or concerted model) and Sequential Model

33
Q

This model assumes the subunits of a cooperatively binding protein are functionally ______, that each subunit can exist in greater than or equal to ___ conformations, and that all subunits undergo simultaneous transition from one ___ to the other

A

MWC model

Functionally identical

greater than or equal to 2 conformations

Simultaneous transition from one conformation to the other

34
Q

In the MWC model, are the subunits in different conformations?

A

No. No protein has subunits in different conformations

35
Q

In the MWC model, the two conformations are in ________

A

Equilibrium

36
Q

In this model of cooperative binding, ligand binding can induce a change of conformation in an individual subunit. A conformational change in one subunit makes a similar change in an adjacent subunit, and the binding of a second ligand is more likely

A

Sequential Model

37
Q

The sequential model has more potential ___ states than the MWC model

A

Intermediate states

38
Q

Hb carries ___ and _____, two end products from cellular respiration, from the tissues to the lungs and kidneys

A

H+ and CO2

39
Q

When Hb carries H+ and CO2 from tissues to the lungs and kidneys, CO2 is hydrated to form

A

Bicarbonate

CO2 + H2O –> H+ + HCO3-

40
Q

If CO2 (insoluble) were no converted to bicarbonate, what would happen?

A

Bubbles of CO2 would form in the tissues and blood

41
Q

Hydration of CO2 results in a/n INCREASE/DECREASE in the H+ concentration

A

Increase in H+ concentration (decrease in pH)

42
Q

Hb transports about what percent of the total H+ and about what percent of the CO2 formed in tissues to the lungs and kidneys?

A

40% of total H+

15-20% of total CO2

43
Q

How is the binding of H+ and CO2 related to the binding of O2?

A

Inversely

44
Q

In _______ (where there is low pH and high CO2), the affinity of Hb for oxygen decreases as H+ and CO2 are bound, causing O2 to be released

A

Peripheral tissues

45
Q

In the _____, CO2 is excreted, blood pH rises, and affinity of Hb for oxygen increases. Hb binds more O2 for transport to tissues

A

The Lungs

46
Q

The effect of pH and CO2 on oxygen binding and release by Hb is called the

A

Bohr Effect

47
Q

What is the Bohr Effect Equation

A

HHb(+) + O2 –> HbO2 + H(+)

48
Q

From the Bohr effect equation, we know the binding of oxygen to Hb is influenced by

A

H+

49
Q

Hb binds to any of several ______ in the protein

A

Amino Acid Residues

50
Q

A major contribution to the Bohr effect is made by ____ of the β subunits.

When protonated, ____ residue forms one of the ion pairs to _____ that stabilizes deoxyHb in the T-state; oxyHb releases O2

A

His 146 (HC3)

His146 forms one of the ion pairs to Asp 94 (FG1)

51
Q

Carbon dioxide binds as a ____ group to the α-amino group at the amino-terminal end
of each globin chain to form carbaminoHb

This reaction produces ___ which contributes to the Bohr effect

A

Carbamate group

H+

52
Q

Bound carbamates also form additional _____ that stabilitze the T state (deoxy T state) and promote O2 release

A

Salt Bridges

53
Q

H+ and CO2 are ___ effector molecules for Hb

A

Allosteric effector molecules

54
Q

____ is another allosteric effecteor molecule for Hb (regulates oxgen binding to Hb)

A

BPG (2,3 bisphosphoglycerate)

55
Q

BPG is present in relatively high concentrations in

A

Erythrocytes

56
Q

BPG greatly reduces the affinity of Hb for oxygen by binding to groups that stabilize the _____ state

A

deoxy (T) state

57
Q

HbBPG + O2 –> HbO2 + BPG

A

!

58
Q

The site of the BPG binding to Hb is the cavity between the ___ subunits in the T state

(positively charged residues interact with negatively charged groups of BPG)

A

β

59
Q

At high altitudes, BPG concentration in the blood rises, leading to an INCREASE/DECREASE in the affinity of Hb for oxygen

At sea level, the situation is reversed

A

Decrease, O2 is released into the tissues

60
Q

Since a fetus must get oxygen from its mother’s blood, fetal hemoglobin must have a greater oxygen affinity than maternal hemoglobin.

Fetal Hb synthesizes __ subunits rather than β, forming ___

A

`γ

α2γ2Hb

61
Q

The α2γ2Hb tetramer in fetuses has a HIGHER/LOWER affinity for BPG corresponding to a HIGHER/LOWER affinity for O2

A

Lower affinity for BPG, higher affinity for O2

62
Q

This is a genetic disease in which an individual inherits the allele for sickle cell Hb from both parents

A

Sickle Cell Anemia

63
Q

Sickle Cell anemia is characterized by a large number of immature cells with many long, thin, crescent shaped _____ that look like a sickle cell blade

A

Erythrocytes

64
Q

When sickle Hb is deoxygenated, it becomes ___ and forms polymers which aggregate into tubular fibers

A

Insoluble

Normal Hb remains soluble on deoxygenation

65
Q

Altered properties of HbS result from a single aa substitution, ___ instead of ____ at position 6 in the two β chains

A

Valine instead of Glutamate

66
Q

HbS has two fewer __ charges. A sticky ____ contact at position 6 is created causing aggregation into bundles of fibers, resulting in serious medical complications

A

Negative Charges

Hydrophobic Contact

67
Q

___ binds to Hb 250 times better than oxygen to form COHb

A

Carbon monoxide (CO)

68
Q

The tight bonding of CO to Hb means that COHb can accumulate over time as people are exposed to a constant low level source of CO

A

!

69
Q

Smokers have increased levels of ___

A

COHb

Biochemistry (27 decks)

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