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Biochemistry > Biochem Protein Lecture 10 > Flashcards

Biochem Protein Lecture 10 Flashcards

1
Q

Is oxygen highly soluble in H2O?

What does this mean for transport to bodily tissues?

A

No, it has limited solubility

It can’t be transported to bodily tissues by dissolving it in blood serum or diffusion through tissues

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2
Q

What are needed to transport and store O2 in the body?

A

Proteins

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3
Q

Reversible binding of O2 requires….

A

A transition metal

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4
Q

Can AA side chains reversibly bind O2?

A

No.

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5
Q

What is incorporated to heme to reversibly bind O2?

A

Iron

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6
Q

This is a complex of protoporphyrin and iron

A

Heme

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7
Q

Free heme (not bound to protein) leaves Fe2+ with how many open coordination bonds?

A

2

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8
Q

Where is heme located in heme-containing proteins? Why?

A

Deep within the protein structure to prevent conversion to Fe3+ (via the air)

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9
Q

In a free heme, one of the two open sites is occupied by a ______

What is the other open site?

A

His (F8) residue (proximal his)

The Open O2 binding site

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10
Q

The imidizole group of a second His (E7) called _______ is located on the O2 binding site of heme

A

Distal His

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11
Q

How does the distal His assist in O2 binding?

A

H-bonds

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12
Q

A single polypeptide with one molecule of heme

A

Myoglobin

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13
Q

The helical segments of myoglobin are labeled __ through ____

A

A through H

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14
Q

This refers to the 8th residue in α helix F

A

His F8

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15
Q

The bends of myoglobin are labeled AB, CD, etc, indicating the α helical segments they connect

A

!

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16
Q

Oxygen is removed from the air in the lungs, transported by ______ in red blood cels to tissues of the body, and then delivered to cells at a pressure not much lower than that found in the atmosphere

A

Hemoglobin

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17
Q

Part of oxygen transported to tissues by Hb is used for _____ in mitochondria

There rest of the oxygen may be stored by ____ and saved for when oxygen demand increases

A

Aerobic metabolism

Myoglobin

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18
Q

Within cells, dissolved oxygen diffuses, or it is bound to _____ which helps transport oxygen to the mitochondria

A

Myoglobin

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19
Q

Carbon dioxide, released from oxidative processes in tissues, is carried back to the lungs by ___ and expired

A

Hemoglobin

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20
Q

As shown in the aerobic metabolism figure 7.4, oxygen is carried by hemoglobin circulatin gin the ____ to the tissues

A

Capillaries

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21
Q

Oxygen diffuses into the muscle cells through the

A

Capillaries

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22
Q

______ is found inside muscle cells. It binds the oxgen and delivers it to the mitochondria

A

Myoglobin

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23
Q

Myoglobin must release O2 when and where it is needed, what two muscle types have higher energy needs and require rapid transport from Hb to mitochondria in the respiring cells. Mb aids in this process

A

Heart and skeletal muscle

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24
Q

What is the equilibrium expression for the reversible binding of a proteins to a ligand?

Apply this concept to Mb and O2

A

P + L —> PL

Mb + O2 —> MbO2

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25
Q

What equation characterizes the equilibrium expression for the reversible binding of Mb and O2?

A

Ka = [MbO2]/[Mb][O2]

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26
Q

This equilibrium constant provides a measure of the affinity of oxygen for Mb

A higher Ka means a HIGHER/LOWER affinity of O2 for Mb

A

Ka

Higher

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27
Q

The fraction of Mb molecules that are oxygenated can be determined by differences in the _______ of Mb in the presence and absence of O2

A

Absorption spectra

28
Q

Θ (peta) = ?

A

Θ = [MbO2]/([MbO2]+[Mb])

Θ = binding sites occupied/total binding sites

29
Q

When substituting Ka values for the Θ equation, what is the final equation after derivation?

A

Θ = [O2]/([O2]+1/Ka)

30
Q

The value of Ka can be determined from a plot of Θ vs. ____

A

[O2]

31
Q

Any equation of the form x=y/(y+z) describes a ____ shape

A

Hyperbola

32
Q

The [O2] at which Θ = ______ corresponds to 1/Ka

A

Θ = 0.5 (half-occupied)

33
Q

What is the equation for the dissociation constant, Kd?

Then, Θ = what?

A

Kd=1/Ka

Θ = [O2]/([O2]+Kd)

34
Q

A lower value of Kd indicates a HIGHER/LOWER affinity of protein for ligand

A

Higher

there is an inverse relationship between Kd and Ka

35
Q

Kd= [O2] at which one half or the binding sites are occupied, or O2

A

Θ= [O2]/ [O2] + [O2]0.5

36
Q

In experiments, the partial pressure of oxygen (pO2) in the gas phase above the solution is varied because it is easier to measure than the concentration of dissolved oxygen in solution

A

[O2] = P(50)

37
Q

What is the equation for Θ in terms of partial pressure

A

Θ= pO2/pO2 + P(50)

38
Q

The P(50) is very HIGH/LOW, corresponding to a HIGH/LOW oxygen affinity

A

Low P50, corresponds to high oxygen affinity

39
Q

The protein/ligand interaction is affected by protein structure and is often accompanied by _____

A

Conformational changes

40
Q

What molecule binds to free heme molecules >20,000 times better than O2?

When heme is bound in myoglobin, the binding of the above molecule is only 200 times better

A

CO

41
Q

What explains the difference in binding affinity for CO that heme has when free and bound to Mb?

What else may affect bonding of CO?

A

Steric Effects of ligands bound to the heme of Mb

H-bonding of O2 to distal His

42
Q

Binding of O2 to the heme in Mb also depends on molecular motion known as _______

Rapid molecular flexing of aa side chains produces transient cavities in protein structure —-> what enters?

A

Breathing

O2

43
Q

Mb has a ____ binding curve for oxygen

It’s relatively SENSITIVE/INSENSITIVE to small changes in the concentration of oxygen, making it function well for oxygen sorage

A

Hyperbolic

Insensitive

44
Q

Is the hyperbolic binding curve of myoglobin for O2 make it a good O2 transporter?

A

No, it doesn’t.

45
Q

Why does Mb not provide efficient transport of O2 from the lungs to the tissues?

A

The partial pressure of O2 in the lungs is 3x that in the tissue, at either pressure, most of the protein is in the bound form. It wouldn’t release enough O2

46
Q

Oxygen is transported in blood by

A

Hemoglobin

47
Q

These cells, aka red blood cells, survive for ~ 120 days

Their main function is to carry

A

Erythrocytes

Hb

48
Q

In arterial blood passing from lungs through the heart to tissues, Hb is how saturated with oxygen? What color is it?

A

96%

Red

49
Q

In venous blood that is returning to the heart, Hb is only ____ % saturated

What color is it?

How much oxygen does 100ml of blood release? Percent total and volume.

A

64%

Dark purple

1/3, or 6.5mL

50
Q

Hemoglobin has multiple subunits and O2 binding sites

A

!

51
Q

Which can respond to changes in ligand concentration and changes in oxygen demand by tissues: Hb or Mb?

A

Hb (good for transport)

52
Q

Hemoglobin is a ____ that contains 4 heme groups, one for each polypeptide chain

It is also called a dimer of _____ protomers

A

Tetramer

αβ

53
Q

When Hb dissociates in urea, the closest and strongest contacts are between α-α and β-β or α-β?

A

α-β

Hence, dimer of α-β protomers

54
Q

Fewer than what percent of aa residues of α and β subunits are identical, even?

Do the non-identical ones have similar structure?

A

Fewer than 50%

Yes

55
Q

Do Mb and Hbα and Hbβ have similar subunit structure?

A

Yes, even though they’re only identical at 27 positions

56
Q

When considering quaternary structure of Hb, there are a few H bonds and salt bonds between chains, but most of the interactions between chains are

A

Hydrophobic

57
Q

Because Hb is a tetramer, each Hb molecule can bind how many oxygens?

What quality does each site display in binding?

A

4

Cooperativity

58
Q

There are two major conformations of Hb which have been confirmed by X-ray crystal structures. ____ means tense and ____ means relaxed

A

T= tense

R= Relaxed

59
Q

Which has higher oxygen affinity, the R state of Hb or the T state?

A

R state

60
Q

Does the binding of oxygen to the R state stabilize or destabilize it?

A

Stabilizes the R state

61
Q

Which state is the predominant conformation of oxyHb, T or R?

A

R state (what’s oxyHb?)

62
Q

The absence of oxygen stabilizes which state?

A

T state

63
Q

Which state is the predominant conformation of deoxyHb, R or T?

A

T state

64
Q

The T state is stabilized by what at many of the α-β interfaces?

A

Ion pairs

65
Q

The binding of O2 to Hb in the T state promotes a change in conformation to the ________

_______ are broken and formed, important for structure and function

A

R state

Ion Pairs

Biochemistry (27 decks)

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