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Biocheem > Lecture 16 > Flashcards

Lecture 16 Flashcards

1
Q

What does the graph in a simple ligand binding behavior?

A

A hyperbolic graph

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2
Q

Which oxygen binding protein has a hyperbolic path?

A

Myoglobin

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3
Q

What does the distal histidine do in Myoglobin?

A

Forms a hydrogen bonding relationship with the oxygen

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4
Q

What coordination position does oxygen occupy?

A

The sixth coordination position

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5
Q

Is binding reversible in myoglobin?

A

Yes

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6
Q

Why is oxygen binding to myoglobin a reversible process?

A

Because we need the myoglobin to release the oxygen in certain conditions

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7
Q

What is the percent of oxygen bound to myoglobin under active muscle conditions?

A

There is a low amount of oxygen bound because the partial pressure of oxygen is low

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8
Q

What is the oxygen concentration bound to myoglobin at resting conditions?

A

It is significantly higher because PO2 is higher and lots of O2 is bound to the myoglobin

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9
Q

What does the value of Kd in the oxygen binding to myoglobin curve represent?

A

When the concentration of the ligand is equal to Kd then we should expect half of our protein to be bound to the ligand and half of the protein to not be bound

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10
Q

How does oxygen bind to myoglobin?

A

By forming an H-bond with the distal histidine

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11
Q

How is the Heme prosthetic group held in the heme binding pocket?

A

By hydrophobic interactions

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12
Q

What decreases carbon monoxide binding to myglobin?

A

The distal histidine

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13
Q

What helps to define the geometry of the oxygen binding site?

A

The distal histidine

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14
Q

What binds with higher affinity to myoglobin: Oxygen or Carbon Monoxide?

A

Carbon Monoxide

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15
Q

What is the Quaternary Structure of Hemoglobin?

A

It is a Tetramer with two types of globin (two alpha and two beta subunits)

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16
Q

What is the biggest thing the differentiates hemoglobin from myoglobin?

A

Hemoglobin has quaternary structure and isn’t just a single polypeptide. Because hemoglobin has four polypeptides

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17
Q

What is each polypeptide in hemoglobin associated with?

A

A heme prosthetic group

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18
Q

Which one of the oxygen carrying proteins is heterotetrameric?

A

Hemoglobin because it has four subunits and they are different from each other

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19
Q

Which type of structure is the same for alpha globin, beta globin and myoglobin?

A

Tertiary structure

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20
Q

What do the Alpha globin, beta globin and myoglobin all have in common?

A

They have 8 alpha helicases with a heme binding pocket between helices E and F

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21
Q

What are Homologous proteins?

A

Proteins that are descendant from a common ancestor

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22
Q

How many O2 can hemoglobin bind to?

A

4 O2 groups

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23
Q

What kind of protein is Myoglobin?

A

A monomeric protein

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24
Q

What is a conservative amino acid substitution?

A

When one amino acid is changed into one that is quite similar

25
Q

How does Conservative substitution affect structure and function?

A

It typically has relatively minor effects on structure/function

26
Q

What is a critical amino acid substitution?

A

When one amino acid is changed into one that is quite different

27
Q

How does Critical substitution affect structure and function?

A

They change the structure and function depending on location

28
Q

How do the alpha and beta subunit of hemoglobin vs myoglobin bind O2?

A

In the exactly same manner

29
Q

What critical residues near the oxygen binding sites are invariant (do not change)?

A 
His F8 (proximal histidine)
His E7 (distal histidine)
30
Q

What does a Hyperbolic curve indicate?

A

A hyperbolic curve indicates a constant affinity

31
Q

What does a Sigmoidal curve indicate?

A

Cooperative binding affinity

32
Q

What is Ligand affinity like in a hyperbolic curve?

A

The ligand affinity does not change

33
Q

What is Ligand affinity like in a sigmoidal curve?

A

Ligand affinity changes as more ligand binds

34
Q

What has a hyperbolic binding curve and what has a sigmoidal binding curve?

A

Hyperbolic - Myoglobin

Sigmoidal - Hemoglobin

35
Q

What is the Proximal Histidine important for?

A

Iron atom coordination and maintaining the oxidation state

36
Q

What is the distal histidine involved in?

A

The H-bonding interaction of the oxygen

37
Q

What does the sigmoidal curve in hemoglobin indicate?

A

Positive cooperativity

38
Q

Aside from hemoglobin where can positive cooperativity be seen?

A

In the denaturation of DNA, where it is difficult to begin denaturation but easy to continue

39
Q

When does Myoglobin bind oxygen?

A

When the tissues are in resting state and the oxygen concentration is very high

40
Q

When does Myoglobin release oxygen?

A

When the tissue is relatively active

41
Q

Where does Hemoglobin transport oxygen from and to?

A

From the lungs to the peripheral tissues

42
Q

When does oxygen bind to hemoglobin and release it?

A

Hemoglobin binds to oxygen in the lungs where concentration is relatively high and lets go in the tissue

43
Q

Why doesn’t the body exclusively use myoglobin?

A

Because myoglobin will happily bind to oxygen in the lungs but as it circulates through the body and gets to the peripheral tissues it won’t let go of the oxygen

44
Q

Which has a higher affinity for oxygen: Myoglobin or Hemoglobin?

A

Myoglobin

45
Q

What are the similar functions of Myoglobin Hemoglobin?

A

They reversibly bind/release O2

46
Q

What are the different function of Myoglobin and Hemoglobin?

A

Mb: O2 transport within tissue
Hb: O2 transport from lungs to tissues

47
Q

What are the two states of Hb?

A

Tense (T) state and Relaxed (R) state

48
Q

What is the Tense (T) state of hemoglobin?

A

The low oxygen affinity state

49
Q

What is the Relaxed (R) state of hemoglobin?

A

The high affinity state

50
Q

What is the Tense state associated with?

A

A higher amount of salt bridge/ion pair interactions

51
Q

What is the difference between the subunits in the tense state and relaxed state?

A

There is a change in how the subunits are interacting with each other. Changing the shape of one subunit changes the shape of another subunit

52
Q

What is the size of the central cavity in the tense state versus the relaxed state?

A

The tense state has a larger central cavity and the relaxed state has smaller central cavity

53
Q

What are Effectors?

A

Compounds which, upon binding, alter affinity at other binding sites

54
Q

What is a Homoallosteric effector?

A

When the binding of the effector effects further binding of the same compound

55
Q

What is Allostery generally associated with?

A

Proteins with quaternary structure

56
Q

What is a Heteroallosteric Effector?

A

When the binding of the effector effects further binding of a different compound

57
Q

What do Activators (positive effectors) do?

A

Increase binding affinity

58
Q

What do Inhibitors (negative effectors) do?

A

Decrease binding affinity

59
Q

What kind of effector is oxygen to hemoglobin?

A

A homoallosteric positive effector

Biocheem (38 decks)

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