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CHEM 350 > Lecture 9 - Examples of Protein Functions > Flashcards

Lecture 9 - Examples of Protein Functions Flashcards

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1
Q

what are 3 main protein functions?

A
  1. myoglobin + hemoglobin
  2. muscle contraction: actin/myosin
  3. immunoglobulins (antibodies)
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2
Q

what is myoglobin?

A

O2 binding protein

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3
Q

how many residues in myoglobin?

A

153

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4
Q

how many helices in myoglobin?

A

8 helices, A through H

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5
Q

what is the functional part of myoglobin?

A

“heme” which contains fe(II)

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6
Q

what happens when Fe(II) is oxidized

A

Fe(III) is inactive

metmyoglobin

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7
Q

what is the fused ring of myoglobin?

A

porphyrin molecule

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8
Q

how is the underside of the porphyrin coordinated?

A

by His93

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9
Q

what is the porphyrin held into place by?

A

a number of hydrophobic residues

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10
Q

what is O2 stabilized by when bound?

A

His64

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11
Q

what does myoglobin facilitate?

A

O2 diffusion in a muscle

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12
Q

What does O2 binding to myoglobin show?

A

typical “saturation” behavior

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13
Q

What is the equilibrium between free and bound O2?

A

MbO2 <> Mb + O2

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14
Q

What is free O2 in muscle measured by?

A

partial pressure PO2

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15
Q

What is PO2?

A

free O2 in muscle

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16
Q

What is YO2?

A

fraction of Mb that has a bound O2

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17
Q

what is hemoglobin?

A

a transport protein

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18
Q

where does hemoglobin transport O2?

A

in the circulatory system

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19
Q

what is hemoglobin responsible for?

A

the red color of erythrocytes

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20
Q

What is mammalian Hb?

A
  • a tetramer

- consists of 2 identical alpha subunits (pink) and 2 identical beta subunits (yellow)

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21
Q

Hb can bind up to _____ O2

A

four

22
Q

What happens when Hb binds O2?

A
  • a major shift occurs in its quaternary structure

- interface between the 2 beta subunits closer together

23
Q

How does hemoglobin bind O2?

A

cooperatively

24
Q

what type of shape does the O2 binding curve on Hb have?

A

sigmoidal shape

25
Q

What does the s-shaped binding curve signal?

A

cooperativity

26
Q

When going toward high PO2, after one O2 binds, what happens to the next?

A

it binds more easily

27
Q

What happens when going toward a low PO2, after one O2 unloads?

A

the next one unloads more easily

28
Q

How does the pattern of PO2 and O2 binding and unloading affect Hb?

A
  • helps Hb deliver more O2 to tissues

- compared against Mg

29
Q

What does the Hill Coefficient describe?

A

cooperativity

Hb(O2)n <> Hb + n O2

30
Q

For the Hill Coefficient,, what does n>1 mean? n<1?

A

n>1 positive cooperativity

n<1 negative cooperativity

31
Q

What is the hill plot?

A

-the rearrangement of the Hill equation to yield a straight-line plot

32
Q

Do hemoglobin T and R conformations have the same affinity for O2?

A

-different affinity

33
Q

T vs. R

A 
T = deoxy form (tense)
R = oxy form (relaxed)
34
Q

What is the effect of the hme and the F helix during the T->R transition?

A
  • makes O2 bind more strongly in R

- disrupts series of ion pairs + H bonds between alpha and beta subunits

35
Q

What happens when the ion pairs and H bonds are disrupted?

A
  • modifies pKa of residues

- alters the O2 binding as a function of pH

36
Q

What is the Bohr effect?

A

-changes the loading of Hb as a function of pH

37
Q

What is O2 binding to Hb accompanied by?

A

-the release of ~0.6 H+

38
Q

What do capillaries have?

A

CO2

39
Q

What happens when CO2 is dissolved in blood?

A

-makes bicarbonate HCO3-

40
Q

what acceleartse the formation of bicarbonate HCO3-?

A

-enzyme carbonic anhydrase

41
Q

When is blood more acidic?

A

-PCO2 is high

42
Q

Where is PCO2 high?

A

-in the capillaries of the muscle

43
Q

Where is PO2 low?

A

in the capillaries in the muscle

44
Q

what happens to O2 in the muscle tissues?

A
  • O2 unbinds
  • Hb takes up H+
  • causes CO2 removal
45
Q

Where is PO2 high?

A

in the lungs

46
Q

What happens to O2 int he lungs?

A
  • O2 binds
  • Hb releases H+
  • releases CO2 into lungs to be expelled when exhaling
47
Q

what are allosteric interactions?

A
  • enable protein subunits to work together

- binding of a ligand at one site affects the binding of another ligand at another site

48
Q

what are two models of allosteric effects?

A
  1. sequential

2. symmetry

49
Q

what is the sequential model of allosteric binding?

A

-assumes binding causes further affinity enhancement

50
Q

what is the symmetry model of allosteric binding?

A

-assumes an equilibrium exists between low and high affinity states

CHEM 350 (22 decks)

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