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Biological Chemistry > Protein Structure > Flashcards

Protein Structure Flashcards

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1
Q

What are the 2 functions of Red Blood Cells?

A
  • transfer O2 from lungs to tissue

- transfer CO2 from tissue to lungs

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2
Q

What were the first proteins to be crystallised?

A

Haemoglobin and Myoglobin

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3
Q

How were Haemoglobin and Myoglobin studied?

A

via ultracentrifugation

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4
Q

Where is myoglobin found in vertebrates?

A
  • skeletal muscle

- heart muscle

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5
Q

How many subunits does myoglobin have?

A

1

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6
Q

What does myoglobin facilitate?

A

rapidly respiring muscle tissue

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7
Q

Is the rate of O2 diffusion slow?

A

Yes

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8
Q

Why is the rate of O2 diffusion slow?

A

due to the solubility of O2

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9
Q

Does myoglobin increase or decrease the solubility of O2?

A

increase

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10
Q

Why is oxygen storage via myoglobin greater in whales and seals?

A

they can slowly release O2 in their bodies

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11
Q

What is the structure of the “haem complex” in myoglobin?

A

two histidine residues (proximal and distal) anchor to haem

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12
Q

What is the ring around Fe called?

A

polyporphyrin

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13
Q

What is “Histidine”?

A

an amino acid with a side chain (imidazole)

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14
Q

What does “Histidine” have a tendency of binding?

A

metal

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15
Q

What genes encode haemoglobin?

A

globin

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16
Q

How many subunits does haemoglobin have?

A

4 (2 alpha, 2 beta)

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17
Q

What type of oligomer is haemoglobin?

A

tetramer

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18
Q

What is an “oligomer”?

A

a molecule consisting of a few similar repeating units

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19
Q

What protein contains iron?

A

ferritin

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20
Q

Is the synthesis of haem and globin synchronised?

A

yes

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21
Q

Where is haem synthesised?

A

mitochondria

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22
Q

Where is globin synthesised?

A

polyribosomes

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23
Q

Do what do mature red blood cells not contain?

A

mitochondria

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24
Q

What does Hb carry excluding O2?

A
  • CO2

- H+

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25
Q

What is haem derived from?

A

protoporphyrin IX

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26
Q

Can Fe3+ bind O2?

A

No

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27
Q

What is the reduced form of iron?

A

Fe2+

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28
Q

What is the oxidised form of iron?

A

Fe3+

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29
Q

What is Fe3+ bound to globin?

A

methemoglobin

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30
Q

What number ligand does protoporphyrin bind O2 to?

A

6th

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31
Q

What is the 5th ligand?

A

histidine F8

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32
Q

What bound to the proximal side of Fe2+?

A

His F8

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33
Q

What bound to the distal side of Fe2+?

A

oxygen

34
Q

What 4 molecules outcompete O2?

A
  • CO
  • NO
  • CN-
  • H2S
35
Q

What can increased methemoglobin be caused by?

A
  • drugs

- environmental agents

36
Q

What does the oxygen dissociation curve of Mb and Hb look like?

A

compare to reference image

37
Q

What is the

binding of O2 abbreviated as?

A

YO2

38
Q

What is the formula of YO2?

A

PO2/ Kd+pO2

39
Q

What do the Hb subunits independently compete for?

A

the first O2 to bind

40
Q

What does it mean if YO2 is close to 1?

A

3 subunits are occupied and the 4th is independent of the other site

41
Q

What is “D-2,3-Bisphosphoglycerate (BPG)”?

A
  • allosteric effector
42
Q

What is the function of “D-2,3-Bisphosphoglycerate (BPG)”?

A
  • modulates (regulates) the affinity of Hb for O2

- providing control and adaptation to environmental factors

43
Q

What does high altitude mean for the abundance of BPG?

A

increased

44
Q

What is “BPG” also known as?

A

DPG

45
Q

What 4 factors affect the position of Hb-O2 dissociation curve?

A
  • [BPG]
  • pH
  • CO2 in RBCs (Bohr effect)
  • structure of Hb
46
Q

What is “stripped Hb”?

A

Hb without BPG

47
Q

How is “stripped Hb” produced?

A

conc. NaCl

48
Q

What causes a right shift in the dissociation curve?

A
  • high BPG
  • high H+
  • high CO2
  • HbS (Sickle Cell)
49
Q

What does a right shift mean?

A

easy O2 delivery (improves release of O2)

50
Q

What causes a left shift in the dissociation curve?

A
  • low BPG

- HbF (fetal Hb)

51
Q

What does the “picket-fence Fe(II)-porphyrin complex” mean?

A

Fe2+ bound within the porphyrin ring is surrounded

by side-chains of the porphyrin molecule to form a “fence” like structure that protects the iron from oxidation

52
Q

Can oxygen bind to tense Hb?

A

not well

53
Q

What binds to tense Hb?

A
  • CO2

- H+

54
Q

What is the maximum capacity of Hb for O2?

A

4

55
Q

Where are the interactions between the alpha and beta subunits occurring in DeoxyHb?

A

alpha1/beta1

56
Q

Where are the changes between the alpha and beta subunits occurring in oxyHb?

A

alpha1/beta2

57
Q

What subunits are unchanged in oxyHb (relaxed form)?

A

alpha1/beta1

58
Q

What occurs when oxygen binds to Hb?

A

conformational shape change

59
Q

How does Hb go from T state to R state?

A

binary switch

60
Q

What drives the T->R transition?

A

energy in the formation of Fe-O2

61
Q

As the lungs become more acidic, what does it mean for O2?

A

it does not bind as well

62
Q

At higher pH (basic) what is promoted?

A

tighter binding of O2 to Hb

63
Q

At lower pH (acidic) what is promoted?

A

easier release of O2 from Hb

64
Q

What is the equation linking the Bohr effect and CO2?

A

CO2 + H20 HCO3- + H+

65
Q

What enzyme catalyses this reaction in erythrocytes?

A

carbonic anhydrase

66
Q

How does HCO3- affect the pH?

A

increases

67
Q

What does the increased pH do to HCO3-?

A

decreases the binding of O2

68
Q

What does the decreased binding of O2 mean for Hb?

A

it’s in T form

69
Q

Where is the forward reaction (CO2 + H20->HCO3- + H+) driven?

A

capillaries

70
Q

Where is the backward reaction (HCO3- + H+-> CO2 + H20) driven?

A

lungs

71
Q

What does deoxyHb bind CO2 as?

A

carbamate

72
Q

High [CO2] in capillaries stimulates Hb to what?

A

release O2

73
Q

What other ion affects the affinity of Hb for O2?

A

Cl-

74
Q

What is Sickle Cell Anaemia (SCA)?

A

a genetic disease that affects Hb

75
Q

What individuals are affected (diseased) by SCA?

A

homozygous

76
Q

What individuals are not affected (carriers) by SCA?

A

heterozygous

77
Q

What does SCA cause?

A

defective Hb (they stick together causing RBCs damage)

78
Q

Heterozygous individuals are protected from what? (By having SCA)

A

malaria

79
Q

What DNA mutation occurs in HbS?

A

point mutation

80
Q

What does the mutation cause in HbS?

A

glutamate (glu) replaced by valine (val)

81
Q

Why is this protein mutation drastic?

A

glu is negatively charged, val has no charge

82
Q

Is Val is hydrophobic or hydrophilic?

A

hydrophobic

Biological Chemistry (6 decks)

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