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MSPC231 > Protein Structure and Function > Flashcards

Protein Structure and Function Flashcards

1
Q

The two Main types of secondary structure

A

Alpha-Helix
Beta-pleated sheet

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2
Q

What is a quatenary structure

A

With more than one polypeptide chain

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3
Q

In the tertiary structure of proteins where can hydrophobic residues be found

A

In the inner part of the protein

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4
Q

In the tertiary structure of proteins where can hydrophilic residues be found

A

On the outer surface of the protein

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5
Q

What is a thiol

A

The sulfur analogue of a hydroxyl group

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6
Q

Why are hydrophilic residues usually found on the outside of the tertiary protein

A

Usually for ionic interactions with water

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7
Q

What do we call a compact tertiary protein

A

A globular protein

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8
Q

What do we call a spindly long tertiary protein

A

A fibrous protein

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9
Q

What is a holoenzyme/holoprotein

A

A complete conjugated protein with its apoprotein and prosthetic group

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10
Q

What is heme

A

a prosthetic group that contains Iron and binds to oxygen

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11
Q

What is a Heme protein

A

Proteins that contain HEME as a prosthetic group

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12
Q

Examples of Heme Proteins

A

Myoglobin and a Hemoglobin

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13
Q

What are the apoproteins in Myoglobins and Hemoglobins

A

Globin

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14
Q

What does heme consist of?

A

A central Fe ion and a protoporphyrin

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15
Q

What is the structure of the protophyrin

A

A cyclic Protoporphyrin RIng which binds a central Fe ion in heme

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16
Q

What is the structure of Hemoglobin(Hb)

A

Quaternary Structure

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17
Q

Hb is considered to have a Quaternary tetrameric structure,

Why is that

A

This is because it is made up of Four subunits

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18
Q

Hb is considered to have a Quaternary tetrameric structure,

Name its Subunits

A

2 α subunits
2 β subunits

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19
Q

Each subunit can bind oxygen

True or False

A

True

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20
Q

Where is Myoglobin found

A

Found in muscle cells

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21
Q

What is the major function of Myoglobin

A

Storage of o2 in muscle cells

Also supply muscle cells with O2

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22
Q

What is the structure of Myoglobin

A

Monomeric Tertiary

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23
Q

What is the name of the environment surrounding heme

A

Heme pocket

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24
Q

What are the main type of amino acids in the heme pocket

A

Hydrophobic amino acid residues

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25
Q

What Other amino acid residues present in
heme pocket

A

Histidine

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26
Q

How many bonds are attached to Fe in heme

A

Six bonds

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27
Q

Name the bonds attached to Fe in heme

A

4 bonds from the pyrrole nitrogen atoms
1 bond from histidine at the fifth site
1 bond from oxygen at the sixth site

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28
Q

What are the two types of histidine residues found in the heme pocket

A

Proximal Histidine
Distal Histidine

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29
Q

What is the function of the Proximal heme

A

Stabilises the Heme

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30
Q

What is the function of the Distal Histidine

A

It weakens the Fe—O bond allowing it to be released, making the bond reversible

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31
Q

How does the distal histidine play its role in the Fe—bond reveribility

A

It causes bent binding hence weaking the bond

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32
Q

What is the function of the heme environment

A

Heme environment protects heme
from oxidation

Specifically rapid oxidation From Fe2+ to Fe3+

Fe3+ cannot bind oxygen

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33
Q

What is oxidized Heme

A

Methemoglobin

Does not bind O2

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34
Q

What is methemoglobinemia

A

A disorder charaterised by an increase in Methemoglobin

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35
Q

When can one be said to have methemoglobinemia

A

When methemoglobin(MetHb)>1% of Total Hb

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36
Q

What is the congenital cause of methemoglinimea

A

MetHb-Reductase Defiency

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37
Q

What is the function of MetHb-Reductase

A

It converts MetHb to normal Hb by reducing Fe3+ to Fe2+

38
Q

Examples of Alpha-like globin Chains and where they can be found

A

α : Major adult form
ζ (zeta): Embryonic form

39
Q

Examples of Beta-like globin Chains and where they can be found

A

β : major adult form
– δ : minor adult form
– γ : major fetal form
– ε : embryonic form

40
Q

What is the subunit structure for HbA1

A

α2β2

41
Q

What is the subunit structure of HbA2

A

α2δ2

42
Q

What is the subunit structure for HbF

A

α2γ2

43
Q

What are the two forms/conformations of hemoglobin

A

T(taut/tense)-form
R(relaxed)-form

44
Q

What are the affinities of oxygen for the two forms of Hb

A

T-form : Low Affinity for Oxygen
R-Form : High Affinity for Oxygen

45
Q

What is an oxygen dissociation curve

A

plot of saturation (Y) (for either Hb or Mb) at different oxygen tension (PO2) values

46
Q

On an Oxygen Dissociation Curve

What is Y ( Fractional saturation/per cent saturation)

A

Fraction of the total binding sites occupied by oxygen

47
Q

What is the shape of the Oxygen Dissociation Curve of Mb

A

Hyperbolic Curve

48
Q

What is the shape of the Oxygen Dissociating curve of Hb

A

Sigmoidal Curve

49
Q

What type of Binding causes the conformational change of Hb from T-form to R-form

A

Cooperative Binding

50
Q

What is the signifcance of P50

A

Measure of oxygen affinity

51
Q

Examples of allosteric effectors of Hb

A

CO₂,
H⁺,
2,3-BPG(2,3-bisphosphoglycerate)

52
Q

How does allosteric Effectors affect Hb

A

They change its conformation from R to T-form causing it to release more oxygen at low PO2

53
Q

Amino acids are weak acids

What makes them acidic at low pKa

A

Their Carboxyl group (COO-)

54
Q

Amino acids are weak acids

What makes them acidic at High pKa

A

Their Amino Group( NH3+)

55
Q

At what pH do Acidic and Basic R groups become acidic and basic

A

Physiological pH (pH of 7.4)

56
Q

What is the effect of increasing [H+] as an allosteric effector of Hb

A

It increases release of Oxygen at tissue level by stabilizing the T conformation

57
Q

H+ is an allosteric effector of Hb

Explain its mechanism

A

H+ bonds with some amino acids and also forms ionic bonds with with other R- groups,

This stabilizes the T-conformation, which has a low affinity for O2, hence releasing oxygen

58
Q

Give an example of an amino acid that bonds with H+

A

Histidine

59
Q

Whats the bohrs effect with relation to allosteric effectors

A

Binding of H+ by Hb and subsequent lowering of its O2 affinity

60
Q

What is the effect of increasing H+ on the Oxygen Dissociation Curve, and what effect is it called

A

It shifts the Oxygen dissociation curve to the right
It is also know as the bohrs effect

61
Q

CO2 is an allosteric effector of Hb

What is its mechanism

A

CO2 binds with the N terminus of Hb globin to form carbamate
Negatively charged carbamate forms ionic bonds with RH+ groups which then stabilizes

Also, it releases H+ when it forms HCO-

62
Q

CO2 is an Hb allosteric Effector

What is the effect of increasing [CO2] on the Oxygen Dissociation Curve

A

Shift of ODC to the right

63
Q

How is 2,3 - bisphosphoglycerate formed

A

A product of glycolysis in RBCs

64
Q

Why does HbF have a lower affintity towards 2,3 -BPG

A

Because it has less Positive amino acids by replacement of Histidine with Serine

65
Q

HbF and HbA which has a higher affinity for Oxygen

A

HbF

66
Q

What has a higher affinity for Hb than Oxygen

A

CArbon Monoxide

67
Q

What is the effect of carbon monoxide on the Oxygen Dissociation Curve

A

It shifts it to the left

68
Q

What is the most abundant example of a glycated Haemoglobin

A

HbA1c

69
Q

Where does glucose attach to in glycated Hb

A

The beta globin chain

70
Q

Is glycation reversible or irreversible

A

Irreversible

71
Q

Why is glucose mainly what glycates hb

A

Because its the predominant carbohydrate in the blood stream

72
Q

What are the two types of hemoglobinopathies, with examples each

A

Qualitative - Sickle Cell Hemoglobin
quantitative- Thalassemia

73
Q

What causes Sickle cell hemoglobin

A

When negatively charge Glutamate at the 6th position is replaced with Hydrophobic Valine in the β chain

74
Q

What type of mutation causes sickle cell

A

Point mutation

75
Q

What is the most common clinical manifestation of Sickle Cell Disease

A

Vaso-Occlusive crisis, which leads to pain, ischemia and infarction

76
Q

What is Ischemia

A

Low supply of oxygen to blood tissue

77
Q

What does Ischemia ultimately lead to

A

It leads to tissue death also referred to as infarction

78
Q

What happens when sickled cells group or clump together in the lungs

A

It leads to Acute chest syndrome, which occurs

79
Q

Why does HbS form polymers and HbA does not

A

This is due to the formation of clefts and exposed Hydrophobic valine which sort of “lock” together, hence polymerization

80
Q

What is the pI for normal Hb

A

6.9

81
Q

What causes the formation of HbC

A

The substitution of Glutamine at postition 6 with lysine on the Beta chain

81
Q
A
82
Q

Give a chemical that helps with sickle cell, and how it works

A

Hydroxyurea, it causes the production of HbF which is less prone too polymerization, allowing blood flow and alleviating pain

83
Q

What is Thalassemia

A

A genetic blood disorder affecting the body’s ability to for adequate amount of hemoglobin

84
Q

What does the severity of Thalassemia depend on

A

The amount of abnormal hemoglobin produced

85
Q

What is the main cause of Thalassemia

A

It is caused by the impairment or imbalance in the production of α or β subunits

86
Q

What are the two main types of thalassemia

A

Alpha thalassemia and
Beta thalassemia

87
Q

What are the two main forms of Hb caused by alpha thalassemia

A

HbBarts in fetal life
HbH postnatal

88
Q

What causes HbH diseases

A

Accumulation pf β-tetramers in RBCs

89
Q

What causes HbBarts d

A

Excess γ tetramers in RBCs

MSPC231 (4 decks)

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