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Biochemistry > Exam 2: Immunoglobulins > Flashcards

Exam 2: Immunoglobulins Flashcards

1
Q

How are immunoglobins (antibodies) made?

A

By B lymphocytes of the adaptive immune system

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2
Q

Why are immunoglobins considered the magic bullets for treating human disease?

A

They recognize and bind to ligands with high affinity + high degree of specificity

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3
Q

What is the structure of an immunoglobin?

A

A heterotetramer comprised of 2 identical light chains and 2 identical heavy chains, held together by non-covalent + disulfide bonds

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4
Q

What are the two regions of an immunoglobulin?

A

A constant sequence (which differs with every immunoglobulin) and and a variable sequence

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5
Q

What is the function of variable sequences and where can they be found?

A

Function: to form antigen-binding sites
Location: amino-terminal

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6
Q

Why are immunoglobulins considered to be bivalent?

A

There are 2 antigen-binding sites

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7
Q

Where are the antigen-binding sites located?

A

On the tips of the two upper domains of the Y-shaped immunoglobulin

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8
Q

What is the base of the Y-shaped structure made up of?

A

Constant regions of heavy chains

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9
Q

Do immunoglobulins exhibit quaternary structure?

A

No, quaternary structure is defined as non-covalent assembly of two or more polypeptide chains, and immunoglobulins are covalently bonded via disulfide bonds

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10
Q

Define epitope

A

Specific part of an antigen recognized by an immunoglobulin

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11
Q

Paratope

A

Specific part of the immunoglobulin that binds epitopes

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12
Q

How do antigens bind to immunoglobulins?

A

Via complementary surfaces (lock and key)

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13
Q

What is a hypervariable region?

A

A region of extreme amino acid sequence variation in the variable region of the immunoglobulin

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14
Q

How many hypervariable regions are there in an immunoglobulin?

A

3

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15
Q

What do the hypervariable regions go on to form?

A

Binding regions for the epitopes

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16
Q

Hypervariable regions are also commonly referred to as:

A

Complementary determining regions

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17
Q

How can immunoglobulins recognize and bind to an array of different molecules?

A

The sequence variation within the complementary determining region

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18
Q

What are B lymphocytes?

A

White blood cells derived from hematopoietic stem cells found in the bone marrow

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19
Q

Are immunoglobulins the same across all B cells?

A

No, immunoglobulins expressed for one particular B cell differ from the ones synthesized in other B cells due to the unique amino acids within the variable domain

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20
Q

What happens when an antigen binds to a B cell receptor?

A

B cell is activated, stimulating proliferation and differentiation into effector (plasma) cells, which begin producing antiibodies

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21
Q

Do antigens bind to immunoglobulins via variable or constant region?

A

Variable. Constant region anchors the immunoglobulin to the plasma membrane

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22
Q

List the 5 main immunoglobulins:

A

IgA, IgD, IgE, IgG, IgM

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23
Q

What is the path immunoglobulins take to reach the cell surface?

A

Endoplasmic reticulum –> golgi –> cell surface

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24
Q

How are proteins trafficked through the cell?

A

They’re packaged in lipid vesicles

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25
Q

What does a protein need in order to enter secretory pathways?

A

A signal sequence at its amino terminus

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26
Q

What happens if the protein signal sequence is cleaved?

A

The protein will be localized to the lumen of the ER and packaged in lipid vesicles for transit through the secretory pathway to the cell surface

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27
Q

What are stop transfer sequences?

A

Hydrophobic stretches of amino acids that stop polypeptide chains from being translocated across the ER membrane

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28
Q

Which two immunoglobins (located on the cell surface) contain targeting information in addition to the signal sequence?

A

IgM and IgD

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29
Q

Are heavy/light chains synthesized dependently or independently?

A

Independently, and each contains a signal peptide directing it to the ER

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30
Q

How are hetero-tetrameric structures formed?

A

In the ER, light chains assemble with heavy chains

31
Q

Which two immunoglobulins are found embedded in the plasma membranes of the B cells in which they are made?

A

IgM and IgD; they fuse with the plasma membrane and remain bound via the stop-transfer sequence which serves as a membrane anchoring domain

32
Q

Which immunoglobulin is the first class to be expressed on immature B cells in the bone marrow?

A

IgM

33
Q

When B cells transit from the bone marrow into the peripheral blood they begin to express which immunoglobulin?

A

IgD

34
Q

Which subclass of B cells can also synthesize secreted from of IgM?

A

B1 lymphocytes

35
Q

Which lymphocyte can produce natural IgM antibodies?

A

B1

36
Q

Are natural IgM antibodies spontaneously produced?

A

Yes, they do not require prior immunization

37
Q

When first synthesized where are IgM antibodies directed against?

A

Self and non-self antigens

38
Q

What is the structure of a secreted IgM antibody?

A

Pentameric form with a joining chain

39
Q

Which domain must be left out of IgM for it to be secreted from cells rather than being localized to the plasma membrane?

A

Stop-transfer sequence

40
Q

How many subclasses of IgG are there and what differentiates them?

A

4; they have slightly different heavy chains

41
Q

Do IgG immunoglobulins contain stop-transfer sequences?

A

No, they are secreted immunoglobulins and lack stop-transfer sequences

42
Q

When are IgG’s produced?

A

Once naive B cells are activated and become effector B cells (plasma cells)

43
Q

Which is the most common antibody?

A

IgG

44
Q

Which is the largest antibody?

A

IgM

45
Q

Light and heavy chains are linked together via?

A

Disulfide bonds

46
Q

Which digestive enzyme can cleave immunoglobulins into Fc and Fab fragments?

A

Papain

47
Q

What is the Fab fragment useful for?

A

Pathogens are recognized by immunoglobulins through sequences in their variable regions which are Fab fragments (top half of the immunoglobulin in monomer form)

48
Q

What is the Fc fragment useful for?

A

Pathogens can be targeted for destruction by macrophages and neutrophils through sequences in the constant region (Fc fragment)

49
Q

Describe the personality of IgE:

A

“Eve gives me allergies”

IgE is monomer-shaped and binds to Fc (constant region) receptors on mast cells promoting cytokine and histamine release and attracting other immune system components

50
Q

Describe IgA personality:

A

“And”

IgA is found most abundantly in bodily secretions (saliva, mucous) and are the first line of defense against inhaled/ingested pathogens

51
Q

Which is the only dimer immunoglobulin?

A

IgA

52
Q

Why are IgA unusual?

A

They are synthesized by mature plasma cells lying beneath epithelial cell surfaces

53
Q

What happens when IgA cells are released from epithelial cells?

A

They are proteolytically cleaved of their IgA receptor and a portion of their receptor remains associated with the secreted IgA (secretory component)

54
Q

IgA are recognized by which basolateral epithelial cells?

A

pIgR cells

55
Q

How many structural motifs (Ig domains) do light/heavy chains contain?

A

Light: 2
Heavy: 4

56
Q

In what element of secondary structure are the hypervariable regions (hypervariable loops) of immunoglobulins found?

A

Random structure

57
Q

Define Ig repertoire:

A

Different immunoglobulin sequence variants formed by naive B cells

58
Q

Define secondary Ig repertoire:

A

When B lymphocytes switch from IgM to IgD to IgG during activation, their affinities for antigens increase through continued amino acid sequence variation in the variable region

59
Q

Which 3 segments of DNA create light chains?

A

Variable, joining, constant

60
Q

Which 3 segments of DNA create heavy chains?

A

Variable, joining, diversity

61
Q

How does the recombination of V, J, and D regions happen?

A

Via an enzyme called V(D)J recombinase

62
Q

How does V(D)J recombinase work?

A

Randomly selects a downstream V site and links it to a J site on the light chain. Upstream V regions are excluded by transcription. Downstream J regions are removed by RNA splicing

63
Q

Define clonal deletion:

A

A mistake made when V and J segments were joined while making a light chain which prevents a functional protein from being expressed will die in the bone marrow

64
Q

When is V(D)J recombinase shut off?

A

When a B cell begins producing a functional immunoglobulin (heavy + light chain combined)

65
Q

Why is the V(D)J recombinase shut off?

A

To ensure that only one single immunoglobulin in made by any individual B cell

66
Q

How are autoimmune diseases caused?

A

When B cells escape the process of having their V(D)J recombinase shut off

67
Q

What is a hyper-mutable state?

A

When B cells are activated by antigen and being making a unique immunoglobulin

68
Q

Which cells are preferentially activated leading to their survival and enhanced proliferation?

A

B cell clones

69
Q

What is the largest change that occurs from class switching?

A

Exchanging 1 heavy chain (constant region) for another and the subsequent production of secreted immunoglobulins instead or membrane-bound

70
Q

Which enzyme promotes class switching?

A

Deaminase which is the same enzyme involved in hypermutation of the variable region

71
Q

What do deamination events cause?

A

Double-stranded breaks in switch sequences between heavy chain constant regions

72
Q

Recombination between which two regions allows class switching?

A

Cu and other C regions

73
Q

Is recombination reversible?

A

No, it’s irreversible because the circular DNA released by the recombinase process is degraded

74
Q

Are high-affinity or low-affinity immunoglobulins the ones commonly used therapeutically?

A

High affinity

Biochemistry (5 decks)

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