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Alex's Genetics > Lecture 8b > Flashcards

Lecture 8b Flashcards

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Biology 101 flashcards
1
Q

What cells make antibodies?

A

B cells

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2
Q

What is another term for antibodies?

A

Immunoglobulins

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3
Q

What are antibodies?

A

Proteins produced to recognize foreign substances (viruses, bacteria, fungi, and other things that don’t belong in the body).

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4
Q

What are antigens?

A

The features in foreign substances that are recognized by antibodies.

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5
Q

T/F: Antigen-antibody recognitions are not very specific.

A

False. Antigen-antibody recognitions are very specific.

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6
Q

How many epitopes can a single antibody recognize?

A

Each type of antibody is said to recognize a single epitope in the antigen.

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7
Q

What does each B cell produce relative to antibody type?

A

Each B cell produces one specific antibody which initially resides in the membrane of the cell.

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8
Q

Describe the antibody structure.

A

Antibodies are tetrameric proteins composed of two ‘heavy’ polypeptide and two ‘light’ polypeptide chains.

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9
Q

What is this?

A

Antibody

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10
Q

Where does the antigen bind?

A

The one end of the heavy chain and light chain highlighted in green.

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11
Q

What is the antibody light chain initially composed of?

A

~300 domains known as Variable (V)
4 domains known as Joining (J)
1 domain known as Constant (C)

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12
Q

What do the Variable and Joining domains do?

A

They are genes that each encode for a different amino acid sequence.

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13
Q

What are the genes of antibody light chains composed of?

A

They are composed of various sequences or domains.

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14
Q

Describe the process for producing a specific antibody light chain up to RNA splicing.

A

1) RAG1 and RAG2 recombinase recognize recombination signal sequences and catalyze the breakage at the end of a variable domain and the beginning of a joining domain.
2) The intervening DNA is lost. NHEJ proteins catalyze the joining of the last V domain and the first J domain in the remaining DNA.

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15
Q

How do we get so much diversity with antibody genes?

A

When the NHEJ is fusing the last V domain and the first J domain in the remaining DNA, the fusion process is not entirely precise. A few bases can be added or lost at the junction.

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16
Q

What removes extra J domains?

A

RNA splicing

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17
Q

Describe the process of producing the antibody light chain after fusion of V and J domains.

A

1) The region between the first joining domain and the constant domain in the pre-mRNA is spliced out.
2) The gene is transcribed into a pre-mRNA starting at the last variable domain. There will be 1 variable, 1 joining, and 1 constant domain.

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18
Q

What makes up a functional antibody protein?

A

2 light-chain polypeptides and 2 heavy-chain polypeptides.

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19
Q

Where is the light chain produced?

A

At the Ig locus

20
Q

Where is the heavy chain produced?

A

IgH locus

21
Q

What is the antibody heavy chain initially composed of?

A

~500 V segments
12 D (diversity) segments
4 J segments
1 C region

22
Q

Describe the process of producing a heavy chain.

A

1) D to J recombination is performed using DNA splicing.
2) V to DJ recombination is performed using DNA splicing.
3) Transcription occurs
4) RNA splicing is performed to splice out any gaps between domains and this produces the mRNA.
5) Translation and assembly will then take place.

23
Q

T/F: V(D)J recombination produces only a few different polypeptides.

A

False, V(D)J recombination produces an enormous diversity in polypeptides.

24
Q

How many possible combinations can we have for a light chain?

A

There are 300 V domains and 4 J domains, so we have 1,200 possible combinations.

300 X 4 = 1,200 possible combinations (not considering variation at the site-specific recombination junctions created by NHEJ proteins).

25
Q

How many possible combinations can we have for a heavy chain?

A

There are 500 V domains, 12 D domains, and 4 J domains, so we have 24,000 possible combinations.

500 X 12 X 4 = 24,000 possible combinations (not considering variation at the site-specific recombination junctions created by NHEJ proteins).

26
Q

Are the light and heavy chains dependent or independent of each other?

A

They are independent of each other.

27
Q

How many light chain-heavy chain combinations are there?

A

1,200 light chain combinations
24,000 heavy chain combinations

1,200 X 24,000 = 28,800,000 possible antibody molecules (not considering variation at the site-specific recombination junctions created by NHEJ proteins).

28
Q

Where does the antibody reside once the B cell produces it? How is it oriented?

A

The antibody is planted in the cell membrane with the “sticky” surface outwards so that it can bind the antigen.

29
Q

T/F: Most antibodies encounter antigens and bind to them.

A

False! Most antibodies never encounter antigens that they can bind to.

30
Q

What does an antibody do once it recognizes an antigen (besides binding to it)?

A

It signals their B cells to proliferate.

31
Q

What happens to B cells during proliferation? What is the purpose of this?

A

The variable regions of the antibody genes are deliberately mutated. The purpose of this is to obtain antibodies with even higher affinities to antigen.

32
Q

What happens after the B cell proliferates and produces the mutated antibodies?

A

The B cells with the antibodies with the highest affinities survive while the ones with lower affinities commit suicide via apoptosis.

33
Q

What do the B cells with the highest affinities do?

A

They give rise to plasma cells and memory B cells.

34
Q

What are memory cells good for? Where do the antibodies sit?

A

The memory cells are good for fighting foreign substances if you’ve already recognized it. This is why we use vaccinations. The antibodies sit in the cell membrane and act as receptors.

35
Q

What do plasma cells do?

A

Secrete antibodies into the blood.

36
Q

What do antibodies in the blood do?

A

They latch onto antigens and serve as a recognition site for macrophages to come eat the antigens.

37
Q

What is the first step in the Western Blot?

A

SDS-PAGE

SDS Polyacrylamide Gel Electrophoresis

38
Q

Describe the process of SDS-PAGE.

A

1) We take protein from a cell and purify it.
2) Then, we take this protein and mix it with SDS (negatively charged detergent), which gloms onto the proteins, causing the proteins to stretch out like DNA. The abundance of negative charges in the SDS overwhelms any positive charges in the protein.
3) The protein/SDS complexes are run out on a polyacrylamide gel.

39
Q

What do polyacrylamide gels work best for?

A

They work better for smaller things. This is fine because most proteins are small compared to DNA.

40
Q

How are polyacrylamide gels similar to agarose gels?

A

It is like an obstacle course for the proteins. The smaller the protein, the faster it runs through the obstacle course.

41
Q

What do we do with the polyacrylamide gel after we run it?

A

We place the gel onto a membrane (nitrocellulose or PVDF) and into the western blot apparatus. An electric current is then used to transfer the protein from the gel onto the membrane.

42
Q

What happens to the membrane after the electric current is applied?

A

The membrane containing all of the protein from the cells or tissue is then exposed to an antibody that only binds to the protein of interest.

43
Q

What happens after the antibody binds to the protein of interest?

A

1) A second antibody that has a chemiluminescent molecule attached to it recognizes the first antibody and is added.
2) The membrane is exposed to a photographic film. The black bands on the film represent the protein of interest.

44
Q

What is the Western Blot used for?

A

Visualizing proteins like the Beta-globin protein

45
Q

What are the lanes used for on the Western Blot?

A

Lane 1: Red blood cells
Lane 2: Brain cells
Lane 3: Intestinal cells

Alex's Genetics (38 decks)

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