Question 1

Which of the following best describes the structure of an IgG antibody?

Accepted Answer

A tetrameric protein composed of two identical heavy chains and two identical light chains, held together by disulfide bonds.

Question 2

In an indirect ELISA designed to detect antibodies against HIV in a patient's blood, which component is immobilized on the ELISA plate first?

Accepted Answer

The HIV antigen (e.g., gp120 protein)

Question 3

Which of the following statements about epitopes is CORRECT?

Accepted Answer

A conformational epitope is only recognized when the protein is in its native folded state.

Question 4

Why are secondary antibodies often conjugated to enzymes such as horseradish peroxidase (HRP) in immunological techniques?

Accepted Answer

To allow detection of the antibody-antigen complex by producing a measurable color or light signal.

Question 5

A researcher wants to determine the subcellular location of a protein in cancer cells. Which technique should they use?

Accepted Answer

Immunofluorescence microscopy

Question 6

In a Western blot, what is the purpose of transferring proteins from an SDS-PAGE gel to a membrane?

Accepted Answer

To immobilize the proteins for detection with antibodies.

Question 7

Which of the following best explains why polyclonal antibodies can recognize multiple epitopes on the same antigen?

Accepted Answer

They are a mixture of antibodies produced by different B cell clones, each recognizing a different epitope.

Question 8

A blood sample is analyzed by flow cytometry using mouse anti-CD4-TRITC and mouse anti-CD8-FITC antibodies. Which cell type will fluoresce green?

Accepted Answer

CD8+ cytotoxic T cells

Question 9

Which of the following steps is unique to sandwich ELISA compared to indirect ELISA?

Accepted Answer

Use of two primary antibodies that recognize different epitopes on the same antigen.

Question 10

In immunoprecipitation, what is the main purpose of using agarose beads coated with antibodies?

Accepted Answer

To selectively bind and isolate a specific protein (antigen) from a cell lysate.

Question 11

A scientist wants to purify hexokinase from a liver cell lysate. Which technique should they use?

Accepted Answer

Immunoaffinity chromatography

Question 12

Which of the following is a critical reason for using a blocking protein such as BSA in ELISA and Western blotting?

Accepted Answer

To prevent non-specific binding of antibodies to the plastic or membrane.

Question 13

Which of the following best describes the detection principle of a flow cytometer?

Accepted Answer

It detects and quantifies fluorescence emitted by individual cells labeled with fluorophore-conjugated antibodies.

Question 14

Why is it important to use primary antibodies from different animal species in co-localization immunofluorescence microscopy?

Accepted Answer

To allow the use of secondary antibodies conjugated to different fluorophores that specifically recognize each primary antibody.

Question 15

Which of the following best explains why a low pH buffer is used to elute proteins from an immunoaffinity chromatography column?

Accepted Answer

Low pH partially denatures the antibodies, causing them to release the bound antigen.

Question 16

A researcher observes a yellow signal in a merged immunofluorescence microscopy image after staining with FITC (green) and TRITC (red). What does this indicate?

Accepted Answer

The two proteins of interest are co-localized in the same cellular compartment.

Question 17

Which of the following is a key advantage of using monoclonal antibodies over polyclonal antibodies in research?

Accepted Answer

Monoclonal antibodies recognize a single epitope, providing higher specificity.

Question 18

Which of the following best describes the role of a secondary antibody in a Western blot?

Accepted Answer

It binds to the primary antibody and is conjugated to an enzyme for detection.

Question 19

In an experiment, a scientist uses immunoprecipitation to identify proteins that interact with Protein X. After SDS-PAGE, two bands are observed: one at 85 kDa and one at 30 kDa. What is the most likely explanation?

Accepted Answer

Protein X (85 kDa) interacts with another protein (30 kDa), which was co-precipitated.

Immunological Techniques in Biochemistry: Antibody-Based Methods and Applications

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