Protein Analysis: SDS-PAGE, 2D Gel Electrophoresis, and ELISA (Vocabulary Flashcards)

A list of vocabulary flashcards covering SDS-PAGE, 2D gels (IEF), and ELISA concepts from the lecture notes.

SDS (sodium dodecyl sulfate)

An anionic detergent that denatures proteins and binds along their length, giving them a uniform negative charge proportional to length; enables separation by size in SDS-PAGE.

Denaturation

The process of unfolding a protein from its native structure, exposing peptide bonds and making it possible for SDS to interact with the protein.

Boiling

Heating step used to provide energy to disrupt stabilizing interactions and unfold proteins during sample prep.

Disulfide bonds

Covalent links between cysteine residues that stabilize protein structure; reduced to allow complete unfolding for SDS-PAGE.

Beta-mercaptoethanol (reducing agent)

A reducing agent used to break disulfide bonds during sample preparation for SDS-PAGE.

SDS-PAGE

Sodium dodecyl sulfate polyacrylamide gel electrophoresis; separates proteins primarily by size after denaturation with SDS.

Polyacrylamide gel

A cross-linked polymer matrix that forms the sieving medium in PAGE.

Wells

Indents in the gel where samples are loaded before electrophoresis.

Coomassie blue staining

A dye that binds proteins in the gel to visualize bands after electrophoresis.

Silver staining

A more sensitive gel stain alternative to Coomassie that can detect smaller amounts of protein.

Cross-linking percentage

The proportion of cross-linker in the gel; higher percentages yield smaller pores and affect resolution.

Native gel

Non-denaturing PAGE where proteins are kept in their native folded state during separation.

Isoelectric focusing (IEF)

First dimension of 2D gel electrophoresis; separates proteins by charge using a pH gradient until they reach their isoelectric point.

Isoelectric point (pI)

The pH at which a protein has zero net charge and stops migrating in the gradient.

Two-dimensional gel electrophoresis (2D-GE)

Two-step separation: first by charge (IEF), then by size (SDS-PAGE) for higher resolution.

ELISA (enzyme-linked immunosorbent assay)

An immunoassay that uses antibodies and an enzyme-coupled detection step to produce a color change indicating presence of a target.

Sandwich ELISA

Format where a coating antibody captures the antigen, and a second enzyme-labeled antibody provides a colorimetric readout.

Indirect ELISA

Format for detecting antibodies in a sample using antigen-coated wells and a labeled secondary antibody for detection.

Antigen

The target protein or molecule recognized by antibodies.

Antibody

A protein that binds specifically to an antigen; can be monoclonal or polyclonal.

Enzyme substrate

A molecule that the enzyme converts into a colored product, enabling detection in ELISA.

Positive result (ELISA)

A color change indicating the presence of the target antigen or antibody in the sample.

Negative result (ELISA)

No color change indicating absence of the target in the sample.

Titer

The concentration or level of antibodies present in a sample.

Subunit

An individual polypeptide that assembles into a larger protein complex; reducing conditions can reveal subunits on SDS-PAGE.

Dimer

A protein consisting of two subunits; may appear as half the total molecular weight if subunits are equal.

Tetramer

A protein composed of four subunits.

Electrode polarity in PAGE

Proteins bound by SDS carry a net negative charge and migrate toward the positive electrode (bottom) during electrophoresis.