An assay is a procedure in molecular biology

Molecular biology

Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...

 for testing or measuring the activity of a drug

Drug

A drug, broadly speaking, is any substance that, when absorbed into the body of a living organism, alters normal bodily function. There is no single, precise definition, as there are different meanings in drug control law, government regulations, medicine, and colloquial usage.In pharmacology, a...

 or biochemical

Biochemistry

Biochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...

 in an organism

Organism

In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

 or organic sample

Sample (material)

In general, a sample is a limited quantity of something which is intended to be similar to and represent a larger amount of that thing. The things could be countable objects such as individual items available as units for sale, or a material not countable as individual items. Samples of countable...

. A quantitative assay may also measure the amount of a substance in a sample. Bioassay

Bioassay

Bioassay , or biological standardization is a type of scientific experiment. Bioassays are typically conducted to measure the effects of a substance on a living organism and are essential in the development of new drugs and in monitoring environmental pollutants...

s and immunoassay

Immunoassay

An immunoassay is a biochemical test that measures the presence or concentration of a substance in solutions that frequently contain a complex mixture of substances. Analytes in biological liquids such as serum or urine are frequently assayed using immunoassay methods...

s are among the many varieties of specialized biochemical assays. Other assays measure processes such as enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 activity, antigen capture, stem cell

Stem cell

This article is about the cell type. For the medical therapy, see Stem Cell TreatmentsStem cells are biological cells found in all multicellular organisms, that can divide and differentiate into diverse specialized cell types and can self-renew to produce more stem cells...

 activity, and competitive protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 binding.
A cytotoxicity assay measures how toxic a chemical compound

Chemical compound

A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 is to cells

Cell (biology)

The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

.

• MTT assay
  MTT assay
  The MTT assay and the MTS assay are colorimetric assays for measuring the activity of enzymes that reduce MTT or close dyes to formazan dyes, giving a purple color. A main application allows to assess the viability and the proliferation of cells...
  
  
• SRB (Sulforhodamine B
  Sulforhodamine b
  Sulforhodamine B or kiton red is a fluorescent dye with uses spanning from laser-induced fluorescence to the quantification of cellular proteins of cultured cells. The red, solid, water-soluble dye is primarily used as a polar tracer.The dye has maximal absorbance at 565 nm light and...
  
  ) assay

Assays for studying interaction

Interaction

Interaction is a kind of action that occurs as two or more objects have an effect upon one another. The idea of a two-way effect is essential in the concept of interaction, as opposed to a one-way causal effect...

s of proteins with DNA

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 include:

• DNase footprinting assay
  DNase footprinting assay
  A DNase footprinting assay is a DNA footprinting technique from molecular biology/biochemistry that detects DNA-protein interaction using the fact that a protein bound to DNA will often protect that DNA from enzymatic cleavage. This makes it possible to locate a protein binding site on a particular...
  
  
• Filter binding assay
  Filter binding assay
  In biochemistry or chemistry, one of the ways to learn about an interaction between two molecules is to determine the binding constant, which is a number that describes the ratio of unbound and bound molecules...
  
  
• Gel shift assay

• Bicinchoninic acid assay
  Bicinchoninic acid assay
  The bicinchoninic acid assay , also known as the Smith assay, after its inventor, Paul K. Smith at the Pierce Chemical Company, is a biochemical assay for determining the total level of protein in a solution , similar to Lowry protein assay, Bradford protein assay or biuret reagent...
  
   (BCA assay)
• Bradford protein assay
  Bradford protein assay
  The Bradford protein assay is a spectroscopic analytical procedure used to measure the concentration of protein in a solution. It is subjective, i.e., dependent on the amino acid composition of the measured protein. The Bradford protein assay was developed by Marion M...
  
  
• Lowry protein assay
  Lowry protein assay
  The Lowry protein assay is a biochemical assay for determining the total level of protein in a solution. The total protein concentration is exhibited by a color change of the sample solution in proportion to protein concentration, which can then be measured using colorimetric techniques. It is...
  
  
• Secretion assay
  Secretion assay
  Secretion assay is a process used in cell biology to identify cells that are secreting a particular protein . It was first developed by Manz et al. in 1995....
  
  

A cell-counting assay may determine the number of living cells, the number of dead cells, or the ratio of one cell type to another, such as numerating and typing red

Red blood cell

Red blood cells are the most common type of blood cell and the vertebrate organism's principal means of delivering oxygen to the body tissues via the blood flow through the circulatory system...

 versus different types of white

White blood cell

White blood cells, or leukocytes , are cells of the immune system involved in defending the body against both infectious disease and foreign materials. Five different and diverse types of leukocytes exist, but they are all produced and derived from a multipotent cell in the bone marrow known as a...

 blood cell

Blood cell

A blood cell, also called a hematocyte, is a cell normally found in blood. In mammals, these fall into three general categories:* red blood cells — Erythrocytes* white blood cells — Leukocytes* platelets — Thrombocytes...

s.