Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Enzyme induction and repression

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The third variation of the ELISA is known as the cap-

ture or sandwich ELISA. As the names imply, the antigen is

sandwiched between the primary and secondary antibodies. In

this technique, the primary antibody is bound to the bottom of

the wells, rather than the antigen. Then, the antigen is added.

Where the bound antibody recognizes the antigen, binding

occurs. A so-called blocking solution is added, which occupies

the vacant antibody sites. Then, an enzyme-labeled secondary

antibody is added. The secondary antibody also recognizes the

antigen, but the antigenic recognition site is different than that

recognized by the primary antibody. The result is that the anti-

gen is sandwiched in between two bound antibodies. Again, a

color reaction reveals the complex.

The ELISA procedure has many applications. The pro-

cedure can provide qualitative (“yes or no”) and quantitative

(“how much”) information on a myriad of prokaryotic and

eukaryotic antibodies. Serum can be screened against a battery

of antigens in order to rapidly assess the range of antibodies

that might be present. For example, ELISA has proven very

useful in the scrutiny of serum for the presence of antibodies

to the Human immunodeficiency virus.

See alsoLaboratory techniques in immunology

EEnzyme induction and repressionNZYME INDUCTION AND REPRESSION

Microorganismshave many enzymesthat function in the myr-

iad of activities that produce a growing and dividing cell.

From a health standpoint, some enzymes are vital for the

establishment of an infection by the microbes. Some enzymes

are active all the time. These are known as constitutive

enzymes. However, other enzymes are active only periodi-

cally, when their product is required. Such enzymes are known

as inducible enzymes.

The ability of microorganisms such as bacteriato con-

trol the activity of inducible enzymes is vital for their survival.

The constant activity of such enzymes could result in the over-

production of a compound, which would be an energy drain on

the microorganism. At the same time, inducible enzymes must

be capable of a rapid response to whatever condition they are

geared to respond.

The twin goals of control of activity and speed of

response are achieved by the processes of induction and

repression.

Induction and repression are related in that they both

focus on the binding of a molecule known as RNApolymerase

to DNA. Specifically, the RNA polymerase binds to a region

that is immediately “upstream” from the region of DNA that

codes for a protein. The binding region is termed the operator.

The operator acts to position the polymerase correctly, so that

the molecule can then begin to move along the DNA, inter-

preting the genetic information as it moves along.

The three-dimensional shape of the operator region

influences the binding of the RNA polymerase. The configu-

ration of the operator can be altered by the presence of mole-

cules called effectors. An effector can alter the shape of the

polymerase-binding region so that the polymerase is more eas-

ELISA assay 96 well test plate.

A technician adds blood samples to a multi-welled sample tray during

an Enzyme-linked ImmunoSorbent Assay (ELISA) test for viral

diseases such as AIDS and Hepatitis B and C. Blood serum of the

patient is added to burst T cells of blood that have been infected with

disease. A color change occurrs if viral antibodies are present.

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