Glossaries

Key Terms and Definitions

The terms and definitions in our glossaries are intended to provide you with a better understanding of words frequently used on this website and/or in reference to published articles and other sources. Information contained in our glossaries is no substitute for your healthcare professional's advice.

ABC
Abacavir.
ADCC
Antibody-dependent cellular cytotoxicity.
ADR
Adverse drug reaction.
AIDS
Acquired immunodeficiency syndrome.
AIDS Dementia Complex (ADC)
HIV encephalopathy.
AIDS-Defining Condition
AIDS-defining illness.
AIDS-Defining Illness
An opportunistic or malignant condition that is included in category C of the CDC (Centers for Disease Control) case definition and is a reason for an AIDS diagnosis. The 26 conditions include candidiasis, cytomegalovirus infection (CMV), Kaposis Sarcoma (KS), mycobacterium avium complex (MAC), pneumocystis jiroveci pneumonia (PCP), progressive multifocal leukoencephalopathy (PML), pulmonary tuberculosis, invasive cervical cancer, and wasting syndrome. cf: AIDS cf: Centers for Disease Control
APV
Amprenavir.
ARS
Acute retroviral syndrome.
ATV
Atazanavir.
Abacavir (ABC)
Generic name for Ziagen®. cf: nucleoside reverse transcriptase inhibitor
Acetylation
During acetylation of proteins, enzymes add an acetyl group (COCH3) to the amino group. Such posttranslational modifications have a strong influence on the properties and functions. For example, acetylated proteins are required to make genes on the DNA accessible for transcription.
Acquired Immunodeficiency Syndrome (AIDS)
The late stage of HIV disease; AIDS involves the loss of function of the immune system as CD4 cells are infected and destroyed, allowing the body to succumb to opportunistic and malignant diseases. The CDC defines AIDS as a CD4 cell count below 200 cells/mm3 or the presence of at least one opportunistic illness in an HIV positive individual (Category C).
Acute
Symptoms that begin abruptly or over a short period of time. Acute bronchitis usually lasts a week or two.
Acute HIV Infection
The initial stage of infection with HIV, prior to the development of antibodies. Acute HIV infection is characterized by a drop in CD4 Cell counts and an increase in HIV levels in the blood. Some, but not all, individuals experience flu-like symptoms during this period of infection. These symptoms can include fever, inflamed lymph nodes, sore throat, and rash. cf: seroconversion acute retroviral syndrome (ARS) asymptomatic HIV infection symptomatic HIV infection acquired immunodeficiency syndrome (AIDS)
Acute Retroviral Syndrome (ARS)
A combination of flu-like symptoms (e.g. fever, sore throat, skin rash, inflamed lymph nodes) that accompanies acute (primary) HIV infection in some patients. These symptoms may last from 7 to 10 days and then go away. Often used as a synonym to acute HIV infection. cf: acute HIV infection.
Adenine
The purine base adenine is a component of the nucleic acids DNA and RNA. In double-stranded DNA molecules, adenine and thymine form a base pair.
Adenoviruses
Adenoviruses are highly infectious for humans and cause diseases of the respiratory tract. The viruses contain a double-stranded DNA molecule. Because they can relatively easily enter the cells of blood vessels, the brain, the liver and the respiratory tract, adenoviruses are used as vectors in gene therapy.
Adherence
Compliance.
Adverse Drug Reaction (ADR)
Any drug effect that is unwanted, unpleasant, or potentially harmful. These effects may be mild and may disappear when the drug is stopped or subside as the body adjusts to the drug (short-term ADR). Other ADRs, such as skin rashes, anemia, or organ damage, are more serious (long-term ADR).
Adverse Effect
Adverse drug reaction.
Adverse Event
Adverse drug reaction.
Agrobacteria
The soil bacterium Agrobacterium tumefaciens is a natural genetic engineer: it incorporates Ti plasmids into plants. The infected, proliferating cells form root collar galls and other tumours on the stem of the plant and produce substances (opines) which the agrobacteria use to grow. Genetic engineers make use of this transfer of genetic information to transport foreign genes into plant cells and incorporate them in the plant genome. To do this, the original tumour genes in the Ti plasmids are replaced by foreign genes. An example of transfection of several genes in the host organism is transgenic rice: Golden Rice Viruses (blue) in infected cells.
Allele
The term allele derives from the Greek allelon (belonging together). An allele is one of several alternative forms of the same gene, located at a particular point on a chromosome. A cell with two identical alleles, i.e. identical genes on its pairs of chromosomes, is homozygous. If the genes differ, the cell is heterozygous.
Amino Acid
An organic compound that is a basic structural unit of peptides and proteins.
Amino acids
Amino acids are the building blocks of proteins. They are water-soluble organic compounds with both acidic and basic properties. There are 20 different natural amino acids. During protein biosynthesis, translation, the individual amino acids are linked together to form a chain. A chain of less than a hundred amino acids is called a peptide. Every amino acid contains at least one amino group (-NH2).
Amplification
The enrichment and copying of a section of nucleic acid molecules with the aid of the PCR is called amplification.
Antibiotic resistance
Among microorganisms, there is fierce competition for resources. Antibiotics are chemical weapons that are often used to suppress the growth of bacteria. The bacteria defend themselves with enzymes that counteract the effects of antibiotics and so give them resistance. For example, the enzyme beta-lactamase cleaves the antibiotic penicillin and thus makes it ineffective. The gene for beta-lactamase is located on a plasmid and can thus be passed from bacterium to bacterium. In the treatment of bacterial infections, resistant organisms are a set-back, as they make the drug ineffective. However, genetic engineers make use of resistance genes: they introduce the resistance gene into a plasmid togetherwith the section of DNA they want to clone. Only bacteria that have taken up the plasmid are able to multiply in the presence of an antibiotic.
Antibodies
Immunoglobulins, so-called antibodies, are one of the most important weapons the immune system has to fight pathogens. Antibodies recognize and bind very specifically to particular well-defined structures, antigens (antibody-antigen reaction). They thus fight off bacteria and viruses on the basis of their characteristic features. They are produced by defensive cells called B Lymphocytes. Each one of these cells produces antibodies of well-defined specificity. Their ability to recognize structures makes antibodies the ideal tools in molecular biology. Thanks to the development of monoclonal antibodies, scientists and physicians have access to precisely characterized antibodies.
Antibody
Also known as immunoglobulin. A protein produced by the body's immune system that recognizes and fights infectious organisms and other foreign substances that enter the body. Each antibody is specific to a particular piece of an infectious organism or other foreign substance.
Antibody-Dependent Cellular Cytotoxicity (ADCC)
An immune response in which antibodies bind to target cells and identify them for attack by other immune cells (natural killer cells and macrophages).
Anticholinergic Bronchodilator
This acts on the cholinergic receptor to help dilate (open) the bronchial tubes (airways), to help move air more easily into and out of the lungs.
Antigen
Any substance that can stimulate the immune system to produce antibodies against it. Antigens include bacteria, viruses, proteins, and other foreign materials. The HIV contains various antigens (e.g. gp120, p24).
Antigen
Antigen is a term derived from antibody and -gen, and refers to a substance that causes the production of antibodies. After entering an organism, antigens trigger a specific immune response. This is expressed in the formation of antibodies (humoral immune response) or the development of specific defensive cells (cellular immune response).
Antigene Presenting Cell
A cell (e.g. dendritic cell) that processes antigen proteins and displays the short peptide fragments on its surface in conjunction with major histocompatibility (MHC) proteins, enabling recognition by T-cells, which iniitiate an immune response.
Antiretroviral Therapy
General term for treatment with antiretroviral drugs that reduce viral replication and hence the progression of disease. The antiretroviral therapy recommended for HIV infection is referred to as highly active antiretroviral therapy (HAART), which uses a combination of medications to attack HIV at different points in its life cycle. cf: highly active antiretroviral therapy cf: replication cycle
Antisense RNA Antisense technique
The antisense technique specifically blocks the production of certain proteins in a cell using artificial antisense RNA with a sequence that is complementary to the sequence of the cellís own mRNA of the target gene. This antisense RNA binds specifically to its target, and so blocks the translation of the mRNA.
Apoptosis
Programmed cell death.
Arabidopsis thaliana - mouse-ear cress
This wild plant found worldwide is a model organism and is the subject of research as a representative dicotyledonous plant. Arabidopsis has a high degree of similarity to important cultivated plants. Its genome consists of five chromosomes with around 25,000 genes. At the end of 2000 the genome of Arabidopsis became the first plant genome to be completely decoded.
Arber, Werner
In 1967, the Swiss microbiologist Werner Arber discovered restriction enzymes: molecular scissors that cut through the DNA molecule in quite specific places. For the discovery, isolation and characterization of these important tools in genetic engineering, Arber, together with D. Nathans and H. Smith, received the Nobel prize for medicine in 1978.
Asilomar conference
In 1975, scientists in Asilomar, USA, discussed how to assess and avoid the possible risks of genetic engineering. They issued recommendations which formed the basis of laws, guidelines and safety requirements all over the world.
Assembly
A step in the replication cycle of HIV. HIV proteins and RNA accumulate on and associate with the inner surface of the plasma membrane. As assembly continues, the new HIV leaves the cell. cf: replication cycle.
Asymptomatic HIV-Infection
A period of varying length after acute infection with HIV during which there are no symptoms of HIV infection. At the same time there is ongoing viral replication and a steady deline in CD4 cells. cf: acute HIV infection symptomatic HIV infection acquired immunodeficiency virus (AIDS)
Asymptomatic Phase
Asymptomatic HIV-Infection.
Attachment
A step in the replication cycle of HIV. HIV's envelope protein binds to the cell surface molecule CD4, which allows binding of another envelope protein gp41 to a chemokine receptor (CCR5, CXCR4). Attachment is followed by fusion of HIV with the cell. cf: replication cycle
Attachment Inhibitor
A class of anti-HIV drugs designed to prevent binding of the viral envelope protein to the CD4 receptor of the host cell. cf: entry inhibitor cf: CD4 receptor
Attenuated
Weakened, made less virulent. An attenuated virus is a virus that is still alive but incapable of causing harm. cf: attenuation
Attenuation
Weakening or reducing the level of virulence of a pathogen. An attenuated virus still posseses immunological properties but has a diminished ability to cause disease. Used in vaccines.
Autoclave
The disinfection of equipment and waste is essential in biotechnology and genetic engineering. This is the only way to avoid undesirable microorganisms spreading in the laboratory or escaping into the environment. So all waste and thermally stable equipment is sterilized in autoclaves: pressure vessels with a saturated steam atmosphere, where no organisms can survive temperatures of 120-140°C and pressures of up to 3 bar.
Autosomes
Autosomes are all the chromosomes of a chromosome set with the exception of the sex chromosomes (heterosomes). Humans have 22 pairs of autosomes and two sex chromosomes.
acetylcholine
The neurotransmitter of the parasympathetic nervous system.
agonist
A chemical substance that simulates the action of a drug or a substance occurring naturally in the body.
alpha 1 -antitrypsin (AAT)
An enzyme that normally prevents loss of the lungsí elastic fibres.
antagonist
A chemical substance that opposes the action on the nervous system of a drug or a substance occurring naturally in the body, combining with and blocking its nervous system receptor.
anti-inflammatory
Describes a drug that treats inflammation.
asthma
A chronic inflammatory disorder of the airways often associated with allergy and onset during childhood.