Neophyte glossary
Here are some terms to help you learn more about neurology, hepatology, oxidative stress or lab techniques.
- ammonia
- Gaz composed by nitrogen and hydrogen (NH3). When it dissolved in water (like blood composition), it become on its soluble form and ionic NH4+, its aqueous base.
- antibody
Biologic molecule from immune system. Its role is to neutralize pathogenes or initiate an immune reaction.
Its properties, mainly to be specific to an unique antigene, make them useful tool in molecular biology. They could be develop easily by animal immunization, they are employed to detect a specific protein.
An antibody recognize an specific antigen by its variables chains (VH and VL). Each antibody possess a different combinaison of variables chains, explaining the available and large antibody diversity.
- astrocyte
Nervous system glial cells. Among roles, we note :
- important part of brain-blood barrier
- support and structure of cerebral tissue
- cells feeder for neurons (energetic source, neurotransmitter synthesis...)
- blood-brain barrier
- Cellular barrier demarking bloodstream and brain tissue. Endothelial cells form tight junctions allowing compounds to flow in by selective and active transport (by opposition to passive diffusion). The vessels are contained by the feet of pericytes and astrocytes, isolating neurons.
- cell
Living unit of an organism. A cell is composed by many organites :
- nucleus : DNA localization.
- mitochondria : energy production site.
- endoplasmic reticulum, ribosomes, Golgi apparatus : proteins synthesis.
- lysosome, peroxisome : destruction of damaged or life-ended proteins.
- membrane : barrier between internal (cytoplasm) and external environment of cell et manage exchanges.
Schematic representation of a cell and its principals organites
- nucleus : DNA localization.
- cirrhosis
- Consequences of chronic attacks affecting liver inducing a loss of liver cells, fibrosis and tissue disruption.
- ELISA
Immunological technique to detect a biological substance.
The sandwich ELISA is started by attaching a first antibody protein X to a plastic plate (1). Each well is then incubated with each sample having to be determined (2). A second anti-X antibody binds to this protein X (3). This antibody is then be detected by an antibody (4) coupled with an enzyme in which the hydrolysis of the substrate causes a color change (5). Thus a dark color reflects a larger concentration of X.
Schematic of a sandwich ELISA
- genome
- All organism pool of genes. Genes are encoded by DNA.
- HPLC
Chromatographic technique used to analysis of complex sample, such as cerebrospinal fluid or blood.
First, we treat the sample, by chemical reaction, to add a fluorophore molecule. Then the sample is loaded on a column coated with a hydrophobic compound (molecules could bind to them). Aqueous buffer flows through the system without affecting the protein-column connections. Thereafter, we introduce a hydrophobic buffer gradually. The molecules from the hydrophobic buffer compete molecular interactions in the column, taking out the sample. Fluorescence will be read by a detector. As percentage of second buffer increases with time, interactions will be destroyed gradually, allowing separation of sample molecules (they all have different properties affecting this link).
Each peak represents a different substance (here, amino acids) while the height of the peak reflects the amount.
- immunohistochemistry
- Immunological technique for localisation of cellular or molecular structures in a tissue or cells.
The cells must be grown on a piece of plastic while the tissues are cut into thin slices. Several methods such as microtome, vibratome, cryotome achieve cuts of about 5-50 um. The cells must be fixed and permeabilized (in the case of an intra-cellular antigen) to provide access in cells to antibodies. An antibody specific to a protein of interest is incubated, followed by a secondary antibody, recognizing the first antibody. By enzymatic reaction with a substrate, color generated can be seen under a microscope. Using a fluorophore allows observation under a fluorescent microscope.
The fluorophore is activated by UV light (excitation) and it emits fluorescence (emission) detected by the microscope. There are many exciting and emitting fluorophores to different wavelengths, generating different colors. It becomes interesting to make double or triple markings, detecting and 2 or 3 parameters simultaneously. - immunoprecipitation
- Immunoassay technique to detect a change or molecular interaction of a specific protein. The protein of interest is first immunoprecipitated from a cell lysate using an antibody specific to it. This antibody-protein mixture is then incubated with agarose beads coupled with G proteins (these proteins have the particularity of a strong antibodies binding). Beads are heavier and can be separated by centrifugation.
After isolation from a complex mixture (cell lysate) of a protein of interest, it's loaded on a SDS-PAGE. By a Western blot procedure, detection of the protein with a different antibody allow to highlight a modification or an interaction. - microdialysis
- Surgical technic where we insert a canula attached to a membrane inside the brain. A physiological liquid is circulating trough pumping and, because membrane pores, small molecules are collected in tubes. This technic allow obtention of alive animal cerebrospinal fluid.
- portal hypertension
High pressure on the portal vein of the liver. It creates a network of collateral vessels that affect the hemodynamic and blood flow and can break more easily, causing bleeding.
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- RT-PCR
Technique used to detect and quantify mRNA levels of specific genes in cells or tissues.
Using an enzyme, transcriptase reverse, we first transcribe RNA into DNA. DNA is after amplified by an another enzyme, polymerase. Final product is separated by its size on a agarose gel and is visualized with a dye under ultra-violets rays.
Schematic representation of DNA amplification by PCR
Example of a typic agarose gel. In 1, a marker of known molecular weigth allow estimation of our sample's fragment.
- tyrosine
- One of the 20 amino acids, structual units of proteine.
Chemical structure of tyrosine. Peptidic unit (NH2-CH-COOH) is link to residue (CH2-C6H4-OH).
When it is modified by ROS, -OH become -NO2 (nitrotyrosine). - urea cycle
- Set of biochemical reactions using ammonia as starting material to transform it into urea. These reactions are catalyzed by enzymes in the liver.
- Western blot
- Immunological technique used to detect a protein. Following the acquisition of a sample of our choice (from cell cultures or animal tissue or human), it's applied on a gel electrophoresis (sodium dodecyl sulfate polyacrylamide gel electrophoresis, SDS-PAGE). The pores of the gel allow separation of proteins by their molecular weight. Proteins migrate down in gel through an electric current (hence the term electrophoresis).
The proteins in the polyacrylamide gel are then transferred to a membrane. This support is more appropriate for the immunologic detection. This membrane is then incubated with an antibody specific to our protein of interest. This antibody is then linked to a second antibody, itself coupled with an enzyme. The addition of a chemoluminescent substrate allow to view the presence of bands representing the protein on a X-ray film.
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