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Biology Definitions

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MacrophageA type of Phagocytic cell that ingests and destroys foreign substances and cells. Also responsible for stimulating T Cells. A type of white blood cell. Although similar to Dendritic Cells, Macrophages are found throughout the body and tissues, whereas Dendritic cells tend to inhabit the Lymph Nodes.Phagocytic Cell, T Cell, Cellular Immunity
Mature mRNAMessenger RNA in a eukaryotic cell that has had certain segments removed and other segments spliced together so as to have the correct formula for the protein which the cell intends to make. Note that certain parts of the original gene are not used.Immature mRNA, RNA Splicing
Mendelian GeneticsA theory, proposed by Mendel in the 1860s, which proposed two laws describing the transmission of hereditary traits: the Law of Segregation (The First Law), and the Law of Independent Assortment (The Second Law). Also known as "Mendelian Inheritance". In the 20th century, small flaws in this theory were improved on with the Chromosomal Theory of Inheritance, which takes into account recombination between homologous chromosomes.Law of Segregation, Law of Independent Assortment, Chromosomal Theory of Inheritance
Meselson-Stahl experimentA 1958 experiment by Matthew Meselson and Franklin Stahl which showed that DNA replication is semiconservative. That is, it showed that when DNA replicates into two copies, each copy contains one strand from the original DNA molecule and one newly created strand of DNA.DNA, Replication
Messenger RNAMessenger RNA (mRNA) is a type of RNA that is created from DNA during transcription. The mRNA sequence complements the section of DNA from which it is transcribed (T->A, C->G, G->C), except that Uracil is used instead of Thymine (A->U). Sections of the RNA polymer may be removed (splicing) before the mRNA leaves the nucleus and enters the cytoplasm where it attaches to a Ribosome and is translated into a protein. As the messenger RNA is "read" by the Ribosome, amino acids are added to the protein based on the last 3 nucleotides (codon) that were read. For example, if the last RNA codon was CAU, a Histidine would be added to the end of the protein.tRNA, RNA, RNAi, DNA, codon, Protein
MetaphaseSub stage of Mitosis during which the chromosomes (each consisting of two identical chromatid from the S phase) are aligned in a 2-D plane (called an "equatorial plane"), and spindles on opposite sides of the cell attach to each of the chromatid.Cell Cycle Phases
Metaphytamulti-cellular, eukaryotic plantsProtozoa, Metazoa, Eukaroyote, Prokaryote
Metazoamulti-cellular, eukaryotic animalsProtozoa, Metaphyta, Eukaryote, Prokaryote
MethylaseAn enzyme that adds methyl groups to DNA or RNA. For example, some bacteria that use restriction enzymes to battle bacteriophage (viruses) use methylase to add methyl groups to its own DNA so that its own restriction enzymes can't bind to and destroy its native DNA. If by accident, methylase adds a methyl group to viral DNA, that virus will become immune to that bacteria's restriction enzymes.Restriction Enzyme
MHC Class IIMolecules on the surface of Dendritic cells which allow these cells to "present" oligopeptides (antigens) from substances or cells that have been digested by the dendritic cell and then broken up into oligopeptides. A Macrophage has many of these MHC Class II receptors on its surface, displaying different sections of the foreign invader it has ingested.Dendritic Cell, Antigen, Oligopeptide, Macrophage, Cellular Immunity, T Helper Cell
MicroarrayA tool used by biologists to analyze a genome (DNA or RNA), antibodies, or proteins. A microarray consists of different probes that are covalently bonded to a substrate (typically, a microchip or glass slide). The probes consist of small sequences of DNA, RNA, or proteins which can hydrogen bond (hybridize) to the target of interest. The targets are labeled in some way (flourescent dye, radioactive) so that the scientist can see where the targets have hybridized to the probes, and thus determine which sequences are present in the target since the locations of the probes are known in advance. Microarrays have lost some popularity as other sequencing techniques have become available and less costly (e.g. Pyrosequencing). Note that Microarray analysis is limited in that you can only look for sequences that you have placed on the "chip" as probes.DNA, RNA, Hydrogen Bond, Polymerase Chain Reaction, Pyrosequencing
Microbea microscopic organism; often used to describe very small organisms that cause disease; examples include bacterium, viruses, protozoaVirus, Bacteria, Protozoa
MicroRNA (miRNA)Small RNA molecules (~22 base pairs) that are able to pair with a messenger RNA (mRNA) and somehow prevent its translation. Gene Regulation, Translational Regulation
MicrosomeIf you centrifuge a cell, the endoplasimic reticulum will be sheared into small particles called microsomes ("small things") which have Ribosomes attached. These "small things" are the vesicles of the Rough Endoplasmic Reticulum.Ribosome
Microtubule AntagonistThe spindle fibers that pull chromatin apart during Mitosis are made from microtubules. A Cell Biologist, studying the process of Mitosis, will often use a Microbule Antagonist to prevent mitosis from progressing to Anaphase (it gets stuck in Metaphase). Colcemid is an example of a drug that can be used as a Microtubule Antagonist.Cell Cycle Phases, Mitosis, Anaphase, Metaphase
Minimal MediaA food source for growing cultures of bacteria and other organisms, which only contains the minimal necessities for growing wild-type. A given organism can sometimes be grown on rich media, and then transferred to minimal media, to discover mutants which have lost the ability to create certain biochemicals.Agar, Rich Media, Wild-Type
Mismatch Detection and Repair EnzymesDNA Polymerase sometimes makes mistakes when creating a new strand of DNA. For example, it may add an Adenine (A) where it should have put a Guanine (G), causing a mutation. Detection and Repair Enzymes look for these kinds of mistakes, and correct them. Because the Adenine-Thymine and Cytosine-Guanine combinations have the same lengths, Detection and Repair Enzymes can look for "bumps" in the DNA strand. In some organisms, the parent strand has been methlyated so that these repair enzymes can determine which strand has the incorrect base and then subsitute the correct base. Some forms of hereditary colon cancer are caused by mutations in the genes that produce these enzymes.DNA Proofreading, Methylate, DNA Polymerase
Missense MutationA mutation which causes one DNA base to be replaced by another, resulting in one amino acid being substituted for another in the translated protein. Note that many single DNA base substitutions do not cause changes in the final amino acid sequence because of the redundancy of the genetic code.Conditional Lethal, Translation, Gene, Mutation, DNA, Amino Acid, Protein, Genetic Code
MitochondriaOrganelles in the cytoplasm of eukaryotic cells which are responsible for energy production (ATP). Mitochondria have their own circular DNA, and are believed to have once been separatic, symbiotic organisms. Both males and females inherit mitochondrial DNA from their mother.Organelle, Cytoplasm, Eukaryote, ATP
MitogenGrowth Stimulatory Agent. An agent that stimulates mitosis. For example, when a B Cell encounters its matching antigen, the antigen acts as a mitogen and causes the B Cell to grow and divide, so that the body will have more B Cells to fight off the foreign invader.Platelet, Cell Cycle, Mitosis, Antigen, Epitope
Mitosis PhaseAlso known as "M Phase". The cell cycle phase which results in two identical daughter cells, by ensuring that equal parts of the replicated DNA (created during S Phase) are distributed to each daugther. The Mitosis Phase consists of several sub-phases: 1.) Interphase 2.) Prophase 3.) Metaphase 4.) Anaphase 5.) Telophase.Cell Cycle Phases, Interphase, Metaphase, Anaphase, Telophase
Molecular BiologyMolecular Biology, also called "new biology", is a branch of biology which focuses on macromolecules (DNA, RNA, proteins, etc.) and their participation in heredity and cell function. This branch of biology helped unify the previously disjointed fields of biochemistry and genetics. It utilizes new, advanced techniques and technologies such as PCR.Biochemistry, Genetics, Protein, DNA, RNA, PCR
Molecular Weight StandardsWhen using Gel electrophoresis to separate molecules by their weights, a biochemist may include known molecules, called "molecular weight standards", so that she can compare the positions of the known and unknown molecules after a charge has been applied to the gel.Gel Electrophoresis
Monoclonal GrowthCancers are called monclonal growths because they form populations of clones from a single malignant ancestor cell.Cancer
MonomerA small, simple molecule that can combine with others similar to itself form a polymer. For example, there are four different nucleotides which are monomers, and they can combine to form DNA sequences.Polymer, DNA, RNA, Nucleotide
mRNAAn abbreviation for Messenger RNA. A type of RNA that is used to carry genetic information from the nucleus, after transcription, to the cytoplasm, where it is translated into protein.Messenger RNA, tRNA, RNAi, Protein
Multiple MyelomaA disease/cancer which causes the blood to have greatly elevated levels of antibody molecules. Note that one particular species of antibody dominates over the others, since the cancer started with a mutation in one particular B Cell (which resulted in an unrestrained monclonal growth), and each B Cell is responsible for producing one particular antibody.B Cell, Plasma Cell, Antibody, Cancer
MurineOf or relating to rats, mice, and other rodents of the Muridae family or Murinae subfamily.XMRV
MutagenA substance that can cause a mutation in DNA. A mutagen can also be a carcinogen (cancer causing).Carcinogen
MutationA change in the genetic code (one of the genes) of an organism, resulting in a change in one or more of the proteins created by cells that use the affected gene. A mutation may result in a new, non-parental trait (phenotype), it may result in cancer, or it may result in the death of the organism.DNA, Gene, Phenotype, Cancer

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