Glossary
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| Term | Definition |
|---|---|
| Haemoglobin | Oxygen-carrying protein found in the red blood cells of vertebrates and some invertebrates, made up from four subunits. [Wikipedia entry] |
| Haemopoietic | (haematopoietic) The formation of blood cellular components. This process occurs in myeloid tissue, which is found in the bone marrow and lymphatic tissue, such as lymph nodes or the spleen. All of the cellular components of the blood are derived from haematopoietic stem cells. [Wikipedia entry] |
| Heterochromatin | A type of chromatin that is darkly staining and tightly packaged or coiled throughout the cell cycle and that is, for the most part, genetically inactive. [Wikipedia entry] |
| Histone | The chief proteins of chromatin that act as spools around which DNA winds; they play a role in gene regulation. [Wikipedia entry] |
| Histone acetylation | See histone acetytransferase. [Wikipedia entry] |
| Histone acetyltransferase | An enzyme that acetylates conserved lysine amino acids on histone proteins. [Wikipedia entry] |
| Histone code | Theory that proposes that specific histone-tail modifications effected by enzymes, control the activity of genes in the nucleus, by providing binding sites for regulatory proteins. [Wikipedia entry] |
| Histone deacetylase | HDACs are enzymes that remove acetyl groups from histone proteins. This has the general effect of increasing the positive charge of histones and increasing their attraction for the negatively charged phosphate groups in DNA (see heterochromatin). [Wikipedia entry] |
| Histone methylation | Modification of the primary protein sequence of a histone protein by the addition of one, two, or three methyl groups. This modification alters the properties of the nucleosome and affects its interactions with other proteins. Specific kinds of methylation, e.g. methylation of lysine 9 within the histone H3 molecule are associated with inactive chromatin (see heterochromatin) where genes are relatively inactive. [Wikipedia entry] |
| Histone methyltransferase | (HMT) Enzymes that catalyze the transfer of methyl groups from certain types of histone proteins. [Wikipedia entry] |
| Histone modification | Acetylation, methylation, poly(ADP-ribose)ylation, phosphorylation, ubiquitylation of specific-amino-acid residues on histones, which are believed to control chromatin states. [Wikipedia entry] |
| Homeostasis | Encompasses physiological processes that allow an organism to maintain internal equilibrium. [Wikipedia entry] |
| Homeotic (homeobox, hox) genes | Homeotic genes in general transform parts of the body into structures appropriate to other positions. Genes with a homeobox or Hox domain involved in embryonic development in many organisms from fruit flies to humans. [Wikipedia entry] |
| Homologue | Describes a gene, protein or morphological structure that is similar in both DNA sequence and amino-acid sequence and function between organisms of different species. Real homologies are based on a common evolutionary descent in contrast to convergent evolution or analogies. Genes discovered initially in fruit flies often have homologues in mammals. [Wikipedia entry] |
| Housekeeping gene | Genes required throughout development for the smooth running of the cell's metabolism. Such genes are expressed continuously. [Wikipedia entry] |
