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Glossary Term
The genetic material of the nucleus, consisting of deoxyribonucleoprotein, which occurs in two forms during the phase between mitotic divisions: 1) as heterochromatin, seen as condensed, readily stainable clumps; 2) as euchromatin, dispersed lightly staining or nonstaining material. During mitotic division the chromatin condenses into chromosomes.
Glossary Term
Major protein component of chromatin. Highly conserved basic proteins, originally classified into classes based on the relative amounts of arginine and lysine in each protein. The various classes are now termed H1, H2A, H2B, H3, and H4. In chromatin, they are found in an octamer, containing two each of H2A, H2B, H3, and H4, complexed with DNA in nucleosomes. The histones in the octamer complex are also known as the core histones. The H1 class of histones, termed the linker histones, is loosely associated with the nucleosome.
Glossary Term
Ubiquitin is a family of widely distributed proteins found in all eukaryotes that contain a highly conserved sequence of 76 amino acids identical in organisms from humans to insects. It participates in diverse cellular functions by conjugation to other proteins through its carboxy terminus. Ubiquitination is associated with many highly regulated biological events including protein degradation, chromatin remodelling, heat shock, cell cycle progression, differentiation, antigen presentation, retrovirus assembly, apoptosis, signal transduction, transcriptional activation, biological clocks, receptor down regulation, and endocytosis. Protein ubiquitination regulates the half-lives of many proteins by targeting them for degradation. Newly discovered families of ubiquitination and deubiquitination enzymes participate in these processes. Ubiquitination enzymes may provide new therapeutic targets and ways of intervention in many human diseases.
Glossary Term
A stretch of repetitive nucleotide sequences (TTAGGG repeats in humans) found at both ends of each chromatid arm that plays a role in chromosome stability during replication.
