A nucleosome is the basic structural unit of DNA packaging in eukaryotes. The structure of a nucleosome consists of a segment of DNA wound around eight histone proteins and resembles thread wrapped around a spool. The nucleosome is the fundamental subunit of chromatin. Each nucleosome is composed of a little less than two turns of DNA wrapped around a set of eight proteins called histones, which are known as a histone octamer. Each histone octamer is composed of two copies each of the histone proteins H2A, H2B, H3, and H4.
In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name organelle comes from the idea that these structures are parts of cells, as organs are to the body, hence organelle, the suffix -elle being a diminutive. Organelles are either separately enclosed within their own lipid bilayers or are spatially distinct functional units without a surrounding lipid bilayer. Although most organelles are functional units within cells, some function units that extend outside of cells are often termed organelles, such as cilia, the flagellum and archaellum, and the trichocyst.
Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself or by forming a template for the production of proteins. RNA and deoxyribonucleic acid (DNA) are nucleic acids. The nucleic acids constitute one of the four major macromolecules essential for all known forms of life. RNA is assembled as a chain of nucleotides. Cellular organisms use messenger RNA (mRNA) to convey genetic information that directs synthesis of specific proteins. Many viruses encode their genetic information using an RNA genome.
Transcription is the process of copying a segment of DNA into RNA. Some segments of DNA are transcribed into RNA molecules that can encode proteins, called messenger RNA (mRNA). Other segments of DNA are transcribed into RNA molecules called non-coding RNAs (ncRNAs).
In molecular biology, RNA polymerase, or more specifically DNA-directed/dependent RNA polymerase (DdRP), is an enzyme that catalyzes the chemical reactions that synthesize RNA from a DNA template.
A DNA polymerase is a member of a family of enzymes that catalyze the synthesis of DNA molecules from nucleoside triphosphates, the molecular precursors of DNA. These enzymes are essential for DNA replication and usually work in groups to create two identical DNA duplexes from a single original DNA duplex. During this process, DNA polymerase "reads" the existing DNA strands to create two new strands that match the existing ones. These enzymes catalyze the chemical reaction
The preinitiation complex is a complex of approximately 100 proteins that is necessary for the transcription of protein-coding genes in eukaryotes and archaea. The preinitiation complex positions RNA polymerase II at gene transcription start sites, denatures the DNA, and positions the DNA in the RNA polymerase II active site for transcription.
Robert G. Roeder is an American biochemist. He is known as a pioneer scientist in eukaryotic transcription. He discovered three distinct nuclear RNA polymerases in 1969 and characterized many proteins involved in the regulation of transcription, including basic transcription factors and the first mammalian gene-specific activator over five decades of research. He is the recipient of the Gairdner Foundation International Award in 2000, the Albert Lasker Award for Basic Medical Research in 2003, and the Kyoto Prize in 2021. He currently serves as Arnold and Mabel Beckman Professor and Head of the Laboratory of Biochemical and Molecular Biology at The Rockefeller University.
RNA polymerase II is a multiprotein complex that transcribes DNA into precursors of messenger RNA (mRNA) and most small nuclear RNA (snRNA) and microRNA. It is one of the three RNAP enzymes found in the nucleus of eukaryotic cells. A 550 kDa complex of 12 subunits, RNAP II is the most studied type of RNA polymerase. A wide range of transcription factors are required for it to bind to upstream gene promoters and begin transcription.
General transcription factors (GTFs), also known as basal transcriptional factors, are a class of protein transcription factors that bind to specific sites (promoter) on DNA to activate transcription of genetic information from DNA to messenger RNA. GTFs, RNA polymerase, and the mediator constitute the basic transcriptional apparatus that first bind to the promoter, then start transcription. GTFs are also intimately involved in the process of gene regulation, and most are required for life.
Patrick Cramer is a German chemist, structural biologist, and molecular systems biologist. In 2020, he was honoured to be an international member of the National Academy of Sciences. He became president of the Max Planck Society in June 2023.
Aled Morgan Edwards is the founder and Chief Executive of the Structural Genomics Consortium, a charitable public-private partnership. He is Professor of Medical Genetics and Medical Biophysics at the University of Toronto, Visiting Professor of Chemical Biology at the University of Oxford, and adjunct professor at McGill University.
Eukaryotic transcription is the elaborate process that eukaryotic cells use to copy genetic information stored in DNA into units of transportable complementary RNA replica. Gene transcription occurs in both eukaryotic and prokaryotic cells. Unlike prokaryotic RNA polymerase that initiates the transcription of all different types of RNA, RNA polymerase in eukaryotes comes in three variations, each translating a different type of gene. A eukaryotic cell has a nucleus that separates the processes of transcription and translation. Eukaryotic transcription occurs within the nucleus where DNA is packaged into nucleosomes and higher order chromatin structures. The complexity of the eukaryotic genome necessitates a great variety and complexity of gene expression control.
Mediator is a multiprotein complex that functions as a transcriptional coactivator in all eukaryotes. It was discovered in 1990 in the lab of Roger D. Kornberg, recipient of the 2006 Nobel Prize in Chemistry. Mediator complexes interact with transcription factors and RNA polymerase II. The main function of mediator complexes is to transmit signals from the transcription factors to the polymerase.
The following outline is provided as an overview of and topical guide to cell biology:
FACT is a heterodimeric protein complex that affects eukaryotic RNA polymerase II transcription elongation both in vitro and in vivo. It was discovered in 1998 as a factor purified from human cells that was essential for productive, in vitro Pol II transcription on a chromatinized DNA template.
In molecular biology, the term macromolecular assembly (MA) refers to massive chemical structures such as viruses and non-biologic nanoparticles, cellular organelles and membranes and ribosomes, etc. that are complex mixtures of polypeptide, polynucleotide, polysaccharide or other polymeric macromolecules. They are generally of more than one of these types, and the mixtures are defined spatially, and with regard to their underlying chemical composition and structure. Macromolecules are found in living and nonliving things, and are composed of many hundreds or thousands of atoms held together by covalent bonds; they are often characterized by repeating units. Assemblies of these can likewise be biologic or non-biologic, though the MA term is more commonly applied in biology, and the term supramolecular assembly is more often applied in non-biologic contexts. MAs of macromolecules are held in their defined forms by non-covalent intermolecular interactions, and can be in either non-repeating structures, or in repeating linear, circular, spiral, or other patterns. The process by which MAs are formed has been termed molecular self-assembly, a term especially applied in non-biologic contexts. A wide variety of physical/biophysical, chemical/biochemical, and computational methods exist for the study of MA; given the scale of MAs, efforts to elaborate their composition and structure and discern mechanisms underlying their functions are at the forefront of modern structure science.
Israel Robert Lehman is a Lithuanian-born American biochemist. His work primarily focused on the study of DNA replication and repair, as well as the replication of phages and the herpes virus. Notably, he collaborated with Arthur Konrberg in the discovery of DNA polymerase and the reaction responsible for genetic material replication. He also made major contributions in characterizing the process of homologous recombination. He served as the head of the Department of Biochemistry at Stanford University from 1974 to 1979 and again from 1984 to 1986. Lehman was awarded the Merk Prize by the American Society for Biochemistry and Molecular Biology.
Sylvy Kornberg née Sylvia Ruth Levy (1917–1986) was an American biochemist who carried out research on DNA replication and polyphosphate synthesis. She discovered and characterized polyphosphate kinase (PPK), an enzyme that helps build long chains of phosphate groups called polyphosphate (PolyP) that play a variety of metabolic and regulatory functions. She worked closely with her husband and research partner, Arthur Kornberg, contributing greatly to the characterization of DNA polymerization that earned him the 1959 Nobel Prize in Physiology or Medicine.
Kevin Struhl is an American molecular biologist and the David Wesley Gaiser Professor of Biological Chemistry and Molecular Pharmacology at Harvard Medical School. Struhl is primarily known for his work on transcriptional and post transcriptional regulatory mechanisms in yeast using molecular, genetic, biochemical, and genomic approaches. In addition, he has used related approaches to study transcriptional regulatory circuits involved in cellular transformation and the formation of cancer stem cells.
