suprachiasmatic nucleus

(noun)

cluster of cells that is considered to be the body's internal clock, which controls our circadian (day-long) cycle

Related Terms

  • optic chiasma
  • superior colliculus

Examples of suprachiasmatic nucleus in the following topics:

  • Visual Processing

    • Finally, there is the pathway from the retina to the suprachiasmatic nucleus (SCN) of the hypothalamus.
  • The Nucleus and Ribosomes

    • Found within eukaryotic cells, the nucleus contains the genetic material that determines the entire structure and function of that cell.
    • One of the main differences between prokaryotic and eukaryotic cells is the nucleus.
    • The nucleus stores chromatin (DNA plus proteins) in a gel-like substance called the nucleoplasm .
    • Lastly, the boundary of the nucleus is called the nuclear envelope.
    • The nucleus is the control center of the cell.
  • Characteristics of Eukaryotic Cells

    • Because a eukaryotic cell's nucleus is surrounded by a membrane, it is often said to have a "true nucleus. " Organelles (meaning "little organ") have specialized cellular roles, just as the organs of your body have specialized roles.
    • Typically, the nucleus is the most prominent organelle in a cell.
    • Eukaryotic cells have a true nucleus, which means the cell's DNA is surrounded by a membrane.
    • The nuclear envelope is a double-membrane structure that constitutes the outermost portion of the nucleus.
    • The nucleoplasm is the semi-solid fluid inside the nucleus where we find the chromatin and the nucleolus.
  • Prokaryotic versus Eukaryotic Gene Expression

    • Prokaryotic organisms are single-celled organisms that lack a defined nucleus; therefore, their DNA floats freely within the cell cytoplasm.
    • In eukaryotic cells, the DNA is contained inside the cell's nucleus where it is transcribed into RNA.
    • The newly-synthesized RNA is then transported out of the nucleus into the cytoplasm where ribosomes translate the RNA into protein.
    • The processes of transcription and translation are physically separated by the nuclear membrane; transcription occurs only within the nucleus, and translation occurs only outside the nucleus within the cytoplasm.
    • Eukaryotic gene expression is regulated during transcription and RNA processing, which take place in the nucleus, and during protein translation, which takes place in the cytoplasm.
  • Fertilization

    • In fertilization, the sperm binds to the egg, allowing their membranes to fuse and the sperm to transfer its nucleus into the egg.
    • The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum.
    • Fusion between the oocyte plasma membrane and sperm follows and allows the sperm nucleus, centriole, and flagellum, but not the mitochondria, to enter the oocyte.
    • (b) Acrosomal reactions help the sperm degrade the glycoprotein matrix protecting the egg and allow the sperm to transfer its nucleus.
  • Reproductive Cloning

    • The zygote nucleus contains the genetic information to produce a new individual.
    • If the haploid nucleus of an egg cell is replaced with a diploid nucleus from the cell of any individual of the same species (called a donor), it will become a zygote that is genetically identical to the donor.
    • Somatic cell nuclear transfer is the technique of transferring a diploid nucleus into an enucleated egg.
    • To create Dolly, the nucleus was removed from a donor egg cell.
    • The nucleus from a second sheep was then introduced into the cell, which was allowed to divide to the blastocyst stage before being implanted in a surrogate mother.
  • Endosymbiotic Theory and the Evolution of Eukaryotes

    • However, the role of endosymbiosis in the development of the nucleus is more controversial.
    • There are several other competing hypotheses as to the origin of eukaryotes and the nucleus.
    • One idea about how the eukaryotic nucleus evolved is that prokaryotic cells produced an additional membrane which surrounded the bacterial chromosome.
    • If the eukaryotic nucleus evolved this way, we would expect one of the two types of prokaryotes to be more closely-related to eukaryotes.
    • Another hypothesis, the nucleus-first hypothesis, proposes the nucleus evolved in prokaryotes first, followed by a later fusion of the new eukaryote with bacteria that became mitochondria.
  • Intracellular Hormone Receptors

    • They then adhere to intracellular receptors residing in the cytoplasm or in the nucleus.
    • Other lipid-soluble hormones that are not steroid hormones, such as vitamin D and thyroxine, have receptors located in the nucleus.
    • The hormones diffuse across both the plasma membrane and the nuclear envelope, then bind to receptors in the nucleus.
    • Upon hormone binding, the receptor dissociates from the heat shock protein and translocates to the nucleus.
    • In the nucleus, the hormone-receptor complex binds to a DNA sequence called a hormone response element (HRE), which triggers gene transcription and translation.
  • Characteristics of Eukaryotic DNA

    • The single characteristic that is both necessary and sufficient to define an organism as a eukaryote is a nucleus surrounded by a nuclear envelope with nuclear pores.
    • All extant eukaryotes have cells with nuclei; most of a eukaryotic cell's genetic material is contained within the nucleus.
    • In contrast, prokaryotic DNA is not contained within a nucleus, but rather is attached to the plasma membrane and contained in the form of a nucleoid, an irregularly-shaped region that is not surrounded by a nuclear membrane .
    • Because eukaryotes have mitochondria and prokaryotes do not, eukaryotic cells contain mitochondrial DNA in addition to DNA contained in the nucleus and ribosomes.
    • Eukaryotic DNA is stored in a nucleus, whereas prokaryotic DNA is in the cytoplasm in the form of a nucleoid.
  • Electron Shells and the Bohr Model

    • Niels Bohr proposed an early model of the atom as a central nucleus containing protons and neutrons being orbited by electrons in shells.
    • The Bohr model shows the atom as a central nucleus containing protons and neutrons with the electrons in circular orbitals at specific distances from the nucleus .
    • For example, 1n represents the first energy level located closest to the nucleus.
    • Under standard conditions, atoms fill the inner shells (closer to the nucleus) first, often resulting in a variable number of electrons in the outermost shell.
    • An electron normally exists in the lowest energy shell available, which is the one closest to the nucleus.
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