Self molecules

Examples of Self molecules in the following topics:

• Elements of Life

  • In such a reducing atmosphere, electrical activity can catalyze the creation of certain basic small molecules (monomers) of life, like amino acids.
  • A fundamental question is about the nature of the first self-replicating molecule.
  • The polymerization of nucleotides into random RNA molecules might have resulted in self-replicating ribozymes (RNA world hypothesis).
  • Using this apparatus, and using conditions thought to approximate the conditions on pre-biotic earth, they were able to catalyze the molecules of life like amino acids.

• Clonal Selection and Tolerance

  • Central tolerance is the mechanism by which newly developing T cells and B cells are rendered non-reactive to self.
  • The theory that self-tolerance is 'learned' during lymphocyte development was a major conceptual contribution to immunology.
  • However, they exert their immune suppression in the periphery on other self (or foreign)-reactive T cells.
  • Positive selection ensures maturation of T cells whose receptors bind weakly to self major histocompatibility complex molecules.
  • "Self"-antigens from the body's own tissues 4.

• T Cell Receptors

  • T lymphocytes have a dual specificity: they recognize polymorphic residues of self major histocompatibility complex (MHC) molecules, which accounts for their MHC restriction; they also recognize residues of peptide antigens displayed by these MHC molecules, which is responsible for their specificity.
  • MHC molecules and peptides form complexes on the surface of antigen presenting cells (APCs).
  • T cells also express other membrane receptors that do not recognize antigens but participate in responses to antigens; these are collectively called 'accessory molecules'.
  • The physiologic role of some accessory molecules is to deliver signals to the T cells that function in concert with signals from the TCR complex to fully activate the cell.

• Natural Killer Cells

  • MHC I molecules are proteins on the surfaces of all nucleated cells which help the immune system distinguish between "self" and "non-self."
  • If the cell is infected, the MHC I molecules display fragments of proteins from the infectious agents to T-cells.
  • Healthy cells do not display any proteins and will be ignored by the immune system, while the cells identified as "non-self" by foreign proteins will be attacked by the immune system.
  • An infected cell (or a tumor cell) is often incapable of synthesizing and displaying MHC I molecules appropriately.
  • This process can deplete host MHC I molecules on the cell surface, which prevents T-cells from recognizing them, but which NK cells detect as "unhealthy" or "abnormal" while searching for cellular MHC I molecules.

• Maturation of T Cells

  • These are expressed by thymic cortical epithelial cells that express both MHC I and MHC II molecules on the surface of cortical cells.
  • Double-positive cells (CD4+/CD8+) that are positively selected on MHC class II molecules will eventually become CD4+ helper T cells, while cells positively selected on MHC class I molecules mature into CD8+ cytotoxic T cells.
  • But if there is a signal interruption, it will instead reduce CD4 molecules, eventually becoming a CD8+, single positive cell.
  • Negative selection removes thymocytes that are capable of strongly binding with self-antigens presented by MHC.
  • While in the medulla, they are again presented with self-antigen in complex with MHC molecules on thymic epithelial cells.

• Acid-Base Properties of Water

  • Water is capable of acting as either an acid or a base and can undergo self-ionization.
  • Under standard conditions, water will self-ionize to a very small extent.
  • The self-ionization of water refers to the reaction in which a water molecule donates one of its protons to a neighboring water molecule, either in pure water or in aqueous solution.
  • The self-ionization of water produces hydronium and hydroxide ions in solution.
  • Explanation of self-ionization of water and the formation of hydronium and hydroxide ions.

• Specialized Equilibrium Constants

  • Common reactions, such as the self-ionization of water, have specially named equilibrium constants.
  • The self-ionization, or autodissociation, of water is a reaction that occurs to a very small extent in neutral water.
  • In this process, one molecule of water donates a proton to a neighboring water molecule, which yields hydronium and hydroxide ions.
  • A water molecule is protonated to form a hydronium ion in the process.
  • A water molecule protonates a neighboring water molecule, yielding hydronium and hydroxide ions.

• Immunoassays for Disease

  • Immunology is the study of molecules, cells, and organs that make up the immune system.
  • The function of the immune system is to recognize self antigens from non-self antigens and defend the body against non-self (foreign) agents.
  • Because antibodies can be produced against any type of macromolecule, antibody-based techniques are useful in identifying molecules in solution or in cells.
  • Recent methods employ pure antibodies or antigens that have been immobilized on a platform and that can be measured using an indicator molecule.

• Antigens and Antigen Receptors

  • Antigens are molecules that initiate the immune response and can be bound by antibodies.
  • "Self" antigens are usually tolerated by the immune system; whereas "non-self" antigens can be identified as invaders and can be attacked by the immune system.
  • Cells present their immunogenic-antigens to the immune system via a histocompatibility molecule.
  • The fragments are then presented on the cell surface in the complex with MHC class I molecules.
  • In order to keep the cytotoxic cells from killing cells just for presenting self-proteins, self-reactive T cells are deleted from the repertoire as a result of tolerance (also known as negative selection).

• Fluid Mosaic Model

  • Hydrophobic, or water-hating molecules, tend to be non-polar.
  • A phospholipid molecule consists of a three-carbon glycerol backbone with two fatty acid molecules attached to carbons 1 and 2, and a phosphate-containing group attached to the third carbon.
  • They interact with other non-polar molecules in chemical reactions, but generally do not interact with polar molecules.
  • When placed in water , hydrophobic molecules tend to form a ball or cluster.
  • This recognition function is very important to cells, as it allows the immune system to differentiate between body cells (called "self") and foreign cells or tissues (called "non-self").