Receptor (biochemistry) Hormone. A hormone (from Greek ὁρμή , "impetus") is a chemical released by a cell, a gland, or an organ in one part of the body that affects cells in other parts of the organism.
Only a small amount of hormone is required to alter cell metabolism . In essence, it is a chemical messenger that transports a signal from one cell to another. [ 1 ] All multicellular organisms produce hormones; plant hormones are also called phytohormones . Hormones in animals are often transported in the blood. Cells respond to a hormone when they express a specific receptor for that hormone.
The hormone binds to the receptor protein , resulting in the activation of a signal transduction mechanism that ultimately leads to cell type-specific responses. Endocrine hormone molecules are secreted (released) directly into the bloodstream , typically into fenestrated capillaries . A variety of exogenous chemical compounds , both natural and synthetic, have hormone-like effects on both humans and wildlife.
Neurotransmitter. Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse . [ 1 ] Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane in the axon terminal, on the presynaptic side of a synapse.
They are released into and diffuse across the synaptic cleft , where they bind to specific receptors in the membrane on the postsynaptic side of the synapse. [ 2 ] Release of neurotransmitters usually follows arrival of an action potential at the synapse, but may also follow graded electrical potentials . Low level "baseline" release also occurs without electrical stimulation. Neurotransmitters are synthesized from plentiful and simple precursors, such as amino acids , which are readily available from the diet and which require only a small number of biosynthetic steps to convert. [ 3 ]
File:Synapse Illustration unlabeled.svg. Cancel Edit Delete Preview revert Text of the note (may include Wiki markup ) Could not save your note (edit conflict or other problem). Please copy the text in the edit box below and insert it manually by editing this page . Neuromodulation. Neuromodulation is the physiological process by which a given neuron uses several different neurotransmitters to regulate diverse populations of central nervous system neurons .
This is in contrast to classical synaptic transmission , in which one presynaptic neuron directly influences a single postsynaptic partner. Neuromodulators secreted by a small group of neurons diffuse through large areas of the nervous system, affecting multiple neurons. Examples of neuromodulators include dopamine , serotonin , acetylcholine , histamine and others. Neuromodulation can be conceptualized as a neurotransmitter that is not reabsorbed by the pre-synaptic neuron or broken down into a metabolite .
Ligand (biochemistry) In biochemistry and pharmacology , a ligand (from the Latin ligandum , binding ) is a substance (usually a small molecule), that forms a complex with a biomolecule to serve a biological purpose. In a narrower sense, it is a signal triggering molecule, binding to a site on a target protein . The binding occurs by intermolecular forces , such as ionic bonds , hydrogen bonds and van der Waals forces . The docking (association) is usually reversible (dissociation). Actual irreversible covalent binding between a ligand and its target molecule is rare in biological systems. Chemical reaction. A thermite reaction using iron(III) oxide.
The sparks flying outwards are globules of molten iron trailing smoke in their wake. A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. [ 1 ] Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms , with no change to the nuclei (no change to the elements present), and can often be described by a chemical equation .
Nuclear chemistry is a sub-discipline of chemistry that involves the chemical reactions of unstable and radioactive elements where both electronic and nuclear changes may both occur. Cell membrane. The cell membrane is a biological membrane that separates the interior of all cells from the outside environment . [ 1 ] The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. [ 2 ] The basic function of the cell membrane is to protect the cell from its surroundings. Enzyme. Enzymes ( pron.: / ˈ ɛ n z aɪ m z / ) are large biological molecules responsible for the thousands of chemical interconversions that sustain life. [ 1 ] [ 2 ] They are highly selective catalysts , greatly accelerating both the rate and specificity of metabolic reactions, from the digestion of food to the synthesis of DNA. Most enzymes are proteins , although some catalytic RNA molecules have been identified. Enzymes adopt a specific three-dimensional structure , and may employ organic (e.g. biotin) and inorganic (e.g. magnesium ion) cofactors to assist in catalysis.
In enzymatic reactions, the molecules at the beginning of the process, called substrates , are converted into different molecules, called products . Almost all chemical reactions in a biological cell need enzymes in order to occur at rates sufficient for life. Structure. Structure is a fundamental, tangible or intangible notion referring to the recognition , observation , nature , and permanence of patterns and relationships of entities .
Carrier protein. Carrier proteins are proteins involved in the movement of ions , small molecules , or macromolecules , such as another protein, across a biological membrane. [ 1 ] Carrier proteins are integral/intrinsic [ 2 ] membrane proteins; that is they exist within and span the membrane across which they transport substances.
The proteins may assist in the movement of substances by facilitated diffusion or active transport . These mechanisms of movement are known as carrier mediated transport . [ 3 ] Each carrier protein is designed to recognize only one substance or one group of very similar substances. Research has correlated defects in specific carrier proteins with specific diseases. [ 4 ] Physiology [ edit ] Active Transport [ edit ] Ion channel. Not to be confused with: Ion Television or Ion implantation . Ion channels are pore-forming membrane proteins whose functions include establishing a resting membrane potential , shaping action potentials and other electrical signals by gating the flow of ions across the cell membrane, controlling the flow of ions across secretory and epithelial cells , and regulating cell volume.
Ion channels are present in the membranes of all cells. Ion channels are considered to be one of the two traditional classes of ionophoric proteins, with the other class known as ion transporters (including the sodium-potassium pump , sodium-calcium exchanger , and sodium-glucose transport proteins , amongst others). [ 1 ] Study of ion channels ( channelomics ) often includes biophysics , electrophysiology and pharmacology , utilizing techniques including voltage clamp , patch clamp , immunohistochemistry , and RT-PCR . Basic features [ edit ] Biological role [ edit ] File:Ion channel.png.