transport protein

(noun)

A protein that binds with a hormone in systemic circulation that facilitates its efficient transport.

Related Terms

Examples of transport protein in the following topics:

  • Transport of Hormones

    • Once within the circulatory system a small proportion of hormones circulate freely, however the majority are bound with a transport protein.
    • Mainly produced in the liver, these transport proteins are hormone specific, such as the sex hormone binding globulin that binds with the sex hormones.
    • When bound with a transport protein hormones are typically inactive, and their release is often triggered in regions of low hormone concentration or can be controlled by other factors.
    • Therefore, transport proteins can act as a reservoir within the circulatory system and help insure an even distribution of hormones within an organ or tissue.
    • Describe the way in which hormones are transported in the endocrine system

  • Blood Plasma

    • It contains proteins and clotting factors, transports nutrients, and removes waste.
    • Plasma contains molecules that are transported around the body.
    • The largest group of solutes in plasma contains three important proteins: albumins, globulins, and clotting proteins.
    • Their main function is to transport various substances in the blood.
    • For example, the beta globulin transferrin can transport iron.

  • RBC Anatomy

    • They are involved in oxygen transport through the body and have features that distinguish them from every other type of human cell.
    • They also lack the components to express genes and synthesize proteins.
    • Hemoglobin is a specialized protein that contains a binding site for the transport of oxygen and other molecules.
    • Each human red blood cell contains approximately 270 million of these hemoglobin biomolecules, each carrying four heme groups (individual proteins).
    • This protein is responsible for the transport of more than 98% of the oxygen, while the rest travels as dissolved molecules through the plasma.

  • Edema Caused by Loss of Plasma Proteins

    • Nephrotic syndrome is a nonspecific disorder in which the kidneys are damaged, causing them to leak large amounts of protein.
    • Human serum albumin is the most abundant protein in human blood plasma.
    • Albumin constitutes about half of the blood serum protein.
    • Albumin transports hormones, fatty acids, and other compounds, buffers pH, and maintains osmotic pressure, among other functions.
    • The various causes of albuminuria, can be discriminated based on the amount of protein excreted.

  • Metabolic Changes

    • Protein and carbohydrate metabolism are affected during pregnancy and maternal insulin resistance can lead to gestational diabetes.
    • During pregnancy, both protein metabolism and carbohydrate metabolism are affected.
    • One kilogram of extra protein is deposited, with half going to the fetus and placenta, and another half going to uterine contractile proteins, breast glandular tissue, plasma protein, and hemoglobin.
    • Insulin binds to its receptor (1) on the cell membrane which in turn starts many protein activation cascades (2).
    • These include: translocation of Glut-4 transporter to the plasma membrane and influx of glucose (3), glycogen synthesis (4), glycolysis (5) and fatty acid synthesis (6).

  • Body Fluid Composition

    • The reason for these specific sodium and potassium ion concentrations are Na+/K ATPase pumps, which facilitate the active transport of these ions.
    • These pumps transport ions against their concentration gradients to maintain cytosol fluid composition of ions.
    • These ions are important for water transport throughout the body.
    • Plasma is mostly water (93% by volume) and contains dissolved proteins (major proteins are fibrinogens, globulins and albumins), glucose, clotting factors, mineral ions (Na+, Ca++, Mg++, HCO3- Cl- etc.), hormones and carbon dioxide (plasma being the main medium for excretory product transportation).
    • Ocular fluid in the eyes contrasts cerebrospinal fluid by containing high concentrations of proteins, including antibodies.

  • Regulation of Blood Cholesterol Levels

    • Cholesterol is transported through the blood by lipoproteins which direct cholesterol to where it is needed.
    • Since cholesterol is insoluble in blood, it is transported in the circulatory system within lipoproteins , which are complex discoidal particles that have an exterior composed of amphiphilic proteins and lipids whose outward-facing surfaces are water-soluble and inward-facing surfaces are lipid-soluble; triglycerides and cholesterol esters are carried internally.
    • The more lipid and less protein a lipoprotein has, the less dense it is.
    • Synthesis of the LDL receptor is regulated by SREBP, the same regulatory protein as was used to control synthesis of cholesterol de novo in response to cholesterol presence in the cell.
    • Also, HDL particles are thought to transport cholesterol back to the liver for excretion or to other tissues that use cholesterol to synthesize hormones in a process known as reverse cholesterol transport (RCT).

  • Lymph Transport

    • Lymph transport refers to the transport of lymph fluid from the interstitial space inside the tissues of the body, through the lymph nodes, and into lymph ducts that return the fluid to venous circulation.
    • In addition to interstitial fluid, pathogens, proteins, and tumor cells may also leak into the lymph capillaries and be transported through lymph.
    • The collecting vessels typically transport lymph fluid either into lymph nodes or lymph trunks.
    • The lymph nodes contain a large number of B and T lymphocytes, which are transported throughout the node during many components of the adaptive immune response.
    • The lymphocytes are transported through lymph fluid and leave the node through the efferent vessels to travel to other parts of the body to perform adaptive immune response functions.

  • Absorption in the Small Intestine

    • Examples of nutrients absorbed by the small intestine include carbohydrates, lipids, proteins, iron, vitamins, and water.
    • The epithelial cells of the villi transport nutrients from the lumen of the intestine into these capillaries (amino acids and carbohydrates) and lacteals (lipids).
    • The absorbed substances are transported via the blood vessels to different organs of the body where they are used to build complex substances such as the proteins required by our body.
    • Absorption of the majority of nutrients takes place in the jejunum, with the following notable exceptions: iron is absorbed in the duodenum; vitamin B12 and bile salts are absorbed in the terminal ileum; water and lipids are absorbed by passive diffusion throughout the small intestine; sodium bicarbonate is absorbed by active transport and glucose and amino acid co-transport; and fructose is absorbed by facilitated diffusion.

  • Mechanisms of Hormone Action

    • The hormones then diffuse to the bloodstream via capillaries and are transported to the target cells through the circulatory system.
    • Hormones exit their cell of origin through the process of exocytosis or by other means of membrane transport.
    • Hormones activate target cells by diffusing through the plasma membrane of the target cells (lipid-soluble hormones) to bind a receptor protein within the cytoplasm of the cell, or by binding a specific receptor protein in the cell membrane of the target cell (water-soluble proteins).
    • Transport of the hormone to the target cells, tissues, or organs.
    • Recognition of the hormone by an associated cell membrane or an intracellular receptor protein.