transport protein

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

• Facilitated transport

  • Facilitated transport is a type of passive transport.
  • The integral proteins involved in facilitated transport are collectively referred to as transport proteins; they function as either channels for the material or carriers.
  • A different group of carrier proteins called glucose transport proteins, or GLUTs, are involved in transporting glucose and other hexose sugars through plasma membranes within the body.
  • Channel and carrier proteins transport material at different rates.
  • Channel proteins transport much more quickly than do carrier proteins.

• ABC Transporters

  • ABC transporters are a protein superfamily that all have an ATP binding cassette and transport substances across membranes.
  • ATP-binding cassette transporters (ABC-transporters) are members of a protein superfamily that is one of the largest and most ancient families with representatives in all extant phyla from prokaryotes to humans.
  • Proteins are classified as ABC transporters based on the sequence and organization of their ATP-binding cassette (ABC) domain(s).
  • The third subgroup of ABC proteins do not function as transporters, but rather are involved in translation and DNA repair processes.
  • Summarize the function of the three major ABC transporter categories: in prokaryotes, in gram-negative bacteria and the subgroup of ABC proteins

• Secondary Active Transport

  • Unlike in primary active transport, in secondary active transport, ATP is not directly coupled to the molecule of interest.
  • If a channel protein exists and is open, the sodium ions will be pulled through the membrane.
  • This movement is used to transport other substances that can attach themselves to the transport protein through the membrane .
  • The potential energy that accumulates in the stored hydrogen ions is translated into kinetic energy as the ions surge through the channel protein ATP synthase, and that energy is used to convert ADP into ATP.
  • An electrochemical gradient, created by primary active transport, can move other substances against their concentration gradients, a process called co-transport or secondary active transport.

• Transport of Electrolytes across Cell Membranes

  • The mechanisms that transport ions across membranes are facilitated diffusion and active transport.
  • Facilitated diffusion of solutes occurs through protein-based channels.
  • Active transport requires energy in the form of ATP conversion, carrier proteins, or pumps in order to move ions against the concentration gradient.
  • Passive transport, such as diffusion, requires no energy as particles move along their gradient.
  • Active transport requires additional energy as particles move against their gradient.

• 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.

• Electron Transport Chain

  • A complex is a structure consisting of a central atom, molecule, or protein weakly connected to surrounding atoms, molecules, or proteins.
  • A prosthetic group is a non-protein molecule required for the activity of a protein.
  • Cytochrome proteins have a prosthetic heme group.
  • Complex III pumps protons through the membrane and passes its electrons to cytochrome c for transport to the fourth complex of proteins and enzymes.
  • The fourth complex is composed of cytochrome proteins c, a, and a3.

• Types and Functions of Proteins

  • Proteins perform essential functions throughout the systems of the human body.
  • Sometimes non-polypeptide groups are also required in the final protein.
  • Because form determines function, any slight change to a protein's shape may cause the protein to become dysfunctional.
  • In the respiratory system, hemoglobin (composed of four protein subunits) transports oxygen for use in cellular metabolism.
  • From the protein data base.

• Regulating Protein Activity and Longevity

  • The addition of a phosphate group to a protein can result in either activation or deactivation; it is protein dependent.
  • The addition of methyl groups to a protein can result in protein-protein interactions that allows for transcriptional regulation, response to stress, protein repair, nuclear transport, and even differentiation processes.
  • Methylation in the proteins negates the negative charge on it and increases the hydrophobicity of the protein.
  • The addition of an ubiquitin group to a protein marks that protein for degradation.
  • These proteins are moved to the proteasome, an organelle that functions to remove proteins to be degraded .

• Primary Active Transport

  • The primary active transport that functions with the active transport of sodium and potassium allows secondary active transport to occur .
  • The secondary transport method is still considered active because it depends on the use of energy as does primary transport.
  • Three sodium ions bind to the protein.
  • The protein now has a higher affinity for sodium ions, and the process starts again.
  • Primary active transport moves ions across a membrane, creating an electrochemical gradient (electrogenic transport).