active transport

Examples of active transport in the following topics:

• Secondary Active Transport

  • In secondary active transport, a molecule is moved down its electrochemical gradient as another is moved up its concentration gradient.
  • Unlike in primary active transport, in secondary active transport, ATP is not directly coupled to the molecule of interest.
  • Both antiporters and symporters are used in secondary active transport.
  • Secondary active transport brings sodium ions, and possibly other compounds, into the cell.
  • 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

  • Ions cannot diffuse passively through membranes; instead, their concentrations are regulated by facilitated diffusion and active transport.
  • For this reason, athletes are encouraged to replace electrolytes and fluids during periods of increased activity and perspiration.
  • The mechanisms that transport ions across membranes are facilitated diffusion and active transport.
  • All movement can be classified as passive or active.
  • Active transport requires additional energy as particles move against their gradient.

• Electrochemical Gradient

  • To move substances against the membrane's electrochemical gradient, the cell utilizes active transport, which requires energy from ATP.
  • Because active transport mechanisms depend on a cell's metabolism for energy, they are sensitive to many metabolic poisons that interfere with the supply of ATP.
  • Primary active transport moves ions across a membrane and creates a difference in charge across that membrane, which is directly dependent on ATP.
  • Secondary active transport describes the movement of material that is due to the electrochemical gradient established by primary active transport that does not directly require ATP.
  • An important membrane adaption for active transport is the presence of specific carrier proteins or pumps to facilitate movement.

• 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.
  • Primary active transport moves ions across a membrane, creating an electrochemical gradient (electrogenic transport).

• Routing

  • This chapter focuses on the role of routing in transportation networks.
  • Transport engineers use mathematical graph theory to analyze a transport network to determine the flow of vehicles (or people) through it.
  • A transport network may combine different modes of transport.
  • At the tactical level of supply chain activities, the transportation strategy of goods must be considered.
  • In order to reduce costs, companies often look for ways to streamline routes and supply chain activities.

• Components of Plasma Membranes

  • The movement of a substance across the selectively permeable plasma membrane can be either "passive"—i.e., occurring without the input of cellular energy—or "active"—i.e., its transport requires the cell to expend energy.
  • The cell employs a number of transport mechanisms that involve biological membranes:
  • Transmembrane protein channels and transporters: transports small organic molecules such as sugars or amino acids
  • Endocytosis: transports large molecules (or even whole cells) by engulfing them
  • These proteins can be receptors, which work as receivers of extracellular inputs and as activators of intracellular processes, or markers, which allow cells to recognize each other.

• Electron Transport Chain

  • The most vital part of this process is the electron transport chain, which produces more ATP than any other part of cellular respiration.
  • Electron transport is a series of redox reactions that resemble a relay race.
  • A prosthetic group is a non-protein molecule required for the activity of a protein.
  • Once it is reduced to QH2, ubiquinone delivers its electrons to the next complex in the electron transport chain.
  • The electron transport chain is a series of electron transporters embedded in the inner mitochondrial membrane that shuttles electrons from NADH and FADH2 to molecular oxygen.

• Supply Chain Management

  • Distribution strategy: questions of operating control (centralized, decentralized or shared); delivery scheme (e.g., direct shipment, pool point shipping, or cross docking), DSD (direct store delivery), closed loop shipping; mode of transportation (e.g., motor carrier, including truckload, LTL, or parcel); railroad; intermodal transport, including TOFC (trailer on flatcar), and COFC (container on flatcar); ocean freight; airfreight; replenishment strategy (e.g., pull, push or hybrid); and transportation control (e.g., owner-operated, private carrier, common carrier, contract carrier, or 3PL).
  • Trade-offs in logistical activities: The above activities must be well coordinated in order to achieve the lowest total logistics cost.
  • Trade-offs may increase the total cost if only one of the activities is optimized.
  • If, however, a full truckload of a product is ordered to reduce transportation costs, there will be an increase in inventory holding costs, which may increase total logistics costs.
  • It is, therefore, imperative to take a systems approach when planning logistical activities.

• Regulatory Mechanisms for Cellular Respiration

  • Access of glucose to the cell can be regulated using the GLUT proteins that transport glucose .
  • This site has an effect on the enzyme's activity, often by changing the conformation of the protein.
  • These regulators, known as allosteric effectors, may increase or decrease enzyme activity, depending on the prevailing conditions, altering the steric structure of the enzyme, usually affecting the configuration of the active site.
  • GLUT4 is a glucose transporter that is stored in vesicles.
  • A cascade of events that occurs upon insulin binding to a receptor in the plasma membrane causes GLUT4-containing vesicles to fuse with the plasma membrane so that glucose may be transported into the cell.

• 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.
  • When a lymphocyte is presented with an antigen (such as by an activated helper T cell), B cells become activated and migrate to the germinal centers of the node, where they proliferate and differentiate to be specific to that antigen.