The Exogenous Pathway

(noun)

Phagocytized pathogens are broken down from within the cell and their broken-down antigens bind with MHC II, which then is expressed on the surface of the antigen-presenting cell.

Related Terms

Examples of The Exogenous Pathway in the following topics:

  • Antigenic Determinants and Processing Pathways

    • The determinants need not be located on the exposed surface of the antigen in its original form, since recognition of the determinant by T cells requires that the antigen be first processed by antigen presenting cells.
    • However, the pathway leading to the association of protein fragments with MHC molecules differs between class I and class II MHC, which are presented to cytotoxic or helper T cells respectively.
    • There are two different pathways for antigen processing:
    • The endogenous pathway occurs when MHC class I molecules present antigens derived from intracellular (endogenous) proteins in the cytoplasm, such as the proteins produced within virus-infected cells.
    • The exogenous pathway occurs when MHC class II molecules present fragments derived from extracellular (exogenous) proteins that are located within the cell.

  • Fever

    • PGE2 release comes from the arachidonic acid pathway, which also produces inflammatory mediators such as thromboxane and leukotriene.
    • This pathway is mediated by the enzymes phospholipase A2 (PLA2), cyclooxygenase-2 (COX-2), and prostaglandin E2 synthase.
    • A pyrogen is a substance that induces fever and can be either internal (endogenous) or external (exogenous) to the body.
    • Exogenous factors s lipopolysaccharide toxin (from gram negative bacteria) which can activate a number of innate immune activation pathways.
    • When TNFα or any of these cytokine factors bind to cells in phospolipids in the brain, the arachidonic acid pathway is activated and PGE2 released to act on the hypothalamus and cause the fever response.

  • Reasons for and Consequences of Shifts in the Aggregate Demand Curve

    • Aggregate Demand/Aggregate Supply Model (AD/AS):The x-axis represents the overall output, while the y-axis represents the price level.
    • Below are some of the driving forces that will shift aggregate demand to the right:
    • An exogenous increase in transfer payments from the government to the people;
    • An exogenous increase in purchases of the country's exports by people in other countries; and
    • However, as the system evolves and aligns itself closer to the highest potential output (optimal utilization of resources or Y*), scarcity will naturally cause the prices to increase more than the overall output in a system.

  • Antigen-Presenting Cells

    • The ability of the adaptive immune system to survey for infection requires specialized pathways of enabling recognition of pathogen-derived antigens by T cells.
    • Dendritic cells (DCs) phagocytose exogenous pathogens such as bacteria, parasites, and toxins in the tissues and then migrate, via chemotactic signals, to T cell-enriched lymph nodes.
    • Exogenous antigens are usually displayed on MHC Class II molecules, which interact with CD4+ helper T cells.
    • In the upper pathway; foreign protein or antigen (1) is taken up by an antigen-presenting cell (2).
    • In the lower pathway; whole foreign proteins are bound by membrane antibodies (5) and presented to B lymphocytes (6), which process (7) and present antigen on MHC II (8) to a previously activated T helper cell (10), spurring the production of antigen-specific antibodies (9).

  • Complement Fixation

    • The first component is an indicator system that uses combination of sheep red blood cells, complement-fixing antibody such as immunoglobulin G produced against the sheep red blood cells and an exogenous source of complement usually guinea pig serum.
    • When these elements are mixed in optimum conditions, the anti-sheep antibody binds on the surface of red blood cells.
    • Patient serum is first added to the known antigen, and complement is added to the solution.
    • If the serum contains antibody to the antigen, the resulting antigen-antibody complexes will bind all of the complement.
    • Describe how the complement fixation assay can be used to test for the presence of a specific antibody in a patient's serum

  • Metabolic Pathways

    • The processes of making and breaking down carbohydrate molecules illustrate two types of metabolic pathways.
    • One example of an anabolic pathway is the synthesis of sugar from CO2.
    • Catabolic pathways involve the degradation of complex molecules into simpler ones, releasing the chemical energy stored in the bonds of those molecules.
    • Some catabolic pathways can capture that energy to produce ATP, the molecule used to power all cellular processes.
    • Both types of pathways are required for maintaining the cell's energy balance.

  • Bacterial Transformation

    • Transformation is the direct uptake, incorporation and expression of exogenous genetic material from its surroundings.
    • In molecular biology, transformation is genetic alteration of a cell resulting from the direct uptake, incorporation and expression of exogenous genetic material (exogenous DNA) from its surroundings and taken up through the cell membrane(s) .
    • Competence refers to the state of being able to take up exogenous DNA from the environment.
    • The transport of the exogeneous DNA into the cells may require proteins that are involved in the assembly of type IV pili and type II secretion system, as well as DNA translocase complex at the cytoplasmic membrane.
    • The exogenous DNA is incorporated into the host cell's chromosome via recombination.

  • The Entner–Doudoroff Pathway

    • The Entner–Doudoroff pathway is an alternate series of reactions that catabolize glucose to pyruvate.
    • Pseudomonas, a genus of Gram-negative bacteria, and Azotobacter, a genus of Gram-negative bacteria use the Entner-Doudoroff pathway
    • The Entner–Doudoroff pathway describes an alternate series of reactions that catabolize glucose to pyruvate using a set of enzymes different from those used in either glycolysis or the pentose phosphate pathway .
    • Most bacteria use glycolysis and the pentose phosphate pathway.
    • There are a few bacteria that substitute classic glycolysis with the Entner-Doudoroff pathway.

  • Substrates for Biosynthesis

    • Major metabolic pathways require substrates to be acted upon for the formation of larger, more complex products.
    • The major metabolic pathways require substrates to be acted upon for the formation of larger, more complex products.
    • Additional pathways that require precursors formed by the TCA include amino acid and nucleotide synthesis .
    • Additional pathways that require substrates or metabolites produced by the glycolytic pathway include: gluconeogenesis, lipid metabolism, the pentose phosphate pathway, and the TCA.
    • An overview of the glycolytic pathway.

  • Connecting Proteins to Glucose Metabolism

    • Excess amino acids are converted into molecules that can enter the pathways of glucose catabolism.
    • Metabolic pathways should be thought of as porous; that is, substances enter from other pathways and intermediates leave for other pathways.
    • Many of the substrates, intermediates, and products in a particular pathway are reactants in other pathways.
    • When deaminated, amino acids can enter the pathways of glucose metabolism as pyruvate, acetyl CoA, or several components of the citric acid cycle.
    • Deaminated amino acids can also be converted into another intermediate molecule before entering the pathways.