Question
In immunology, which class of MHC proteins presents exogenous antigens?
Solution
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In immunology, the class of Major Histocompatibility Complex (MHC) proteins that presents exogenous antigens is known as Class II MHC. These proteins are primarily found on the surface of antigen-presenting cells (APCs) such as dendritic cells, macrophages, and B cells. The process of antigen presentation by Class II MHC molecules is a critical component of the immune response to pathogens that exist outside of the body's cells.
In immunology, the class of Major Histocompatibility Complex (MHC) proteins that presents exogenous antigens is known as Class II MHC. These proteins are primarily found on the surface of antigen-presenting cells (APCs) such as dendritic cells, macrophages, and B cells. The process of antigen presentation by Class II MHC molecules is a critical component of the immune response to pathogens that exist outside of the body's cells.
Here is a step-by-step explanation of how exogenous antigens are processed and presented by Class II MHC molecules:
1. Uptake of the Antigen: Antigen-presenting cells take up exogenous antigens from their surroundings through processes such as phagocytosis or endocytosis.
2. Antigen Processing: Once inside the APC, the antigen is enclosed in a vesicle called a phagosome or endosome. This vesicle then fuses with a lysosome, which contains digestive enzymes that degrade the antigen into smaller peptide fragments.
3. MHC Class II Synthesis: While the antigen is being processed, MHC Class II molecules are synthesized within the endoplasmic reticulum (ER) of the APC. A specialized protein called the invariant chain (Ii) binds to the MHC Class II molecule's peptide-binding groove to prevent it from binding to peptides within the ER.
4. Formation of MHC Class II-Peptide Complex: The invariant chain is then degraded in an acidic compartment, leaving a small fragment known as CLIP (Class II-associated invariant chain peptide) still bound to the MHC Class II molecule. The vesicle containing the processed antigen fuses with the vesicle containing the MHC Class II molecule. An exchange then occurs where CLIP is replaced by one of the antigenic peptides, forming the MHC Class II-peptide complex.
5. Transport to the Cell Surface: The MHC Class II-peptide complex is transported to the cell surface of the APC in a vesicle.
6. Presentation to T Cells: Once on the cell surface, the MHC Class II-peptide complex can be recognized by CD4+ T cells (also known as helper T cells). The T cell receptor (TCR) on the CD4+ T cell binds to the antigenic peptide presented by the MHC Class II molecule, while the CD4 co-receptor binds to the MHC Class II molecule itself. This interaction is crucial for the activation of the CD4+ T cells, which then help orchestrate the immune response.
In summary, Class II MHC molecules are responsible for presenting exogenous antigens to CD4+ T cells, leading to the activation of the immune system to combat pathogens that are located outside of the host's cells. This process is a fundamental aspect of the adaptive immune response.
Here is a step-by-step explanation of how exogenous antigens are processed and presented by Class II MHC molecules:
1. Uptake of the Antigen: Antigen-presenting cells take up exogenous antigens from their surroundings through processes such as phagocytosis or endocytosis.
2. Antigen Processing: Once inside the APC, the antigen is enclosed in a vesicle called a phagosome or endosome. This vesicle then fuses with a lysosome, which contains digestive enzymes that degrade the antigen into smaller peptide fragments.
3. MHC Class II Synthesis: While the antigen is being processed, MHC Class II molecules are synthesized within the endoplasmic reticulum (ER) of the APC. A specialized protein called the invariant chain (Ii) binds to the MHC Class II molecule's peptide-binding groove to prevent it from binding to peptides within the ER.
4. Formation of MHC Class II-Peptide Complex: The invariant chain is then degraded in an acidic compartment, leaving a small fragment known as CLIP (Class II-associated invariant chain peptide) still bound to the MHC Class II molecule. The vesicle containing the processed antigen fuses with the vesicle containing the MHC Class II molecule. An exchange then occurs where CLIP is replaced by one of the antigenic peptides, forming the MHC Class II-peptide complex.
5. Transport to the Cell Surface: The MHC Class II-peptide complex is transported to the cell surface of the APC in a vesicle.
6. Presentation to T Cells: Once on the cell surface, the MHC Class II-peptide complex can be recognized by CD4+ T cells (also known as helper T cells). The T cell receptor (TCR) on the CD4+ T cell binds to the antigenic peptide presented by the MHC Class II molecule, while the CD4 co-receptor binds to the MHC Class II molecule itself. This interaction is crucial for the activation of the CD4+ T cells, which then help orchestrate the immune response.
In summary, Class II MHC molecules are responsible for presenting exogenous antigens to CD4+ T cells, leading to the activation of the immune system to combat pathogens that are located outside of the host's cells. This process is a fundamental aspect of the adaptive immune response.
Exercise 13 - The four classes of protein structures
Exercise 14 - The true statement about proteins' organization
Exercise 4 - Create a class called Pen which inherits from the Item class
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Exercise 13 - The four classes of protein structures
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We have an exercise testing on knowledge on structure classification.
What are the 4 classes protein structures are divided into?
At the highest level of classification,
protein structures are divided into 4 classes.
You have the all Alpha: These are structures that are made of all Alpha-helices,
and if you remember in the lesson itself,
we showed multiple figures of this.
You have the all Beta forms.
You have the Alpha over Beta in which
the Alpha and Beta segments are interspersed or alternate,
and you have the Alpha and Beta in which
the Alpha and B- regions are somewhat segregated.
Again, you have all Alpha,
so these are protein structures that are made of all Alpha-helices.
You have all Beta,
structures that are made of all Beta sheets, Beta forms.
You have Alpha over Beta,
protein structures that have Alpha and Beta segments interspersed, alternating,
mixed together, or you have the fourth,
which is Alpha and Beta,
in which the Alpha and Beta regions are somewhat segregated.
In each class are tens to hundreds of different folding arrangements,
built up from increasingly identifiable substructures.
Some substructure arrangements are very common,
others have been found in just 1 protein.
This video discusses the four classes of protein structures and their substructures. At the highest level of classification, protein structures are divided into four classes: all Alpha, all Beta, Alpha over Beta, and Alpha and Beta. All Alpha structures are made of all Alpha-helices, all Beta structures are made of all Beta sheets, Alpha over Beta structures have Alpha and Beta segments interspersed, and Alpha and Beta structures have Alpha and Beta regions segregated. Each class contains tens to hundreds of different folding arrangements, built up from increasingly identifiable substructures. Some substructure arrangements are very common, while others have been found in only one protein.
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