Examples of receptor-mediated endocytosis in the following topics:
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- A targeted variation of endocytosis, known as receptor-mediated endocytosis, employs receptor proteins in the plasma membrane that have a specific binding affinity for certain substances .
- In receptor-mediated endocytosis, as in phagocytosis, clathrin is attached to the cytoplasmic side of the plasma membrane.
- If uptake of a compound is dependent on receptor-mediated endocytosis and the process is ineffective, the material will not be removed from the tissue fluids or blood.
- Some human diseases are caused by the failure of receptor-mediated endocytosis.
- In receptor-mediated endocytosis, uptake of substances by the cell is targeted to a single type of substance that binds to the receptor on the external surface of the cell membrane.
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- When a protein in the viral capsid binds to its receptor on the host cell, the virus may be taken inside the cell via a vesicle during the normal cell process of receptor-mediated endocytosis.
- An alternative method of cell penetration used by non-enveloped viruses is for capsid proteins to undergo shape changes after binding to the receptor, creating channels in the host cell membrane.
- Enveloped viruses also have two ways of entering cells after binding to their receptors: receptor-mediated endocytosis and fusion.
- Many enveloped viruses enter the cell by receptor-mediated endocytosis in a fashion similar to some non-enveloped viruses.
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- As plant viruses have a cell wall to protect their cells, their viruses do not use receptor-mediated endocytosis to enter host cells as is seen with animal viruses.
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- The plasma membrane protects the cell from its external environment, mediates cellular transport, and transmits cellular signals.
- 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.
- Membrane receptors provide extracellular attachment sites for effectors like hormones and growth factors, which then trigger intracellular responses.
- Some viruses, such as Human Immunodeficiency Virus (HIV), can hijack these receptors to gain entry into the cells, causing infections.
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- There are two types of receptors: internal receptors and cell-surface receptors.
- Once inside the cell, many of these molecules bind to proteins that act as regulators of mRNA synthesis to mediate gene expression.
- There are three general categories of cell-surface receptors: ion channel-linked receptors, G-protein-linked receptors, and enzyme-linked receptors.
- Enzyme-linked receptors are cell-surface receptors with intracellular domains that are associated with an enzyme.
- An example of this type of enzyme-linked receptor is the tyrosine kinase receptor.
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- Lipid-insoluble hormones bind to receptors on the outer surface of the plasma membrane, via plasma membrane hormone receptors.
- When a hormone binds to its membrane receptor, a G protein that is associated with the receptor is activated.
- These activated molecules can then mediate changes in cellular processes.
- Hormone binding to receptor activates a G protein, which in turn activates adenylyl cyclase, converting ATP to cAMP. cAMP is a second messenger that mediates a cell-specific response.
- Describe the events that occur when a hormone binds to a plasma hormone receptor
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- Hormones mediate changes in target cells by binding to specific hormone receptors.
- Cells can have many receptors for the same hormone, but often also possess receptors for different types of hormones.
- Cells respond to a hormone when they express a specific receptor for that hormone.
- Depending on the location of the protein receptor on the target cell and the chemical structure of the hormone, hormones can mediate changes directly by binding to intracellular hormone receptors and modulating gene transcription, or indirectly by binding to cell surface receptors and stimulating signaling pathways.
- The hormone insulin binds to its receptor (1), which starts many protein activation cascades (2).
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- One known mechanism involves a type of postsynaptic glutamate receptor: NMDA (N-Methyl-D-aspartate) receptors .
- These receptors are normally blocked by magnesium ions.
- Activated AMPA receptors allow positive ions to enter the cell.
- One mechanism known to cause LTD also involves AMPA receptors.
- The calcium that does flow through NMDA receptors initiates a different calcineurin and protein phosphatase 1-dependent cascade, which results in the endocytosis of AMPA receptors.
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- They then adhere to intracellular receptors residing in the cytoplasm or in the nucleus.
- For example, the active vitamin D metabolite, calcitriol, mediates its biological effects by binding to the vitamin D receptor (VDR), which is principally located in the nuclei of target cells.
- An intracellular nuclear receptor (NR) is located in the cytoplasm bound to a heat shock protein (HSP).
- The corresponding protein product can then mediate changes in cell function.
- Describe how hormones alter cellular activity by binding to intracellular receptors
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- B and T cells, parts of the adaptive immune response, contain receptors that can identify antigens derived from pathogens.
- There are two types of adaptive responses: the cell-mediated immune response, which is controlled by activated T cells, and the humoral immune response, which is controlled by activated B cells and antibodies.
- On B cells, these receptors contain antibodies, which are responsible for antigen binding .
- Meanwhile, T cell receptors are responsible for the recognition of pathogenic antigens by T cells .
- B cells are involved in the humoral immune response, which targets pathogens loose in blood and lymph, while T cells are involved in the cell-mediated immune response, which targets infected cells.