https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3456489/

As the antibodies only bind to the protein of interest, only one band should be visible. The thickness of the band corresponds to the amount of protein present; thus doing a standard can indicate the amount of protein present.

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Note added at 2 hrs (2020-09-14 10:16:04 GMT)
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I am not clear which technique is being used here, Western Blotting?

However it is clearly an "immuno" technique (eg immunohistochemistry) involving the use of antibodies selective for specific proteins, involving the binding of these Abs to these proteins and their subsequent visualisation by various means. The blocking process involves prior application of a solution to prevent the antibodies binding non-specifically to the wrong proteins.

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Note added at 2 hrs (2020-09-14 10:17:25 GMT)
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tglab.com/support/immunohistochemistry-protocol/ihc-blocking/#:~:text=What%20is%20blocking%20in%20Immunohistochemistry,specific%20binding%20to%20other%20molecules.

What is blocking in Immunohistochemistry?
Blocking is essential for preventing non-specific binding of antibodies or other reagents to the tissue. Even if the antibody has high specificity towards the target, intermolecular forces can promote non-specific binding to other molecules. Consequently, non-specific binding prevents visualization of the antigen-antibody binding of interest. To mitigate nonspecific binding, a blocking step should be carried out before incubation with the primary antibody.

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Note added at 2 hrs (2020-09-14 10:21:37 GMT)
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https://en.wikipedia.org/wiki/Immunohistochemistry

Immunohistochemistry (IHC) is the most common application of immunostaining. It involves the process of selectively identifying antigens (proteins) in cells of a tissue section by exploiting the principle of antibodies binding specifically to antigens in biological tissues

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Note added at 10 hrs (2020-09-14 17:56:26 GMT)
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https://www.sciencedirect.com/topics/medicine-and-dentistry/...

The separated protein is then transferred onto the membrane [polyvinylidene difluoride (PVDF) or nitrocellulose], where they bind to antibodies specific to the target proteins. Western blotting can detect target proteins as low as 1 ng in concentration due to high-resolution capacity of gel electrophoresis and strong sensitivity and specificity of the immunoassay.

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Note added at 10 hrs (2020-09-14 18:07:29 GMT)
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finally binding is specified as a translation of fixation on Terrmium
https://www.btb.termiumplus.gc.ca/tpv2alpha/alpha-fra.html?l...

ubject field(s)
Nervous System
Biochemistry
binding
correct
CONT
Neurotransmitter receptors are proteins that span the neuronal membrane. These proteins have ligand binding regions that are accessible to extracellular messengers and other regions involved in transducing the binding interaction into an intercellular effect. The reversible binding of the neurotransmitter to the receptor causes a conformational change that triggers the transmembrane signaling event.

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Note added at 10 hrs (2020-09-14 18:08:48 GMT)
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see fiche 2 in Termium