Signaling hydrophilic substance

As peptides or proteins, the cytokines are hydrophilic signaling substances that act by binding to receptors on the cell surface (see p. 380). Binding of a cytokine to its receptor (1) leads via several intermediate steps (2 -5) to the activation of transcription of specific genes (6). 

Hydrophilic hormones and other water-soluble signaling substances have a variety of biosynthetic pathways. Amino acid derivatives arise in special metabolic pathways (see p. 352) or through post-translational modification (see p. 374). Proteohormones, like all proteins, result from translation in the ribosome (see p. 250). Small peptide hormones and neuropeptides, most of which only consist of 3-30 amino acids, are released from precursor proteins by proteolytic degradation. 

Fig. 6.1 Function and formation of intracellular messenger substances in signaling pathways. Starting from the activated receptor, effector proteins next in sequence are activated that create an intracellular signal in the form of diffusible messenger substances. The hydrophilic messenger substances diffuse to target proteins in the cytosol...

In MALDI-MSI, a liquid or powder matrix is deposited on top of the sample, incorporating the analyte into the matrix crystals. When illuminated with the laser, the matrix and analyte are vaporized and ionized. Although longer exposure of the sample to matrix facilitates extraction of the analyte of interest from the tissue, it can also delocalize the analyte. Shorter extraction times ameliorate this problem, but result in poorer signal. This issue is particularly problematic when investigating small hydrophilic substances that diffuse during matrix application. Recent advances in MALDI matrix solution application approaches have helped to create uniform MALDI matrix layers these include spray coating... 

Cell membrane The cell membrane serves to separate and protect a cell from its surrounding environment, and is made mostly from a double layer of lipids and hydrophilic phosphorus molecules as such, the layer is called a phospholipid bilayer. Embedded within this membrane is a variety of protein molecules that act as channels and pumps to move different molecules in and out of the cell. The membrane is said to be semipermeable, in that it can either let a substance pass through freely, pass through to a limited extent, or not pass through at all. Cell surface membranes also contain receptor proteins that allow cells to detect external signaling molecules such as hormones. 

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