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Protein is a nutrient needed by the human body for growth and maintenance. Aside from water, proteins are the most abundant kind of molecules in the body. Protein can be found in all cells of the body and is the major structural component of all cells in the body, especially muscle. This also includes body organs, hair and skin.
The binding of a divalent cation, almost always magnesium, strongly affects the interaction of ATP with various proteins. Due to the strength of the ATP-Mg 2+ interaction, ATP exists in the cell mostly as a complex with Mg 2+ bonded to the phosphate oxygen centers. [6] [8] A second magnesium ion is critical for ATP binding in the kinase domain. [9]
Cells are capable of synthesizing new proteins, which are essential for the modulation and maintenance of cellular activities. This process involves the formation of new protein molecules from amino acid building blocks based on information encoded in DNA/RNA. Protein synthesis generally consists of two major steps: transcription and translation.
A particular biosynthetic pathway may be located within a single cellular organelle (e.g., mitochondrial fatty acid synthesis pathways), while others involve enzymes that are located across an array of cellular organelles and structures (e.g., the biosynthesis of glycosylated cell surface proteins).
An example is the glucose symporter SGLT1, which co-transports one glucose (or galactose) molecule into the cell for every two sodium ions it imports into the cell. [27] This symporter is located in the small intestines, [28] heart, [29] and brain. [30] It is also located in the S3 segment of the proximal tubule in each nephron in the kidneys. [31]
Once formed, proteins only exist for a certain period and are then degraded and recycled by the cell's machinery through the process of protein turnover. A protein's lifespan is measured in terms of its half-life and covers a wide range. They can exist for minutes or years with an average lifespan of 1–2 days in mammalian cells.
Outbound proteins from the endoplasmic reticulum will bud off into transport vesicles that travel along the cell cortex to reach their specific destinations. [3] Since the ER is the site of protein synthesis, it would serve as the parent organelle, and the cis face of the golgi, where proteins and signals are received, would be the acceptor.
The process of signal transduction involves around 560 known protein kinases and pseudokinases, encoded by the human kinome [33] [34] As is the case with GPCRs, proteins that bind GTP play a major role in signal transduction from the activated RTK into the cell.