Proteins are synthesised on ribosomes in the cell cytoplasm, and must be targeted to the appropriate compartment of the cell by special targeting sequences. What is likely to be the fate of a protein that contains no such targeting sequence?
Answers
All eucaryotic cells have an endoplasmic reticulum (ER). Its membrane typically constitutes more than half of the total membrane of an average animal cell (see Table 12-2). The ER is organized into a netlike labyrinth of branching tubules and flattened sacs extending throughout the cytosol (Figure 12-35). The tubules and sacs are all thought to interconnect, so that the ER membrane forms a continuous sheet enclosing a single internal space. This highly convoluted space is called the ER lumen or the ER cisternal space, and it often occupies more than 10% of the total cell volume (see Table 12-1). The ER membrane separates the ER lumen from the cytosol, and it mediates the selective transfer of molecules between these two compartments.
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Proteins are synthesised on ribosomes in the cell cytoplasm, and must be targeted to the appropriate compartment of the cell by special targeting sequences. What is likely to be the fate of a protein that contains no such targeting sequence?
Answer.
It remains in the cytoplasm.
Explanation:-
While many proteins need to be sorted to the endoplasmic reticulum, the Golgi apparatus, or the extracellular space, some proteins exist in the cytoplasm as part of their normal function. Such proteins include actin (a structural protein) and ribosomal proteins (which assist protein synthesis). A lack of a targeting sequence leads to cytosolic localisation and should be viewed as a default response.
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