for modification Golgi apparatus use carbohydrates from where carbohydrates it get?
from plasma membrane or from extracellular material
Answers
Answer:
Cells have extensive sets of intracellular membranes, which together compose the endomembrane system. The endomembrane system was first discovered in the late 1800s when scientist Camillo Golgi noticed that a certain stain selectively marked only some internal cellular membranes. Golgi thought that these intracellular membranes were interconnected, but advances in microscopy and biochemical studies of the various membrane-encased organelles later made it clear the organelles in the endomembrane system are separate compartments with specific functions. These structures do exchange membrane material, however, via a special type of transport.
Today, scientists know that the endomembrane system includes the endoplasmic reticulum (ER), Golgi apparatus, and lysosomes. Vesicles also allow the exchange of membrane components with a cell's plasma membrane.
How Are Cell Membranes Synthesized?
Membranes and their constituent proteins are assembled in the ER. This organelle contains the enzymes involved in lipid synthesis, and as lipids are manufactured in the ER, they are inserted into the organelle's own membranes. This happens in part because the lipids are too hydrophobic to dissolve into the cytoplasm.
Similarly, transmembrane proteins have enough hydrophobic surfaces that they are also inserted into the ER membrane while they are still being synthesized. Here, future membrane proteins make their way to the ER membrane with the help of a signal sequence in the newly translated protein. The signal sequence stops translation and directs the ribosomes — which are carrying the unfinished proteins — to dock with ER proteins before finishing their work. Translation then recommences after the signal sequence docks with the ER, and it takes place within the ER membrane. Thus, by the time the protein achieves its final form, it is already inserted into a membrane (Figure 1).
The proteins that will be secreted by a cell are also directed to the ER during translation, where they end up in the lumen, the internal cavity, where they are then packaged for vesicular release from the cell. The hormones insulin and erythropoietin (EPO) are both examples of vesicular proteins.
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