FRANCIS LEROY, BIOCOSMOS / SCIENCE PHOTO LIBRARY FRANCIS LEROY, BIOCOSMOS / SCIENCE PHOTO LIBRARY
Illustration of membrane structures in a cell: endoplasmic reticulum, golgi apparatus and plasma membrane. At top, the nucleus is seen with pores, & ribosomes (pink dots) on its surface. Continuous with the nuclear membrane is endoplasmic reticulum (ER, top left) which forms a network through the cytoplasm. ER transports glycoproteins to the golgi body (red, centre). Glycoproteins processed in the golgi body are formed into vesicles, which pass through the cytoplasm to the plasma membrane (lower frame). In this way the cell secretes sub- stances in a process whose instructions were originally given by the nucleus.
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