Essential Cell Biology 5th edition

20 CHAPTER 1 Cells: The Fundamental Units of Life
Figure 1–22 The endoplasmic reticulum
produces many of the components of a
eukaryotic cell. (A) Schematic diagram of an
animal cell shows the endoplasmic reticulum
(ER) in green. (B) Electron micrograph of a
thin section of a mammalian pancreatic cell
shows a small part of the ER, of which there
are vast amounts in this cell type, which is
specialized for protein secretion. Note that
the ER is continuous with the membranes
of the nuclear envelope. The black particles
studding the region of the ER (and nuclear
envelope) shown here are ribosomes,
structures that translate RNAs into proteins.
Because of its appearance, ribosome-coated
ER is often called “rough ER” to distinguish
it from the “smooth ER,” which does not
have ribosomes bound to it. (B, courtesy of
Lelio Orci.)
(A)
nucleus nuclear envelope endoplasmic reticulum
(B)
ribosomes
1 µm
profusion of other organelles that are surrounded by single membranes
(see Figure 1–8A). Most of these structures are involved with the cell’s
ability to import raw materials and to export both useful substances and
waste products that are produced by the cell (a topic we discuss in detail
in Chapter 12).
The endoplasmic reticulum (ER) is an irregular maze of interconnected
spaces enclosed by a membrane (Figure 1–22). It is the site where most
cell-membrane components, as well as materials destined for export
from the cell, are made. This organelle is enormously enlarged in cells
that are specialized for ECB5 the secretion e1.21/1.22 of proteins. Stacks of flattened,
membrane-enclosed sacs constitute the Golgi apparatus (Figure 1–23),
nuclear
envelope
(A)
Figure 1–23 The Golgi apparatus is
composed of a stack of flattened,
membrane-enclosed discs. (A) Schematic
diagram of an animal cell with the Golgi
apparatus colored red. (B) More realistic
drawing of the Golgi apparatus. Some of
the vesicles seen nearby have pinched off
from the Golgi stack; others are destined to
fuse with it. Only one stack is shown here,
but several can be present in a cell.
(C) Electron micrograph that shows the
Golgi apparatus from a typical animal cell.
(C, courtesy of Brij L. Gupta.)
(B)
membraneenclosed
vesicles
Golgi apparatus
endoplasmic reticulum
(C)
1 µm