85
CHAPTER THREE
Cells
Golgi
apparatus
Rough
endoplasmic
reticulum
Nucleus
Cytosol
Transport
vesicle
Secretion
Cell membrane
Nuclear
envelope
(a)
(b)
Carbohydrates
Cell membrane
Mitochondrion
Lysosome
Nuclear pore
Nuclear envelope
mRNA
Milk
protein
Milk
protein
in Golgi
vesicle
Lipids are
synthesized
in the smooth
endoplasmic
reticulum (ER).
Most proteins are synthesized
on ribosomes associated with
membranes of the rough ER,
using amino acids in the cytosol.
Sugars are synthesized in the
smooth ER and Golgi apparatus
and may be attached to proteins
or secreted in vesicles.
Proteins are secreted from
vesicles that bud off of the
Golgi apparatus.
Fat droplets pick up a layer of
lipid from the cell membrane
as they exit the cell.
2
3
4
5
6
7
Milk protein genes are
transcribed into mRNA.
1
mRNA exits through
nuclear pores.
FIGURE 3.10
The Golgi apparatus. (
a
) A transmission electron
micrograph of a Golgi apparatus (48,500×). (
b
) The Golgi apparatus
consists of membranous sacs that continually receive vesicles from the
endoplasmic reticulum and produce vesicles that enclose secretions.
FIGURE 3.11
Milk secretion illustrates how organelles interact to
synthesize, transport, store, and export biochemicals (
1–7
). When the
baby suckles, he or she receives a chemically complex secretion—milk.
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