64
Chapter 3
This binding restarts the process of protein assembly, and the
growing polypeptide chain is fed through a protein complex
in the endoplasmic reticulum membrane into the lumen of the
reticulum (
Figure 3–25
). Upon completion of protein assem-
bly, proteins that are to be secreted end up in the lumen of
the rough endoplasmic reticulum. Proteins that are destined
to function as integral membrane proteins remain embedded
in the reticulum membrane.
Cytoplasm
Extracellular fluid
mRNA from gene A
mRNA from gene B
Free ribosome
Signal sequence
Rough
endoplasmic
reticulum
Growing
polypeptide
chain
Carbohydrate
group
Cleaved signal
sequences
Vesicle
Golgi apparatus
Additional carbohydrate
groups
Secretory vesicle
Plasma membrane
Exocytosis
Digestive
protein
from
gene B
Lysosome
Secreted protein
from gene A
Figure 3–25
Pathway of proteins destined to be secreted by cells or transferred to lysosomes. An example of the latter might be a protein important in
digestive functions in which a cell degrades other intracellular molecules.
previous page 92 Vander's Human Physiology The Mechanisms of Body Function read online next page 94 Vander's Human Physiology The Mechanisms of Body Function read online Home Toggle text on/off