BIO230H1 Lecture Notes - Lecture 1: Endoplasmic Reticulum, Endosome, Exocytosis

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16 May 2018
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Lecture One: Membrane Trafficking
Why is Membrane Trafficking Important?
Cells must engage with other cells
o Communicate with other cells
o Acquire resources
Referring to the diagram:
Apical Domain = pink
Basolateral Domain = green
o They are each going to contain different proteins
and lipids
Ex. On the apical side, you absorb nutrients
and on the basolateral side, you transmit the
nutrients to the rest of the body
these processes require control and dynamic changes to the plasma membrane
Biosynthetic-Secretory and Endocytic Pathways: Change the Plasma Membrane
1. Endoplasmic Reticulum
Produces proteins
2. Plasma Membrane & Lysosomes
Break down proteins
Basic Principles of the Biosynthetic-Secretory and Endocytic Pathways
1. They have polarized trafficking routes
The ends are different
(there is a start/end point different)
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2. They have sorting stations
Ex.
Trans Golgi Network
(will sort proteins to certain
locations of the cell) some will
go to early endosomes, late
endosomes, plasma membrane etc.
3. They have retrieval mechanisms and general balancing among routes
There is more than one route
(can release and bring back proteins)
Balanced route not only
endocytosis, but also exocytosis
Secretory Pathways: Constitutive and Regulated
These two secretory pathways
diverge at the trans golgi network
(at the sorting station)
1. Constitutive Secretory Pathway
(does not require a signal keeps on going)
o Functions in all cells
Soluble proteins
Transmembrane proteins
Newly synthesized lipids
(vesicle made up of lipids
so when it fuses with the PM
the cell membrane gets extra
lipids gets bigger)
2. Regulated Secretory Pathway
(requires a signal to release)
o Functions in specialized
cells
Soluble proteins
Transmembrane proteins
Newly synthesized lipids
(vesicle made up of lipids
so when it fuses with the PM
the cell membrane gets extra
lipids gets bigger)
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Mature Secretory Vesicle:
This occurs in both pathways (constitutive and regulated)
A mature secretory vesicle is made by retrieving Golgi
components and concentrating cell cargo
This will allow it to conserve the secretory vesicle
with concentrated cargo to reduce the waste of
cell membrane
Regulated Secretion Provides Extra Plasma Membrane When Needed:
For certain secretion you can concentrate
the cargo and save cell membrane
however for others, it requires extra
cell membrane
A. Cleavage Furrow:
o One cell is dividing into two
o They each require additional
cell membrane
B. Phagocytosis
o The “yellow” thing is being engulfed, it will form a vesicle within the cell
(hence every time phagocytosis occurs the cells will continuously shrink)
o Therefore, it will require additional cell membrane to make up for the cell membrane
lost in phagocytosis
C. Wound Repair:
o When the cell membrane is damage it will require additional cell membrane to repair
the cell
A & B typically receive the extra cell membrane from endosomes
C typically receive the extra cell membrane from lysosomes
Endocytic Pathways Counterbalance Secretory Pathways and Perform Specific Functions:
Endocytosis:
o Process of engulfment;
when something enters
the cell
Secretion:
o Process of secretion;
when something leaves
the cell
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BIO230H1 Full Course Notes
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Document Summary

Why is membrane trafficking important: cells must engage with other cells, communicate with other cells, acquire resources. Referring to the diagram: apical domain = pink, basolateral domain = green, they are each going to contain different proteins and lipids, ex. On the apical side, you absorb nutrients and on the basolateral side, you transmit the nutrients to the rest of the body these processes require control and dynamic changes to the plasma membrane. Biosynthetic-secretory and endocytic pathways: change the plasma membrane: endoplasmic reticulum, produces proteins, plasma membrane & lysosomes, break down proteins. Mature secretory vesicle: this occurs in both pathways (constitutive and regulated, a mature secretory vesicle is made by retrieving golgi components and concentrating cell cargo. This will allow it to conserve the secretory vesicle with concentrated cargo to reduce the waste of cell membrane. A & b typically receive the extra cell membrane from endosomes. C typically receive the extra cell membrane from lysosomes.

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