Unit 4: Microscopes, Structure
and Function of Cells
Endomembrane System (EMS)
Monkemeier
Which cellular structures are part of
the Endomembrane system?
Answer
Endoplasmic Reticulum (smooth and
rough)
 The Golgi Apparatus
 Lysosomes (animal cells only)
 Transport vesicles

Contrast the structure and functions of rough
endoplasmic reticulum with those of smooth
endoplasmic reticulum
Rough Endoplasmic
Reticulum (RER)
 Contains ribosomes
 Produces proteins
 Attaches sugars to
proteins
 Proteins fold into their
three dimensional shape
 Packages proteins in
transport vesicles which
go to Golgi Apparatus
Smooth Endoplasmic
Reticulum (SER)
 Produces Lipids
 In testes produces
testosterone
 In liver helps detoxify
drugs
Describe the relationship between the
components of the Endomembrane system

Proteins synthesized on ribosomes on RER
are via transport vesicles to Golgi Apparatus.
 The Golgi Apparatus receives the vesicles
from the cis side. The Golgi Apparatus
modifies the proteins.
 The modified proteins leave the Golgi
Apparatus from the trans side via transport
vesicles.
 The Transport Vesicles then transport the
modified proteins either back to RER or to the
cell membrane for export.
Describe the relationship between the
components of the Endomembrane system

The smooth endoplasmic reticulum is involved
with synthesis of lipids.
 The lipids (such as testosterone) leave the
SER via transport vesicles.
 The transport vesicles transport the lipids to
the Golgi apparatus. The Golgi Apparatus
receives the transport vesicles from the cis
side and releases the modified lipids from the
trans side.
 The modified lipids within the transport
vesicles get transported out of the cell.
Describe the relationship between the
components of the Endomembrane system
The Golgi Apparatus in animal cells
makes lysosomes.
 Lysosomes have a very low pH and are
filled with hydrolytic enzymes.
 The lysosomes fuse with worn out cell
parts and with transport vesicles to break
down structures.

Other Vesicles and Vacuoles Peroxisomes

Made by ribosomes in the cytoplasm. Contain
enzymes. Hydrogen peroxide (H2O2) is a
natural by-product of cellular metabolism.
Enzymes in peroxisomes break hydrogen
peroxide into water and oxygen gas.
 Prevalent in cells that are synthesizing and
breaking down lipids.
 In germinating seeds the peroxisomes break
down fatty acids into sugars needed by the
growing plant.
Other Vesicles and Vacuoles Vacuoles
Are larger than vesicles
 Some are specialized (as in Protists –
the contractile vacuole) to perform
specific functions.
 Usually store substances
 Some animal cells contain vacuoles that
store fat.

Other Vesicles and Vacuoles –
Plant Cell Large Central Vacuole
Contains water, salt, sugars and can
contain enzymes.
 The membrane surrounding the large
central vacuole is called the tonoplast.
 The large central vacuole helps plants
maintain their tonicity – water balance.

Endomembrane System
Human Diseases
Tay Sachs disease involves enzymes in
the lysosomes. Within the lysosome is a
faulty enzyme that cannot properly break
down a specific lipid. This lipid builds up
in the brain and causes nerve
degeneration.
 Children born with Tay Sachs Disease
show symptoms at 6 months and usually
do not live past four years old.

Connections
The mutation that causes Tay Sachs
disease is the HEXA gene on
chromosome number 15.
 The mutation is a change in the
sequence of the DNA nucleotides. This
causes a change in the protein.
 The protein = the enzyme that does not
break down lipids properly.
