The Endomembrane System
The Endomembrane System
A series of membranes found in the
interior of a eukaryotic cell. It
divides the cell into compartments,
channels the passage of molecules
through the interior of the cell and
provides surfaces for the synthesis
of lipids and some proteins.
The Endomembrane System
One of the fundamental distinctions
between eukaryotes and prokaryotes.
The Endomembrane System
1.
Nuclear Envelope
2.
Endoplasmic reticulum (ER)
3.
Golgi Apparatus
4.
Vesicles (Vacuoles)
Nuclear Envelope
• Double membrane
• Pores permit exit of
ribosomal subuints
• Separates nucleoplasm from cytoplasm
Endoplasmic Reticulum
System of membrane channels
continuous with outer membrane
of the nuclear envelope.
Rough ER is:
Contiguous with the outer membrane
of the nuclear envelope.
Studded with ribosomes
cytoplasm side.
on
the
Function of Rough ER
Protein synthesis and modification.
Function of Rough ER
1. Protein synthesis and modification.
2. Membrane Synthesis
3. Distributes Transport Vesicles
Destinations of Rough ER
Proteins
• Exported from the cell
• Sent to lysosomes or vacuoles
• Embedded in plasma membrane
Smooth ER
Continuous with rough ER
No ribosomes (hence smooth)
Function of smooth ER
1. Synthetic processes
Phospholipids
Steroids
Fatty acids
2. Forms transport vesicles
3. Stores Calcium
4. Detoxifies poisons
Golgi Apparatus
Delivery System Of the Cell
Discovered in 1898
Named
For
Camillo Golgi
Golgi Apparatus
• Stack of 3-20 slightly
curved saccules.
• 1 to few (protists)
• 20 or more - animal cells
• Several hundred – plant
cells
Golgi Apparatus
Receives protein-filled vesicles that bud from the
ER.
Vesicles fuse with membrane of Golgi apparatus
cis face.
Golgi Apparatus
• Proteins modified as they pass
through (form glycoproteins)
• Move to outer (trans) face after
modification.
• Vesicles form & move to different
locations in cell.
• At plasma membrane, vesicles
discharge
contents
as
secretions.
Vesicles
Enzyme Storehouses
Lysosomes –
Intracellular
digestion
centers;
bud
from
endomembrane system
Microbodies
 Peroxisomes – Enzymes catalyze the removal of
hydrogen atoms.
 Glyoxysomes – Found in plants. Enzymes convert
fats into carbohydrates
Lysosomes
Intracellular digestion centers
Produced by Golgi
Membrane-enclosed
vesicles
Contains digestive enzymes
(function best in acidic
environment)
Break down organelles
Animation: Lysosome Formation
Lysosomes
Intracellular digestion centers
Eliminates cells engulfed by phagocytosis.
White blood cells use lysosomes to digest
engulfed bacteria.
Autodigestion - when lysosomes digest
parts of cells.
Apoptosis - programmed cell death, a normal part of
development
Tadpole tail absorption.
Degeneration of webbing between fingers
Peroxisomes
• Abundant in cells that metabolize lipids
• Detoxify alcohol in liver and yeast cells
• Forms hydrogen peroxide that is broken
down to water and oxygen by catalase.
RH2 + O2  R + H2O2  H2O + O2
Glyoxysomes
(Peroxisomes in plants)
In leaves carry out reactions the uses up O2
and releases CO2 that can be used in
photosynthesis
In germinating seeds - convert oils into
sugars used as nutrients by growing plants.
Vacuoles
• Large membranous sac
• Larger than vesicles
• Store substances
• Vacuoles in protozoans
include digestive
vacuoles and waterregulating contractile
vacuoles.
Vacuoles
In protozoans include digestive vacuoles
and water-regulating contractile vacuoles.
Vacuoles
Plant cell vacuoles (usually
one or two) more
prominenet; water-filled and
give support to cell.
Plant vacuoles store water,
sugars, salt, pigments, and
toxic substances to protect
plant from herbivores.