The Endomembrane System

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The Endomembrane System
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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.

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The Endomembrane System

• One of the fundamental distinctions between
  eukaryotes and prokaryotes.

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The Endomembrane System

1. Nuclear Envelope
2. Endoplasmic reticulum (ER)
3. Golgi Apparatus
4. Vesicles (Vacuoles)

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Nuclear Envelope

• Double membrane
• Pores permit exit of
• ribosomal subuints
• Separates nucleoplasm from cytoplasm

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Endoplasmic Reticulum

• System of membrane channels continuous with outer
  membrane of the nuclear envelope.

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Rough ER is

• Contiguous with the outer membrane of the nuclear
  envelope.
• Studded with ribosomes on the cytoplasm side.

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Function of Rough ER

• Protein synthesis and modification.

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Function of Rough ER

1. Protein synthesis and modification.
2. Membrane Synthesis
3. Distributes Transport Vesicles

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Destinations of Rough ER Proteins

• Exported from the cell
• Sent to lysosomes or vacuoles
• Embedded in plasma membrane

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Smooth ER

• Continuous with rough ER
• No ribosomes (hence smooth)

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Function of smooth ER

• 1. Synthetic processes
• Phospholipids
• Steroids
• Fatty acids
• Forms transport vesicles
• Stores Calcium
• Detoxifies poisons

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Golgi ApparatusDelivery System Of the Cell

• Discovered in 1898
• Named
• For
• Camillo Golgi

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Golgi Apparatus

• Stack of 3-20 slightly curved saccules.
• 1 to few (protists)
• 20 or more - animal cells
• Several hundred plant cells

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Golgi Apparatus

• Receives protein-filled vesicles that bud from
  the ER.
• Vesicles fuse with membrane of Golgi apparatus
  cis face.

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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.

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VesiclesEnzyme 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

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Lysosomes Intracellular digestion centers

• Produced by Golgi
• Membrane-enclosed vesicles
• Contains digestive enzymes (function best in
  acidic environment)
• Break down organelles

Animation Lysosome Formation
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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

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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

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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.

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Vacuoles

• Large membranous sac
• Larger than vesicles
• Store substances
• Vacuoles in protozoans include digestive
  vacuoles and water- regulating contractile
  vacuoles.

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Vacuoles

• In protozoans include digestive vacuoles and
  water-regulating contractile vacuoles.

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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.

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