Endoplasmic Reticulm

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Endoplasmic Reticulm

• Complex mass of membranes with cytoplasm of cell
• Extension of nuclear membranes and perinuclear
  space
• Two varieties
• Rough-coated with ribosomes
• Smooth-no ribosomes
• Complex structure with
• Tubules-thin tubes of membrane
• Cisternae-large holding vats

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Roles of ER

• Rough
• Ribosomes synthesize excreted proteins
• Stored in cisternae or vesicle
• Modify proteins
• Glycosylation of proteins
• Delivery of membrane associated proteins
• Often interacts with the Golgi

• Smooth
• Tissue-specific uses
• Storage of carbohydrates
• Detoxification reactions in liver
• Synthesizes much of the new membrane material
• Modification of existing molecules

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ER and Golgi

• Often adjacent in cytoplasm of cell
• Both are membrane producers
• Membrane has sides
• Vesicles are produced inside out
• Vesicle fuses with surface and excreted proteins
  are released and integral proteins are added
  along with membrane
• ER often performs first steps of modification
  that is later finished in Golgi

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Golgi apparatus

• Complex collection of membrane
• Has polarity
• Cis and trans surfaces
• Responsible for secretion
• Very prominent in cells that serve secretory
  functions-such as epithelial cells
• Modifies structures previously synthesized in the
  ER

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Golgi Function

• Cis face is nearer the center of cell
• Cis face is often adjacent to ER
• Trans face is nearer the cell membrane
• Activity is directional
• Starts at cis face and moves to trans

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ER and Golgi

• Synthesis in ER but modification in Golgi
• Similar to an assembly line
• Options packages are added in Golgi
• Sequential passage through cisternae (cis to
  trans)
• Each cisternae contains different enzymes

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Examples of Golgi Function

• Replace sugars placed on glycoproteins
• Modification of phospholipid acylgroups and head
  groups
• Molecule targeting and assembly
• Production of vesicles to delivery membrane
  associated molecules and excreted molecules to
  cell surface

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Cell Renewal

• Cells and their molecules age and become less
  effective
• An important cellular function is renewal
• Old molecules and organelles are recycled
• New phospholipids are produced for the membrane
• Toxic molecules need to be collected and
  detoxified
• Sometimes a cell needs to commit suicide
• Called autolysis or apoptosis

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Vesicle Organelles

• Perform many of the renewal functions
• Lysosome
• Peroxisome
• Glyoxisome

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Lysosome

• Contains digestive enzymes used to degrade
  macromolecules or organelles
• Originates in ER but enzymes are activated in
  Golgi
• Important in macrophages
• Used to degrade organelles

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Cell Death

• Sometimes used in development of organism
• Hand development
• Certain cells are programmed to die at
  appropriate times
• Defense against viral or intracellular bacterial
  infections
• Self-destruct
• Program is started by T cells
• Apoptosis is often accomplished by leaky or
  popping lysosomes

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Peroxisomes

• Contain enzymes to collect free hydrogen and
  oxygen and combine into H2O2 (peroxide)
• Peroxide is also toxic so they contain enzymes to
  degrade into water and oxygen molecules
• Catalase experiment in lab
• Peroxisomes are formed by aggregation of lipids
  and proteins (not formed in ER)
• Many are found in liver cells
• Degrade alcohols into peroxide then into water
  and oxygen

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Peroxisome pt 2

• Also responsible for degradation of fatty acids
  in cytosol
• Modify fatty acids and phospholipids and
  incorporate into peroxisome membrane
• Divide by binary fission

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Glyoxysomes

• Specialized peroxisomes found in plant seeds
• Recognize appropriate signals and begin to
  degrade stored fat in seed
• Fat is converted to sugars which allows seedling
  to sprout
• Once photosynthesis starts, glyoxysomes degrade