Roles of ER Rough Ribosomes synthesize excreted proteins Stored in cisternae or vesicle Modify...
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Transcript of Roles of ER Rough Ribosomes synthesize excreted proteins Stored in cisternae or vesicle Modify...
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
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
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
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
Fig. 6-13
cis face(“receiving” side of Golgi apparatus) Cisternae
trans face(“shipping” side of Golgi apparatus)
TEM of Golgi apparatus
0.1 µm
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
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
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
Vesicle Organelles
Perform many of the renewal functions Lysosome Peroxisome Glyoxisome
Lysosome Contains digestive enzymes used to degrade
macromolecules or organelles Originates in ER but enzymes are activated in
Golgi Important in macrophages for degradation of
particles acquired via phagocytosis Used to degrade organelles-autophagy
Fig. 6-14a
Nucleus 1 µm
Lysosome
Lysosome
Digestive enzymes
Plasma membrane
Food vacuole
Digestion
(a) Phagocytosis
Fig. 6-14b
Vesicle containingtwo damaged organelles
Mitochondrion fragment
Peroxisome fragment
Peroxisome
Lysosome
DigestionMitochondrionVesicle
(b) Autophagy
1 µm
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
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
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
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