Endomembrane System & Energy
Production
• The endomembrane system is an internal membrane system within
the cell that carries out a variety of functions such as:
– synthesis of proteins and their transport
– metabolism and movement of lipids
– the detoxification of poisons.
• The membranes of the system are either directly in contact with
each other or can communicate through the formation of vesicles
(enclosed sacs made of membrane material).
• There are 5 major compartments:
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endoplasmic reticulum (smooth&rough),
golgi apparatus,
Lysosomes
vacuoles.
Endoplasmic Reticulum(ER)
• largest of the endomembrane systems (over 1/2of the
total)
• contains a network of tubes called cisternae (contains the
inner lumen)
• connected to the nuclear envelope separating the cytosol
from the inner lumen (much like our digestive system)
• self proliferating making its components from precursors
(pieces of phospholipids) found in the cytosol
• 2 distinct compartments smooth & rough
Smooth ER
• Cisternae are rich in enzymes that carry out specialized
tasks
– Functions
• Synthesis of lipids
– oils, phospholipids, & steroids
– cells that produce and secrete these will be "rich" in smooth ER
• Metabolism of carbohydrates
• Detoxification of drugs and poisons
– primary area is in the liver
– detoxification occurs through adding hydroxyl functional groups (increases
water solubility)
– increased used (drugs & alcohol) causes proliferation of smooth ER in the liver
which increases tolerance through faster clearance
• Storage of calcium ions
– stored in muscle for use in contraction
Rough ER
• growing chain of polypeptides is threaded into the
cisternae lumen from the ribosome
– makes secretory proteins called glycoproteins (proteins
with a carbohydrate covalently bonded)
– makes membrane proteins that are anchored by
hydrophobic attraction
– once completed the proteins are transported through
vesicles to their destination
The Golgi Apparatus
(shipping & receiving)
• Consists of flattened sacs of cisternae
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2 distinct sides - CIS (receiving)&TRANS (shipping)
each side has different polarity and thickness
CIS face is close to the ER to receive incoming vesicles
packaged vesicles leave from the trans face
• Site of ER product modification (may modify the glycoprotein to
make it better suited for its final destination)
• Produces its own polysaccharides to be fused with plasma
membranes
– molecular identification tags (phosphate groups or external molecules)
aid in delivery to the correct location
Lysosomes
• A sac of hydrolytic enzymes
– made in the rough ER & modified in the golgi
– Acidic in nature
– Special inner membrane with a 3D conformation that
resists auto digestion
– Can carry out intracellular digestion via phagocytosis
(enfolding of membrane around an object) of membrane
bound food vacuoles
• Digestion products (simple sugars, amino acids, & other
monomers) pass back to the cytosol via exocytosis
Vacuoles
• Food storage structures in plants, protist, and fungal cells.
• Contain hydrolytic enzymes much like lysosomes
• Can be specialized in different animals to perform specific functions
– Contractile vacuole
• protists use this structure to maintain salinity by adding and removing water
– Central vacuole
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found in mature plants
enclosed in a specialized membrane called a tonoplast
enclosed material is called sap not cytosol
can be used to store molecules, ions, waste, pigments, or anything needed for
growth
• plays a major growth role
Mitochondria
• transform energy from their environment to be used by the
host organism. They produce their own energy, are mobile,
and divide (bud) to create new structures.
– found in all Eukaryotes
– site of cellular respiration
– produces ATP through redox reactions in the mitochondrial
membranes
– the # of mitochondria present is based on the cell's (organism's)
need for energy
– has a smooth outer membrane and a folded inner membrane
called cristae
– contains its own DNA & ribosomes in the mitochrondrial matrix
(an enclosed area in the inner membrane)
Chloroplasts
• transform energy from their environment to be used by the
host organism
– specialized member of the plastid family (chromoplasts &
amyloplasts)
– contain the green pigment chlorophyll
– function in the photosynthetic production of sugar
– consists of many flattened sacks called thalokoids (stacks are
called granum)
– fluid outside is called the stroma (contains the DNA &
ribosomes)
Peroxisomes
• Structures is much like lysosomes.
– Produce peroxide (H2O2) for the breakdown of fatty acids by
oxidation for use in the mitochondria.
– Also found in the liver as sites of detoxification.
– Glycoxysomes are specialized structures in plant seeds that
convert fatty acids to sugar used as a source of energy
• Cannot self replicate - product of lipids from the ER,
proteins from the cytosol, & lipids made in the peroxisomes
– they may split (bud) once the necessary parts are assembled
and the size is sufficient