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Structures of the Endomembrane System

Nuclear Envelope, Plasma Membrane, Endoplasmic Reticulum, Golgi Apparatus, Lysosomes, and Vacuoles

Functions of the Endomembrane System

1. synthesis of proteins and transports into membranes, organelles, or out of cells.
2. Metabolism and movement of lipids
3. Detoxification of poisons.

Endoplasmic Reticulum

Cisternae- network of membranous tubules and sacs.
ER lumen cavity- internal/cisternal space separated from cytosol.
Membrane is continuous with the Nuclear Envelope.
Consists of Smooth and Rough ER.

Smooth ER

lacks ribosomes.
FUNCTION: synthesizes lipids (likes oils, phosolipids, and steroids; glands and testes/ovaries are rich in smooth ER because they secrete hormones), metabolizes carbs, and detoxes drugs and poisons by adding a hydroxyl group to make it more soluble (liver cells; the increase in "barbituates" means increase in proliferation of smooth ER meaning it takes longer to achieve a particular effect).

Rough ER

has ribosomes.
FUNCTION: Secretory Proteins- (pancreas cells make insulin) glycoproteins- secretory proteins with carbs covalently bonded to them.
Polypeptide chain is brought into the ER lumen through pore complex and folds and the protein is wrapped in membrane of vesicles that bud from transitional ER

Membrane Factory: grows by adding membrane proteins and phospholipids.

transitional ER

where vesicles are formed


proteins with carbs covalently bonded to them

transport vesicle

vesicles that move from one place to another

Golgi Apparatus

center of maufacturing, warehousing, sorting and shipping
STRUCTURE: has cisternae that are not connected unlike ER. Has cells special for secretion.
FUNCTION: makes non-cellulose polysaccharides (cellulose made by plasma membrane)
secretes certain molecules.

Delivery function of ER and Golgi (Structural/Functional Polarity/ Cisternal Maturation Model)

vesicles from ER come to golgi on the cis face (towards ER) then the vesicles bud from the trans face of the golgi.

ER----[transport vesicle (ER)]---> cis golgi ---[changes and modifies]--->trans golgi---[golgi transport vesicle]----> plasma membrane.

Before fully budding it adds molecular ID tags (ex: phosphate groups) to show where to go


membranous sac of hydrolytic enzymes that is used to digest macromolecules (the enzymes are made from rough ER and processed in golgi apparatus).
lysosomes fuse with food vacuoles so the enzymes can break the macromolecules into monomers.


to eat/engulf


Since pH in the lysosomes are acidic when it breaks it inhibits the enzymes from either working or it begins to break apart the cell.


carry out phagocytosis like white blood cells


lysosomes use their enzymes to recycle own organic material. A lysosome breaks apart a damaged organelle and reuses the organic material.

Lysosomal storage diseases

Tay Sachs Diease- lack/ in-activeness of lipid digesting enzymes which causes an accumulation of lipids in the brain.


Food vacuoles- material digested by lysosomes
Contractile vacuoles- pump excecss water out to maintain a suitable concentration of ions and molecules in cell
Central Vacuole: (plants) derived from smaller vacuoles from ER and golgi --> big vacuole

disposal site
contains pigments to attract
can contain poisonous compounds that are toxic or unpalatable to animals

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