The Endomembrane System

•Regulates protein traffic and performs metabolic functions in the cell• Includes many different structures:

– Endoplasmic Reticulum (and vesicles)– Golgi Apparatus (and vesicles)– Lysosomes– Vacuoles

Endoplasmic Reticulum

• Function– Manufactures membranes and performs many bio-

synthesis functions• Structure

– Membrane connected to nuclear envelope & extends throughout cell

– Accounts for 50% of membranes in eukaryotic cells• Types

– Rough ER= has ribosomes bound to it– Smooth ER=does not have ribosomes bound to it

Endoplasmic Reticulum

Smooth Endoplasmic Reticulum

• Functions• Metabolic processes

• Synthesis and hydrolysis• Enzymes of smooth ER

• Synthesize lipids, oils, phospholipids, steroids & sex hormones

• Hydrolysis of glycogen into glucose in liver

• Detoxify drugs and poisons (in liver)• Pumps calcium ions for muscle function

Rough Endoplasmic Reticulum• Function

• Produce proteins for export out of cell• Protein secreting cells• Packaged into transport vesicles for export

Membrane Factory

• Synthesize membrane phospholipids– Build new membrane– As ER membrane expands, bud off & transfer

to other parts of cell that need membranes• Synthesize membrane proteins

– Membrane bound proteins synthesized directly into membrane

– Processing to make glycoproteins

Endoplasmic reticulum

• Which types of cells have a lot of rough ER?

• How might smooth ER play a role in “alcohol tolerance”?

Golgi Apparatus

• Function:• Finishes, sorts &

ships cell products• Shipping and

receiving department

• Extensive in cells specialized for secretion

Golgi Apparatus

• Structure– Flattened membranous sac=cisternae

• Look like stacks of pita bread

– 2 sides=2 functions• Cis=receives material by fusing with vesicles=“receiving”• Trans=buds off vesicles that travel to other

sites=“shipping”

Golgi Processing

• During path from cis to trans, products from ER are modified into final form

• Tags, sorts, & packages materials into transport vesicles– Golgi=“UPS headquarters”– Transport vesicles=“UPS trucks”

• Delivering packages that have been tagged with their own barcode

Inside of cell

Outside of cell

Roughendoplasmicreticulum

Flow of material

Golgi apparatuscis region

Cisternae

Protein-carrying vesicles from the endoplasmic reticulumtransfer substances to the cis region of the Golgi apparatus.

The Golgi chemically modifies proteins in its lumen…

trans region

…and “targets” them to the correct addresses.

Proteins for usewithin the cell Proteins for use

outside the cellPlasmamembrane

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Lysosomes

• Function:• A little “stomach”for the cell

• Lyso-=breaking things apart

• -some=body• Clean up crew of the

cell

Lysosome• Structure

– Membrane bounded sac of hydrolytic enzymes and molecules that digests macromolecules

• Enzymes & membrane of lysosomes are synthesized by rough ER & transferred to the golgi

Only in animal cells

Lysosomes in the Cell

Cellular digestion

• Lysosomes fuse with food vacuoles

• Polymers are digested into monomers– Pass to cytosol to

become nutrients of cell

Lysosomal enzymes

• Lysosomal enzymes work best at pH 5– Organelle creates custom pH– Enzymes are very pH sensitive

• Why evolve digestive enzymes which function at pH different from cytosol– Digestive enzymes won’t function well if leak

into cytosol=don’t want to digest yourself

Cell death…

• Apoptosis=cell death– Critical role in programmed destruction of

cells in multicellular organisms• Auto-destruct mechanism

– “cell suicide”• Some cells have to die in an organized fashion

especially during development– Ex. Development of space between your fingers during

embryonic development– ex. If cell grows improperly this self destruct mechanism

is triggered to remove damaged cell» Cancer over rides this to enable tumor growth

When things go wrong…• What if a lysosome digestive

enzyme didn’t function– Don’t digest a biomolecule

• Instead biomolecule collects in lysosomes

• Lysosomes fill up with undigested material

– Lysosomes grow larger & larger

• Eventually disrupt cell & organ function

• Lysosomal storage diseases are usually fatal– Tay-Sachs disease

• Lipids build up in brain cells• Child dies before age 5

Peroxisomes• Other digestive enzyme

sacs– In both plants and

animals– Breakdown fatty acids to

sugars• Easier to transport & use as

energy source

– Detoxify cell• Detoxifies alcohol & other

poisons

– Produce perioxide (H2O2)

Central Vacuole

• Functions in plants• Storage

• Stockpiling proteins or inorganic ions

• Depositing metabolic byproducts• Storing pigments• Storing defensive compounds

against herbivores• Selective membrane (tonoplast)

• Control what comes in and out

• Maintains turgor pressure• Often largest structure in plant

cell

Other Types of Vacuoles

• Food vacuoles– Are formed by phagocytosis

• Contractile vacuoles– Pump excess water out of protist cells

The Endomembrane System: A Review

• The endomembrane system is a complex and dynamic player in the cell’s compartmental organization