Chapter 6 The Cell: Endomembrane System–. Endoplasmic Reticulum, Chapter 6 The Cell: Endomembrane System– Endoplasmic Reticulum, Golgi Apparatus, Lysosomes, Peroxisomes, Vacuoles, Vesicles 2005-2006

Overview Play key role in synthesis (& hydrolysis) of macromolecules in cell Various “players” modify macromolecules for various functions 2005-2006

Endoplasmic Reticulum Function manufactures membranes & performs many bio-synthesis functions Structure membrane connected to nuclear envelope & extends throughout cell accounts for 50% membranes in eukaryotic cell rough ER = bound ribosomes smooth ER = no ribosomes

Types of ER 2005-2006

Smooth ER function Factory processing operations many metabolic processes synthesis & hydrolysis enzymes of smooth ER… synthesize lipids, oils, phospholipids, steroids & sex hormones hydrolysis (breakdown) of glycogen (in liver) into glucose detoxify drugs & poisons (in liver) ex. alcohol & barbiturates

which cells have a lot of rough ER? Rough ER function Produce proteins for export out of cell protein secreting cells packaged into transport vesicles for export which cells have a lot of rough ER? Which cells have a lot of ER? protein production cells like pancreas = production of digestive enzymes (rough endoplasmic reticulum from a cell of exocrine pancreas (88000X)) 2005-2006

Membrane Factory 2005-2006 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 2005-2006

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which cells have a lot of Golgi? Golgi Apparatus Function finishes, sorts, & ships cell products “shipping & receiving department” center of manufacturing, warehousing, sorting & shipping extensive in cells specialized for secretion Cells specialized for secretion? endocrine glands: produce hormones pituitary, pancreas, adrenal, testes, ovaries exocrine glands: produce digestive enzymes& other products pancreas, mammary glands, sweat glands which cells have a lot of Golgi? 2005-2006

Golgi Apparatus Structure flattened membranous sacs = cisternae look like stack 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” (transport) cis 2005-2006 trans

Golgi Apparatus

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 barcodes 2005-2006

Putting it together… 2005-2006

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Lysosomes Structure membrane-bounded sac of hydrolytic enzymes that digests macromolecules enzymes & membrane of lysosomes are synthesized by rough ER & transferred to the Golgi only in animal cells 2005-2006

Lysosomes 1960 | 1974 Function a little “stomach” for the cell lyso– = breaking things apart –some = body also the “clean up crew” of the cell Lysosomes were discovered quite recently, in 1960s, by Christian de Duve. This discovery was so important that he was awarded the 1974 Nobel prize. Why was this discovery so important? 1974 Nobel prize: Christian de Duve Lysosomes discovery in 1960s 2005-2006

Cellular digestion Lysosomes fuse with food vacuoles Polymers are digested into monomers pass to cytosol to become nutrients of cell 2005-2006

Where old proteins go to die! “Let’s go to the video tape!” The Recycler “Let’s go to the video tape!” (play movie here) Fuse with organelles or macromolecules in cytosol to recycle materials 2005-2006

Lysosomal enzymes Lysosomal enzymes work best at pH 5 organelle creates custom pH how? proteins in lysosomal membrane pump H+ ions from the cytosol into lysosome why? enzymes are very sensitive to pH enzymes are proteins — pH affects structure 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! lysosomes create a space where cell can digest macromolecules safely rupturing a few lysosomes has little impact on a cell (pH of cytosol affects functionality of the lysosomal enzymes), but massive leakage from lysosomes can destroy cell why evolve digestive enzymes which function at pH so different from cytosol? digestive enzymes won’t function well if leak into cytosol = most times don’t want to digest yourself! low pH = acid environment cause oxidation (removing electrons) & promotes hydrolysis

When things go wrong… Tay-Sachs What if a lysomome digestive enzyme doesn’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 2005-2006

Sometimes its supposed to work that way… 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 Feedback mechanism There are sensors in the cell that monitor growth. They trigger self-destruct when they sense processes gone awry. Brown spots on leaves too. Virus infected plant cell auto-destructs and even kills cells around it to wall off virus.

syndactyly Fetal development 15 weeks 6 weeks 2005-2006

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Peroxisomes Other digestive enzyme sacs in both animals & plants breakdown fatty acids to sugars easier to transport & use as energy source detoxify cell detoxifies alcohol & other poisons produce peroxide (H2O2) must breakdown H2O2  H2O 2005-2006

“Let’s go to the video tape!” Vacuoles & vesicles Function little “transfer ships” Food vacuoles phagocytosis, fuse with lysosomes Contractile vacuoles in freshwater protists, pump excess H2O out of cell Central vacuoles in many mature plant cells “Let’s go to the video tape!” (play movie here) 2005-2006

Vacuoles in plants Functions storage stockpiling proteins or inorganic ions depositing metabolic byproducts storing pigments storing defensive compounds against herbivores selective membrane control what comes in or goes out 2005-2006

Vacuole 2005-2006

Vesicles Vesicles 2005-2006

Putting it all together… “Let’s go to the video tape!” (play movie here) Putting it all together… 2005-2006

Any Questions??