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

Why organelles? Special structures with special functions mitochondria Why organelles? Special structures with special functions Containers with different local environments (pH, ionic conditions, etc) Ex: lysosome & its digestive enzymes Sites for chemical reactions Ex: chloroplasts & mitochondria chloroplast Golgi Why organelles? There are several reasons why cells evolved organelles. First, organelles can perform specialized functions. Second, membrane bound organelles can act as containers, separating parts of the cell from other parts of the cell. Third, the membranes of organelles can act as sites for chemical reactions. Organelles as specialized structures An example of the first type of organelle is cilia, these short filaments act as "paddles" to help some cells move. Organelles as Containers Nothing ever invented by man is as complex as a living cell. At any one time hundreds of incompatible chemical reactions may be occurring in a cell. If the cell contained a uniform mixture of all the chemicals it would not be able to survive. Organelles surrounded by membranes act as individual compartments for these chemical reactions. An example of the second type of organelle is the lysosome. This structure contains digestive enzymes, these enzymes if allowed to float free in the cell would kill it. Organelle membranes as sites for chemical reactions An example of the third type of organelle is the chloroplast. The molecules that conduct the light reactions of photosynthesis are found embedded in the membranes of the chloroplast. ER

Endoplasmic Reticulum Function Many building functions (like membranes) Structure Extends from nuclear membrane throughout cell rough ER = bound ribosomes smooth ER = no ribosomes

Smooth ER function Metabolic processing factory Synthesis (build) & hydrolysis (break) enzymes … build lipids, oils, phospholipids, steroids In liver  breakdown of glycogen into glucose In liver  detoxify drugs & poison

Rough ER function Build proteins for export out of cell protein secreting cells packaged into transport vesicles for export 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

Golgi Apparatus Function Finishes, sorts, ships cell products 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 2005-2006

Golgi Apparatus Structure flattened membrane sacs = cisternae 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 processing While moving 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” 2005-2006

Lysosomes  cell digestion and recycling Structure sacs of enzymes that hydrolyze/digest macromolecules enzymes made by rough ER only in animal cells 2005-2006

Cell digestion Lysosomes fuse with food vacuoles Polymers digested into monomers 2005-2006

Where old organelles go to die! 1960 | Lysosomes little “stomach” lyso– = breaking things apart –some = body digests macromolecules “clean up crew” cleans up broken down organelles Nobel Prize1974 Where old organelles go to die! only in animal cells

Lysosome enzymes work best at pH 5 organelle creates custom pH how? proteins in lysosomal membrane pump in H+ ions from the cytosol adaptation: digestive enzymes from lysosomes won’t work if they 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

But sometimes cells need to die… Lysosomes can kill cells when they need to die  for proper development apoptosis “self-destruct” lysosomes break open & kill cell ex: tadpole tail gets re-absorbed when it turns into a frog ex: loss of webbing between fingers during fetal development Feedback mechanism There are sensors in the cell that monitor growth. They trigger self-destruct when they sense processes. Brown spots on leaves too. Virus infected plant cell auto-destructs and even cells around it to wall off virus.

syndactyly Fetal development 6 weeks 15 weeks

Peroxisomes Other digestive enzyme sacs in both animals & plants breakdown fatty acids to sugars Why? Sugars are easier energy source detoxify cell  alcohol/poisons produce peroxide (H2O2) must breakdown H2O2  H2O + O (bubbles) 2005-2006

Vacuoles & Vesicles Vesicles store, transport, or digest cellular products and waste. Vacuoles contain water Food vacuoles phagocytosis, fuse with lysosomes Contractile vacuoles pump excess H2O out of cell in protists Central vacuole in plants Stockpile byproducts 2005-2006