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The Cell

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  1. The Cell

  2. Why are cells so small?Why can’t they be as huge as an hippo?

  3. Overview: The Fundamental Units of Life • All organisms are made of cells • The cell is the simplest collection of matter that can be alive • Cell structure is correlated to cellular function

  4. Concept 6.1: Biologists use microscopes and the tools of biochemistry to study cells • In a light microscope (LM), visible light is passed through a specimen and then through glass lenses • -Lenses refract (bend) the light, so that the image is magnified • Scanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen, providing images that look 3-D • Scanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen, providing images that look 3-D

  5. Human height 1 m Length of somenerve andmuscle cells 0.1 m Unaided eye Chicken egg 1 cm Frog egg 1 mm Human egg 100 m Most plant andanimal cells Light microscopy 10 m Nucleus Most bacteria Mitochondrion 1 m Smallest bacteria Electron microscopy Super-resolutionmicroscopy 100 nm Viruses Ribosomes 10 nm Proteins Lipids 1 nm Small molecules Atoms 0.1 nm

  6. Cell Fractionation • Cell fractionation takes cells apart and separates the major organelles from one another

  7. TECHNIQUE Figure 6.4 Homogenization Tissuecells Homogenate Centrifuged at1,000 g(1,000 times theforce of gravity)for 10 min Centrifugation Supernatantpoured intonext tube Differentialcentrifugation 20,000 g 20 min 80,000 g 60 min Pellet rich innuclei andcellular debris 150,000 g 3 hr Pellet rich inmitochondria(and chloro-plasts if cellsare from a plant) Pellet rich in“microsomes”(pieces of plasmamembranes andcells’ internalmembranes) Pellet rich inribosomes

  8. What limits cell size? • Surface to volume ratio • as cell gets bigger its volume increases faster than its surface area • smaller objects have greaterratio of surface area to volume 6:1 ~1:1 6:1 s:v

  9. Cell characteristics • All cells: • surrounded by a plasma membrane • have cytosol • semi-fluid substance within the membrane • cytoplasm = cytosol + organelles • contain chromosomes which have genes in the form of DNA • have ribosomes • tiny “organelles” that make proteins using instructions contained in genes

  10. Prokaryotebacteria cells Types of cells - no organelles - organelles Eukaryoteanimal cells Eukaryoteplant cells

  11. Prokaryotic cell DNA in nucleoid region, without a membrane separating it from rest of cell Cell wall present in all (type differs) Eukaryotic cell chromosomes in nucleus, membrane-enclosed organelle Cell walls present in fungi and plants only More complex Membrane bound organelles present Types of cells • Prokaryotic vs. eukaryotic cells

  12. The prokaryotic cell is much simpler in structure, lacking a nucleus and the other membrane-enclosed organelles of the eukaryotic cell.

  13. Golgi mitochondria chloroplast ER Why organelles? • Specialized structures • specialized functions • cilia or flagella for locomotion • Containers • partition cell into compartments • create different local environments • separate pH, or concentration of materials • distinct & incompatible functions • lysosome & its digestive enzymes • Membranes as sites for chemical reactions • unique combinations of lipids & proteins • embedded enzymes & reaction centers • chloroplasts & mitochondria

  14. Cells gotta work to live! • What jobs do cells have to do? • make proteins • proteins control everycell function • make energy • for daily life • for growth • make more cells • growth • repair • renewal

  15. The Protein Assembly Line Golgiapparatus ribosome ER Building Proteins • Organelles involved • nucleus • ribosomes • endoplasmic reticulum (ER) • Golgi apparatus • vesicles nucleus vesicles

  16. cisternal space polypeptide signal sequence ribosome membrane of endoplasmic reticulum mRNA cytoplasm Synthesizing proteins ribosome

  17. large subunit small subunit ribosome Nucleolus • Function • ribosome production • build ribosome subunits from rRNA & proteins • exit through nuclear pores to cytoplasm & combine to form functional ribosomes rRNA & proteins nucleolus

  18. Types of Ribosomes • Freeribosomes • suspended in cytosol • synthesize proteins that function in cytosol • Bound ribosomes • attached to endoplasmic reticulum • synthesize proteins for export or for membranes membrane proteins

  19. Rough ER function • Finalize protein formation and prepare for export out of cell (protein folding) • protein secreting cells will have lots • packaged into transport vesicles to golgi

  20. secretory vesicles transport vesicles Golgi Apparatus • Function • finishes, sorts, tags & ships cell products • like “UPS shipping department” • ships products in vesicles • membrane sacs • “UPS trucks”

  21. nucleus cell membrane nuclear pore protein secreted rough ER vesicle ribosome proteins smooth ER transport vesicle Golgi apparatus cytoplasm Putting it together… Making proteins

  22. Smooth ER function • Membrane production • Many metabolic processes • synthesis • synthesize lipids • oils, phospholipids, steroids & sex hormones • hydrolysis • hydrolyze glycogen into glucose • in liver • detoxify drugs & poisons • in liver • ex. alcohol & barbiturates

  23. Lysosomes • Function • little “stomach” of the cell • digests macromolecules • “clean up crew” of the cell • cleans up broken down organelles • Structure • vesicles of digestive enzymes synthesized by rER, transferred to Golgi only in animal cells

  24. Cellular digestion • Lysosomes fuse with food vacuoles • polymers digested into monomers • pass to cytosol to become nutrients of cell vacuole • lyso– = breaking things apart • –some = body

  25. When cells need to die… • Lysosomes can be used to kill cells when they are supposed to be destroyed • some cells have to die for proper development in an organism • apoptosis • “auto-destruct” process • lysosomes break open & kill cell • ex: tadpole tail gets re-absorbed when it turns into a frog • ex: loss of webbing between your fingers during fetal development

  26. + Making Energy • Cells must convert incoming energy to forms that they can use for work • mitochondria: from glucose to ATP • chloroplasts: from sunlight to ATP & carbohydrates • ATP = active energy • carbohydrates = stored energy ATP ATP

  27. Mitochondria & Chloroplasts • Important to see the similarities • transform energy • generate ATP • double membranes = 2 membranes • semi-autonomous organelles • move, change shape, divide • internal ribosomes, DNA & enzymes

  28. Mitochondria • Function • cellular respiration • generate ATP • from breakdown of sugars, fats & other fuels • in the presence of oxygen • break down larger molecules into smaller to generate energy = catabolism • generate energy in presence of O2 = aerobic respiration

  29. Mitochondria • Almost all eukaryotic cells have mitochondria • there may be 1 very large mitochondrion or 100s to 1000s of individual mitochondria • number of mitochondria is correlated with aerobic metabolic activity • more activity = more energy needed = more mitochondria What cells would have a lot of mitochondria? active cells: • muscle cells • nerve cells

  30. Chloroplasts • Chloroplasts are plant organelles • class of plant structures = plastids • amyloplasts • store starch in roots & tubers • chromoplasts • store pigments for fruits & flowers • chloroplasts • store chlorophyll & function in photosynthesis • in leaves, other green structures of plants & in eukaryotic algae

  31. Chloroplasts • Function • photosynthesis • generate ATP & synthesize sugars • transform solar energy into chemical energy • produce sugars from CO2 & H2O • Semi-autonomous • moving, changing shape & dividing • can reproduce by pinching in two Who else divides like that? bacteria!

  32. Mitochondria & chloroplasts are different • Organelles not part of endomembrane system • Grow & reproduce • semi-autonomous organelles • Proteins primarily from free ribosomes in cytosol & a few from their own ribosomes • Own circular chromosome • directs synthesis of proteins produced by own internal ribosomes • ribosomes like bacterial ribosomes Who else has a circular chromosome not bound within a nucleus? bacteria

  33. Endosymbiosis theory • Mitochondria & chloroplasts were once free living bacteria • engulfed by ancestral eukaryote • Endosymbiont • cell that lives within another cell (host) • as a partnership • evolutionary advantage for both • one supplies energy • the other supplies raw materials & protection Lynn Margulis U of M, Amherst

  34. Endosymbiosis theory Evolution of eukaryotes

  35. food vacuoles Food & water storage plant cells central vacuole animal cells contractilevacuole

  36. 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

  37. 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

  38. Putting it all together, try labeling.. animal cells plant cells