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Cell Structure and Function: An Overview

This outline provides an overview of cell structure and function, including the cell theory, cell sizes, microscopy techniques, and an introduction to prokaryotic cells.

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Cell Structure and Function: An Overview

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  1. Cell Structure and Function

  2. Outline • Cell Theory • Cell Size • Prokaryotic Cells • Eukaryotic Cells • Organelles • Nucleus • Endomembrane System • Cytoskeleton • Centrioles, Cilia, and Flagella

  3. Cell Theory • A unifying concept in biology • Originated from the work of biologists Schleiden and Schwann in 1838-9 • States that: • All organisms are composed of cells • German botanist Matthais Schleiden in 1838 • German zoologist Theodor Schwann in 1839 • All cells come only from preexisting cells • German physician Rudolph Virchow in 1850’s • Smallest unit of life

  4. Organisms and Cells

  5. Sizes of Living Things

  6. Cell Size • Most much smaller than one millimeter (mm) • Some as small as one micrometer (mm) • Size restricted by Surface/Volume (S/V) ratio • Surface is membrane, across which cell acquires nutrients and expels wastes • Volume is living cytoplasm, which demands nutrients and produces wastes • As cell grows, volume increases faster than surface • Cells specialized in absorption modified to greatly increase surface area per unit volume

  7. Surface to Volume Ratio TotalSurfaceArea (HeightWidthNumberOfSidesNumberOfCubes) 96 cm2 192 cm2 384 cm2 TotalVolume (HeightWidthLengthXNumberOfCubes) 64 cm3 64 cm3 64 cm3 SurfaceAreaPerCube/VolumePerCube (SurfaceArea/Volume) 1.5/1 3/1 6/1

  8. Microscopy Today:Compound Light Microscope • Light passed through specimen • Focused by glass lenses • Image formed on human retina • Max magnification about 1000X • Resolves objects separated by 0.2 mm, 500X better than human eye

  9. Microscopy Today:Transmission Electron Microscope • Abbreviated T.E.M. • Electrons passed through specimen • Focused by magnetic lenses • Image formed on fluorescent screen • Similar to TV screen • Image is then photographed • Max magnification 1000,000s X • Resolves objects separated by 0.00002 mm, 100,000X better than human eye

  10. Microscopy Today:Scanning Electron Microscope • Abbreviated S.E.M. • Specimen sprayed with thin coat of metal • Electron beam scanned across surface of specimen • Metal emits secondary electrons • Emitted electrons focused by magnetic lenses • Image formed on fluorescent screen • Similar to TV screen • Image is then photographed

  11. Microscopy Today:Immunofluorescence Light Microscope • Antibodies developed against a specific protein • Fluorescent dye molecule attached to antibody molecules • Specimen exposed to fluorescent antibodies • Ultra-violet light (black ligt) passed through specimen • Fluorescent dye glows in color where antigen is located • Emitted light is focused by glass lenses onto human retina • Allows mapping distribution of a specific protein in cell

  12. Microscopy Today:Confocal Microscopy • Narrow laser beam scanned across transparent specimen • Beam is focused at a very thin plane • Allows microscopist to optically section a specimen • Sections made at different levels • Allows assembly of 3d image on computer screen that can be rotated

  13. Microscopy Today:Video-enhanced Contrast Microscopy • Great for specimens with low contrast, like living cells • Image is captured by TV camera instead of eye • Image is then “tweaked” by adjusting contrast • Darkest part of image is made black • Lightest part of image is made white • All parts in between made shades of gray • Also allows various shades to be converted to different colors for more contrast

  14. Microscopy Today:Phase Contrast Microscopy • Great for transparent specimens with low contrast, like living cells • Some organelles have higher density than others • Speed of light is affected by density • Light passes more slowly through high density than low density • Light waves entering a specimen “in phase” exit some parts of the specimen out of phase • Microscope shows only light that is slower or faster • Causes transparent organelles to “glow”

  15. Microscopy and Amoeba proteus

  16. Microscopy and Cheek Cells

  17. Prokaryotic Cells:Domains • Lack a membrane-bound nucleus • Structurally simple • Two domains: • Bacteria • Three Shapes • Bacillus (rod) • Coccus (spherical) • Spirilla (spiral) • Archaea • Live in extreme habitats

  18. Shapes of Bacterial Cells

  19. Prokaryotic Cells: Visual Summary

  20. Prokaryotic Cells:The Envelope • Cell Envelopes • Glycocalyx • Layer of polysaccharides outside cell wall • May be slimy and easily removed, or • Well organized and resistant to removal (capsule) • Cell wall • Plasma membrane • Like in eukaryotes • Form internal pouches (mesosomes)

  21. Prokaryotic Cells:Cytoplasm & Appendages • Cytoplasm • Semifluid solution • Bounded by plasma membrane • Contains inclusion bodies – Stored granules of various substances • Appendages • Flagella – Provide motility • Fimbriae – small, bristle-like fibers that sprout from the cell surface • Sex pili – rigid tubular structures used to pass DNA from cell to cell

  22. Eukaryotic Cells • Domain Eukarya • Protists • Fungi • Plants • Animals • Cells contain: • Membrane-bound nucleus • Specialized organelles • Plasma membrane

  23. Eukaryotic Cells :Organelles • Compartmentalization: • Allows eukaryotic cells to be larger than prokaryotic cells • Isolates reactions from others • Two classes: • Endomembrane system: • Organelles that communicate with one another • via membrane channels • Via small vesicles • Energy related organelles • Mitochondria & chloroplasts • Basically independent & self-sufficient

  24. Plasma Membrane

  25. Hypothesized Origin of Eukaryotic Cells

  26. Cell Fractionation, andDifferential Centrifugation • Cell fractionation is the breaking apart of cellular components • Differential centrifugation: • Allows separation of cell parts • Separated out by size & density • Works like spin cycle of washer • The faster the machine spins, the smaller the parts that settled out

  27. Cell Fractionation, andDifferential Centrifugation Grindcells Figure 4C Thencentrifugelonger@ 15,000 g Thencentrifugeeven longer@ 100,000 g Centrifuge@ 600 g Sedimentcontainsnuclei Sedimentcontainsmitochondria,lysosomes Sedimentcontainsribosomes,ER Solubleportion ofcytoplasm.Nosediment

  28. Animal Cell Anatomy

  29. Plant Cell Anatomy

  30. Nucleus • Command center of cell, usually near center • Separated from cytoplasm by nuclear envelope • Consists of double layer of membrane • Nuclear pores permit exchange between nucleoplasm & cytoplasm • Contains chromatin in semifluid nucleoplasm • Chromatin contains DNA of genes • Condenses to form chromosomes • Dark nucleolus composed of rRNA • Produces subunits of ribosomes

  31. Anatomy of the Nucleus

  32. Ribosomes • Serve in protein synthesis • Composed of rRNA • Consists of a largesubunit and a smallsubunit • Subunits made in nucleolus • May be located: • On the endoplasmic reticulum (thereby making it “rough”), or • Free in the cytoplasm, either singly or in groups called polyribosomes

  33. Nucleus, Ribosomes, & ER Figure 4.9

  34. Endomembrane System • Restrict enzymatic reactions to specific compartments within cell • Consists of: • Nuclear envelope • Membranes of endoplasmic reticulum • Golgi apparatus • Vesicles • Several types • Transport materials between organelles of system

  35. Endomembrane System:The Endoplasmic Reticulum • Rough ER • Studded with ribosomes on cytoplasmic side • Protein anabolism • Synthesizes proteins • Modifies proteins • Adds sugar to protein • Results in glycoproteins • Smooth ER • No ribosomes • Synthesis of lipids

  36. Endoplasmic Reticulum

  37. Golgi Apparatus

  38. Lysosomes

  39. Endomembrane System:The Golgi Apparatus • Golgi Apparatus • Consists of 3-20 flattened, curved saccules • Resembles stack of hollow pancakes • Modifies proteins and lipids • Packages them in vesicles • Receives vesicles from ER on cis face • Prepares for “shipment” in vesicles from trans face • Within cell • Export from cell (secretion, exocytosis)

  40. Endomembrane System:Lysosomes • Membrane-bound vesicles (not in plants) • Produced by the Golgi apparatus • Low pH • Contain lytic enzymes • Digestion of large molecules • Recycling of cellular resources • Apoptosis (programmed cell death, like tadpole losing tail) • Some genetic diseases • Caused by defect in lysosomal enzyme • Lysosomal storage diseases (Tay-Sachs)

  41. Endomembrane System: A Visual Summary

  42. Peroxisomes • Similar to lysosomes • Membrane-bounded vesicles • Enclose enzymes • However • Enzymes synthesized by free ribosomes in cytoplasm (instead of ER) • Active in lipid metabolism • Catalyze reactions that produce hydrogen peroxide H2O2 • Toxic • Broken down to water & O2 by catalase

  43. Peroxisomes

  44. Vacuoles • Membranous sacs that are larger than vesicles • Store materials that occur in excess • Others very specialized (contractile vacuole) • Plants cells typically have a central vacuole • Up to 90% volume of some cells • Functions in: • Storage of water, nutrients, pigments, and waste products • Development of turgor pressure • Some functions performed by lysosomes in other eukaryotes

  45. Vacuoles

  46. Energy-Related Organelles:Chloroplast Structure • Bounded by double membrane • Inner membrane infolded • Forms disc-like thylakoids, which are stacked to formgrana • Suspended in semi-fluid stroma • Green due to chlorophyll • Green photosynthetic pigment • Found ONLY in inner membranes of chloroplast

  47. Energy-Related Organelles:Chloroplasts • Captures light energy to drive cellular machinery • Photosynthesis • Synthesizes carbohydrates from CO2 & H2O • Makes own food using CO2 as only carbon source • Energy-poor compounds converted to enery rich compounds

  48. Energy-Related Organelles:Chloroplast Structure

  49. Energy-Related Organelles:Mitochondria • Bounded by double membrane • Cristae – Infoldings of inner membrane that encloses matrix • Matrix – Inner semifluid containing respiratory enzymes • Involved in cellular respiration • Produce most of ATP utilized by the cell

  50. Energy-Related Organelles:Mitochondrial Structure

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