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Cell Structure

Cell Structure. Chapter 5. Cell Theory. All organisms are composed of one or more cells. Cells are the smallest living units of all living organisms. Cells arise only by division of a previously existing cell. Cell Characteristics. Genetic material

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Cell Structure

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  1. Cell Structure Chapter 5

  2. Cell Theory • All organisms are composed of one or more cells. • Cells are the smallest living units of all living organisms. • Cells arise only by division of a previously existing cell.

  3. Cell Characteristics • Genetic material • single circular molecule of DNA in prokaryotes • double helix located in nucleus in eukaryotes – nuclear envelope (double membrane • Cytoplasm fills cell interior – • sugars, amino acids, • proteins - organelles • Plasma membrane encloses • the cell – phospholipid bilayer Phospholipid Membrane proteins

  4. Generalized Eukaryotic Cell

  5. Cell Size • Most cells are relatively small because as size increases, volume increases much more rapidly. • longer diffusion time

  6. Visualizing Cells • Resolution - minimum distance two points can be apart and still be distinguished as two separate points • Compound microscopes - magnify in stages using multiple lenses • Transmission electron microscope - electrons transmitted through specimen • Scanning electron microscope - electrons beamed onto surface of the specimen

  7. Visualizing Cells

  8. Prokaryotic Cells • Simplest organisms • Cytoplasm is surrounded by plasma membrane and encased in a rigid cell wall composed of peptidoglycan. • no distinct interior compartments • gram-positive – thick single layer wall that retains a violet dye from Gram stain procedure • gram-negative – multilayered wall does not retain dye • Susceptibility of bacteria to antibiotics depends on cell wall structure.

  9. Prokaryotic Cells • Some use flagellum for locomotion • threadlike structures protruding from cell surface Bacterial cell wall Rotary motor Sheath Flagellin

  10. Eukaryotic Cells • Characterized by compartmentalization by an endomembrane system, and the presence of membrane-bound organelles. • Central vacuole – plants, storage • Vesicles (smaller) • Chromosomes - DNA and protein • Cytoskeleton (internal protein scaffolding) • Cell walls – plants and fungi

  11. Nucleus • Repository for genetic material • Directs activities of the cell • Usually single, some cells several, RBC none • Nucleolus - region of intensive ribosomal RNA synthesis • Surface of nucleus bound by two phospholipid bilayer membranes • nuclear membrane • Nuclear pores – protein gatekeepers • Usually proteins going in and RNA going out

  12. Nucleus

  13. Chromosomes • DNA of eukaryotes is divided into linear chromosomes. • exist as strands of chromatin, except during cell division • associated with packaging histones, packaging proteins • nucleosomes

  14. Endomembrane System • Compartmentalizes cell, channeling passage of molecules through cell’s interior. • Endoplasmic reticulum • Rough ER - studded with ribosomes • Smooth ER - few ribosomes

  15. Endoplasmic reticulum • Largest internal membrane • Composed of Lipid bilayer • Serves as system of channels from the nucleus • Functions in storage and secretion • Rough ER is “rough” because of associated ribosomes (sites of protein synthesis • Smooth ER - lack associated ribosomes – contained embedded enzymes, catalyze synthesis of carbohydrate and lipid molecules

  16. Endomembrane System • Golgi apparatus • collection of Golgi bodies • collect, package, and distribute molecules synthesized at one location in the cell and utilized at another location • Front - cis , Back – trans • Cisternae – stacked membrane folds

  17. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cisternae cis face Proteins trans face Golgi apparatus Transport vesicle Protein Vesicle budding from rough endoplasmic reticulum Migrating transport vesicle Fusion of vesicle with Golgi apparatus Ribosome

  18. Endomembrane System • Vesicles • Lysosomes - membrane-bound vesicles containing digestive enzymes – from Golgi • Microbodies - enzyme-bearing, membrane-enclosed vesicles. • Peroxisomes - contain enzymes that catalyze the removal of electrons and associated hydrogen atoms • Peroxisome – named for hydrogen peroxide produced as a by-product • Enzyme breaks down to water and oxygen

  19. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cytoplasm Endoplasmic reticulum Phagocytosis Golgi apparatus Food vesicle Lysosomes Transport vesicle Old or damaged organelle Plasma membrane Digestion of phagocytized food particles or cells Breakdown of old organelle Extracellular fluid

  20. Ribosomes • Ribosomes are RNA-protein complexes composed of two subunits that join and attach to messenger RNA. • site of protein synthesis • assembled in nucleoli

  21. Organelles With DNA • Mitochondria • bounded by exterior and interior membranes • interior partitioned by cristae • Chloroplasts • have enclosed internal compartments of stacked grana, containing thylakoids • found in photosynthetic organisms

  22. Mitochondria A. "Powerhouse of the cell" - cellular metabolism B. Structure- outer and inner membranes, cristae C. Have their own DNA

  23. Chloroplasts • Chloroplasts are larger and more complex than mitochondria • Grana – closed compartments of stacked membranes • Thylakoids – disc shaped structure – light capturing pigment • Stroma – fluid matrix

  24. Endosymbiosis • Endosymbiotic theory suggests engulfed prokaryotes provided hosts with advantages associated with specialized metabolic activities.

  25. Theory of Endosymbiosis

  26. Evidence for the endosymbiont theory is that mitochondria and chloroplasts: - Are appropriate size to be descendants of eubacteria. - Have inner membranes similar to those on prokaryotic plasma membranes. - Replicate by splitting, as in prokaryotes. - DNA is circular and different from the DNA of the cell's nucleus. - Contain their own components for DNA transcription and translation into proteins . - Have ribosomes similar to prokaryotic ribosomes. - Molecular systematics lend evidence to support this theory. - Many extant organisms are involved in endosymbiotic relationships.

  27. Microtubules Intermediate filaments Actin Cytoskeleton • Network of protein fibers supporting cell shape and anchoring organelles • Actin filaments • cell movement • Microtubules • Hollow tubes • Facilitate cell movement • Centrioles – barrel shaped • organelles occur in pairs – • help assemble animal cell’s microtubules • Intermediate filaments • Stable - don’t break down

  28. Cytoskeleton

  29. Plant Cells • Central vacuole • often found in the center of a plant, and serves as a storage facility for water and other materials • Cell wall • primary walls – laid down while cell is growing • middle lamella – glues cells together • secondary walls – inside the primary cell walls after growth

  30. Plant Cell

  31. Animal Cells • Animal cells lack cell walls. • form extracellular matrix • provides support, strength, and resilience

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