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Chapter 6

Chapter 6. A Tour of the Cell. Overview: The Importance of Cells. All organisms are made of cells Cell structure is correlated to cellular function All cells are related by their descent from earlier cells

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Chapter 6

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  1. Chapter 6 A Tour of the Cell

  2. Overview: The Importance of Cells • All organisms are made of cells • Cell structure is correlated to cellular function • All cells are related by their descent from earlier cells • There is an opinion that cell is the simplest formation that can live (but others say it’s virus)

  3. Concept 6.2: Eukaryotic cells have internal membranes that compartmentalize their functions • The basic structural and functional unit of every organism is one of two types of cells: prokaryotic or eukaryotic • Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells • Protists, fungi, animals, and plants all consist of eukaryotic cells

  4. Comparing Prokaryotic and Eukaryotic Cells • Basic features of all cells: • Plasma membrane • Cytosol • Chromosomes (carry genes) • Ribosomes (make proteins)

  5. Prokaryotic cells have no nucleus • In a prokaryotic cell, DNA is in an unbound region called the nucleoid • Prokaryotic cells lack membrane-bound organelles

  6. Eukaryotic cells have DNA in a nucleus that is bounded by a membranous nuclear envelope • Eukaryotic cells have membrane-bound organelles • Eukaryotic cells are generally much larger than prokaryotic cells

  7. The plasma membrane is a selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of the cell

  8. A Panoramic View of the Eukaryotic Cell • A eukaryotic cell has internal membranes that partition the cell into organelles • Plant and animal cells have most of the same organelles

  9. LE 6-9a ENDOPLASMIC RETICULUM (ER Nuclear envelope Flagellum Rough ER Smooth ER NUCLEUS Nucleolus Chromatin Centrosome Plasma membrane CYTOSKELETON Microfilaments Intermediate filaments Microtubules Ribosomes: Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome In animal cells but not plant cells: Lysosomes Centrioles Flagella (in some plant sperm)

  10. LE 6-9b Nuclear envelope Rough endoplasmic reticulum NUCLEUS Nucleolus Chromatin Smooth endoplasmic reticulum Centrosome Ribosomes (small brown dots) Central vacuole Golgi apparatus Microfilaments Intermediate filaments CYTOSKELETON Microtubules Mitochondrion Peroxisome Chloroplast Plasma membrane Cell wall Plasmodesmata Wall of adjacent cell In plant cells but not animal cells: Chloroplasts Central vacuole and tonoplast Cell wall Plasmodesmata

  11. Concept 6.3: The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes • The nucleus contains most of the DNA in a eukaryotic cell • Ribosomes use the information from the DNA to make proteins

  12. The Nucleus: Genetic Library of the Cell • The nucleus contains most of the cell’s genes and is usually the most conspicuous organelle • The nuclear envelope encloses the nucleus, separating it from the cytoplasm

  13. Ribosomes: Protein Factories in the Cell • Ribosomes are particles made of ribosomal RNA and protein • Ribosomes carry out protein synthesis in two locations: • In the cytosol (free ribosomes) • On the outside of the endoplasmic reticulum (ER) or the nuclear envelope (bound ribosomes)

  14. http://genome.imim.es/courses/Madrid04/exercises/ensembl/images/ribosome.jpghttp://genome.imim.es/courses/Madrid04/exercises/ensembl/images/ribosome.jpg

  15. LE 6-11 Ribosomes ER Cytosol Endoplasmic reticulum (ER) Free ribosomes Bound ribosomes Large subunit Small subunit 0.5 µm TEM showing ER and ribosomes Diagram of a ribosome

  16. Concept 6.4: The endomembrane system regulates protein traffic and performs metabolic functions in the cell • Components of the endomembrane system: • Nuclear envelope • Endoplasmic reticulum • Golgi apparatus • Lysosomes • Vacuoles • Plasma membrane • These components are either continuous or connected via transfer by vesicles

  17. LE 6-12 Smooth ER Nuclear envelope Rough ER ER lumen Cisternae Ribosomes Transitional ER Transport vesicle 200 nm Rough ER Smooth ER

  18. The Endoplasmic Reticulum: Biosynthetic Factory • The endoplasmic reticulum (ER) accounts for more than half of the total membrane in many eukaryotic cells • The ER membrane is continuous with the nuclear envelope • There are two distinct regions of ER: • Smooth ER, which lacks ribosomes • Rough ER, with ribosomes studding its surface

  19. Functions of Smooth ER • The smooth ER • Synthesizes lipids • Metabolizes carbohydrates • Stores calcium • Detoxifies poison

  20. Functions of Rough ER • The rough ER • Has bound ribosomes • Produces proteins and membranes, which are distributed by transport vesicles • Is a membrane factory for the cell

  21. http://sun.menloschool.org/~cweaver/cells/c/rough_er/picture.jpghttp://sun.menloschool.org/~cweaver/cells/c/rough_er/picture.jpg

  22. The Golgi Apparatus: Shipping and Receiving Center • The Golgi apparatus consists of flattened membranous sacs called cisternae • Functions of the Golgi apparatus: • Modifies products of the ER • Manufactures certain macromolecules • Sorts and packages materials into transport vesicles

  23. http://micro.magnet.fsu.edu/cells/golgi/images/golgifigure1.jpghttp://micro.magnet.fsu.edu/cells/golgi/images/golgifigure1.jpg

  24. Lysosomes: Digestive Compartments • A lysosome is a membranous sac of hydrolytic enzymes • Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids • Lysosomes also use enzymes to recycle organelles and macromolecules, a process called autophagy

  25. Vacuoles: Diverse Maintenance Compartments • Vesicles and vacuoles (larger versions of vacuoles) are membrane-bound sacs with varied functions • A plant cell or fungal cell may have one or several vacuoles

  26. Food vacuoles are formed by phagocytosis • Central vacuoles, found in many mature plant cells, hold organic compounds and water

  27. LE 6-15 Central vacuole Cytosol Tonoplast Central vacuole Nucleus Cell wall Chloroplast 5 µm

  28. Endomembrane system Nucleus Rough ER Smooth ER Nuclear envelope

  29. LE 6-16-2 Nucleus Rough ER Smooth ER Nuclear envelope cis Golgi Transport vesicle trans Golgi

  30. LE 6-16-3 Nucleus Rough ER Smooth ER Nuclear envelope cis Golgi Transport vesicle Plasma membrane trans Golgi

  31. Concept 6.5: Mitochondria and chloroplasts change energy from one form to another • Mitochondria are the sites of cellular respiration • Chloroplasts, found only in plants and algae, are the sites of photosynthesis • Mitochondria and chloroplasts are not part of the endomembrane system • Peroxisomes are oxidative organelles

  32. LE 6-17 Mitochondrion Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Inner membrane Cristae Matrix Mitochondrial DNA 100 nm

  33. Mitochondria: Chemical Energy Conversion • Mitochondria are in nearly all eukaryotic cells • They have a smooth outer membrane and an inner membrane folded into cristae • The inner membrane creates two compartments: intermembrane space and mitochondrial matrix • Some metabolic steps of cellular respiration are catalyzed in the mitochondrial matrix • Cristae present a large surface area for enzymes that synthesize ATP

  34. Chloroplasts: Capture of Light Energy • The chloroplast is a member of a family of organelles called plastids • Chloroplasts contain the green pigment chlorophyll, as well as enzymes and other molecules that function in photosynthesis • Chloroplast structure includes: • Thylakoids, membranous sacs • Stroma, the internal fluid

  35. LE 6-18 Chloroplast Ribosomes Stroma Chloroplast DNA Inner and outer membranes Granum 1 µm Thylakoid

  36. Concept 6.6: The cytoskeleton is a network of fibers that organizes structures and activities in the cell • The cytoskeleton is a network of fibers extending throughout the cytoplasm • It organizes the cell’s structures and activities, anchoring many organelles • It is composed of three types of molecular structures: • Microtubules • Microfilaments • Intermediate filaments

  37. Roles of the Cytoskeleton: Support, Motility, and Regulation • The cytoskeleton helps to support the cell and maintain its shape • It interacts with motor proteins to produce motility • Recent evidence suggests that the cytoskeleton may help regulate biochemical activities

  38. Components of the Cytoskeleton • Microtubules are the thickest of the three components of the cytoskeleton • Microfilaments, also called actin filaments, are the thinnest components • Intermediate filaments are fibers with diameters in a middle range

  39. Microtubules

  40. Cilia and Flagella • Microtubules control the beating of cilia and flagella, locomotor appendages of some cells

  41. LE 6-21a Vesicle ATP Receptor for motor protein Motor protein (ATP powered) Microtubule of cytoskeleton

  42. Microfilaments

  43. Intermediate filaments

  44. Microfilaments (Actin Filaments) • Microfilaments are solid rods about 7 nm in diameter, built as a twisted double chain of actin subunits • The structural role of microfilaments is to bear tension, resisting pulling forces within the cell • They form a 3D network just inside the plasma membrane to help support the cell’s shape

  45. Microfilaments that function in cellular motility contain the protein myosin in addition to actin • In muscle cells, thousands of actin filaments are arranged parallel to one another • Thicker filaments composed of myosin interdigitate with the thinner actin fibers

  46. LE 6-27a Muscle cell Actin filament Myosin filament Myosin arm Myosin motors in muscle cell contraction

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