Chapter 6


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Chapter 6

  1. 1. Chapter 6 A Tour of the CellPowerPoint® Lecture Presentations for Biology Eighth EditionNeil Campbell and Jane ReeceLectures by Chris Romero, updated by Erin Barley with contributions from Joan SharpCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
  2. 2. Eukaryotic cells have internal membranes thatcompartmentalize their functions• Basic features of all cells: plasma membrane, cytosol, chromosomes, ribosomes• Prokaryotic vs Eukaryotic cells – prokaryotic cells  Bacteria and Archaea • No nucleus • DNA in an unbound region called the nucleoid • No membrane-bound organelles • Cytoplasm bound by the plasma membrane – eukaryotic cells  Protists, fungi, animals and plants • DNA in a nucleus bounded by nuclear envelope • Membrane-bound organelles • Cytoplasm in the region between the plasma membrane and nucleusCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
  3. 3. Fig. 6-6 Prokaryotic cell Fimbriae Nucleoid Ribosomes Plasma membrane Bacterial Cell wall chromosome Capsule 0.5 µm Flagella
  4. 4. Fig. 6-9a Eukaryotic Animal Cell Nuclear envelope ENDOPLASMIC RETICULUM (ER) Nucleolus NUCLEUS Rough ER Smooth ER Flagellum*** Chromatin (not in plants) Centrosome Plasma membrane CYTOSKELETON: Microfilaments Intermediate filaments Microtubules Ribosomes Microvilli Golgi Peroxisome apparatus Mitochondrion Lysosome*** (not in plants/prokaryotes)
  5. 5. Fig. 6-9b Eukaryotic Plant Cell Nuclear envelope Rough endoplasmic reticulum NUCLEUS Nucleolus Chromatin Smooth endoplasmic reticulum Ribosomes Central Golgi vacuole*** apparatus Microfilaments Intermediate CYTO-SKELETON filaments Microtubules Mitochondrion Peroxisome Chloroplast*** Plasma membrane Cell wall*** Plasmodesmata*** Wall of adjacent cell ***specific to plants
  6. 6. Organelles to know• Nucleus – Genetic information• Ribosomes – protein factories• Endoplasmic Reticulum – protein trafficking and metabolic functions• Golgi Apparatus – shipping and receiving center• Lysosomes – digestive compartments• Vacuoles – maintenance compatments• Mitochondria – chemical energy conversion (site of cellular respiration)• Chloroplasts – light energy conversion (site of photosynthesis)• Peroxisomes - oxidation• Cytoskeleton – support, motility and regulation• Extracellular Matrix – support, adhesion, movement, regulation• Intercellular Junctions – facilitate contact between cells
  7. 7. Nucleus: Information Central – nuclear envelope encloses the nucleus, separating it from the cytoplasm – nuclear membrane is a double membrane; each membrane consists of a lipid bilayer – Pores regulate the entry and exit of molecules from the nucleus – The shape of the nucleus is maintained by the nuclear lamina, which is composed of protein – In the nucleus, DNA and proteins form genetic material called chromatin – Chromatin condenses to form discrete chromosomes – The nucleolus is located within the nucleus and is the site of ribosomal RNA (rRNA) synthesisCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
  8. 8. Fig. 6-10 Nucleus 1 µm Nucleolus Chromatin Nuclear envelope Nuclear pore Pore complex Surface of nuclear envelope Ribosome 1 µm 0.25 µm Close-up of nuclear envelope Pore complexes Nuclear lamina
  9. 9. Ribosomes: Protein factories – particles made of ribosomal RNA and protein – Protein synthesis occurs here • Free ribosomes are localized to the cytosol • Bound ribosomes are on the ER or the nuclear envelope Cytosol Endoplasmic reticulum (ER) Free ribosomes Bound ribosomes Large subunit Fig. 6-11 Small subunit Diagram of a ribosome
  10. 10. Endoplasmic Reticulum (ER): Protein Trafficking – The ER membrane is attached to the nuclear envelope – There are two distinct regions of ER: • Smooth ER  lacks ribosomes – Synthesizes lipids – Metabolizes carbohydrates – Detoxifies poison – Stores calcium • Rough ER with ribosomes – Secretes glycoproteins (proteins covalently bonded to carbohydrates) – Distributes transport vesicles, proteins surrounded by membranes – membrane factory for the cellCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
  11. 11. Fig. 6-12 Smooth ER Rough ER Nuclear envelope Ribosomes Transport vesicle Rough ER Smooth ER
  12. 12. Golgi apparatus: Shipping and Receiving Center – shipping and receiving center – consists of flattened membranous sacs called cisternae – Functions: • Modifies products of the ER • Manufactures certain macromolecules • Sorts and packages materials into transport vesicles CisternaeCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
  13. 13. Lysosome: Digestive Compartment – a membranous sac of hydrolytic enzymes that can digest macromolecules – Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids • After phagocytosis (engulfing of another cell) lysosomes fuse with the food vacuole and digests the molecules • Autophagy uses enzymes to recycle the cell’s own organelles and macromolecules (a) Phagocytosis (b) Autophagy Digestive enzymesLysosome Lysosome Plasma Peroxisome membrane Digestion Food vacuole Digestion Mitochondrion VesicleCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
  14. 14. Fig. 6-15Vacuoles: Maintenance Compartment – Diverse Maintenance Compartments Central – Food vacuole vacuoles are Cytosol formed by phagocytosis – Contractile vacuoles Nucleus Central vacuole pump excess water out of Cell wall cells Chloroplast – Central vacuoles (in many mature plant cells) hold organicCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
  15. 15. The Endomembrane System: A Review• The endomembrane system is a complex and dynamic player in the cell’s compartmental organization – Nuclear envelope – ER – Golgi apparatus – Lysosomes – Vacuoles – Plasma membraneCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
  16. 16. Fig. 6-16-3 Nucleus Rough ER Smooth Golgi ER Transport vessicle Transport vessicle Lysosome Plasma membrane •Nuclear envelope is connected to rough ER •Proteins produced by the ER flow in transport vessicles to the Golgi •Golgi pinches off vessicles that give rise to lysosomes, vessicles and vacuoles •Lysosomes can fuse with another vessicle for digestion •Transport vessicle carries proteins to plasma membrane for secretion •Plasma membrane expands by fusion of vessicles; proteins are secreted from the cell
  17. 17. Mitochondria: Chemical Energy Conversion – sites of cellular respiration, a metabolic process that generates ATP – Have a double membrane – Contain their own DNA – Mitochondria are in nearly all eukaryotic cells – They have a smooth outer membrane and an inner membrane folded into cristae • Cristae present a large surface area for enzymes that synthesize ATP – The inner membrane creates two compartments: intermembrane space and mitochondrial matrix • Some metabolic steps of cellular respiration are catalyzed in the mitochondrial matrixCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
  18. 18. Fig. 6-17 Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Inner membrane Cristae Matrix 0.1 µm
  19. 19. Chloroplasts: Light Energy Conversion – Capture light energy, are the sites of photosynthesis – found in plants and algae – Have a double membrane (similar to mitochondria) – Contain their own DNA (similar to mitochondria) – contain chlorophyll and other molecules that function in photosynthesis – found in leaves and other green organs of plants and in algae Ribosomes Stroma Inner and outer membranes Granum 1 µm ThylakoidCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
  20. 20. Peroxisome: Oxidation – oxidative organelles Chloroplast Peroxisome – specialized Mitochondrion metabolic compartments bounded by a single membrane – produce hydrogen peroxide and convert it to water 1 µm – Oxygen is used to break down different types of moleculesCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
  21. 21. Cytoskeleton: Support, Motility and Regulation – a network of fibers extending throughout the cytoplasm – organizes the cell’s structures and activities, anchoring many organelles – composed of three types of molecular structures: • Microtubules are the thickest of the three components • Microfilaments, also called actin filaments, are the thinnest components • Intermediate filaments are fibers with diameters in a middle range – helps to support the cell and maintain its shape – interacts with motor proteins to produce motilityCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
  22. 22. Microtubules• Functions – Shaping the cell – Guiding movement of organelles – Separating chromosomes during cell division• Centrosomes – The centrosome is a “microtubule-organizing center” – microtubules grow out from a centrosome near the nucleus and attach to chromosomes during mitosis• Cilia and Flagella – Microtubules control the beating of cilia and flagella – A core of microtubules sheathed by the plasma membrane Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
  23. 23. Microtubules separate chromosomes during mitosis Centrosome microtubules Microtubule centrosome Fig. 6-22
  24. 24. Microtubules assist in motility (a) EX: Motion of flagella in sperm (b) EX: Motion of cilia in aquatic lifeFig. 6-23
  25. 25. Fig. 6-24 Microtubule structure in cilia Plasma membrane Microtubules (b) Cross section of Plasma cilium membrane Basal body (a) Longitudinal section of cilium (c) Cross section of basal body
  26. 26. Microfilaments (Actin Filaments)• Microfilaments are solid rods Microvillus built as a twisted double chain of actin subunits• The structural role: bear tension and resist pulling forces within the cell Microfilaments• (actin filaments) Cellular function: cellular motility – Myosin and actin contribute to this• Examples – Muscle contraction Intermediate filaments – Ameoboid movement occurs through Pseudopodia – Cytoplasmic streaming Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
  27. 27. Intermediate Filaments• They support cell shape and fix organelles in place• more permanent cytoskeleton fixtures than the other two classesCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
  28. 28. Cell Walls of Plants• Prokaryotes, fungi, and some protists also have cell walls• Functions: protects the plant cell, maintains its shape, prevents excessive uptake of water• made of cellulose fibers• Plant cell walls may have multiple layers: – Primary cell wall: relatively thin and flexible – Middle lamella: thin layer between primary walls of adjacent cells – Secondary cell wall (in some cells): added between the plasma membrane and the primary cell wallCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
  29. 29. Fig. 6-28 Secondary cell wall Primary cell wall Middle lamella 1 µm Central vacuole Cytosol Plasma membrane Plant cell walls Plasmodesmata
  30. 30. The Extracellular Matrix (ECM) of Animal Cells• Functions – Support – Adhesion Proteoglycan Collagen EXTRACELLULAR MATRIX complex – Movement – Regulation• made up of Fibronectin glycoproteins (collagen, proteoglycans, and fibronectin) Integrins• ECM proteins bind to receptor proteins in the plasma Micro- CYTOPLASM membrane called filaments integrinsCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
  31. 31. Intercellular Junctions• Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact• Intercellular junctions facilitate this contact• There are several types of intercellular junctions – Plasmodesmata – channels that perforate cell walls – Tight junctions - membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid – Desmosomes (anchoring junctions) fasten cells together into strong sheets – Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cellsCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
  32. 32. Fig. 6-32 Tight Tight junctions prevent junction fluid from moving across a layer of cells 0.5 µm Tight junction Desmosomes fasten cells together in sheets Intermediate filaments Desmosome Gap Desmosome junctions Gap junctions all cells to communicate with one Space Extracellular another via cytoplasmic matrix between Gap channels cells junction Plasma membranes of adjacent cells 0.1 µm
  33. 33. Fig. 6-UN1 Cell Component Structure Function Concept 6.3 Nucleus Surrounded by nuclear Houses chromosomes, made of The eukaryotic cell’s genetic envelope (double membrane) chromatin (DNA, the genetic instructions are housed in perforated by nuclear pores. material, and proteins); contains the nucleus and carried out The nuclear envelope is nucleoli, where ribosomal by the ribosomes continuous with the subunits are made. Pores endoplasmic reticulum (ER). regulate entry and exit of materials. (ER) Ribosome Two subunits made of ribo- Protein synthesis somal RNA and proteins; can be free in cytosol or bound to ER Concept 6.4 Endoplasmic reticulum Extensive network of Smooth ER: synthesis of The endomembrane system membrane-bound tubules and lipids, metabolism of carbohy- regulates protein traffic and (Nuclear sacs; membrane separates drates, Ca2+ storage, detoxifica- performs metabolic functions envelope) lumen from cytosol; tion of drugs and poisons in the cell continuous with the nuclear envelope. Rough ER: Aids in synthesis of secretory and other proteins from bound ribosomes; adds carbohydrates to glycoproteins; produces new membrane Golgi apparatus Stacks of flattened Modification of proteins, carbo- membranous hydrates on proteins, and phos- sacs; has polarity pholipids; synthesis of many (cis and trans polysaccharides; sorting of Golgi faces) products, which are then released in vesicles. Lysosome Membranous sac of hydrolytic Breakdown of ingested substances, enzymes (in animal cells) cell macromolecules, and damaged organelles for recycling Vacuole Large membrane-bounded Digestion, storage, waste vesicle in plants disposal, water balance, cell growth, and protection Concept 6.5 Mitochondrion Bounded by double Cellular respiration Mitochondria and chloro- membrane; plasts change energy from inner membrane has one form to another infoldings (cristae) Chloroplast Typically two membranes Photosynthesis around fluid stroma, which contains membranous thylakoids stacked into grana (in plants) Peroxisome Specialized metabolic Contains enzymes that transfer compartment bounded by a hydrogen to water, producing single membrane hydrogen peroxide (H2O2) as a by-product, which is converted to water by other enzymes in the peroxisome