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Chapter 6

Chapter 6. A Tour of the Cell. The Importance of Cells. Cell Theory:. 1. All organisms are composed of one or more cells 2. Cells are the smallest living things 3. Cells arise only by division of a previously existing cell. Cell Size. 1. Cell size

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Chapter 6

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  1. Chapter 6 A Tour of the Cell

  2. The Importance of Cells Cell Theory: 1. All organisms are composed of one or more cells 2. Cells are the smallest living things 3. Cells arise only by division of a previously existing cell

  3. Cell Size 1. Cell size • from a few micrometers to several centimeters 2. Most cells are small because larger cells do not function efficiently 3. It is advantageous to have a large surface-to-volume ratio • Smaller sizes have greater Surface for volume

  4. Surface area increases while total volume remains constant 5 1 1 Total surface area (height  width  number of sides  number of boxes) 6 150 750 Total volume (height  width  length  number of boxes) 125 125 1 Surface-to-volume ratio (surface area  volume) 6 12 6 • A smaller cell • Has a higher surface to volume ratio, which facilitates the exchange of materials into and out of the cell Figure 6.7

  5. 10 µm • Cell structure is correlated to cellular function Figure 6.1

  6. 10 m Human height 1 m Length of some nerve and muscle cells 0.1 m Light microscope Chicken egg 1 cm Frog egg 1 mm 100 µm Most plant and Animal cells Electron microscope 10 µ m NucleusMost bacteriaMitochondrion 1 µ m Electron microscope Smallest bacteria 100 nm Viruses 10 nm Ribosomes Proteins Lipids 1 nm Small molecules Figure 6.2 Atoms 0.1 nm Visualizing Cells • Different types of microscopes • Can be used to visualize different sized cellular structures Unaided eye Measurements 1 centimeter (cm) = 102 meter (m) = 0.4 inch 1 millimeter (mm) = 10–3 m 1 micrometer (µm) = 10–3 mm = 10–6 m 1 nanometer (nm) = 10–3 mm = 10–9 m

  7. RESULT TECHNIQUE (a) Brightfield (unstained specimen). Passes light directly through specimen. Unless cell is naturally pigmented or artificially stained, image has little contrast. [Parts (a)–(d) show a human cheek epithelial cell.] 50 µm (b) Brightfield (stained specimen).Staining with various dyes enhances contrast, but most staining procedures require that cells be fixed (preserved). (c) Phase-contrast. Enhances contrast in unstained cells by amplifying variations in density within specimen; especially useful for examining living, unpigmented cells. Figure 6.3 • Use different methods for enhancing visualization of cellular structures

  8. (d) (e) Fluorescence. Shows the locations of specific molecules in the cell by tagging the molecules with fluorescent dyes or antibodies. These fluorescent substances absorb ultraviolet radiation and emit visible light, as shown here in a cell from an artery. 50 µm (f) Confocal. Uses lasers and special optics for “optical sectioning” of fluorescently-stained specimens. Only a single plane of focus is illuminated; out-of-focus fluorescence above and below the plane is subtracted by a computer. A sharp image results, as seen in stained nervous tissue (top), where nerve cells are green, support cells are red, and regions of overlap are yellow. A standard fluorescence micrograph (bottom) of this relatively thick tissue is blurry. 50 µm Differential-interference-contrast (Nomarski). Like phase-contrast microscopy, it uses optical modifications to exaggerate differences in density, making the image appear almost 3D.

  9. TECHNIQUE RESULTS 1 µm Cilia (a) Scanning electron micro- scopy (SEM). Micrographs taken with a scanning electron micro- scope show a 3D image of the surface of a specimen. This SEM shows the surface of a cell from a rabbit trachea (windpipe) covered with motile organelles called cilia. Beating of the cilia helps move inhaled debris upward toward the throat. Electron Microscopes • 1. The scanning electron microscope (SEM) • Provides for detailed study of the surface of a specimen Figure 6.4 (a)

  10. Longitudinal section of cilium Cross section of cilium 1 µm (b) Transmission electron micro- scopy (TEM). A transmission electron microscope profiles a thin section of a specimen. Here we see a section through a tracheal cell, revealing its ultrastructure. In preparing the TEM, some cilia were cut along their lengths, creating longitudinal sections, while other cilia were cut straight across, creating cross sections. Electron Microscopes 2. The transmission electron microscope (TEM) • Provides for detailed study of the internal ultrastructure of cells Figure 6.4 (b)

  11. Types of Cells Two types: 1. Prokaryotic – NO NUCLEUS 2. Eukaryotic - NUCLEUS

  12. Common features Prokaryotic & Eukaryotic Cells share: • Bound by plasma membrane • Contain cytosol – semifluid substance where organelles found • Have ribosomes • Contain chromosomes

  13. Prokaryotes • 1. Plasma Membrane • 2. Ribosomes • 3. Cytoplasm • 4. Cell wall of peptidoglycan • 5. Some have flagella (for movement) • 6. Pili (small hair-like appendages found on surface of bacteria) • Aid in ADHERANCE

  14. Pili: attachment structures on the surface of some prokaryotes Nucleoid: region where the cell’s DNA is located (not enclosed by a membrane) Ribosomes: organelles that synthesize proteins Plasma membrane: membrane enclosing the cytoplasm Cell wall: rigid structure outside the plasma membrane Capsule: jelly-like outer coating of many prokaryotes Bacterialchromosome 0.5 µm Flagella: locomotion organelles of some bacteria (a) A typical rod-shaped bacterium (b) A thin section through the bacterium Bacillus coagulans (TEM) Figure 6.6 A, B

  15. Eukaryotic sub cell structures • NUCLEUS a. Surrounded by a double membrane called NUCLEAR MEMBRANE or Nuclear envelope Studded with nuclear PORES (mRNA exit here) b. Nucleolus – dark staining region within the nucleus * site for ribosome assembly c. DNA - usually in the for of chromatin (with histone proteins) - DNA in this state is uncondensed Chromosomes – condensed DNA only visualized during MITOSIS (cell division that makes exact copies)

  16. Nucleus Nucleus 1 µm Nucleolus Chromatin Nuclear envelope: Inner membrane Outer membrane Nuclear pore Pore complex Rough ER Surface of nuclear envelope. 1 µm Ribosome 0.25 µm Close-up of nuclear envelope Nuclear lamina (TEM). Pore complexes (TEM). • The nuclear envelope • Encloses the nucleus, separating its contents from the cytoplasm Figure 6.10

  17. Eukaryotic Sub Structures • Enzymes that interact w/DNA (transcription & DNA replication)

  18. Endoplasmic Reticulum (ER) a. Huge collection of membrane bound “tubes” that snake throughout the cytoplasm

  19. Smooth ER Nuclear envelope Rough ER ER lumen Cisternae Ribosomes Transitional ER Transport vesicle 200 µm Smooth ER Rough ER • The ER membrane • Is continuous with the nuclear envelope Figure 6.12

  20. b. Types of ER 1. Rough ER covered with Ribosomes (little circles) Main site for protein synthesis Newly made proteins are pushed into the LUMEN (opening or empty center region or the Rough ER) carry out initial modifications of newly manufactured protein

  21. 2. Smooth ER No Ribosomes – looks exactly like rough ER w/o ribo site for synthesis of lipids & carbohydrates site for toxin inactivation ex. Alcohol dehydrogenase

  22. Ribosomes a. Composed of ribosomal RNA and protein 2 Sub units (large and small) b. Carry out protein synthesis (aka protein factories) • Two types • Free ribosomes – located in cytosol (proteins will function within cytosol) • Bound ribosomes - located on Rough ER (proteins will be packaged for insertion into membranes, packaging within organelles)

  23. Ribosomes Cytosol Free ribosomes Bound ribosomes Large subunit Small subunit 0.5 µm TEM showing ER and ribosomes Diagram of a ribosome • Carry out protein synthesis ER Endoplasmic reticulum (ER) Figure 6.11

  24. Golgi (complex, body, appartus) a. stack of flattened membrane sacs called cisternae completes all modifications to newly made macromolecules b. * Packages molecules into vessicles & places a molecular address onto package *Sends vessicle to ultimate destination (w/in cell or to be secreted) c. Two faces 1. cis face – incoming/receiving 2. trans face - shipping

  25. cis face (“receiving” side of Golgi apparatus) 5 3 4 6 2 1 Vesicles coalesce to form new cis Golgi cisternae Vesicles move from ER to Golgi 0.1 0 µm Vesicles also transport certain proteins back to ER Cisternae Cisternal maturation: Golgi cisternae move in a cis- to-trans direction Vesicles form and leave Golgi, carrying specific proteins to other locations or to the plasma mem- brane for secretion trans face (“shipping” side of Golgi apparatus) Vesicles transport specific proteins backward to newer Golgi cisternae • Functions of the Golgi apparatus Golgi apparatus Figure 6.13 TEM of Golgi apparatus

  26. Lysosomes (membranous sacs) Contain hydrolytic enzymes that “digest” macromolecules Recycle of “worn out” cell components Apoptosis – cell suicide in cells infected w/viruses or transformed into cancer Can arise from “budding” off the Golgi apparatus

  27. 1 µm Nucleus Lysosome Hydrolytic enzymes digest food particles Food vacuole fuses with lysosome Lysosome contains active hydrolytic enzymes Digestive enzymes Lysosome Plasma membrane Digestion Food vacuole (a) Phagocytosis: lysosome digesting food • Lysosomes carry out intracellular digestion by • Phagocytosis Figure 6.14 A

  28. Lysosome containing two damaged organelles 1 µ m Mitochondrion fragment Peroxisome fragment Lysosome fuses with vesicle containing damaged organelle Hydrolytic enzymes digest organelle components Lysosome Digestion Vesicle containing damaged mitochondrion (b) Autophagy: lysosome breaking down damaged organelle • Autophagy Figure 6.14 B

  29. 1 Nuclear envelope is connected to rough ER, which is also continuous with smooth ER Nucleus Rough ER 2 Membranes and proteins produced by the ER flow in the form of transport vesicles to the Golgi Smooth ER cis Golgi Nuclear envelop 3 Golgi pinches off transport Vesicles and other vesicles that give rise to lysosomes and Vacuoles Plasma membrane trans Golgi 4 5 6 Lysosome available for fusion with another vesicle for digestion Transport vesicle carries proteins to plasma membrane for secretion Plasma membrane expands by fusion of vesicles; proteins are secreted from cell • Relationships among organelles of the endomembrane system Figure 6.16

  30. Peroxisomes (type of vessicle) Contains collection of enzymes that inactivate toxic byproducts of oxygen presence ex. Catalase

  31. Chloroplast Peroxisome Mitochondrion 1 µm Peroxisomes: Oxidation • Peroxisomes • Produce hydrogen peroxide and convert it to water Figure 6.19

  32. Vacuoles – they are like your garage and often look like balloons! Found in plant or fungal cells Three types: 1. Food Vacuole – form by phagocytosis 2. Contractile Vacuole – pump out excess water (freshwater protists) 3. Central Vacuole – found in PLANTS hold reserves of important organic molecules can contain by-products or pigments can also be protection – hold poisonous compounds

  33. Nuclear envelope ENDOPLASMIC RETICULUM (ER) NUCLEUS Nucleolus Rough ER Smooth ER Chromatin Flagelium Plasma membrane Centrosome CYTOSKELETON Microfilaments Intermediate filaments Ribosomes Microtubules Microvilli Golgi apparatus Peroxisome In animal cells but not plant cells: Lysosomes Centrioles Flagella (in some plant sperm) Lysosome Mitochondrion • A animal cell Figure 6.9

  34. Nuclear envelope Rough endoplasmic reticulum Nucleolus NUCLEUS Chromatin Smooth endoplasmic reticulum Centrosome Ribosomes (small brwon dots) Central vacuole Tonoplast Golgi apparatus Microfilaments Intermediate filaments Microtubules Mitochondrion Peroxisome Plasma membrane Chloroplast Cell wall Plasmodesmata Wall of adjacent cell • A plant cell CYTOSKELETON In plant cells but not animal cells: Chloroplasts Central vacuole and tonoplast Cell wall Plasmodesmata Figure 6.9

  35. Mitochondria – Powerhouse of the cell • Location for aerobic respiration (cellular respiration) Use oxygen to produce ATP Three parts: inner membrane, outer membrane, matrix • Krebs cycle occurs in matrix biochem reactions that converts energy into usable forms for the cell • Electron Transport system in the inner membrane last biochemical step in production of ATP *oxygen is the FINAL ELECTRON RECEPTOR

  36. Mitochondrion Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Inner membrane Cristae Matrix Mitochondrial DNA 100 µm • Mitochondria are enclosed by two membranes • A smooth outer membrane • An inner membrane folded into cristae Figure 6.17

  37. Mitochrondria • Have their own DNA (circular and single stranded) • Replicate INDEPENDENTLY of the cell • Endosymbiotic theory – scientists think mitochrondria and chloroplasts were once a cell and then engulfed by eukaryotes about a billion years ago

  38. Chloroplasts Found only in plants ( also in a few protists) Site for photosynthesis Parts: Stroma – light independent rxns occur Grana – composed of thylakoid membrane light dependent rxns occur here via electron transport chain Contain own DNA, reproduce independently

  39. Chloroplast Ribosomes Stroma Chloroplast DNA Inner and outer membranes Granum 1 µm Thylakoid • Chloroplasts • Are found in leaves and other green organs of plants and in algae Figure 6.18

  40. Microtubule Microfilaments 0.25 µm Figure 6.20 • The cytoskeleton • Is a network of fibers extending throughout the cytoplasm Figure 6.20

  41. Cyotskeleton – the FRAMEWORK collection of proteins fibers that confer shape & mvmt to the cell Parts: 1. Microtublules fat hollow polymers of the protein TUBULIN *main support of cell & form cilia & flagella *can function as “tracks” along which other subcellular structures can be transported

  42. Parts: • Intermediate filaments Composed of strong proteins like KERRATIN Functions to hold other cytoskeletal components together (like rope) Found in large quantities in nucleoplasm

  43. Parts: 3. Microfilaments Composed of polymers of the protein ACTIN Usually involved in movement Found under plasma membrane Cell shape, muscle movement

  44. Table 6.1 • There are three main types of fibers that make up the cytoskeleton

  45. Muscle cell Actin filament Myosin filament Myosin arm (a) Figure 6.27 A Myosin motors in muscle cell contraction. • Microfilaments that function in cellular motility • Contain the protein myosin in addition to actin

  46. Vesicle ATP Receptor for motor protein Motor protein (ATP powered) Microtubule of cytoskeleton (a) Motor proteins that attach to receptors on organelles can “walk” the organelles along microtubules or, in some cases, microfilaments. Vesicles Microtubule 0.25 µm (b) Vesicles containing neurotransmitters migrate to the tips of nerve cell axons via the mechanism in (a). In this SEM of a squid giant axon, two  vesicles can be seen moving along a microtubule. (A separate part of the experiment provided the evidence that they were in fact moving.) Figure 6.21 A, B • Is involved in cell motility, which utilizes motor proteins

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