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A TOUR OF THE CELL OVERVIEW: THE IMPORTANCE OF CELLS All organisms are made of cells The cell is the simplest collection of matter that can live Cell structure is correlated to cellular function All cells are related by their descent from earlier cells 1 MICROSCOPY Light Microscope Resolution Magnification Staining Organelles? LE 6-2 10 m Human height 1m Unaided eye Length of some nerve and muscle cells 0.1 m Chicken egg 1 cm Frog egg 1 mm 100 µm Most plant and animal cells 10 µm Nucleus Most bacteria 1 µm 100 nm Mitochondrion Smallest bacteria Viruses Ribosomes 10 nm Electron microscope Light microscope 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 µm = 10–9 m Proteins Lipids 1 nm Small molecules 0.1 nm Atoms LE 6-3A Brightfield (unstained specimen) 50 µm Brightfield (stained specimen) Phase-contrast 2 LE 6-3B Differentialinterferencecontrast (Nomarski) Fluorescence 50 µm Confocal 50 µm ELECTRON MICROSCOPES Scanning Transmission LE 6-4 Scanning electron microscopy (SEM) Transmission electron microscopy (TEM) Cilia Longitudinal section of cilium 1 µm Cross section of cilium 1 µm 3 CELL FRACTIONATION What is it? Why? LE 6-5A Homogenization Tissue cells Homogenate Differential centrifugation LE 6-5B 1000 g (1000 times the force of gravity) 10 min Supernatant poured into next tube 20,000 g 20 min 80,000 g 60 min Pellet rich in nuclei and cellular debris 150,000 g 3 hr Pellet rich in mitochondria (and chloroplasts if cells are from a plant) Pellet rich in “microsomes” (pieces of plasma membranes and cells’ internal membranes) Pellet rich in ribosomes 4 INTERNAL COMPARTMENTALIZATION? The basic structural and functional unit Prokaryotic Eukaryotic COMPARING PROKARYOTIC AND EUKARYOTIC CELLS Basic features of all cells: 1. 2. 3. 4. PROKARYOTIC CELLS 1. 2. 3. 5 LE 6-6 Pili Nucleoid Ribosomes Plasma membrane Cell wall Bacterial chromosome Capsule 0.5 µm Flagella A typical rod-shaped bacterium A thin section through the bacterium Bacillus coagulans (TEM) EUKARYOTIC 1. 2. 3. 4. LE 6-7 Surface area increases while Total volume remains constant 5 1 1 Total surface area (height x width x number of sides x number of boxes) 6 150 750 Total volume (height x width x length X number of boxes) 1 125 125 6 1.2 6 Surface-to-volume ratio (surface area volume) 6 A 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 LE 6-9A ENDOPLASMIC RETICULUM (ER Nuclear envelope Rough ER Flagellum 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) LE 6-9B Nuclear envelope NUCLEUS Nucleolus Chromatin Centrosome Rough endoplasmic reticulum Smooth endoplasmic reticulum Ribosomes (small brown dots) Central vacuole Golgi apparatus Microfilaments Intermediate filaments Microtubules CYTOSKELETON 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 7 THE NUCLEUS: GENETIC LIBRARY OF THE CELL Function? Nuclear envelope LE 6-10 Nucleus Nucleus 1 µm Nucleolus Chromatin Nuclear envelope: Inner membrane Outer membrane Nuclear pore Pore complex Rough ER Surface of nuclear envelope Ribosome 1 µm 0.25 µm Close-up of nuclear envelope Pore complexes (TEM) Nuclear lamina (TEM) RIBOSOMES Structure Function Where? 8 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 ENDOMEMBRANE SYSTEM Components of the endomembrane system: 1. 2. 3. 4. 5. 6. These components are either continuous or connected via transfer by vesicles ENDOPLASMIC RETICULUM More than half of the total membrane Continuous with the nuclear envelope Two distinct regions 1. 2. 9 LE 6-12 Smooth ER Rough ER Nuclear envelope ER lumen Cisternae Ribosomes Transport vesicle Smooth ER Transitional ER Rough ER 200 nm FUNCTIONS OF SMOOTH ER 1. 2. 3. 4. FUNCTIONS OF ROUGH ER 1. 2. 10 GOLGI APPARATUS Structure Functions 1. 2. 3. LE 6-13 Golgi apparatus cis face (“receiving” side of Golgi apparatus) Vesicles also transport certain proteins back to ER Vesicles move from ER to Golgi Vesicles coalesce to form new cis Golgi cisternae 0.1 µm Cisternae Cisternal maturation: Golgi cisternae move in a cisto-trans direction Vesicles form and leave Golgi, carrying specific proteins to other locations or to the plasma membrane for secretion Vesicles transport specific proteins backward to newer Golgi cisternae trans face (“shipping” side of Golgi apparatus) TEM of Golgi apparatus LYSOSOME Structure Function 1. 2. 11 LE 6-14A 1 µm Nucleus Lysosome Lysosome contains Food vacuole Hydrolytic active hydrolytic enzymes digest fuses with enzymes food particles lysosome Digestive enzymes Plasma membrane Lysosome Digestion Food vacuole Phagocytosis: lysosome digesting food LE 6-14B Lysosome containing two damaged organelles 1 µm Mitochondrion fragment Peroxisome fragment Lysosome fuses with vesicle containing damaged organelle Hydrolytic enzymes digest organelle components Lysosome Digestion Vesicle containing damaged mitochondrion Autophagy: lysosome breaking down damaged organelle VACUOLE Structure One or many? 12 Functions LE 6-15 Central vacuole Cytosol Tonoplast Nucleus Central vacuole Cell wall Chloroplast 5 µm LE 6-16-1 Nucleus Rough ER Smooth ER Nuclear envelope 13 LE 6-16-2 Nucleus Rough ER Smooth ER Nuclear envelope cis Golgi Transport vesicle trans Golgi LE 6-16-3 Nucleus Rough ER Smooth ER Nuclear envelope cis Golgi Transport vesicle Plasma membrane trans Golgi MITOCHONDRIA Where? Who? Structure 14 Function LE 6-17 Mitochondrion Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Inner membrane Cristae Matrix Mitochondrial DNA 100 nm CHLOROPLASTS Where? Who? Plastids Structure 15 Function LE 6-18 Chloroplast Ribosomes Stroma Chloroplast DNA Inner and outer membranes Granum 1 µm Thylakoid PEROXISOMES Structure Function 16 LE 6-19 Chloroplast Peroxisome Mitochondrion 1 µm CYTOSKELETON Network of fibers Organization Three types of molecular structures: 1. 2. 3. LE 6-20 Microtubule Microfilaments 0.25 µm 17 ROLES OF THE CYTOSKELETON 1. 2. 3. 4. LE 6-21A Vesicle ATP Receptor for motor protein Motor protein (ATP powered) Microtubule of cytoskeleton LE 6-21B Microtubule Vesicles 0.25 µm 18 COMPONENTS OF THE CYTOSKELETON 19 MICROTUBULES Structure Functions: 1. 2. 3. CENTROSOMES AND CENTRIOLES Centrosome Centrioles LE 6-22 Centrosome Microtubule Centrioles 0.25 µm Longitudinal section Microtubules of one centriole Cross section of the other centriole 20 CILIA AND FLAGELLA Common Ultrastructure 1. 2. 3. LE 6-23A Direction of swimming Motion of flagella 5 µm LE 6-23B Direction of organism’s movement Direction of active stroke Motion of cilia Direction of recovery stroke 15 µm 21 LE 6-24 0.1 µm Outer microtubule doublet Dynein arms Central microtubule Plasma membrane Cross-linking proteins inside outer doublets Microtubules Plasma membrane Basal body Radial spoke 0.5 µm 0.1 µm Triplet Cross section of basal body How dynein “walking” moves flagella and cilia: 1. 2. 3. LE 6-25A Microtubule doublets ATP Dynein arm Dynein “walking” 22 LE 6-25B Cross-linking proteins inside outer doublets ATP Anchorage in cell Effect of cross-linking proteins Wavelike motion MICROFILAMENTS (ACTIN FILAMENTS) Structure LE 6-26 Microvillus Plasma membrane Microfilaments (actin filaments) Intermediate filaments 0.25 µm 23 Function LE 6-27A Muscle cell Actin filament Myosin filament Myosin arm Myosin motors in muscle cell contraction LE 6-27B Cortex (outer cytoplasm): gel with actin network Inner cytoplasm: sol with actin subunits Extending pseudopodium Amoeboid movement 24 LE 6-27C Nonmoving cytoplasm (gel) Chloroplast Streaming cytoplasm (sol) Vacuole Parallel actin filaments Cell wall Cytoplasmic streaming in plant cells INTERMEDIATE FILAMENTS Structure Function CELL WALLS OF PLANTS Extracellular Function Basic structure 25 CELL WALLS OF PLANTS May have multiple layers Primary cell wall: Middle lamella: Secondary cell wall (in some cells): Plasmodesmata LE 6-28 Central vacuole of cell Plasma membrane Secondary cell wall Primary cell wall Central vacuole of cell Middle lamella 1 µm Central vacuole Cytosol Plasma membrane Plant cell walls Plasmodesmata THE EXTRACELLULAR MATRIX (ECM) Animal cells Structure Function 1. 2. 3. 4. 26 LE 6-29A Collagen fiber Proteoglycan complex EXTRACELLULAR FLUID Fibronectin Plasma membrane Integrin CYTOPLASM Microfilaments LE 6-29B Proteoglycan complex Polysaccharide molecule Carbohydrates Core protein Proteoglycan molecule INTERCELLULAR JUNCTIONS Functions 27 PLANTS: PLASMODESMATA What are they? What do they do? LE 6-30 Cell walls Interior of cell Interior of cell 0.5 µm Plasmodesmata Plasma membranes ANIMALS Tight junctions Desmosomes Gap junctions 28 LE 6-31 Tight junctions prevent fluid from moving across a layer of cells Tight junction 0.5 µm Tight junction Intermediate filaments Desmosome 1 µm Space between cells Gap junctions Plasma membranes of adjacent cells Gap junction Extracellular matrix 0.1 µm THE CELL: A LIVING UNIT GREATER THAN THE SUM OF ITS PARTS Cells rely on the integration of structures and organelles in order to function For example, a macrophage’s ability to destroy bacteria involves the whole cell, coordinating components such as the cytoskeleton, lysosomes, and plasma membrane 5 µm LE 6-32 29
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