* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Chapter 6 A Tour of the Cell
Survey
Document related concepts
Tissue engineering wikipedia , lookup
Cytoplasmic streaming wikipedia , lookup
Signal transduction wikipedia , lookup
Cell growth wikipedia , lookup
Cell membrane wikipedia , lookup
Cell encapsulation wikipedia , lookup
Cellular differentiation wikipedia , lookup
Cell culture wikipedia , lookup
Cell nucleus wikipedia , lookup
Organ-on-a-chip wikipedia , lookup
Extracellular matrix wikipedia , lookup
Cytokinesis wikipedia , lookup
Transcript
Chapter 6 A Tour of the Cell The Fundamental Units of Life Concept 6.1: Biologists use microscopes and the tools of biochemistry to study cells Cells are usually too small to be seen by the naked eye All organisms are made of cells The cell is the simplest collection of matter that can be alive Electron microscopy Light microscopy All cells are related by their descent from earlier cells Unaided eye Cells can differ substantially from one another but share common features Human height © 2014 Pearson Education, Inc. Microscopy Microscopes are used to visualize cells In a light microscope (LM), visible light is passed through a specimen and then through glass lenses Lenses refract (bend) the light, so that the image is magnified © 2014 Pearson Education, Inc. Superresolution microscopy Length of some nerve and muscle Chicken egg cells © 2014 Education, 10 Pearson m 1 m Inc.0.1 m 1 cm Nucleus Most bacteria Frog Human egg egg 1 mm Most plant and animal cells 100 µm 10 µm Smallest bacteria Small Viruses Proteins molecules Mitochondrion 1 µm Ribosomes 100 µm Lipids 10 nm Atoms 1 nm 0.1 nm Three important parameters of microscopy Magnification, the ratio of an object’s image size to its real size Resolution, the measure of the clarity of the image, or the minimum distance of two distinguishable points Contrast, visible differences in brightness between parts of the sample © 2014 Pearson Education, Inc. 1 Brightfield (unstained specimen) 50 µm Brightfield (stained specimen) Fluorescence © 2014 Pearson Education, Inc. Phase-contrast Differentialinterference-contrast (Nomarski) Confocal (without) 10 µm Confocal microscopy and deconvolution microscopy provide sharper images of three-dimensional tissues and cells Deconvolution New techniques for labeling cells improve resolution 10 µm © 2014 Pearson Education, Inc. Figure 6.3c Confocal (with) Super-resolution (without) Super-resolution (with) 1 µm Various techniques enhance contrast and enable cell components to be stained or labeled Recent advances in light microscopy 50 µm Light microscopes can magnify effectively to about 1,000 times the size of the actual specimen Light Microscopy (LM) Two basic types of electron microscopes (EMs) are used to study subcellular structures Scanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen, providing images that look 3-D Transmission electron microscopes (TEMs) focus a beam of electrons through a specimen TEMs are used mainly to study the internal structure of cells Electron Microscopy (EM) Scanning electron microscopy (SEM) © 2014 Pearson Education, Inc. 2 µm Transmission 2 µm electron microscopy (TEM) © 2014 Pearson Education, Inc. 2 Figure 6.4 Cell Fractionation Homogenization Tissue cells Cell fractionation takes cells apart and separates the major organelles from one another Homogenate Centrifugation Centrifuges fractionate cells into their component parts 1,000 g 10 min Supernatant poured into next tube 20,000 g 20 min Cell fractionation enables scientists to determine the functions of organelles Pellet rich in nuclei and cellular debris Biochemistry and cytology help correlate cell function with structure 80,000 g 60 min 150,000 g 3 hr Pellet rich in mitochondria and chloroplasts Differential centrifugation Pellet rich in “microsomes” Pellet rich in ribosomes © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. Concept 6.2: Eukaryotic cells have internal membranes that compartmentalize their functions Comparing Prokaryotic and Eukaryotic Cells 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 Basic features of all cells Plasma membrane Semifluid substance called cytosol Chromosomes (carry genes) Ribosomes (make proteins) Protists, fungi, animals, and plants all consist of eukaryotic cells © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 3 Figure 6.5 Fimbriae Prokaryotic cells are characterized by having Nucleoid No nucleus Ribosomes DNA in an unbound region called the nucleoid Plasma membrane No membrane-bound organelles Cell wall Bacterial chromosome Capsule 0.5 µm Cytoplasm bound by the plasma membrane Flagella (a) A typical rod-shaped bacterium (b) A thin section through the bacterium Bacillus coagulans (TEM) © 2014 Pearson Education, Inc. Eukaryotic cells are characterized by having DNA in a nucleus that is bounded by a membranous nuclear envelope © 2014 Pearson Education, Inc. The plasma membrane is a selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell Membrane-bound organelles Cytoplasm in the region between the plasma membrane and nucleus Eukaryotic cells are generally much larger than prokaryotic cells © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 4 Figure 6.6 Outside of cell (a) TEM of a plasma membrane Metabolic requirements set upper limits on the size of cells Inside of cell 0.1 µm Carbohydrate side chains The surface area to volume ratio of a cell is critical As a cell increases in size, its volume grows proportionately more than its surface area Hydrophilic region Hydrophobic region Hydrophilic region Phospholipid Proteins (b) Structure of the plasma membrane © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. Figure 6.8a ENDOPLASMIC RETICULUM (ER) A Panoramic View of the Eukaryotic Cell Rough ER Smooth ER A eukaryotic cell has internal membranes that partition the cell into organelles The basic fabric of biological membranes is a double layer of phospholipids and other lipids Plant and animal cells have most of the same organelles Flagellum Nuclear envelope Nucleolus NUCLEUS Chromatin Centrosome Plasma membrane CYTOSKELETON: Microfilaments Intermediate filaments Microtubules Ribosomes Microvilli Golgi apparatus Peroxisome Mitochondrion © 2014 Pearson Education, Inc. Lysosome © 2014 Pearson Education, Inc. 5 Figure 6.8c Ribosomes Human cells from lining of uterus (colorized TEM) Central vacuole Mitochondrion Peroxisome Chloroplast Plasma membrane Cell wall Nucleus Mitochondrion A single yeast cell (colorized TEM) Cell wall Mitochondrion Nucleus Nucleolus Cells from duckweed (colorized TEM) 1 μm Cell Chloroplast 8 μm CYTOSKELETON Plant Cells Microtubules Cell wall Vacuole Yeast cells budding (colorized SEM) Unicellular Eukaryotes Microfilaments Nucleus Nucleolus 5 μm Golgi apparatus Cell 1 μm Buds 5 μm Smooth ER Parent cell Fungal Cells Rough ER Animal Cells Nuclear envelope NUCLEUS Nucleolus Chromatin 10 μm Figure 6.8b Flagella Nucleus Nucleolus Vacuole Chlamydomonas (colorized SEM) Chloroplast Cell wall Chlamydomonas (colorized TEM) Plasmodesmata Wall of adjacent cell Concept 6.3: The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes © 2014 Pearson Education, Inc. The Nucleus: Information Central Nucleus 1 μm Nucleus Nucleolus Chromatin The nucleus contains most of the DNA in a eukaryotic cell Nuclear envelope: Inner membrane Outer membrane Nuclear pore Ribosomes use the information from the DNA to make proteins Rough ER Surface of nuclear envelope (TEM) Pore complex Ribosome 0.25 μm Close-up of nuclear envelope Pore complexes (TEM) Chromatin 0.5 μm © 2014 Pearson Education, Inc. Nuclear lamina (TEM) © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 6 Ribosomes: Protein Factories Ribosomes are complexes made of ribosomal RNA and protein Ribosomes carry out protein synthesis in two locations Concept 6.4: The endomembrane system regulates protein traffic and performs metabolic functions in the cell The endomembrane system consists of In the cytosol (free ribosomes) Nuclear envelope On the outside of the endoplasmic reticulum or the nuclear envelope (bound ribosomes) Endoplasmic reticulum Golgi apparatus 0.25 μm Ribosomes Free ribosomes in cytosol Endoplasmic reticulum (ER) ER Lysosomes Vacuoles Ribosomes bound to ER Large subunit Plasma membrane Small subunit TEM showing ER and ribosomes Diagram of a ribosome Computer model of a ribosome © 2014 Pearson Education, Inc. These components are either continuous or connected via transfer by vesicles © 2014 Pearson Education, Inc. The Endoplasmic Reticulum: Biosynthetic Factory Functions of ER The smooth ER Synthesizes lipids Metabolizes carbohydrates Smooth ER Rough ER Nuclear envelope Smooth ER Rough ER Detoxifies drugs and poisons Stores calcium ions The rough ER ER lumen Cisternae Ribosomes Transport vesicle Has bound ribosomes, which secrete glycoproteins (proteins covalently bonded to carbohydrates) Transitional ER 0.20 μm Distributes transport vesicles, secretory proteins surrounded by membranes Is a membrane factory for the cell © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 7 The Golgi Apparatus: Shipping and Receiving Center The Golgi apparatus consists of flattened membranous sacs called cisternae Golgi apparatus cis face (“receiving” side of Golgi apparatus) The Golgi Apparatus: Shipping and Receiving Center Functions of the Golgi apparatus Modifies products of the ER 0.1 μm Manufactures certain macromolecules Cisternae Sorts and packages materials into transport vesicles © 2014 Pearson Education, Inc. trans face (“shipping” side of Golgi apparatus) TEM of Golgi apparatus © 2014 Pearson Education, Inc. Lysosomes: Digestive Compartments A lysosome is a membranous sac of hydrolytic enzymes that can digest macromolecules Lysosomal enzymes work best in the acidic environment inside the lysosome Hydrolytic enzymes and lysosomal membranes are made by rough ER and then transferred to the Golgi apparatus for further processing © 2014 Pearson Education, Inc. Some types of cell can engulf smaller organisms or food particles by phagocytosis; this forms a food vacuole A lysosome fuses with the food vacuole and digests the molecules Lysosomes also use enzymes to recycle the cell’s own organelles and macromolecules, a process called autophagy © 2014 Pearson Education, Inc. 8 Figure 6.13 Vacuoles: Diverse Maintenance Compartments Vesicle containing two damaged organelles 1 μm Nucleus 1 μm Mitochondrion fragment Vacuoles perform a variety of functions in different kinds of cells Peroxisome fragment Lysosome Digestive enzymes Food vacuoles are formed by phagocytosis Lysosome Lysosome Plasma membrane Peroxisome Digestion Food vacuole Mitochondrion Vesicle (a) Phagocytosis: lysosome digesting food Vacuoles are large vesicles derived from the ER and Golgi apparatus Digestion (b) Autophagy: lysosome breaking down damaged organelles © 2014 Pearson Education, Inc. Contractile vacuoles, found in many freshwater protists, pump excess water out of cells Central vacuoles, found in many mature plant cells, hold organic compounds and water © 2014 Pearson Education, Inc. Figure 6.14 The Endomembrane System: A Review The endomembrane system is a complex and dynamic player in the cell’s compartmental organization Central vacuole Nucleus Cytosol Rough ER Nucleus Central vacuole Smooth ER cis Golgi Cell wall Chloroplast 5 μm trans Golgi © 2014 Pearson Education, Inc. Plasma membrane © 2014 Pearson Education, Inc. 9 Concept 6.5: Mitochondria and chloroplasts change energy from one form to another Mitochondria are the sites of cellular respiration, a metabolic process that uses oxygen to generate ATP The Evolutionary Origins of Mitochondria and Chloroplasts Mitochondria and chloroplasts have similarities with bacteria Enveloped by a double membrane Chloroplasts, found in plants and algae, are the sites of photosynthesis Contain free ribosomes and circular DNA molecules Peroxisomes are oxidative organelles Grow and reproduce somewhat independently in cells These similarities led to the endosymbiont theory © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. Figure 6.16 The endosymbiont theory suggests that an early ancestor of eukaryotes engulfed an oxygen-using nonphotosynthetic prokaryotic cell The engulfed cell formed a relationship with the host cell, becoming an endosymbiont The endosymbionts evolved into mitochondria Endoplasmic reticulum Nucleus Nuclear envelope Ancestor of eukaryotic cells (host cell) Mitochondrion Engulfing of photosynthetic prokaryote Chloroplast At least Mitochondrion one cell At least one of these cells may have then taken up a photosynthetic prokaryote, which evolved into a chloroplast Engulfing of oxygenusing nonphotosynthetic prokaryote, which becomes a mitochondrion Nonphotosynthetic eukaryote Photosynthetic eukaryote © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 10 Figure 6.17b Mitochondria: Chemical Energy Conversion Mitochondria Mitochondrion 10 μm Intermembrane space Outer membrane DNA Mitochondrial DNA Inner membrane Free ribosomes in the mitochondrial matrix Nuclear DNA Cristae Matrix (b) Network of mitochondria in Euglena (LM) 0.1 μm (a) Diagram and TEM of mitochondrion © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. Figure 6.18b Chloroplasts: Capture of Light Energy Ribosomes 50 μm Stroma Inner and outer membranes Granum DNA Intermembrane space Thylakoid (a) Diagram and TEM of chloroplast © 2014 Pearson Education, Inc. Chloroplasts (red) 1 μm (b) Chloroplasts in an algal cell © 2014 Pearson Education, Inc. 11 Figure 6.19 Peroxisomes: Oxidation Peroxisome Peroxisomes are specialized metabolic compartments bounded by a single membrane Mitochondrion Peroxisomes produce hydrogen peroxide and convert it to water Peroxisomes perform reactions with many different functions How peroxisomes are related to other organelles is still unknown © 2014 Pearson Education, Inc. Chloroplasts 1 μm © 2014 Pearson Education, Inc. Concept 6.6: The cytoskeleton is a network of fibers that organizes structures and activities in the cell Roles of the Cytoskeleton: Support and Motility The cytoskeleton is a network of fibers extending throughout the cytoplasm The cytoskeleton helps to support the cell and maintain its shape It organizes the cell’s structures and activities, anchoring many organelles It interacts with motor proteins to produce motility © 2014 Pearson Education, Inc. 10 μm Inside the cell, vesicles can travel along tracks provided by the cytoskeleton © 2014 Pearson Education, Inc. 12 Figure 6.21 ATP Components of the Cytoskeleton Vesicle Receptor for motor protein Three main types of fibers make up the cytoskeleton Motor protein Microtubule (ATP powered) of cytoskeleton (a) Motor proteins “walk” vesicles along cytoskeletal fibers. Microtubule Vesicles 0.25 μm 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 (b) SEM of a squid giant axon © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. Table 6.1 Microtubules Microtubules are hollow rods about 25 nm in diameter and about 200 nm to 25 microns long Functions of microtubules Shaping the cell Guiding movement of organelles Separating chromosomes during cell division © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 13 Centrosomes and Centrioles Centrosome Cilia and Flagella In animal cells, microtubules grow out from a centrosome near the nucleus In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a ring Longitudinal section of one centriole © 2014 Pearson Education, Inc. Figure 6.23 Microtubule Centrioles 0.25 μm Microtubules Cross section of the other centriole Microtubules control the beating of flagella and cilia, microtubule-containing extensions that project from some cells Cilia and flagella differ in their beating patterns © 2014 Pearson Education, Inc. Cilia and flagella share a common structure (a) Motion of flagella Direction of swimming 0.1 μm Outer microtubule doublet Motor proteins (dyneins) Central microtubule 5 μm Radial spoke Microtubules (b) Motion of cilia Direction of organism’s movement Power stroke Plasma membrane Plasma membrane Basal body Recovery stroke (b) Cross section of motile cilium 0.1 μm Cross-linking proteins between outer doublets Triplet 0.5 μm (a) Longitudinal section of motile cilium 15 μm © 2014 Pearson Education, Inc. (c) Cross section of basal body © 2014 Pearson Education, Inc. 14 Cilia and flagella share a common structure How dynein “walking” moves flagella and cilia A core of microtubules sheathed by the plasma membrane Dynein arms alternately grab, move, and release the outer microtubules A basal body that anchors the cilium or flagellum Cross-linking proteins limit sliding A motor protein called dynein, which drives the bending movements of a cilium or flagellum Forces exerted by dynein arms cause doublets to curve, bending the cilium or flagellum © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 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 3-D network called the cortex just inside the plasma membrane to help support the cell’s shape Microvillus 0.25 µm Figure 6.25 Microfilaments (Actin Filaments) Plasma membrane Microfilaments (actin filaments) Intermediate filaments Bundles of microfilaments make up the core of microvilli of intestinal cells © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 15 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 Figure 6.26 Cortex (outer cytoplasm): gel with actin network 100 µm Inner cytoplasm (more fluid) Extending pseudopodium Muscle cell 0.5 µm Amoeboid movement 30 µm Chloroplast Cytoplasmic streaming in plant cells Actin filament Myosin filament Myosin head © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. Intermediate Filaments Concept 6.7: Extracellular components and connections between cells help coordinate cellular activities Intermediate filaments range in diameter from 8–12 nanometers, larger than microfilaments but smaller than microtubules They support cell shape and fix organelles in place Most cells synthesize and secrete materials that are external to the plasma membrane Intermediate filaments are more permanent cytoskeleton fixtures than the other two classes These extracellular structures are involved in a great many cellular functions © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 16 Cell Walls of Plants Plant cell walls may have multiple layers The cell wall is an extracellular structure that distinguishes plant cells from animal cells Primary cell wall: Relatively thin and flexible Prokaryotes, fungi, and some unicellular eukaryotes also have cell walls Middle lamella: Thin layer between primary walls of adjacent cells The cell wall protects the plant cell, maintains its shape, and prevents excessive uptake of water Plant cell walls are made of cellulose fibers embedded in other polysaccharides and protein © 2014 Pearson Education, Inc. Secondary cell wall (in some cells): Added between the plasma membrane and the primary cell wall Secondary cell wall Primary cell wall Middle lamella 1 μm Central vacuole Cytosol Plasma membrane Plasmodesmata are channels between adjacent plant cells © 2014 Pearson Education, Inc. Plant cell walls Plasmodesmata Figure 6.28 The Extracellular Matrix (ECM) of Animal Cells Animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM) The ECM is made up of glycoproteins such as collagen, proteoglycans, and fibronectin ECM proteins bind to receptor proteins in the plasma membrane called integrins EXTRACELLULAR FLUID Collagen A proteoglycan complex Polysaccharide molecule Carbohydrates Fibronectin Core protein Plasma membrane Proteoglycan molecule Microfilaments CYTOPLASM Integrins © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 17 Cell Junctions The ECM has an influential role in the lives of cells ECM can regulate a cell’s behavior by communicating with a cell through integrins Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact The ECM around a cell can influence the activity of gene in the nucleus Mechanical signaling may occur through cytoskeletal changes, that trigger chemical signals in the cell © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. Plasmodesmata in Plant Cells Tight Junctions, Desmosomes, and Gap Junctions in Animal Cells Plasmodesmata are channels that perforate plant cell walls Through plasmodesmata, water and small solutes (and sometimes proteins and RNA) can pass from cell to cell Cell walls Interior of cell At 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 cells Interior of cell 0.5 μm © 2014 Pearson Education, Inc. Three types of cell junctions are common in epithelial tissues Plasmodesmata Plasma membranes © 2014 Pearson Education, Inc. 18 Figure 6.30 Tight junctions prevent fluid from moving across a layer of cells. The Cell: A Living Unit Greater Than the Sum of Its Parts Tight junction Cells rely on the integration of structures and organelles in order to function TEM 0.5 μm Tight junction Intermediate filaments For example, a macrophage’s ability to destroy bacteria involves the whole cell, coordinating components such as the cytoskeleton, lysosomes, and plasma membrane Desmosome Gap junction Desmosome 1 μm (TEM) Plasma membranes of adjacent cells Extracellular matrix Space between cells TEM Ions or small molecules 0.1 μm Gap junctions © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 19