A Tour of the Cell Lecture Notes PDF

Chapter 6 A Tour of the Cell Lecture 2 PowerPoint® Lecture Presentations Biology Presented by: for Dr. Same...

Chapter 6 A Tour of the Cell Lecture 2 PowerPoint® Lecture Presentations Biology Presented by: for Dr. Samer Yousef Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Overview: The Fundamental Units of Life 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Concept 6.1: To study cells, biologists use microscopes and the tools of biochemistry Though usually too small to be seen by the unaided eye, cells can be complex Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Microscopy Scientists use microscopes to visualize cells too small to see with the naked eye In a light microscope (LM), visible light passes through a specimen and then through glass lenses, which magnify the image Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  The quality of an image depends on – 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 parts of the sample Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-2 10 m Human height 1m U Length of some n nerve and ai muscle cells d 0.1 m e Chicken egg d e 1 cm y e Frog egg 1 mm Li g 100 µm ht m Most plant and ic animal cells ro 10 µm Nucleus s c El Most bacteria o e 1 µm Mitochondrion p ct e ro n Smallest bacteria m 100 nm Viruses ic ro Ribosomes s 10 nm c Proteins o Lipids p 1 nm e Small molecules 0.1 nm Atoms  LMs can magnify effectively to about 1,000 times the size of the actual specimen Various techniques enhance contrast and enable cell components to be stained or labeled Most subcellular structures, including organelles (membrane-enclosed compartments), are too small to be resolved by an LM Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-3ab TECHNIQUE RESULTS (a) Brightfield (unstained specimen) 50 µm (b) Brightfield (stained specimen) known as a compound light microscopy, by using 2 lenses to focus visible light thru specimens Fig. 6-3cd TECHNIQUE RESULTS (c) Phase-contrast Used to enhance the contrast of images of transparent and colorless specimens. (d) Differential-interference- contrast (Nomarski) introduces contrast to images of specimens which have little or no contrast when viewed using brightfield microscopy. Fig. 6-3e TECHNIQUE RESULTS (e) Fluorescence Exciting a fluorophore with light at a shorter wavelength, which causes it to emit light at a longer wavelength. Fig. 6-3f TECHNIQUE RESULTS (f) Confoc For al increasing optical resolution and contrast of a micrograph by means of using a spatial pinhole to block out-of-focus light in image formation. 50 µm  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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-4 TECHNIQUE RESULTS 1 µm (a) Scanning electron Cilia microscopy (SEM) (b) Transmission electron Longitudinal Cross section microscopy (TEM) section of of cilium 1 µm cilium  Cell Fractionation Cell fractionation takes cells apart and separates the major organelles from one another Ultracentrifuges fractionate cells into their component parts Cell fractionation enables scientists to determine the functions of organelles Biochemistry and cytology help correlate cell function with structure Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-5 TECHNIQUE Homogenization Tissue Homogenate cells 1,000 g (1,000 times the force of gravity) 10 min Differential Supernatant centrifugation poured into next tube 20,000 g 20 min 80,000 g Pellet rich in 60 min nuclei and cellular debri s 150,000 g Pellet rich in 3 hr mitochondria (and chloro- plasts if cells are from a plant) Pellet rich in “microsomes” (pieces of plasma membranes and cells’ internal membranes) Pellet rich in ribosomes Fig. 6-5a TECHNIQUE Homogenization Tissue cells Homogenate Differential centrifugation Fig. 6-5b TECHNIQUE (cont.) 1,000 g (1,000 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 chloro- plasts if cells are from a plant) Pellet rich in “microsomes” (pieces of plasma membranes and cells’ internal membranes) Pellet rich in ribosomes  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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Chapter 6 A Tour of the Cell Lecture 3 PowerPoint® Lecture Presentations Biology Presented by: for Dr. Samer Yousef Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Comparing Prokaryotic and Eukaryotic Cells Basic features of all cells: – Plasma membrane – Semifluid substance called cytosol – Chromosomes (carry genes) – Ribosomes (make proteins) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Prokaryotic cells are characterized by having – No nucleus – DNA in an unbound region called the nucleoid – No membrane-bound organelles – Cytoplasm bound by the plasma membrane Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-6 Fimbriae Nucleoid Ribosomes Plasma membrane Bacterial Cell wall chromosome Capsule 0.5 µm Flagella (a) A typical (b) A thin section rod-shaped through the bacterium bacterium Bacillus coagulans (TEM)  Eukaryotic cells are characterized by having – DNA in a nucleus that is bounded by a membranous nuclear envelope – Membrane-bound organelles – Cytoplasm in the region between the plasma membrane and nucleus Eukaryotic cells are generally much larger than prokaryotic cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  The plasma membrane is a selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell The general structure of a biological membrane is a double layer of phospholipids Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-7 (a) TEM of a plasma Outside of cell membrane Inside of cell 0.1 µm Carbohydrate side chain Hydrophilic region Hydrophobic region Hydrophilic Phospholipid Proteins region (b) Structure of the plasma membrane  The logistics of carrying out cellular metabolism sets limits on the size of cells The surface area to volume ratio of a cell is critical As the surface area increases by a factor of n2, the volume increases by a factor of n3 Small cells have a greater surface area relative to volume Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-8 Surface area increases while total volume remains constant 5 1 1 Total surface area [Sum of the surface areas (height width) of all 6 150 750 boxes sides number of boxes] Total volume [height width length 1 125 125 number of boxes] Surface-to-volume (S-to-V) ratio [surface area ÷ volume] 6 1.2 6  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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-9a Nuclear envelope ENDOPLASMIC RETICULUM (ER) Nucleolus NUCLEUS Rough ER Smooth ER Flagellum Chromatin Centrosome Plasma membrane CYTOSKELETON: Microfilaments Intermediate filaments Microtubules Ribosomes Microvilli Golgi Peroxisome apparatus Mitochondrion Lysosome  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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  The Nucleus: Information Central 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 The nuclear membrane is a double membrane; each membrane consists of a lipid bilayer Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-10 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)  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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  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) synthesis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Ribosomes: Protein Factories 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 or the nuclear envelope (bound ribosomes) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-11 Cytosol Endoplasmic reticulum (ER) Free ribosomes Bound ribosomes Large subunit Small 0.5 µm subunit TEM showing ER and ribosomes Diagram of a ribosome  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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-12 Smooth ER Rough ER Nuclear envelope ER lumen Cisternae Ribosomes Transitional ER Transport vesicle 200 nm Smooth ER Rough ER  Functions of Smooth ER The smooth ER – Synthesizes lipids – Metabolizes carbohydrates – Detoxifies poison – Stores calcium Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Functions of Rough ER The rough ER – Has bound ribosomes, which secrete glycoproteins (proteins covalently bonded to carbohydrates) – Distributes transport vesicles, proteins surrounded by membranes – Is a membrane factory for the cell Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-13 cis face (“receiving” side of 0.1 µm Golgi apparatus) Cisternae trans face (“shipping” side of TEM of Golgi apparatus Golgi apparatus)  Lysosomes: Digestive Compartments A lysosome is a membranous sac of hydrolytic enzymes that can digest macromolecules Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids Animation: Lysosome Formation Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Some types of cell can engulf another cell 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-14 Nucleus 1 µm Vesicle containing 1 µm two damaged organelles Mitochondrion fragment Peroxisome fragment Lysosome Digestive enzymes Lysosome Lysosome Plasma Peroxisome membrane Digestion Food Digestion Mitochondrion vacuole Vesicle (a) Phagocytosis (b) Autophagy Fig. 6-14a Nucleus 1 µm Lysosome Digestive enzymes Lysosome Plasma membrane Digestion Food vacuole (a) Phagocytosis Fig. 6-14b Vesicle containing 1 µm two damaged organelles Mitochondrion fragment Peroxisome fragment Lysosome Peroxisome Mitochondrion Digestion Vesicle (b) Autophagy  Vacuoles: Diverse Maintenance Compartments A plant cell or fungal cell may have one or several vacuoles Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Food vacuoles are formed by phagocytosis 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 Video: Paramecium Vacuole Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-15 Central vacuole Cytosol Nucleus Central vacuole Cell wall Chloroplast 5 µm  The Endomembrane System: A Review The endomembrane system is a complex and dynamic player in the cell’s compartmental organization Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-16-1 Nucleus Rough ER Smooth ER Plasma membrane Fig. 6-16-2 Nucleus Rough ER Smooth ER cis Golgi Plasma membrane trans Golgi Fig. 6-16-3 Nucleus Rough ER Smooth ER cis Golgi Plasma membrane trans Golgi  Concept 6.5: Mitochondria and chloroplasts change energy from one form to another Mitochondria are the sites of cellular respiration, a metabolic process that generates ATP Chloroplasts, found in plants and algae, are the sites of photosynthesis Peroxisomes are oxidative organelles Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Mitochondria and chloroplasts – Are not part of the endomembrane system – Have a double membrane – Have proteins made by free ribosomes – Contain their own DNA Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-17 Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Inner membrane Cristae Matrix 0.1 µm  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 Chloroplasts are found in leaves and other green organs of plants and in algae Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Chloroplast structure includes: – Thylakoids, membranous sacs, stacked to form a granum – Stroma, the internal fluid Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-18 Ribosomes Stroma Inner and outer membranes Granum 1 µm Thylakoid  Peroxisomes: Oxidation Peroxisomes are specialized metabolic compartments bounded by a single membrane Peroxisomes produce hydrogen peroxide and convert it to water Oxygen is used to break down different types of molecules Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-19 Chloroplast Peroxisome Mitochondrion 1 µm  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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-20 Microtubule Microfilaments 0.25 µm  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 Inside the cell, vesicles can travel along “monorails” provided by the cytoskeleton Recent evidence suggests that the cytoskeleton may help regulate biochemical activities Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-21 Vesicle ATP Receptor for motor protein Motor protein Microtubule (ATP powered) of cytoskeleton (a) Microtubule Vesicles 0.25 µm (b)  Components of the Cytoskeleton Three main types of fibers make up 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Table 6-1 10 µm 10 µm 10 µm Column of tubulin dimers Keratin proteins Actin subunit Fibrous subunit (keratins 25 nm coiled together) 7 nm 8–12 nm Tubulin dimer Table 6-1a 10 µm Column of tubulin dimers 25 nm Tubulin dimer Table 6-1b 10 µm Actin subunit 7 nm Table 6-1c 5 µm Keratin proteins Fibrous subunit (keratins coiled together) 8–12 nm  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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Centrosomes and Centrioles In many cells, microtubules grow out from a centrosome near the nucleus The centrosome is a “microtubule-organizing center” In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a ring Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-22 Centrosome Microtubule Centrioles 0.25 µm Longitudinal section Microtubules Cross section of one centriole of the other centriole  Cilia and Flagella Microtubules control the beating of cilia and flagella, locomotor appendages of some cells Cilia and flagella differ in their beating patterns Video: Video: Paramecium Chlamydomonas Cilia Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-23 Direction of swimming (a) Motion of flagella 5 µm Direction of organism’s movement Power stroke Recovery stroke (b) Motion of cilia 15 µm  Cilia and flagella share a common ultrastructure: – A core of microtubules sheathed by the plasma membrane – A basal body that anchors the cilium or flagellum – A motor protein called dynein, which drives the bending movements of a cilium or flagellum Animation: Cilia and Flagella Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-24 Outer microtubule 0.1 µm Plasma doublet membrane Dynein proteins Central microtubule Radial spoke Protein cross- Microtubules linking outer doublets (b) Cross section of Plasma cilium membrane Basal body 0.5 µm (a) Longitudinal 0.1 µm section of cilium Triplet (c) Cross section of basal body  How dynein “walking” moves flagella and cilia: − Dynein arms alternately grab, move, and release the outer microtubules – Protein cross-links limit sliding – Forces exerted by dynein arms cause doublets to curve, bending the cilium or flagellum Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-25 Microtubule doublets ATP Dynein protein (a) Effect of unrestrained dynein movement ATP Cross-linking proteins inside outer doublets Anchorage in cell (b) Effect of cross-linking proteins 1 3 2 (c) Wavelike motion Fig. 6-25a Microtubule doublets ATP Dynein protein (a) Effect of unrestrained dynein movement Fig. 6-25b ATP Cross-linking proteins inside outer doublets Anchorage in cell (b) Effect of cross-linking proteins 1 3 2 (c) Wavelike motion  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 3-D network called the cortex just inside the plasma membrane to help support the cell’s shape Bundles of microfilaments make up the core of microvilli of intestinal cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-26 Microvillus Plasma membrane Microfilaments (actin filaments) Intermediate filaments 0.25 µm  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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-27 Muscle cell Actin filament Myosin filament Myosin arm (a) Myosin motors in muscle cell contraction Cortex (outer cytoplasm): gel with actin network Inner cytoplasm: sol with actin subunits Extending pseudopodium (b) Amoeboid movement Nonmoving cortical cytoplasm (gel) Chloroplast Streaming cytoplasm (sol) Vacuole Parallel actin filaments Cell wall (c) Cytoplasmic streaming in plant cells Fig, 6-27a Muscle cell Actin filament Myosin filament Myosin arm (a) Myosin motors in muscle cell contraction Fig. 6-27bc Cortex (outer cytoplasm): gel with actin network Inner cytoplasm: sol with actin subunits Extending pseudopodium (b) Amoeboid movement Nonmoving cortical cytoplasm (gel) Chloroplast Streaming cytoplasm (sol) Vacuole Parallel actin filaments Cell wall (c) Cytoplasmic streaming in plant cells  Localized contraction brought about by actin and myosin also drives amoeboid movement Pseudopodia (cellular extensions) extend and contract through the reversible assembly and contraction of actin subunits into microfilaments Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Cytoplasmic streaming is a circular flow of cytoplasm within cells This streaming speeds distribution of materials within the cell In plant cells, actin-myosin interactions and sol- gel transformations drive cytoplasmic streaming Video: Cytoplasmic Streaming Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Intermediate Filaments 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 Intermediate filaments are more permanent cytoskeleton fixtures than the other two classes Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Concept 6.7: Extracellular components and connections between cells help coordinate cellular activities Most cells synthesize and secrete materials that are external to the plasma membrane These extracellular structures include: – Cell walls of plants – The extracellular matrix (ECM) of animal cells – Intercellular junctions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Cell Walls of Plants The cell wall is an extracellular structure that distinguishes plant cells from animal cells Prokaryotes, fungi, and some protists also have cell walls 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  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 wall Plasmodesmata are channels between adjacent plant cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-28 Secondary cell wall Primary cell wall Middle lamella 1 µm Central vacuole Cytosol Plasma membrane Plant cell walls Plasmodesmata Fig. 6-29 RESULTS 10 µm Distribution of cellulose Distribution of microtubules synthase over time over time  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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-30 Collagen Proteoglycan Polysaccharide EXTRACELLULAR FLUID complex molecule Carbo- hydrates Fibronectin Core protei n Integrins Proteoglycan molecule Plasma membrane Proteoglycan complex Micro- CYTOPLASM filaments Fig. 6-30a Collagen Proteoglycan EXTRACELLULAR FLUID complex Fibronectin Integrins Plasma membrane Micro- CYTOPLASM filaments Fig. 6-30b Polysaccharide molecule Carbo- hydrates Core protein Proteoglycan molecule Proteoglycan complex  Functions of the ECM: – Support – Adhesion – Movement – Regulation Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  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 – Tight junctions – Desmosomes – Gap junctions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Plasmodesmata in Plant 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-31 Cell walls Interior of cell Interior of cell 0.5 µm Plasmodesmata Plasma membranes  Tight Junctions, Desmosomes, and Gap Junctions in Animal Cells 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 Animation: Tight Junctions Animation: Desmosomes Animation: Gap Junctions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-32 Tight junction Tight junctions prevent fluid from moving across a layer of cells 0.5 µm Tight junction Intermediate filaments Desmosome Gap Desmosome 1 µm junctions Extracellula Space r between matrix Gap junction cells Plasma membranes of adjacent cells 0.1 µm Fig. 6-32a Tight junctions prevent fluid from moving across a layer of cells Tight junction Intermediate filaments Desmosome Gap junctions Extracellular Space matrix between cells Plasma membranes of adjacent cells Fig. 6-32b Tight junction 0.5 µm Fig. 6-32c Desmosome 1 µm Fig. 6-32d Gap junction 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-33 5 µ m 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 regulate entry and exit of endoplasmic reticulum (ER). 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 envelope) sacs; membrane separates drates, Ca2+ storage, detoxifica- performs metabolic functions 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 inner membrane has from infoldings (cristae) one form to another Chloroplast Typically two membranes Photosynthesis around fluid stroma, which contains membranous thylakoids Peroxisom stacked Specialized into grana metabolic (in plants) Contains enzymes that transfer e 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 Fig. 6-UN1a 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 os materials. (ER ) Ribosome Two subunits made of ribo- Protein somal RNA and proteins; can be synthesis free in cytosol or bound to ER Fig. 6-UN1b Cell Component Structure Function 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, envelope) lumen from cytosol; detoxifica- performs metabolic functions continuous with tion of drugs and poisons in the cell the nuclear envelope. Rough ER: Aids in sythesis 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 faces) Golgi products, which are then released in vesicles. Breakdown of ingested sub- Lysosome Membranous sac of stances cell macromolecules, hydrolytic and damaged organelles for enzymes (in animal cells) recycling Vacuole Large membrane-bounded Digestion, storage, waste vesicle in plants disposal, water balance, cell growth, and protection Fig. 6-UN1c Cell Component Structure Function 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 Fig. 6-UN2 Fig. 6-UN3  You should now be able to: 1. Distinguish between the following pairs of terms: magnification and resolution; prokaryotic and eukaryotic cell; free and bound ribosomes; smooth and rough ER 2. Describe the structure and function of the components of the endomembrane system 3. Briefly explain the role of mitochondria, chloroplasts, and peroxisomes 4. Describe the functions of the cytoskeleton Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 1. Compare the structure and functions of microtubules, microfilaments, and intermediate filaments 2. Explain how the ultrastructure of cilia and flagella relate to their functions 3. Describe the structure of a plant cell wall 4. Describe the structure and roles of the extracellular matrix in animal cells 5. Describe four different intercellular junctions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings