Topic 5 Cell Structure and Function PDF

Topic 5 The Cell: Structure and function Prokaryotic vs Eukaryotic cells...

Topic 5 The Cell: Structure and function Prokaryotic vs Eukaryotic cells Cellular organelles: structure vs function Cytoskeleton and PowerPoint Lectures for extracellular Biology, Seventh Edition Neil Campbell and Jane Reece components Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Learning Objectives (LOBs) 1. Describe the different types of light and electron microscopes and compare their application in studying cell morphology. 2. Compare the basic structure of prokaryotic and eukaryotic cells. Part A 3. Compare the structure of plant vs animal cells and identify the function of the different cell structures and organelles. 4. Describe the structure and function of the different components and filaments of the cytoskeleton, including the role of the centrosome, the flagella and the cilia. 5. Describe the structure and function of the different Part B extracellular components (of animal and plant cells). 6. Identify the different types of intercellular junctions in animal cells vs plant cells and their function. Recommended reading: Chapter 7 (Campbell Biology) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Topics to be covered Part 1. Scientific study of cells (Microscopy) Part 2. Cell types and structure Part 3. Cytoskeleton, extracellular components, cell junctions Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Part I Scientific study of cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Overview: The Importance of Cells All organisms are made of cells Cell: the basic structural and functional unit of every organism The cell is the simplest collection of living matter Cell structure is related to cellular function All cells are related by their descent from earlier cells Techniques used for scientific study of cells : 1. Microscopy 2. Cell fractionation (isolation of subcellular structures) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  1. Microscopy Cells are usually too small to be seen by the naked eye To study cells biologists use microscopes and biochemical tools Different types of microscopes can be used to visualize different sized cellular structures 1. Light microscopes (LMs): – Visible light passes through a specimen – Magnification of cellular structures using lenses 2. Electron microscopes (EMs): – Focus a beam of electrons through a specimen (TEM) or onto its surface (SEM) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Microscopes 10 m UnaidedUnaided eye Human height 1m Length of some eye nerve and 0.1 m muscle cells Chicken egg 1 cm Frog egg 1 mm Light microscope 100 µm Most plant and Animal cells Measurements 10 µm Nucleus 1 centimeter (cm) = 10−2 meter (m) = 0.4 inch Electron microscope Most bacteria Mitochondrion 1 millimeter (mm) = 10–3 m 1 µm 1 micrometer (µm) = 10–3 mm = 10–6 m 1 nanometer (nm) = 10–6 mm = 10–9 m 100 nm Smallest bacteria Viruses 1 Å (Angstrom) =10–10 m Ribosomes 10 nm Proteins 1 nm Lipids Small molecules 0.1 nm Atoms Figure 7.2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Comparison of the size of cellular and acellular forms of living organisms Bacterium (0.1-10 μm) Phage Virus Eukaryotic cell (10-100 μm) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Microscopy Factors affecting image quality: – Magnification: the ratio of an object’s image size to its real size – Resolution: the measure of the clarity of the image (minimum distance of two distinguishable points) – Contrast: visible differences in parts of the sample Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Light Microscopes Use different methods for enhancing visualization of cellular structures TECHNIQUE RESULT (1a) 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 (1b) Brightfield (stained specimen). Staining with various dyes enhances contrast, but most staining 2D procedures require that cells be fixed (preserved). (2) Phase-contrast. Enhances contrast in unstained cells by amplifying variations in density within specimen; especially useful for examining Figure 7.3 living unpigmented cells (e.g. dividing cells). Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Light Microscopes (3) Differential-interference-contrast (Nomarski). Like phase-contrast microscopy, it uses optical modifications to exaggerate differences in density, making the image appear almost 3D. (4) Fluorescence. Shows the locations of specific 2D molecules in the cell by tagging the molecules with fluorescent dyes or antibodies. These fluorescent substances absorb ultraviolet (UV) radiation and emit visible light, as shown here in a cell from an artery. 50 µm (5) 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. 3D A sharp image results, as seen in stainednervous 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. It enables the reconstruction of three-dimensional structures from the obtained images. 50 µm Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Fluorescent Microscopy images Mumps virus protein in the endoplasmic reticulum (ER) of a cultured cell Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Light Microscopes (LM) LMs can magnify samples about 1000 times (1000x) the size of the actual specimen LM resolution: 0.2 µm = 200 nm 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 © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Electron Microscope (EM) Discovered in 1930s Uses a beam of electrons concentrated by applying a strong magnetic field Magnification: up to 250 000 x Can detect structure as small as 0.1 nm (e.g. viruses) Can detect macromolecules (e.g. proteins, DNA and polysaccharides) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Electron Microscopes Two basic types of electron microscopes (EMs) are used to study subcellular structures: 1. Transmission electron microscope (TEM): - focus a beam of electrons through a specimen - are used mainly to study the internal structure of cells (2D image) 2. Scanning electron microscope (SEM): - focus a beam of electrons onto the surface of a specimen providing 3D images=> used to study of the surface of the specimen. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Electron Microscopes (EM) The transmission electron microscope (TEM): – Provides image the internal ultrastructure of cells (2D images) (e.g. specimen section) Longitudinal Cross section section of of cilium 1 cilium µm (b) Transmission electron micro- scopy (TEM). A transmissionelectron 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. Figure 7.4 (b) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Electron Microscopes The scanning electron microscope (SEM): – Provides image of the surface of a specimen (3D images) TECHNIQUE RESULTS 1 Cilia µm (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. Figure 7.4 (a) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Resolution of Microscopes Light microscope: 200 nm 100 x improvement in resolution Electron microscope: 2 nm Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Electron Microscopy images SEM SEM Clostridium difficile bacteria Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Electron Microscopy images TEM TEM Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  2. Isolating Organelles by Cell Fractionation Cell fractionation: enables isolation of subcellular components and determination of the organelle functions Fractionates cells and separates the major organelles from one another – Separation is based on size and density Centrifugation: the centrifuge is used to fractionate cells into their component parts (e.g. ultracentrifuges) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cell fractionation: using centrifugation Centrifuge Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Cell Fractionation: Differential centrifugation Homogenization Tissue cells 1000 g Homogenate (1000 times the force of gravity) 10 min Differential centrifugation Supernatant poured into next tube 20,000 g 20 min Separation of cell 80,000 g Pellet rich in 60 min components based nuclei and cellular debris 150,000 g on size 3 hr Pellet rich in mitochondria (and chloro- plasts if cells are from a Pellet rich in plant) “microsomes” (pieces of g= 9.81 m/s2 plasma mem- branes and Pellet rich in cells’ internal ribosomes membranes) Figure 7.5 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Differential vs Density gradient centrifugation Differential Density gradient centrifugation centrifugation Separation Separation based on based on size only (sucrose density (size concentration and shape) constant) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Density gradient centrifugation Increasing sucrose gradient Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Differential vs Density gradient centrifugation Differential Density gradient centrifugation centrifugation Solvent concentration Stabilizing solvent Steep solvent gradient gradient (stable solvent concentration; e.g. 0.5 M sucrose) Centrifugation steps Multiple centrifugation Single centrifugation step steps (increasing acceleration and time) Separation basis Size Density (size and shape)  Part II Cell types and structure Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Cell types Two types of cells make up every organism – Prokaryotic (Bacteria and Archaea domains) – Eukaryotic (Protists, Fungi, Plants, Animals kingdoms) Bacteria and Archaea: unicellular prokaryotic organisms Protists: unicellular (include Protozoa and Algae) Fungi: can be unicellular (e.g. yeasts) or multicellular (e.g. mushrooms) Plants and Animals: multicellular organisms Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  The 3 domains (previously 5 kingdoms) descended from the same ancestor Plants Animals Fungi Eukaryotes Protists Bacteria and Prokaryotes Archaea Copyright © 2005 Pearson Educati on, Inc. publishing as Benjamin Cummings  Prokaryotic and Eukaryotic cells The first cells that appeared were prokaryotic 109 years after the appearance of prokaryotic cells, the eukaryotic cells appeared 109 years Mutations Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Comparing Prokaryotic and Eukaryotic Cells All cells have several basic features in common: – bounded by a plasma membrane – contain a semifluid substance called the cytosol – They contain chromosomes – They all have ribosomes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Comparing Prokaryotic and Eukaryotic Cells Prokaryotic cells: – Do not contain a nucleus (no nuclear membrane) – Have their DNA located in an unbound region called the nucleoid – Do not have any membrane-bound organelles Eukaryotic cells: – Contain a nucleus bounded by a membranous nuclear envelope – Generally bigger than prokaryotic cells – have internal membranes that compartmentalize their functions (e.g. ER, Golgi) and membrane-bound organelles (e.g. mitochondria, chloroplasts) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Prokaryotic vs Eukaryotic Cell structure Prokaryotic Ribosomes cell Εukaryotic cell Golgi apparatus Lysosome Εndoplasmic Copyright reticulum © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Comparing Prokaryotic and Eukaryotic Cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Prokaryotic cell structure 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 Bacterial of many prokaryotes chromosome 0.5 µm Flagella: locomotion (b) A thin section through the organelles of bacterium Bacillus coagulans some bacteria (TEM) (a) A typical rod-shaped bacterium Figure 7.6 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Eukaryotic cell structure: animal cell lysosome Nuclear membrane centrosome Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Cytoplasm vs Cytosol Cytoplasm: the region between the plasma membrane and nucleus => Includes all the subcellular structures except the nucleus Cytosol: the intracellular fluid component of cytoplasm - excludes organelles and other subcellular membranes (eg. Golgi/ER) - contains ribosomes, proteasomes, cytoskeletal filaments, soluble molecules, and water Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  A Panoramic View of the Eukaryotic Cell Nucleus Cytoplasm Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Differences between animal and plant cells Animal and plant cells are eukaryotic and have most of the same organelles Copyright © 2005 Pearson Education, Inc. publis hing as Benjamin Cummings  Differences between animal and plant cells ▪ Plant cells have: - Chloroplasts - Central vacuoles (instead of lysosomes) - Cell wall - Different cell junctions (plasmodesmata) Animal cells have : - Lysosomes - Centrosome (composed of centrioles) - Some have a flagella (e.g. sperm cell) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Animal cell structure ENDOPLASMIC RETICULUM (ER) Nuclear envelope Nucleolus NUCLEUS Rough ER Smooth ER Chromatin Flagelium Plasma membrane Centrosome CYTOSKELETON Microfilaments Intermediate filaments Microtubules Ribosomes Microvilli Golgi apparatus Peroxisome In animal cells but not plant cells: Lysosome Lysosomes Figure 7.9 Mitochondrion Centrioles Flagella (in some plant sperm) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Plant cell structure Nuclear envelope Rough NUCLEUS Nucleolus endoplasmic Chromatin reticulum Smooth Centrosome endoplasmic reticulum Ribosomes (small brown dots) Central vacuole Tonoplast Golgi apparatus Microfilaments Intermediate CYTOSKELETON filaments Microtubules Mitochondrion Peroxisome Plasma membrane Chloroplast Cell wall Plasmodesmata In plant cells but not animal cells: Wall of adjacent cell Chloroplasts Central vacuole and tonoplast Figure 7.9 Cell wall Plasmodesmata Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Plasma membrane (Cytoplasmic membrane) Plasma membrane: a selective barrier that allows sufficient passage of oxygen, nutrients, and waste in and out of the cell Consists of a double layer of phospholipids (phospholipid bilayer) Proteins allow communication with the external environment Semi-permeable (selectively permeable) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Fig. 7-7 Outside of cell Plasma membrane structure (a) TEM of a plasma membrane Inside of cell 0.1 µm Carbohydrate side chain Hydrophilic region Hydrophobic region Hydrophilic region Phospholipid Proteins (b) Structure of the plasma membrane Copyright © 20 05 Pearson Education, Inc. publishing as Benjamin Cummings Cytoplasmic membrane proteins phospholipids Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  The Nucleus: Genetic Library of the Cell The nucleus: – Contains most of the DNA in the eukaryotic cell – Genes are found on chromosomes – Gene: DNA unit that leads to the production of a functional product (protein or RNA product) – Genes contain the directions for the synthesis of proteins – Each chromosome is made of a complex of proteins and DNA = chromatin – Chromatin condenses to form discrete chromosomes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chromosomes, Genes, DNA Copyright © 2005 Pearson Education, Inc. publishi ng as Benjamin Cummings  What is synthesized in the nucleus DNA replication and transcription take place in the nucleus - DNA is replicated before every cell division (in nucleus) - DNA is transcribed to mRNA in the nucleus Translation: in the cytoplasm -mRNA exits the nucleus, moves to the cytoplasm and attaches to ribosomes which translate the information to protein Central dogma of transfer of genetic information: DNA transcription mRNA translation Protein nucleus cytoplasm Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nucleolus Ribosomal RNA (rRNA) is synthesized in the nucleolus, a denser area in the nucleus After rRNA is synthesized, it is assembled with proteins These subunits exit the nucleus and form ribosomes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Nucleolus Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  The nuclear envelope Encloses the nucleus, separating its contents from the cytoplasm Has nuclear pores 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 Figure 6.10 Pore complexes (TEM). Nuclear lamina (TEM). Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nuclear pores Pores regulate the entry and exit of molecules from the nucleus Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Ribosomes: Protein Factories in the Cell Ribosomes: – particles made of ribosomal RNA (rRNA) and protein – Consist of a small and a large subunit which are assembled in the nucleolus Function: protein synthesis 2 cellular locations of ribosomes: -Free ribosomes (in the cytosol): synthesize cytosolic proteins -Bound ribosomes (bound to the RER): synthesize secreted or membrane-bound proteins Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Ribosomes carry out protein synthesis Ribosomes ER Cytosol Endoplasmic reticulum (ER) Free ribosomes Bound ribosomes Large subunit Small 0.5 µm subunit Figure 7.11 TEM showing ER and ribosomes Diagram of a ribosome Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  The Endoplasmic Reticulum:Biosynthetic Factory The endoplasmic reticulum (ER): – Network of membranous tubules and sacs Smooth ER – Inside space is called the lumen Rough ER Nuclear envelope – ER membrane: continuous with the nuclear envelope Two distinct regions of ER: ER lumen Cisternae Ribosomes – Smooth ER (SER): lacks Transport vesicle Transitional ER 200 µm ribosomes Smooth ER Rough ER – Rough ER (RER): contains bound ribosomes Figure 7.12 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Functions of Smooth ER The smooth ER: – Does not have any bound ribosomes – Function: Synthesizes lipids Metabolizes carbohydrates Stores calcium Detoxifies poisons Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Functions of Rough ER: protein production, modification and targeting The rough ER (RER) has bound ribosomes Function: Protein synthesis (by bound ribosomes): Synthesis of secreted proteins or membrane-bound proteins (proteins of the endomembrane system= ΕR, Golgi) Some post-translational modifications: protein processing to become functional Protein targeting (sorting): transports and distributes proteins other cell compartments (e.g. Golgi) by producing membrane-bound transport vesicles (cell trafficking) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Functions of Rough ER Post-translational modifications that occur in the RER: Polypeptide cleavage: some polypeptides are activated by enzymes that cleave them in order to become functional (e.g. insulin) Protein folding (tertiary structure): e.g. disulphide bond formation. Subunit assembly (protein quaternary structure) : Some polypeptides come together to form the subunits of a functional protein (e.g. haemoglobin) Some chemical modifications: addition of chemical groups to proteins (e.g. glycosylation, hydroxylation) => formation of glycoproteins (some in RER but most in Golgi apparatus). Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  ANIMAL Nuclear CELL envelope ENDOPLASMIC RETICULUM (ER) Nucleolus NUCLEUS Rough ER Smooth ER Fig. 7- Flagellum Chromatin 9a Centrosome Plasma membrane CYTOSKELETON: Microfilaments Intermediate filaments Microtubules Ribosomes Microvilli Golgi Peroxisome apparatus Mitochondrion Lysosome Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  The Golgi Apparatus Consists of flattened membranous sacs (cisternae) Receives many of the transport vesicles produced in the rough ER TGN (trans Golgi network) CGN (cis Golgi network) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  The Golgi Apparatus cis face (“receiving” side of 0.1 µm Golgi apparatus) Cisternae trans face (“shipping” side of TEM of Golgi apparatus Golgi apparatus) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  The Golgi Apparatus: Shipping and Receiving Center Functions : – Protein and macromolecule processing (chemical modifications): Receives and modifies protein and other mecromolecule products of the ER by addition of chemical groups to proteins (e.g. glycosylation, phosphorylation, hydroxylation) - e.g. addition of carbohydrates (protein/lipid glycosylation) or lipids to proteins => production of glycoproteins, glycolipids, lipoproteins, etc (some processing in RER but most in Golgi apparatus) – Macromolecule sorting and targeting: Sorts and packages biomolecules into transport vesicles and sends them to other parts of the cell or the organism (targeting= transport to their cellular destination) – Manufacture of certain macromolecules. e.g. polysaccharides Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  The Golgi Apparatus Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Lysosomes: Digestive Compartments Lysosomes: membranous vesicles containing hydrolytic enzymes => digestion of macromolecules (or even microorganisms) => Release simple sugars, aminoacids, nucleotides and fatty acids to be reused by the cell for building new macromolecules (recycling) Lysosomal enzymes functional only at the acidic environment of the lysosome (pH=4) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Lysosomal functions: Phagocytosis and Autophagy Phagocytosis: - intracellular digestion carried out by lysosomes - used by some protists (e.g.amoeba) to digest food - human macrophages use lysosomes to ingest pathogenic microorganisms (immune cells) Autophagy: – Destruction of damaged organelles – Recycling of cell’s organic material Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Phagocytosis Figure 7.14A Nucleus 1 µm Lysosome Lysosome contains Food vacuole Hydrolytic active hydrolytic fuses with enzymes digest enzymes lysosome food particles Digestive enzymes Lysosome Digestion Food vacuole Plasma membrane (phagosome) (a) Phagocytosis: lysosome digesting food Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Autophagy Lysosome containing 1µm two damaged organelles Mitochondrion fragment Peroxisome fragment Lysosome fuses with Hydrolytic enzymes vesicle containing digest organelle damaged organelle components Lysosome Digestion Vesicle containing damaged mitochondrion Figure 7.14 B (b) Autophagy: lysosome breaking down damaged organelle Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PLANT Nuclear envelope Rough endoplasmic Nucleolus reticulum CELL NUCLEUS Chromatin Smooth endoplasmic reticulum Fig. 6- 9b Ribosomes Central vacuole Golgi apparatus Microfilaments Intermediate CYTO- filaments SKELETON Microtubules Mitochondrion Peroxisome Chloroplast Plasma membrane Cell wall Plasmodesmata Wall of adjacent cell Copyright © 20 05 Pearson Education, Inc. publishing as Benjamin Cummings  Vacuoles: Diverse Maintenance Compartments A vacuole is a large membrane- bounded vesicle in plants Involved in digestion, storage, Central vacuole waste disposal, water balance, cell growth and protection Vacuoles have similar role to lysosomes Plant and fungal cell have one or more vacuoles instead of lysosomes Plant cells usually have one large central vacuole Plant cell Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Types of vacuoles Food vacuoles (phagosomes): formed by phagocytosis Contractile vacuoles: pump excess water out of protist cells Central vacuole: – found in plant cells (1 central vacuole per plant cell) – hold reserves of important organic compounds and water – Stores ions and dangerous byproducts that could damage the cell – Some store poisons as a defense against predators (herbivore animals) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Central vacuole: storage compartment Central vacuole Cytosol Tonoplast Nucleus Central vacuole Cell wall Chloroplast 5 µm Figure 7.15 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  The Endomembrane System: A Review The endomembrane system function: - important role in the cell’s compartmental organization - regulates protein traffic (trafficking) and performs metabolic functions in the cell Endomembrane system components: – Nuclear envelope – Endoplasmic reticulum – Golgi apparatus – Lysosomes/vacuoles – Plasma membrane Components are either continuous or connected via vesicle-mediated transfer Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Fig. 7-9a 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Relationships among organelles of the endomembrane system 1 Nuclear envelope is connected to rough ER, Nucleus which is also continuous with smooth ER Rough ER 2 Membranes and proteins produced by the ER flow in Smooth ER the form of transport vesicles cis Golgi to the Golgi Nuclear envelop 3 Golgi pinches off transport vesicles and other vesicles that give rise to lysosomes and Vacuoles Plasma trans Golgi membrane 4 Lysosome available 5Transport vesicle carries 6 Plasma membrane expands for fusion with another proteins to plasma by fusion of vesicles; proteins vesicle for digestion membrane for secretion are secreted from cell Figure 7.16 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Mitochondria and chloroplasts Mitochondria and chloroplasts change energy from one form to another Mitochondria: - the sites of cellular respiration - found in nearly all eukaryotic cells (including animal and plant cells) Chloroplasts: - the sites of photosynthesis - only found only in plant cells and algae Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Mitochondria and chloroplasts Mitochondria and chloroplasts: – Not part of the endomembrane system – Have a double membrane – Contain their own DNA (circular double-stranded mtDNA) – Their proteins are made by their own free ribosomes (in mitochondrial matrix and chloroplast stroma) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Mitochondria: Chemical Energy Conversion Mitochondria are enclosed by two membranes: – A smooth outer membrane – An inner membrane folded into cristae Mitochondrion Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Inner membrane Cristae Matrix Mitochondrial DNA 100 µm Figure 7.17 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Mitochondria: Chemical Energy Conversion Cell respiration: the metabolic process that generates ATP by extracting energy from sugars, fats and other fuels with the help of oxygen Intermembrane space Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Chloroplasts: Capture of Light Energy Chloroplasts: member of a family of closely related plant organelles called plastids Plastids: plant organelles - Chloroplasts: contain chlorophyll - Chromoplasts: contain other pigments (e.g. carotenoids) - Amyloplasts (leucoplasts): contain starch granules Chloroplasts: - found in leaves and other green organs of plants and in algae - contain the green pigment chlorophyll which absorbs solar energy - perform photosynthesis: synthesis of organic compounds (sugars) from CO2 and H2O (inorganic compounds) => conversion of solar energy to chemical energy Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Fig. 7-9b Nuclear envelope Rough endoplasmic reticulum NUCLEUS Nucleolus Chromatin Smooth endoplasmic reticulum Ribosomes Central vacuole Golgi apparatus Microfilaments Intermediate CYTO- filaments SKELETON Microtubules Mitochondrion Peroxisome Chloroplast Plasma membrane Cell wall Plasmodesmata Wall of adjacent cell Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Chloroplasts: photosynthesis Οrganelles with double membrane Have chlorophyll Absorb light energy from sun Function: photosynthesis EM picture Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Chloroplast structure Chloroplast structure includes: – Thylakoids: membranous sacs stacked to form a granum – Stroma: the internal fluid Chloroplast Ribosomes Stroma Chloroplast Inner and outer DNA membranes Granum 1 µm Figure 7.18 Thylakoid Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Chloroplast structure (thylakoid space) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Chloroplasts Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Fig. 7-9b Nuclear envelope Rough endoplasmic reticulum NUCLEUS Nucleolus Chromatin Smooth endoplasmic reticulum Ribosomes Central vacuole Golgi apparatus Microfilaments Intermediate CYTO- filaments SKELETON Microtubules Mitochondrion Peroxisome Chloroplast Plasma membrane Cell wall Plasmodesmata Wall of adjacent cell Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Peroxisomes: Oxidation Peroxisomes: specialized membrane-bound metabolic compartments Peroxisomes functions: – Produce hydrogen peroxide (H2O2) and convert it to H2O by their enzymes (catalase and oxidase) – Detoxification: e.g. liver peroxisomes detoxify alcohol and other harmful compounds – Fatty acid breakdown (β-oxidation of very long fatty acids) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Peroxisomes: hydrocarbon oxidation RH2 + O2 oxidase R + H2O2 RH2 + H202 catalase R + 2H20 H202 catalase H20 + 1/2 O2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Peroxisome structure Chloroplast Peroxisome Mitochondrion Figure 7.19 1 µm Peroxisomes in liver cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Proteasome:Protein degradation Proteasomes: giant protein complexes that bind to protein molecules and degrade them Protein degradation: - Short-lived cytosolic proteins and non-functional (misfolded) proteins are attached to ubiquitin (ubiquitination) => targeted to the proteasome for degradation Ubiquitin Proteasome and ubiquitin to Proteasome be recycled Protein Protein to be Ubiquitinated fragments Protein entering a degraded protein (peptides) proteasome Fig. 18-12. Degradation of a protein by a proteasome.  Summary.Cellular organelles: structure vs function Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Summary. Cell structure vs function Microscopy: Light vs Electron microscope (different types) Cell structure and function: Prokaryotic vs Eukaryotic cells Plant vs Animal cells Cellular organelles: structure and function Nucleus (including nucleolus) Endoplasmic Reticulum (SER vs RER) Golgi apparatus Lysosomes/ Vacuoles Peroxisomes Mitochondria/Chloroplasts Subcellular structures: Ribosomes Proteasomes  Glossary Suffix “-some” = body. Prefix refers to their role Cellular organelles: Lysosomes: Lysis body Peroxisomes: Peroxide body Subcellular structures: Ribosomes: Ribonucleic (RNA) bodies Proteasomes: Protein bodies