ASIM'S WEBWORLD View: Main School Main AP Biology Chapter Guides RELATED LINKS Review Questions and Answers		AP BIOLOGY: Chapter Five Outline INTRODUCTION All Organisms Composed of Cells fig 5.1 Integral Part of Definition of Life AN OVERVIEW OF CELL STRUCTURE The Plasma Membrane Surrounds the Cell Phospholipid bilayer contains embedded proteins Appear as two dark lines separated by lighter area fig 5.2 Major proteins have large hydrophobic domains Proteins enable cell to interact with environment Transport proteins facilitate passage across membrane Receptors induce cell changes with contact by molecules Markers provide cell identity The Central Portion of the Cell Contains the Genetic Material Genetic material in prokaryotes Single, circular molecule of DNA Is concentrated in the nucleoid, not membrane bound Genetic material in eukaryotes Contained within the nucleus Surrounded by two membranes The Cytoplasm Comprises the Rest of the Cell's Interior Cytoplasm is a semifluid matrix Contains chemicals to carry out growth and reproduction MOST CELLS ARE VERY SMALL Small Size a Characteristic Trait fig 5.3 The Cell Theory Robert Hooke First seen with invention of microscope in 1665 Observed honeycomb of empty compartments in cork Antonie Van Leeuwenhoek First observance of living cells Called organisms "animalcules" fig 5.4 Matthias Schleiden Observed plant tissues All plants aggregates of separate cells Theodor Schwann Observed animal tissues All animals composed of individual cells Modern principles of cell theory All organisms composed of one or more cells Cell is smallest living organizational unit Cells arise only from division of other cells Why Aren't Cells Larger? Limitations of molecular diffusion Faster passage through small cells More efficient communication Limitations of surface-to-volume ratio With increase in size, greater increase in volume than surface area Interaction with outside occurs only at surface Insufficient exchange of materials at plasma membrane for survival THE STRUCTURE OF SIMPLE CELLS: BACTERIA Simplest Cellular Organisms Great diversity fig 5.5 Similar organization, small size May adhere in masses, but are fundamentally separate from one another fig 5.6 Strong Cell Walls Carbohydrate matrix cross linked with peptide units Gram positive, thick cell wall, retains stain Gram negative, thinner cell wall, releases stain Simple Interior Organization Lack internal compartmentalization Cell strength due to cell wall fig 5.6 Reactions not separated, single metabolic unit Lack membrane-bound organelles Infolding of plasma membrane Associated with cell division Location of bacterial photosynthetic pigments fig 5.7 Rotating Flagella Long, threadlike organelles that protrude from cell surface Cell movement results from screw-like rotation fig 5.8 THE STRUCTURE OF EUKARYOTIC CELLS: AN OVERVIEW tbl 5.1 Eukaryotes Are More Complex Than Prokaryotes fig 5.9,10 Hallmark is compartmentalization Possess internal membrane-bound organelles Golgi complex and lysosomes created by folding endoplasmic reticulum Mitochondria and chloroplasts associated with cellular energy Central vacuole in plants stores protein and wastes Vesicles in animals store and transport many materials Nucleus contains chromosomes made of DNA and histone proteins Cytoskeleton is an internal scaffold of proteins Cell walls: cellulose/chitin fibers embedded in polysaccharides, proteins Flagella undulate THE ENDOPLASMIC RETICULUM: COMPARTMENTALIZATION OF THE CELL fig 5.11 General Characteristics Thin membranes not visible in light microscope Divide interior into compartments Lipid bilayer with embedded proteins Abbreviated ER Rough ER: Manufacturer of Proteins for Export Ribosomes assist manufacture of proteins Aggregates of protein and RNA Translate RNA copies of genes into proteins Exported proteins contain signal sequences fig 5.12 Initial translation by free ribosome Signal sequence attaches recognition factor Aggregation travels to ER docking site Protein directed to Golgi complex Smooth ER: Organizer of Internal Activities Lack ribosomes Contain embedded enzymes Associated with detoxification, carbohydrate and lipid synthesis THE NUCLEUS: INFORMATION CENTER FOR THE CELL Spherical Appearance in Most Cells Largest organelle, readily visible Centrally located, positioned by filaments fig 5.13 Lacking in mature red blood cells Getting In and Out: The Nuclear Envelope fig 5.13 Double layer of membranes, outer continuous with ER Membranes pinched together at nuclear pores Embedded with proteins, serve as molecular channels Restrict passage of molecules to proteins and RNA The Chromosomes of Eukaryotes Are Complex fig 5.14 Contain hereditary information specifying structure and function Divided intolinear chromosomes, associated with histone protein Enables condensation during cell division Uncoiled at other times Uncoiling permits RNA polymerase to access DNA, making RNA Proteins Are Synthesized on the Ribosomes fig 5.15 Read mRNA copy of DNA gene to direct synthesis of protein DNA coding for ribosomal RNA (rRNA) clustered to maximize synthesis Greater number of ribosomes with increased protein synthesis The Nucleolus Manufactures Ribosomal Subunits fig 5.16 Location of ribosome synthesis Dark-staining region visible in protein producing cells Present when chromosomes are uncoiled and invisible THE GOLGI COMPLEX: THE DELIVERY SYSTEM OF THE CELL Golgi Bodies fig 5.17 Individual, flattened stacks of membranes Abundant in glandular secretory cells Collectively called the Golgi complex Function in Molecule Collection, Packaging, Distribution fig 5.18 Manufactured products of ER transported into it Bind to polysaccharides forming glycoproteins and glycolipids Molecules collect at flattened, stacked folds of membranous cisternae Folds pinch together forming distribution vesicles called liposomes LYSOSOMES: PRODUCERS OF DIGESTIVE ENZYMES FOR THE CELL fig 5.19 Membrane-Bound Organelles Containing Hydrolytic Enzymes Enzymes catalyze breakdown of macromolecules within cell Digest worn-out cell components and recycle material into new structures Alter internal pH to effect control of digestion Primary lysosome has high pH and is inactive Secondary lysosome has low pH and is active Avoiding Self Digestion Unknown process that requires energy Metabolically inactive eukaryotes die Lysosome membrane digested by enzymes within Cell destroyed by released enzymes Bacteria lack lysosomes can be metabolically inactive Eliminate Other Substances Including Whole Cells Digest pathogens engulfed by white blood cells Participate in selective cell death Associated with organismal development Cells internally directed to commit suicide PEROXISOMES: DETOXIFIERS OF HYDROGEN PEROXIDE Enzyme-Bearing, Membrane-Bound Vesicles Called Microbodies Arise from pre-existing microbodies Peroxisomes in animals Glyoxysomes in plants Functionally Organizes Cellular Metabolism Convert fat to carbohydrates Destroy harmful hydrogen peroxide SOME ORGANELLES CONTAIN DNA Mitochondria: The Cell's Chemical Furnaces fig 5.20 Occur in all organisms Bounded by double membrane Outer membrane is smooth Inner membrane is folded into contiguous layers Called cristae Divides into inner matrix and outer compartment Associated with proteins of oxidative metabolism Possesses own genome Genes direct production of own RNA and ribosomal components Genes for oxidative metabolism are in nucleus Capable of replication Distributed between halves of dividing cells Replenish numbers by simple fission division Components for division are governed by genes in nucleus Not completely autonomous, cannot be cultured separately Chloroplasts: Where Photosynthesis Takes Place fig 5.21 Occur in photosynthetic organisms, plants and algae Bounded by double membrane Internal membranes form disk-shaped thylakoids Photosynthetic pigments on thylakoid surface Stack of thylakoids called granum Possess own genome Genes for chloroplast components located in nucleus RNA and protein components for photosynthesis on chloroplast DNA Become leucoplasts when deprived of light Lamellae reabsorbed Specialized amyloplasts store starch Plastids are derived from proplastids Centrioles: Microtubular Assembly Plants fig 5.22 Present in animal and protist cells Occur in pairs at right angles near nuclear envelope, forms the centrosome Associated with assembly and organization of microtubules Form basal bodies that anchor flagella and cilia Absent in plant and fungal cells THE CYTOSKELETON: INTERIOR FRAMEWORK OF THE CELL Network of Protein Fibers fig 5.23 Anchor organelles to fixed location Formed by polymerization of identical protein subunits Also disassembled subunit by subunit Three Types of Cytoskeleton Fibers fig 5.24 Actin filaments fig 5.24a Fibers composed of two chains like two intertwined strands of pearls Actin proteins are the pearl molecules Form spontaneously Cell controls polymerization via other proteins Microtubules fig 5.24b Spontaneously form hollow tubes of 13 protein protofilaments Alpha and beta tubulin subunits polymerize to form protofilaments Form from nucleation centers In constant flux, polymerizing and depolymerizing Stabilized when guanine triphosphate (GTP) binds to ends + end is away from the nucleating center - end is toward the nucleating center Help move materials within the cell itself Kinesin protein moves organelles to + end (periphery) Dynein protein moves organelles to - end (center) Intermediate filaments fig 5.24c Composed of various subunits of intermediate size Fibrous proteins twined together to form overlapping tetrameres Fibers very stable do not break down readily Vimentin subunits make filaments that provide structural stability Examples: keratin and neurofilaments Provide Mechanical Support for Cell Fibers anchored to plasma membrane proteins Intermediate fibers prevent excessive stretching Actin fibers determine cell shape Rapid changes in filament length changes cell shape quickly fig 5.25 Involved in Cell Locomotion Movement of white blood cells is good example Results in regional changes in gel-sol state Interior is usually very fluid (sol) Periphery is usually more rigid (gel) Formation of pseudopods to move cell May have implications in healing and slowing spread of cancer Cell motion tied to movement of actin filaments and/or microtubules Provide Scaffold for Anchoring Cell Enzymes Metabolic enzymes and ribosomes bind to actin filaments Organize metabolic activities of cell by relocating elements FLAGELLA AND CILIA: MOTILITY FOR THE CELL Eukaryotic Flagella 9+2 structure of microtubules fig 5.26 Undulating movement results from sliding of filaments Projection enclosed by cell membrane Derived from basal body below cell membrane Cilia and Centrioles Also Show 9+2 Arrangement Numerous, short projections called cilia fig 5.1 Have functions other than locomotion Pass fluids over tissue surface Bend in response to sound waves SYMBIOSIS AND THE ORIGIN OF EUKARYOTES tbl 5.2 Eukaryotes Have Radically Different Cell Structure Internally complex Possess organelles that resemble bacteria, endosymbiont theory Symbionts Provided Metabolic Advantage to Host Mitochondria are energy factories Chloroplasts photosynthesize Evidence Supporting Theory Mitochondria and chloroplasts surrounded by double membrane fig 5.27 Mitochondria and bacteria have similar size Mitochondrial ribosomes resemble bacterial ribosomes Mitochondria and chloroplast DNA circular like bacteria Mitochondria divide by simple fission Centrioles resemble spirochaete bacteria