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Transcript
Prokaryotes vs. Eukaryotes Process of Life • • • • Growth (increase in size) Reproduction Responsiveness _Metabolism___ Both prokaryotes and eukaryotes undergo these processes Prokaryote • Simple structure • No nucleus • Small; ~1.0 µm in diameter • One circular chromosome, not in a membrane • No histones • No _membrane___ bound organelles • Peptidoglycan cell walls • Binary fission • Comprised of bacteria and archaea Eukaryote • • • • • • • • • Complex Structure Nucleus Larger; 10-100 µm in diameter Paired_ chromosomes, in nuclear membrane Histones Organelles Polysaccharide cell walls Mitotic spindle__ Comprised of algae, protozoa, fungi, animals, and plants Comparing Prokaryotes and Eukaryotes Figure 3.2ab Comparing Prokaryotes and Eukaryotes Figure 3.2ab Prokaryotes • Average size: 0.2 -1.0 µm × 2 - 8 µm • Basic shapes: Arrangements External Structures of Prokaryotic Cells • Glycocalyx • Flagella • Fimbriae and Pili Glycocalyx • Gelatinous, sticky substance surrounding the outside of the cell • Composed of polysaccharides, polypeptides, or both • Two types – Slime Layer – Capsule Slime Layer • Loosely attached to cell surface • Thinner • Water soluble • Protects cells from drying out • Sticky layer that allows prokaryotes to attach to surfaces Capsule • Composed of organized repeating units of organic chemicals • Thicker • Firmly attached to cell surface • Protects cells from drying out • May prevent bacteria from being recognized and destroyed by host Flagella • Responsible for movement • Long, whiplike structures that extend beyond surface of cell Flagella Structure • Composed of filament, hook, and basal body • Flagellin protein (filament) arranged in chains and forms helix around hollow core • Base of filament inserts into hook • Basal body anchors filament and hook to cell wall by a rod and a series of either two or four rings • Filament capable of _rotating_ 360º Motile Cells • Rotate flagella to run or tumble • Move toward or away from stimuli (taxis) – Move toward food (+) – Move away from harmful chemicals (-) • Flagella proteins are H antigens (e.g., E. coli O157:H7) • Not all bacteria are motile – Only those with a flagellum • _Cocci_ do not have flagella Motile Cells Figure 4.9 Arrangements of Flagella Monotrichous Lophotrichous Figure 3.6 Arrangements of Flagella Amphitrichous Peritrichous Figure 3.6 Axial Filaments • Endoflagella = flagellum covered in a sheath • In spirochetes • Anchored at one end of a cell • Rotation causes cell to move Figure 4.10a Fimbriae and Pili • Nonmotile extensions • Fimbriae – Sticky, proteinaceous, bristlelike projections – Used by bacteria to adhere to one another, to hosts, and to substances in environment – May be hundreds per cell and are shorter than flagella – Serve an important function in biofilms Fimbriae Versus Flagella Figure 3.9 Pili • Long hollow tubules composed of pilin • Longer than fimbriae but shorter than flagella • Bacteria typically only have one or two per cell • Join two bacterial cells and mediate the transfer of DNA from one cell to another (conjugation) • Also known as conjugation pili or sex pili Pilus Versus Fimbriae Figure 3.10 Prokaryotic Cell Walls • Provides structure and shape • Protects cell from osmotic forces • Assists some cells in attaching to other cells or in eluding antimicrobial drugs • Animal cells do not have cell walls – target cell wall of bacteria with antibiotics • Bacteria and archaea have different cell wall chemistry Bacterial Cell Walls • Most have cell wall composed of peptidoglycan_; a few lack a cell wall entirely • Peptidoglycan composed of sugars, NAG and NAM • Chains of NAG and NAM attached to other chains by tetrapeptide crossbridges – Bridges may be covalently bonded to one another – Bridges may be held together by short connecting chains of amino acids Peptidoglycan • Polymer of disaccharide N-acetylglucosamine (NAG) & N-acetylmuramic acid (NAM) • Linked by _____________ Figure 4.13a Structure of Peptidoglycan Bacterial Cell Walls • Gram-Positive Cell Walls – Relatively thick layer of peptidoglycan – Contains unique polysaccharides called teichoic acids • Some covalently linked to lipids, forming lipoteichoic acids that anchor _peptidoglycan_ to cell membrane – Retains crystal violet dye in Gram staining procedure; appear purple – Acid-fast bacteria contain up to 60% mycolic acid; helps cells survive dessication Bacterial Cell Walls – Gram positive Figure 3.13a Bacterial cell walls • Gram-Negative Cell Walls – Have only a thin layer of peptidoglycan – Have a bilayer membrane composed of phospholipids, channel proteins _(porins)_, and lipopolysaccharide (LPS) – May be impediment to the treatment of disease – Following Gram staining procedure, cells appear pink Bacterial Cell Walls Gram Negative Figure 3.13b LPS • Union of lipid with sugar • Also known as endotoxin • Lipid portion known as lipid A – Released from dead cells when cell wall disintegrates – May trigger fever, vasodilation, inflammation, shock, and blood clotting – Can be released when antimicrobial drugs kill bacteria Periplasmic Space • Between outer membrane and cell membrane – Contains peptidoglycan and periplasm – Contains water, nutrients, and substances secreted by the cell, such as digestive enzymes and proteins involved in transport Archael Cell Walls • Do not have peptidoglycan • Cell walls contain variety of specialized polysaccharides and proteins • Gram-positive archaea stain purple • Gram-negative archaea stain pink Prokaryotic Cytoplasmic Membrane • Phospholipid bilayer - composed of lipids and associated proteins • Proteins act as – recognition proteins, enzymes, receptors, carriers, or channels – Integral proteins – Peripheral proteins – Glycoproteins • Fluid mosaic model describes current understanding of membrane structure Phospholipid Bilayer of Cytoplasmic Membrane Figure 3.14 Cytoplasmic Membrane Function • Controls passage of substances into and out of the cell; selectively permeable • Functions in energy production • Harvests light energy in photosynthetic prokaryotes Control of Substances Across Cytoplasmic Membrane • Naturally impermeable to most substances • Proteins allow substances to cross membrane • Occurs by passive or active processes • Maintains a concentration gradient and electrical gradient; collectively known as electrochemical gradient – Chemicals concentrated on one side of the membrane or the other – Voltage exists across the membrane Passive Processes of Transport • Diffusion • Facilitated Diffusion • Osmosis – Isotonic solution – Hypertonic solution – Hypotonic solution • Active Transport • Group Translocation Movement Across Membranes • Simple diffusion: Movement of a solute from an area of high concentration to an area of low concentration. Movement Across Membranes Facilitated diffusion: Solute combines with a transporter protein in the membrane. Figure 4.17 Movement Across Membranes • Osmosis – Movement of water across a selectively permeable membrane from an area of high water concentration to an area of lower water concentration. Figure 4.18a Figure 4.18c-e Effects of Solutions on Organisms – Osmotic Pressure Figure 3.18 Movement Across Membranes • Active transport of substances requires a transporter protein and ATP. • Group translocation of substances requires a transporter protein and PEP. – Substance chemically modified during transport Cytoplasm of Prokaryotes • Cytoplasm is the substance inside the plasma membrane – Cytosol is the liquid portion Figure 4.6a, b Nuclear Area • Nuclear area (nucleoid) Figure 4.6a, b Ribosomes Figure 4.6a Ribosomes Differ slightly in size from Eukaryotic ribosomal subunits Streptomycin & gentamycin attach to 30S subunit Erythromycin & Chloramphenicol attach to 50S subunit Figure 4.19 Inclusions • Metachromatic granules (volutin) • Polysaccharide granules • Lipid inclusions • Sulfur granules • Carboxysomes •Phosphate reserves • Gas vacuoles • Magnetosomes •Protein covered cylinders •Iron oxide (destroys H2O2) •Energy reserves •Energy reserves •Energy reserves •Ribulose 1,5-diphosphate carboxylase for CO2 fixation Eukaryotic Cells External Structures of Eukaryotic Cells • Glycocalyx • Flagella • Cilia Glycocalyx • Not as organized as prokaryotic capsules • Helps anchor animal cells adhere to each other • Strengthens cell surface • Provides protection against dehydration • Function in cell-to-cell recognition and communication Flagella • Shaft composed of tubulin arranged from microtubules • “9 + 2” arrangement of microtubules • Filaments anchored to cell by basal body; no hook • Basal body has “9 + 0” arrangement of microtubules • Originate inside the cell (not extensions outside the cell) • May be single or multiple • Generally found at one pole of cell • Do not rotate, but undulate rhythmically Eukaryotic Flagella and Cilia Figure 3.23 Flagella & Cilia Eukaryotic Flagella and Cilia Figure 3.23 Cilia • Shorter and more numerous than flagella • Composed of tubulin in “9 + 2” and “9 + 0” arrangements • Coordinated beating propels cells through their environment • Also used to move substances past the surface of the cell Eukaryotic Flagella and Cilia Figure 3.23 Eukaryotic Cell Walls • Fungi, algae, and plants have cell walls but no glycocalyx • Composed of various polysaccharides – Cellulose found in plant cell walls – Fungal cell walls composed of cellulose, chitin, and/or glucomannan – Algal cell walls composed of cellulose, agar, carrageenan, silicates, algin, calcium carbonate, or combination of these What is not present in a eukaryotic cell wall? Eukaryotic Cell Membranes • All eukaryotic cells have cell membrane • Fluid mosaic of phospholipids and proteins • Contains steroid lipids to help maintain fluidity • Controls movement into and out of cell – Use diffusion, facilitated diffusion, osmosis, and active transport – Endocytosis • Phagocytosis if solid substance • Pinocytosis if liquid substance – Exocytosis enables substances to be exported from cell Phagocytosis Cytoplasm of Eukaryotes – Nonmembranous Organelles • Ribosomes • Cytoskeleton • Centrioles and Centrosome Ribosomes • Eukaryotic cells have two types of ribosomes • 80S – Composed of 60S and 40S subunits – Membrane-bound Attached to ER – Free In cytoplasm • 70S – In chloroplasts and mitochondria Cytoskeleton • Extensive • Functions – Provides basic shape – Anchor organelles – Cytoplasmic streaming and movement of organelles – Cell contraction – Movement during endocytosis – Amoeboid action (pseudopodia) • Made up of microtubules, microfilaments, and intermediate filaments Centrioles and Centrosome • Centrioles play a role in mitosis, cytokinesis, and in formation of flagella and cilia • Centrioles composed of “9 + 0” arrangement of microtubules • Centrosome – region of cytoplasm where centrioles are found Cytoplasm of Eukaryotes – Membranous Organelles • • • • Nucleus Endoplasmic Reticulum Golgi Body Lysosomes, Peroxisomes, Vacuoles, and Vesicles • Mitochondria • Chloroplasts Nucleus • • • • Often largest organelle in cell Contains most of the cell’s DNA Semi-liquid portion called nucleoplasm One or more nucleoli – RNA synthesized • Chromatin – DNA associated with histones • Double membrane bound – two phospholipid bilayers – nuclear envelope • Nuclear envelope contains nuclear pores Nucleus Endoplasmic Reticulum • Continuous with the nuclear envelope • Netlike arrangement of hollow tubules • Functions – Protein modification – As transport system • Two forms – Smooth endoplasmic reticulum (SER) – plays role in lipid synthesis – Rough endoplasmic reticulum (RER) – ribosomes attached to its outer surface; protein modification Rough and Smooth Endoplasmic Reticulum Figure 3.32 Golgi Body • Receives, processes, and packages large molecules for export from cell • Protein modification and trafficking • Composed of flattened hollow sacs surrounded by phospholipid bilayer Lysosomes, Peroxisomes, Vacuoles, and Vesicles • Vacuoles – store chemicals within cells – Vesicles – transport chemicals within cells • Lysosomes contain catabolic enzymes • Peroxisomes contain enzymes that degrade poisonous wastes Mitochondria • Powerhouse of the cell – Produce most of cell’s ATP • Double membrane bound • Interior matrix contains – 70S ribosomes – circular molecule of DNA Chloroplasts • Used by algae and plants for photosynthesis • Double membrane bound • Contain – 70S ribosomes – DNA Prokaryote • Simple structure • No nucleus • Small; ~1.0 µm in diameter • One circular chromosome, not in a membrane • No histones • No membrane bound organelles • Peptidoglycan cell walls • Binary fission • Comprised of bacteria and archaea Eukaryote • Complex Structure • Nucleus • Larger; 10-100 µm in diameter • Paired chromosomes, in nuclear membrane • Histones • Organelles • Polysaccharide cell walls • Mitotic spindle • Comprised of algae, protozoa, fungi, animals, and plants Endosymbiotic Theory • Eukaryotes formed from phagocytosis of small aerobic prokaryotes – lost ability to exist independently – Retained portion of DNA, ribosomes, and cytoplasmic membranes – Larger cell became dependent on for aerobic ATP production – Aerobic prokaryotes evolved into mitochondria – Similar scenario for origin of chloroplasts • Not universally accepted Endosymbiotic Theory Figure 10.2 Prokaryotic membranes