MICROBIOLOGY THIRD EDITION WITH DISEASES BY BODY SYSTEM SECOND Chapter 3 Cell Structure and Function Why is this important All living things are composed of cells In order to understand disease and its treatment we must understand cell structure and how cells live Processes of Life Prokaryotic and Eukaryotic Cells An Overview Cells are living entities surrounded by a membrane that are capable of growing reproducing responding and metabolizing All cells may be described as either prokaryotes or eukaryotes Prokaryotic and Eukaryotic Cells An Overview Prokaryotes Consist of Domain Archaea and Domain Bacteria A typical prokaryote does not have a nucleus Typically lack various types of internal structures bound with phospholipid membranes that are present in eukaryotic cells Bacteria and archaea differ fundamentally from one another Normally 1 0 m in diameter or smaller Prokaryotic and Eukaryotic Cells An Overview Prokaryotic and Eukaryotic Cells An Overview Eukaryotes Have membrane surrounding their DNA have a nucleus Domain Eukarya Have internal membrane bound organelles Are larger 10 100 m in diameter Have more complex structure Composed of algae protozoa fungi animals and plants Prokaryotic and Eukaryotic Cells An Overview External Structures of Bacterial Cells Glycocalyces Flagella Fimbriae and Pili Glycocalyces Gelatinous sticky substance surrounding the outside of the cell Composed of polysaccharides polypeptides or both Two Types Capsule Composed of organized repeating units of organic chemicals Firmly attached to cell surface May mediate adherence of cells to surfaces Protects cells from engulfment and can protect some cells from drying Slime layer Loosely attached to cell surface water soluble Provides protection from antibiotics and desiccation Sticky layer that allows prokaryotes to attach to surfaces Glycocalyces Glycocalyces Glycocalyces play an important role in the ability of pathogenic bacteria to survive and to cause disease Slime layers are often sticky and provide a means by which bacteria attach to surfaces Chemicals in many capsules are similar to those normally found in the body they may prevent bacteria from being recognized or devoured by defensive cells in the host Glycocalyces Copyright Gary E Kaiser Flagella Cell s motility may enable it to flee from a harmful environment or move towards a favorable one The most notable structures responsible for bacterial movement are flagella Long structures that extend beyond the surface of a cell and its glycocalyx and propel the cell through its environment Not all bacteria have flagella Flagella Structure Composed of filament hook and basal body Filament Long hollow shaft that extends out into the environment Composed of flagellin Deposited in a clockwise helix at the lengthening tip Not covered by a membrane Hook Base of filament inserts into hook Basal body Anchors filament and hook to cell wall and cytoplasmic membrane by a rod and a series of either two or four rings of integral proteins Hook and basal body enable the filament to rotate 360 Flagella Structure Flagella Structure Flagellar Structure Flagella Arrangement Flagella Function Rotation propels bacterium through environment Flow of hydrogen ions or of sodium ions through the cytoplasmic membrane near the basal body powers the rotation Flagella rotate at more than 100 000 rpm Rotation reversible can be clockwise or counterclockwise Bacteria move in response to stimuli taxis Runs counterclockwise Tumbles clockwise Flagella Function Flagella Movement Fimbriae and Pili Rodlike proteinaceous extensions Fimbriae are sticky bristlelike projections composed of protein with adhesive tips Used by bacteria to adhere to one another and to substances in environment May be hundreds per cell and are usually shorter than flagella May use fimbriae to move across a substrate or toward another bacterium via a process similar to pulling an object with a rope Serve an important function in biofilms because some fimbriae conduct electrical signals among cells in a biofilm Fimbriae and Pili Pili are a special type of fimbria Longer than fimbriae but shorter than flagella Bacteria typically only have one or a few per cell Mediate the transfer of DNA from one cell to another conjugation Also known as conjugation pili or sex pili Fimbriae and Pili Fimbriae and Pili Copyright Gary E Kaiser Fimbriae and Pili Bacterial Cell Walls Provides structure and shape and protects cell from osmotic forces Assist some cells in attaching to other cells or in resisting antimicrobial drugs Not present in animal cells so can target cell wall of bacteria with antibiotics Give bacterial cells characteristic shapes cocci rods spirilla Bacterial Cell Walls Cell wall is composed of peptidoglycan complex polysaccharide Peptidoglycan is 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 Scientists describe two basic types of bacterial cell walls Gram positive and Gram negative Distinguished by the use of the Gram stain procedure Bacterial Cell Walls Gram Positive Bacterial Cell Walls Relatively thick layer of peptidoglycan Contain unique chemicals called teichoic acids Some covalently linked to lipids forming lipoteichoic acids that anchor peptidoglycan to cytoplasmic membrane Retain crystal violet dye in Gram staining procedure so appear purple Acid fast bacteria have walls with up to 60 mycolic acid a waxy lipid Helps these organisms survive desiccation Gram Positive Cell Walls Gram Negative Cell Walls Have only a thin layer of peptidoglycan but have an asymmetric bilayer membrane outside this layer outer membrane Appear pink following Gram staining procedure Outer Membrane Inner leaflet composed of phospholipids and proteins Outer leaflet composed of lipopolysaccharide LPS Porins form channels through both leaflets allowing for the movement of glucose and other monosaccharide across the membrane Acts as a protective permeability barrier Impermeable to large molecules and hydrophobic compounds such as antimicrobial compounds Structure of LPS Lipid A endotoxin Released from dead cells when outer membrane disintegrates Can be released when antimicrobial drugs kill bacteria May trigger fever vasodilation inflammation shock and blood clotting O side chain Core polysaccharide Gram Negative Cell Walls Periplasmic Space In Gram negatives