Chapter 3: Cell Structure and FunctionWhy Is This Important?- All living things are composed of living cells- In order to understand disease and its treatment, we must understand cell structure and how cells liveProcesses of LifeProkaryotic and Eukaryotic Cells: An Overview- Cells are living entities, surrounded by a membrane, that are capable of growing, reproducing, responded, and metabolizing- The smallest living things are single-celled microorganisms- There are many different kinds of cells, but all cells may be described as either prokaryotes or eukaryotesProkaryotes- Consist of the domain arachaea and domain bacteria- A typical prokaryote doesn’t 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- Typically 1.0 um in diameter or smaller- Have DNA but aren’t organized into a structure- Archaea and bacteria are very differentEukaryotes- Have a membrane called a nuclear envelope surrounded their DNA, forming anucleuso Domain Eukarya- Defined boundarieso True membrane bound nucleus - Have numerous other internal membrane-bound organelles- Are larger, 10-100 um in diameter- Have more complex structure- Composed of algae, protozoa, fungi, animals, and plantsExternal Structures of Bacterial Cells- Glycocalyces- Flagella - Fimbriae and pili- Doesn’t have to have all of themGlycocalyces- Gelatinous, sticky substance surrounding the outside of the cell - Composed of polysaccharides, polypeptides, or both- Protect cells from drying- All bacteria have a glycocalyx - Bacteria is composed of about 90% water- Two types (have one or the other, but not both)o Capsule Composed of organized repeating units of organic chemicals (sugar) Makes bacteria slippery Firmly attached to cell surface Composition may be similar to chemicals found in the human body preventing bacteria from being recognized as foreign- Hard to determine where bacteria is from due to similar compositiono Virulence factor: structures and substance – easyto cause infection and disease in humanso Slime layer Loosely attached to cell surface (water soluble) Sticky layer that allows prokaryotes to attach to surfaces as biofilms- Plaque on tootho Bacteria adhered to surface of teeth Less organized, easier to remove, breaks in layersFlagella- Used for movemento Towards nutrientso Virulence factor – ability to move- 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 andpropel the cell through its environment- Not all bacteria have flagella- Some can produce them at some timesFlagella Structure- Composed of filament, hook, and basal body- Filamento Long, hollow shaft that extends out into the environmento Composed of flagellin - proteino Deposited in a clockwise helix at the lengthening tipo Not covered by a membrane- Hooko Base of filament inserts into hook- Basal bodyo 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 (from the hook)Gram + : 2 rings in basal body: only in cytoplasmic membraneGram - : 4 rings in basal body with more anchorsFlagella Arrangementa) Completely covers surfaceb) Just one end c) Tufteda) Wraps around cytoplasmic membraneFlagella Function- Rotation propels bacterium through environment- Flow of hydrogen ions 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)o Runs (counterclockwise) – one direction, longero Tumbles (clockwise) – sensing their environment, less frequent, switching directions- Taxis: when bacteria moves- Chemotaxis: towards/away from chemicals- Phototaxis: towards/away from light- + : towards something it wants- - : away from something it doesn’t wantFimbriae and Pili (not interchangeable)- Rodlike proteinaceous extensions (from plasma membrane)- Fimbriae are sticky, bristlelike projections composed of protein with adhesivetipso Used by bacteria to adhere to one another and to substances in the environment May use fimbriae to move across a surfaceo May be hundreds per cell and are usually shorter than flagella o Some carry enzymes that cause soluble, toxic metal ions to change into insoluble, nontoxic formso Serve an important function in biofilms by conducting electrical signals among cells in a biofilm Biofilm: adhesive to solid surface in liquid environmento Fimbriae Ends are sticky Used to adhere Can completely go around the cell- Pilus is a special type of fimbriao Longer than fimbriae but shorter than flagella o Bacteria typically only have one or a few per cello Mediate the transfer of DNA from one cell to another (conjugation)o Also known as conjugation pillusBacterial Cell Walls- Animals don’t have 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- Some antibiotics – all bacterial infections – have target toxicity that target (bacteria) cell walls since animals don’t have them- Cell wall is composed of peptidoglycan (complex polysaccharide)- Peptidoglycan is composed of sugars, NAG and NAM - Chains of NAG and NAM (alternating) are attached to other chains by tetrapeptide (4 amino acids-adds additional stability) cross bridgeso Bridges may be covalently bonded to one anothero 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-negativeo Distinguished by the use of the Gram stain procedureGram-Positive Bacterial Cell Walls- Relatively thick layer of peptidoglycan- Contain unique chemicals called teichoic acidso Some covalently linked to lipids, forming lipoteirchoic acids that anchor peptidoglycan to the cytoplasmic membrane- Retain crystal violet dye in Gram staining procedure so they appear