All cells can be placed into one of two categories: Prokaryotes : Bacteria: Archae: extreme environment

Eukaryotes: any organism with a fundamental cell type containing membrane-enclosed organelles

Protista: ameba Animalia Plantea Fungi

One circular chromosome, not in a membraneNo histonesNo organellesPeptidoglycan cell wallsBinary fissionProkaryoteEukaryotePaired chromosomes, in nuclear membraneHistonesOrganellesPolysaccharide cell wallsMitotic spindle

ArchaeaProkaryoticSingluar circular chromosomeUnique rRNA sequencesUnique Cell membrane lipidsNo peptidoglyc an in cell wallsOften live under extreme environmental conditions

Archaea

Average size: 0.2 -1.0 m 2 - 8 mBasic shapes:Procaryotes (Bacteria)

Procaryotes (Bacteria)

Size relationships among prokaryotes

Bacterial morphologies (1)

Bacterial morphologies (2)Staphylococcus aureus Escherichia coli Bacillus Anthracis Vibrio cholerae Treponema pallidum Streptococcus mutans

Bacterial Cell StructureAppendages - flagella, pili or fimbriaeSurface layers - capsule, cell wall, cell membraneCytoplasm - nuclear material, ribosome, mesosome, inclusions etc.Special structure - endospore

Appendages1. FlagellaSome rods and spiral form have this.a) function: motilityb) origin : cell membrane flagella attach to the cell by hook and basal body which consists of set(s) of rings and rods Gram - : 2 sets of ring and rods, L, P, S, M rings and rods e.g. E. coliGram + : S, M rings and rodse.g. B. megaterium

Structure of the flagellum

Rotation propels bacterium through environmentRotation can be clockwise or counterclockwise; reversibleBacteria move in response to stimuli (taxis)Runs movements of cell in single direction for some time due to counterclockwise flagellar rotation; increase with favorable stimuli (positive chemotaxis, positive phototaxis)Tumbles abrupt, random, changes in direction due to clockwise flagellar rotation; increase with unfavorable stimuli (negative chemotaxis, negative phototaxis)Flagella movement(3)

PositionMonotrichous

LophotrichousPeritrichous

2. Pili or Fimbriae Shorter than flagella and straighter , smaller. Only on some gram- bacteria.

Function: adhere. One of the invasive mechanism on bacteria. Some pathogens cause diseases due to this. If mutant (fimbriae) not virulent. Prevent phagocytosis. Serve an important function in biofilms

Long hollow tubules composed of pilinIt belongs to a class of protein Lectin which bond to cell surface polysaccharidLonger than fimbriae but shorter than flagellaBacteria typically only have one or two per cellJoin two bacterial cells and mediate the transfer of DNA from one cell to another (conjugation)Also known as conjugation pili or sex piliPili

CELL SURFACE LAYER1. Capsule or slime layerMany bacteria are able to secrete material that adheres to the bacterial cell but is actually external to the cell. Capsule: Composed of organized repeating units of organic chemicalsFirmly attached to cell surfaceProtects cells from drying outMay prevent bacteria from being recognized and destroyed by host

Slime layer:Loosely attached to cell surfaceWater solubleProtects cells from drying outSticky layer that allows prokaryotes to attach to surfaces

2. Cell WallProvides structure and shape and protects cell from osmotic forcesAssists some cells in attaching to other cells or in eluding antimicrobial drugsAnimal cells do not have; can target cell wall of bacteria with antibioticsBacteria and archaea have different cell wall chemistry

Most have cell wall composed of peptidoglycan; a few lack a cell wall entirelyPeptidoglycan composed of sugars, NAG, and NAMChains of NAG and NAM attached to other chains by tetrapeptide crossbridgesBridges may be covalently bonded to one anotherBridges may be held together by short connecting chains of amino acidsScientists describe two basic types of bacterial cell walls: gram-positive and gram-negative

Gram-Positive Cell WallRelatively thick layer of peptidoglycanContains unique polyalcohols called teichoic acidsSome covalently linked to lipids, forming lipoteichoic acids that anchor peptidoglycan to cell membraneRetains crystal violet dye in Gram staining procedure; appear purpleAcid-fast bacteria contain up to 60% mycolic acid; helps cells survive desiccation

Gram-Negative Cell WallsHave only a thin layer of peptidoglycanBilayer membrane outside the peptidoglycan contains phospholipids, proteins, and lipopolysaccharide (LPS) May be impediment to the treatment of diseaseFollowing Gram staining procedure, cells appear pink

LPSUnion of lipid with sugarAlso known as endotoxinLipid portion known as lipid ADead cells release lipid A when cell wall disintegratesMay trigger fever, vasodilation, inflammation, shock, and blood clottingCan be released when antimicrobial drugs kill bacteriaPeriplasmic SpaceLocated between outer membrane and cell membraneContains peptidoglycan and periplasmContains water, nutrients, and substances secreted by the cell, such as digestive enzymes and proteins involved in transport

Bacterial Cell WallsFigure 3.13a

Gram Positive Cell WallThick layer peptidoglycanTeichoic acid Lipoteichoic acid

Bacterial Cell Walls

Gram Negative Cell wall Outer Membrane LPS-lipopolysaccharide (Endotoxin) Porins Periplasm

Cell walls of bacteria(2)

3. Cell membraneReferred to as phospholipid bilayer; composed of lipids and associated proteinsApproximately half the membrane is composed of proteins that act as recognition proteins, enzymes, receptors, carriers, or channelsIntegral proteins Peripheral proteins Glycoproteins Fluid mosaic model describes current understanding of membrane structure

Phospholipid Bilayer of Cytoplasmic Membrane

Function:Controls passage of substances into and out of the cell; selectively permeableHarvests light energy in photosynthetic prokaryotes

Control of substrate across cell membraneNaturally impermeable to most substancesProteins allow substances to cross membraneOccurs by passive or active processesMaintains a concentration gradient and electrical gradientChemicals concentrated on one side of the membrane or the otherVoltage exists across the membrane

Functions of the cytoplasmic membrane(1)

Active TransportUtilizes permease proteins and expends ATPUniport Antiport Symport Group Translocation Substance chemically modified during transport

Transport proteins

Classes of membrane transporting systems(1)

Classes of membrane transporting systems(2)

4. Cytoplasm

Cytosol liquid portion of cytoplasmInclusions may include reserve deposits of chemicalsRibosomes sites of protein synthesisCytoskeleton plays a role in forming the cells basic shapeSome bacterial cells produce dormant form called endospore

Bacterial chromosomesa single large circular double stranded DNA no histone proteins. The only proteins associated with the bacterial chromosomes are the ones for DNA replication, transcription etc.

MesosomesA large invaginations of the plasma membrane, irregular in shape. a. increase in membrane surface, which may be useful as a site for enzyme activity in respiration and transport.b. may participate in cell replication by serving as a place of attachment for the bacterial chromosome.

InclusionsNot separate by a membrane but distinct.Granules of various kinds: * glycogen,*polyhydroxybutyric acid droplets (PHB) i.e. fat droplets* inorganic metaphosphate (metachromatic granules) - in general, starvation of cell for almost any nutrients leads to the formation of this to serve as an intracellular phosphate reservoir.

Special Structure

*EndosporesSpore former: sporobactobacilli and sporosarcinae - no medical importance. bacillus and clostridium have medical importance.

*Position: median, sub-terminal and terminal have small water, high calcium content and dipicolinic acid (calcium dipicolinate) extremely resistant to heat, UV, chemicals etc. may be due to many S containing A.A for disulfide groups.

Hardiest of all life forms For escape from unfavorable environmental conditions Germination = return to the vegetative state from the spore state NOT reproductive (1 cell forms 1 endospore which return to reform 1 cell)

Detailed stepsin endospore formation(1)

Detailed stepsin endospore formation(2)

Eucaryotes

Membranous OrganellesNucleusEndoplasmic reticulumGolgi bodyLysosomes, peroxisomes, vacuoles, and vesiclesMitochondriaChloroplasts

NucleusOften largest organelle in cellContains most of the cells DNASemiliquid portion called nucleoplasmOne or more nucleoli present in nucleoplasm; RNA synthesized in nucleoliNucleoplasm contains chromatin masses of DNA associated with histonesSurrounded by double membrane composed of two phospholipid bilayers nuclear envelopeNuclear envelope contains nuclear pores

Endoplasmic ReticulumNetlike arrangement of flattened, hollow tubules continuous with nuclear envelopeFunctions as transport systemTwo formsSmooth endoplasmic reticulum (SER) plays role in lipid synthesisRough endoplasmic reticulum (RER) ribosomes attached to its outer surface; transports proteins produced by ribosomes

Rough and Smooth Endoplasmic Reticulum

Golgi BodyReceives, processes, and packages large molecules for export from cellPackages molecules in secretory vesicles that fuse with cytoplasmic membraneComposed of flattened hollow sacs surrounded by phospholipid bilayer

Golgi BodyFigure 3.33

MitochondriaHave two membranes composed of phospholipid bilayerProduce most of cells ATPInterior matrix contains 70S ribosomes and circular molecule of DNA

ChloroplastsLight-harvesting structures found in photosynthetic eukaryotesHave two phospholipid bilayer membranes and DNAHave 70S ribosomes

Classification of Eukaryotic Organisms

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