Chapter 4 Characteristics of prokaryotic and Eukaryotic cells Basic cells Type Both prokaryotic and eukaryotic cells have membranes that define the bounds of the living cell, and both contain genetic information stored in DNA. Prokaryotic cells differ from eukaryotic cells in that they 1. lack a defined nucleus 2. lack membrane-bound organells (except for a few membrane-covered bodies in certain type of prokaryotes). 3. Peptidoglycan is found in prokaryotic cells only. Three Domains - Bacteria, Archaea and Eukarya (Protista, Fungi, Plantae and Animalia) - Bacteria and Archaea are prokaryotic , Eukarya is eukaryotic - “bacteria” applies to Bacteria and Archaea Six Kindoms: Bacteria, Archaea, Protista, Fungi, Plantae and Animalia) Size, Shape, and Arrangement Prokaryotes are the smallest living organisms, 0.5 to 2 microns (however some spiral ones are much bigger; some cyanobacteria can be as long as 60 microns). Shape: Coccus (cocci - spherical), Bacillus (bacilli - rod-shaped), Spirillum (spirilli - rigid wavy-shaped), Vibrio (vibrios - comma-shaped), and Spirochete (spirochetes - cockscrew-shaped), Square bacteria – discovered on the shores of the Red sea. Note pleomorphism in some bacteria – a variety of form even within a single species; in aging cultures this may be also be observed. Arrangement: Diplo – 2 in pair Staphylo - grapelike clusters Strepto - long chains Tetrad – four cells in a cube Sarcinae – 8 in cluster An Overview of Structures - cell membrane, usually surround by a cell wall and sometimes by an additional outer layer - cytoplasm with ribosomes, nuclear region, granules and/or vesicles - external structures, such as capsules, flagella and pili. Write the name of bacteria in Italic.ex. E. coli. The Cell Wall - Complex, semirigid, maintain shape - maintains osmotic pressure by inhibiting lysis - Transport (pores) - protect COMPONENTES OF CELL WALLS Peptidoglycan - murein - N-actetylglucosamine alternates with N-acetylmuramic acid ( 2 polysaccharides) as backbone then joined by peptide chains with tetrapeptides. Outer Membrane - found primarily in Gram-negative bacteria - bilayer membrane, forms the outmost layer of cell wall, attached to the peptidoglycan – protects against certain antibodies (penicillin), lysozyme. Lipopolysaccharide (LPS) – diagnostic importance (salmonella sero variance) – also called endotoxin – important part of outer membrane – not released until the cell walls of dead bacteria are broken down – consists of polysaccharide and lipid A – polysaccharides are used for the identification of Gram-negative – Lipid A is responsible for the toxic properties, cause septic shock Periplasmic space – Between the cell wall and cell membrane – contains a high concentration of degrading enzymes and transport proteins. Distinguishing Bacteria by Cell Walls - certain properties of cell walls produce different staining reactions - Gram-positive, Gram-negative and acid fast bacteria After enzyme digestion - Gram-positive bacteria become protoplast – cell with cell membrane , no cell wall. - Gram-negative bacteria become spheroplast – cell with cell membrane and most of outer membrane Gram Positive Gram negetive Thick layer of peptidoglycan Thin layer of peptidoglycan Teichoic acid No teichoic acid No Lipopolysaccharide Lipopolysaccharide No Periplasmic membrane Periplasmic membrane No Outer membrane Outer membrane High sensitivity to penicillin Low sensitivity to penicillin Low sensitivity to streptomycin High sensitivity to streptomycin Gram-negative bacteria fail to retain the crystal violet-iodine dye during the decolorizing procedure due to the thin layer of peptidoglycan and many liposaccharides. Penicillin blocks the final stages of peptidoglycan synthesis. Lysozyme, found in tears and other human body fluids can digests peptidoglycan. Acid –Fasts bacteria - Mycobacterium tuberculosis causes tuberculosis - can be diagnosed by acid-fast stain, - cell walls – unique waxy layer made of mycolic acid - 60% lipids - Grow slow, lipid impede entry of nutrients - Gram positive - Skin test of an induration of 15 mm in diameter is positive. - Isoniazid (INH) daily for 9 months to treat. which inhibits synthesis of components of the waxy layer. . Wall-Deficient Organisms Mycoplasma - filterable - no cell wall, no outer membrane - plasma membrane strengthened with sterols to maintain shape. - Extreme pleomorphism - Form colonies look like egg fried sunny-side up. L-forms -- suddenly lose their ability to form cell walls - Gram positive or gram-negative bacteria that do not make a cell wall. - occur naturally or be caused by chemical treatment - when treatment is discontinued, the L-forms can convert to walled forms and regrow - Mycobacterium paratuberculosis with Crohn’s disease, a chronic disorder of the intestine CELL MEMBRANE - Unit membrane, have the same general structure as other cell membrane, - Phospholipids bilayer, hydrophilic head (phosphate), hydrophobic tail (fatty acid - fluid-mosaic structure with mobile proteins moved like fluid, and proteins embedded in a mosaic pattern. - No sterol. Internal Structures Cytoplasm - semifluid substance inside the cell membrane, - 80% water, contains organic materials, ribosomes , cytoplasmic inclusions. - Ribosomes - consist of RNA and protein - sites for protein synthesis - grouped in long chains, polyribosomes - size measured by sedimentation rate, Svedberg (S) unit - bacteria: 70S, streptomucin and erythromycin bind to 70S ribosomes, disrupt protein synthesis - antibiotics do not affect 80S in Eukaryotic cells, they kill bacteria without harming host cells, subunits : 30S & 50S - Nuclear Region (Nucleoid) - one circular double strands DNA (20% of cell volume) - small circular DNA called plasmids, encode specialized, nonessential functions. - One chromosome Internal membrane Systems - in photosynthetic bacteria and cyanobacteria - chromatophores, derived from cell membrane - capture sunlight energy for synthesis of sugars Inclusions - granules, not bounded by membrane, store glycogen - vesicles (have membrane), filled with iron compounds (magnetosomes) - volutin, or metachromatic granules, polyphosphate granules, display metachromasia – exhibit different intensities of color Endopores - Dormant structures (resting cells) - found in three Gram positive genera: Clostridium, Bacillus and Sporosarcina - formed in response to adverse condition. They are durable, have thick walls, survive extreme heat, toxic chemicals, radiation. - Sporulation, or endospore formation - germination, when environment conditions are favorable - help bacteria survive is not a means of reproduction - Fungus produces many spores, which help the organism survive and provide a means of reproduction - The core of an endopore contain living material and is surrounded by a cortex, spore coat, and exosporium( a delicate thin layer), DNA, ribosomes, large amounts of dipicolinic acid, calcium ions. External Structure to the Cell Wall Falgella – monotrichous (one), lophotrichous (with tuft at one end or both ends), amphitrichous ( two, one at each ends), peritrichous (all over), atrichous (no flahella) – Parts of flagellum – filament, hook, and basal body (anchors flagellum to cell wall/plasma membrane) – Flagellin protein organized into hollow cylinders (9 + 2 pattern) motility Chemotaxis movement toward attractions and away from repellents Phototaxis movement toward or away from light Axial filament - In spirochetes - bundles of fibrils that arise at the ends of the cell beneath the outer sheath and spiral around the cell - rotation propels spirochetes in a spiral motion Pili – hairlike appendages (for attachment rather than motility) – long conjugation pili ,sex pili, furnish a pathway for DNA transfer - conjugation – short attachment fimbriae, allow cell to attach to surfaces - hemagglutination – cause red blood cells to clump - in Neisseria gonorrhoeae, strains with pili are highly infectious, attach to epithelial cells of urogential system, also attach to sperm, can spread to next individual - some bacteria form a thin layer at the air-water interface of a broth culture called pellicle – many bacteria adhere to the surface by attachment pili, near air, where the oxygen concentration is greatest. Glycocalyx – viscous gelatinous polymer (polysaccharides and small proteins) – makes a thick capsule or thin slime layer. – Function (capsules) – bacterial virulence, protect against phagocytes, slows dehydration – (slime layer) – loosely arranged polysaccharide, protect the cell against drying, help trap nutrients, and bind cells together, as in dental plaque, trap nutrients. ARCHAEON CELL - Archaeon cell walls are composed of either protein or a peptidoglycan called pseudomurein, not found in any other living things. Some archaea do not have cell walls. - The bonds in the cytoplasmic membrane of archaea cells enter linkages, which are stronger than the ester bonds fond in bacteria.,hydrocarbon molecules are joined to glycerol by ether linkage instead ester linkage. EUKARYOTIC CELLS An Overview of Structure Eukaryotic cells, which are generally larger and more complex than prokaryotic cells are the basic structural unit of microscopic and macroscopic organisms of the kingdoms Protista, Plantae, Fungi, and Animalia. The Plasma Membarne Plasma membranes of eukaryotic cells are almost identical to those of prokaryotic cells, except that they contains sterol. The function of eukarotic plasma membranes, however, is limited primarily to regulating movement of substances into and out of cells. Internal Structure Eukaryotic cells are characterized by the presence of a membrane-enclosed cell nucleus, with a nuclear envelope, nucleoplasm, nucleoli (stor RNA), and chromosomes (typically paired) that contain DNA and proteins called histones. chromatin (uncoiled chromosomes, fine threads) In body cell division by mitosis, each cell receives one of each chromosomes found in parent cells. In sex cell division by meiosis, each cell receives one chromosomes from each pair - haploid, and can become gametes ( in sexual reproduction, two gametes form a diploid zygote)or spores ( dormant or by mitosis as haploid vegetative cells) Mitochondria, the powerhouse of eukaryotic cells, carry out the oxidative reactions that capture energy in ATP.Has outer and inner membrane and matrix. Inner membrane folded to form cristae, embedded in matrix. Photosynthetic cells contain chloroplasts, which capture energy from light. Thylakoids: inner membrane of a choloplast is arranged in stacks. Cholorophyll is embedded in thylakoids. Eukaryotic ribosomes (80S)are larger than those of prokaryotes (70S) and can be free or attached to endoplasmic reticulum. Free ribosomes make protein to be used in the cell; those that are attached to endoplasmic reticulum make proteins to be secreted. The endoplasmic reticulum is an extensive membrane network. Without ribosomes (smooth ER), the endoplasmic reticulum synthesize lipids; when combined with ribosomes (rough ER), it produces protein. The Golgi apparatus is a set of stacked membranes that are receive, modify, and package proteins into secretory vesicles. Lysosomes, in animal cells, are organelles that contain digestive enzymes, which destroy dead cells and digest contents of vacuoles. Peroxisomes are membrane-enclosed organelles that convert peroxides to water and oxygen and sometimes oxidize amino acids and fats. Vacuoles contain various stored substances and materials engulfed by phagocytosis. The cytoskeleton is a network of microfilaments and microtubles that support and give rigidity to cells and provide for cell movements. External Structure Eukaryotic cells do not have pili or axial filaments, but some have flagella and smaller versions called cilia that also function for locomotion. Most external components of eukaryotic cells are concerned with movement. Eukaryotic flagella are composed of microtubules; sliding of proteins at their bases causes them to move. Cilia are shorter and more than flagella and beat in coordinated waves, same structure of microtubule. Pseudopodia are projections into which cytoplasm flows, causing a creeping movement. Eukaryotic cells of the plant and fungi kingdoms have cell walls, as do the algal protests. Cell Walls - do not contain peptidoglycan like bacteria - algal cell walls consist cellulose - fungi consist of cellulose, chitin or both - some protozoa have a pellicle, which functions much as a cell wall, though it is more flexible and skin-like EVOLUTION BY ENDOSYMBIOSIS The endosymbiont theory holds that organelles of eukaryotic cells arose from prokaryotes that had been engulfed and survived to develop a symbiotic relationship by living inside the larger cell. Mitochondria, chloroplasts, flagella, and microtubules are believed to have originated from endosymbiont prokaryotes. Many examples exist of modern prokaryotes living endosymbiotically inside eukaryotes. THE MOVEMENT OF SUBSTANCES ACROSS MEMBRANES Simple diffusion Simple diffusion results from the molecular kinetic energy and random movement of particles. The role of diffusion in living cells depends on the size of particles, nature of membranes, and distances substances must move inside cells. Facilitated Diffusion Facilitated diffusion uses protein carrier molecules or protein-lined pores in membranes in moving ions or molecules from high to low concentrations. Osmosis Osmosis is the net movement of water molecules through a selective permeable membrane from a region of higher concentration of water to a region of lower concentration.The osmotic pressure of a solution is the pressurerequired to prevent such a flow. Active transport Active processes that move substances across membranes generally result in movement from regions of lower concentration of the substances to regions of higher concentration and require the cell to expand energy. Active transport requires a protein carrier molecule in a membrane, a siurce of ATP, and an enzyme that releases energy from ATP. Active transport is important in cell functions because it allows cells to take up substances that are in low concentration in the environment and to concentrate those substances within the cell. Endocytosis and Exocytosis Endocytosis and exocytosis , which occur only in eukaryotic cells, involve formation of vesicles from fragments of plasma membrane and fusion of vesicles with the plasma membranes, respectively. In endocytosis the vesicles enters the cell, as in phagocytosis. In exocytosis the vesicle leaves the cell, as in secretion. Endocytosis and exocytosis are important because they allow the movement of relatively large quantities of materials across plasma membranes.