Prokaryotic Cells Characteristics PDF

Characteristics of Prokaryotic and Eukaryotic Cells Characteristics of Prokaryotic and Eukaryotic Cells Basic Cell Types Prokaryotic Cells Eukaryotic Cells Evolution of Endosymbiosis The Movement by Substances Across Membranes  Basic Cell Types Pro...

Characteristics of Prokaryotic and Eukaryotic Cells Characteristics of Prokaryotic and Eukaryotic Cells Basic Cell Types Prokaryotic Cells Eukaryotic Cells Evolution of Endosymbiosis The Movement by Substances Across Membranes  Basic Cell Types Prokaryote: single-celled organisms, and all are bacteria. Eukaryote: single-celled or multi- cellular organisms Pro = before Eu = true Karyon = nucleus  Similarities: Plasma membrane, DNA and cell wall (plant cells) Differences: 1. Eukaryotic DNA is in a nucleus surrounded by a nuclear membrane 2. Prokaryotic DNA is in a nuclear region not surrounded by a membrane  Table 4.1:Similarities and Differences Between Prokaryotic/Eukaryotic Cells Prokaryotic cells have a single circular chromosome; Eukaryotic cells have paired chromosomes Prokaryotic cells lack histone proteins; Eukaryotic cells have histone proteins Prokaryotic cell wall has peptidoglycan; plant and fungal cells have both cellulose and chitin  Domains A relatively new concept in biological classification, domain is the highest category Three domains: 1. Archaea (ancient) 2. Bacteria (eubacteria) 3. Eukarya  Size, Shape and Arrangement Prokaryotes are among the smallest of all organisms Prokaryotes range from 0.5 – 2.0 µm in diameter and from 1.0 – 60 µm in length Exception: 1991- Epulopiscium fishelsoni is a bacterial symbiont of sturgeon fish (80 µm in diameter and 600 µm in length THE MOST COMMON BACTERIAL SHAPES  Arrangements of Bacteria 1. Cocci in pairs (diplococci): Neisseria sp. 2. Cocci in chains (streptococci): Streptococcus sp. 3. Rods in chains: Lactobacillus sp. 4. Cocci in clusters: Staphylococcus sp. Neisseria (22,578X) Streptococcus (9605X) Staphylococcus (5,400X) Bacillus megaterum (10,000X)  An Overview of Structure Structurally, bacterial cells consist of the following: 1. Cell membrane, usually surrounded by a cell wall 2. Internal cytoplasm with ribosomes, nuclear region, and in some cases granules and/or vesicles 3. Capsules, flagella, and pili (external) TYPICAL PROKARYOTIC CELL  The Cell Wall Lies outside the cell membrane in nearly all bacteria Two important functions: 1. Maintains the characteristic shape 2. Prevents the cell from bursting when fluids flow into the cell by osmosis  Components of Bacterial Cell Walls Peptidoglycan (murein): The single most important component This polymer is made up of two alternating sugar units: 1. N-acetylglucosamine (NAG) 2. N-acetylmuramic acid (NAM) The sugars are joined by short peptide chains that consist of four amino acids (tetrapeptides) PEPTIDOGLYCAN LAYER  Teichoic Acid An additional component found in cell walls of gram-positive bacteria Consists of glycerol, phosphates, and ribitol (sugar alcohol) This polymer extends beyond the rest of the cell wall Two functions: 1. Attachment site for bacteriophages 2. Passageway for movement of ions in/out of cell  Outer Membrane (OM) A bilayer membrane found in gram- negative bacteria Forms the outermost layer of the cell wall; is attached to the peptidoglycan by a continuous layer of lipoprotein molecules Proteins called porins form channels through the OM OM has surface antigens and receptors  Lipopolysaccharide (LPS) An important component of the OM Also called endotoxin; used to ID gram- negative bacteria Released when the cell walls of bacteria are broken down Consists of polysaccharides and Lipid A LIPOPOLYSACCHARIDE  Periplasmic Space The area between the cytoplasmic membrane and the plasma membrane in gram-negative bacteria Active area of cell metabolism Contains the cell wall, digestive enzymes and transport proteins Gram-positive bacteria lack both an OM and a periplasmic space  Distinguishing Bacteria by Cell Walls Gram-positive Bacteria have a relatively thick layer of peptidoglycan (60-90%) Gram-negative Bacteria have a more complex cell wall with a thin layer of peptidoglycan (10-20%) Acid-fast Bacteria is thick, like that of gram- positive bacteria, but has much less peptidoglycan and about 60% lipid BACTERIAL CELL WALL  Acid-Fast Bacteria Found in bacteria that belong to the genus, Mycobacterium sp. Cell wall is mainly composed of lipid Lipid component is mycolic acid Acid-fast bacteria stain gram- positive Controlling Bacteria by Damaging Cell Walls The antibiotic penicillin blocks the final stages of peptidoglycan synthesis The enzyme lysozyme, found in tears and other human body secretions, digests peptidoglycan  Wall-Deficient Organisms Bacteria that belong to the genus Mycoplasma have no cell walls They are protected from osmotic swelling and bursting by a strengthened cell membrane that contains sterols Wall deficient strains are called L-forms The Basic Structural Component of the Membrane: Phospholipid Molecule The Fluid-Mosaic Model of the Membrane Structure  Internal Structure Bacterial cells typically contain (in their cytoplasm): 1. Ribosomes 2. Nucleoid region 3. Vacuoles 4. Certain bacteria sometimes contain endospores  Ribosomes Consist of ribonucleic acid and protein; serve as sites of protein synthesis Abundant in the cytoplasm of bacteria Often grouped in long chains called polyribosomes 70S in bacteria; 80S in eukaryotes Streptomycin & Erythromycin bind specifically to 70S ribosomes and disrupt bacterial protein synthesis A Centrifuge  Nuclear Region (Nucleoid) This centrally located nuclear region consists mainly of DNA, but also contains RNA and protein DNA: Usually one large, circular chromosome Vibrio cholerae: Two chromosomes, one large and one small Plasmids: Extrachromosomal pieces of smaller, circular DNA BACTERIAL NUCLEAR REGION  Internal Membrane Systems Photosynthetic bacteria and cyanobacteria contain internal membrane systems Referred to as chromatophores (Fig. 4.10) Derived from the cell membrane and contain the photosynthetic pigments Nitrifying bacteria also have internal membranes Internal Membrane Systems (Chromatophores)  Inclusions Within the bacterial cytoplasm are a variety of small bodies: 1. Granules: Not membrane bound and contain densely compacted substances (glycogen or polyphosphate) 2. Vesicles: Specialized membrane- enclosed structures that contain gas or poly-B-hydroxybutyrate (lipid)  Endospores A specialized resting structure found in bacteria such as Bacillus sp. and Clostridium sp. Helps the bacterial cell survive when conditions become unfavorable Highly resistant to heat, drying, acids, bases, certain disinfectants and radiation  External Structure Many bacteria have structures that extend beyond or surround the cell wall 1. Flagella and pili extend from the cell membrane through the cell wall and beyond 2. Capsules and slime layers surround the cell wall  Arrangements of Bacterial Flagella 1. Monotrichous: Bacteria with a single polar flagellum located at one end (pole) 2. Amphitrichous: Bacteria with two flagella, one at each end 3. Peritrichous: Bacteria with flagella all over the surface 4. Atrichous: Bacteria without flagella 5. Cocci shaped bacteria rarely have flagella Polar, monotrichous flagellum Pseudomonas (3,300X)  Polar, amphitrichous flagellum Spirillum (694X) Lophotrichous flagella  Peritrichous flagella Salmonella (1200X)  Structure of Two Different Bacterial Flagella Gram-negative bacterium Gram-positive bacterium ELECTRON MICROGRAPH  Chemotaxis Sometimes bacteria move toward or away from substances in their environment by this nonrandom process 1. Positive chemotaxis: net result is movement towards the attractant (nutrients) 2. Negative chemotaxis: net result is movement away from the repellent CHEMOTAXIS  Pili Pilus (singular) Tiny, hollow projections Used to attach bacteria to surfaces Not involved in movement 1. Long conjugation pili (F-pili) 2. Short attachment pili (fimbriae) E. coli (14,300X)  Glycocalyx Used to refer to all polysaccharide/polypeptide-containing substances found external to the cell wall: 1. Capsules 2. Slime Layers 3. All bacteria have at least a thin slime layer  Capsule Protective structure outside the cell wall of the organism that secretes it Only certain bacteria are capable of forming capsules Chemical composition of each capsule is unique to the strain of bacteria that secreted it Encapsulated bacteria are able to evade host defense mechanisms (phagocytosis)  Slime Layer Less tightly bound to the cell wall and is usually thinner than a capsule Protects the cell against drying, traps nutrients and binds cells together (biofilm) Slime Layer: Bacteria growing on tooth enamel A Generalized Eukaryotic Cell Mitosis and Meiosis Compared Mitochondria TEM of Mitochondrion in Longitudinal Section Prokaryotic and Eukaryotic Flagella Compared  The Ciliated Protozoan Oxytricha The Stroke-and-Recovery Motion of a Cilium Cilia on an Organism Move in a Synchronized Fashion, Creating a Wave that Propels the Organism Forward Pseudopodia Amoeba (132X) DNA filaments inside the mitochondrion of a frog cell  Movement of Substances Across Membranes Passive Transport: Cell expends no energy to move substances down a concentration gradient (high to low concentration) 1. Simple Diffusion 2. Facilitated Diffusion 3. Osmosis Active Transport: Cell expends energy from ATP, enabling it to transport substances against a concentration gradient Simple Diffusion: The random movements of molecules cause them to spread out (diffuse) from an area of high concentration to area of low concentration Facilitated Diffusion: Carrier protein molecules aid in the movement of substances through cell membrane from high to low concentration Osmosis: The diffusion of water from an area of high water concentration to an area of low water concentration Experiments that examine the effects of tonicity on osmosis Active Transport: Carrier Protein molecules aid in movement of molecules against a concentration gradient  Endocytosis and Exocytosis Eukaryotic cells move substances by forming membrane-enclosed vesicles 1. Endocytosis: Form by invagination (poking in) and surrounding substances from outside the cell 2. Exocytosis: Vesicles inside the cell fuse with the plasma membrane and extrude contents from the cell