Prokaryote Cell Structure & Function Lecture 5 Prokaryote Cell Structure & Function Cell Diagram: Mariana Ruiz, pub domain

Size of Living Things 1 m = 100 cm = 1,000mm = 1,000,000 µm = 1,000,000,000nm 1mm = 1000 µm = 1000000nm 1 µm = 1000nm Diagrams: http://www.cellsalive.com/howbig.htm

The Cellular Level of Organization Living things are constructed of cells. Living things may be unicellular or multicellular. Cell structure is diverse but all cells share common characteristics. Cells are small so they can exchange materials with their surroundings. Surface area relative to the volume decreases as size of cell increases. - limits the size of cells Cell Theory states: 1. All organisms are composed of one or more cells. 2. Cells are the basic unit of structure and function in organisms. 3. All cells come only from other cells. Cell Theory

Two basic types of cells Prokaryotic Cells (Prokaryotes) Eukaryotic Cells (Eukaryotes) Prokaryotic Eukaryotic Diagrams: Prokaryotic & Eukaryotic Cell, Mariana Ruiz

Prokaryotes Binary Fission Prokaryotes Almost always single-celled (except for prokaryote colonies). Always reproduces by means of binary fission. Does not have a cell nucleus or any other organelles within membranes. DNA travels openly around the cell. - All bacteria are prokaryotes. Diagrams: Prokaryotic Mariana Ruiz Binary Fission, JW Schmidt

Prokaryote Genetics - Antibiotic resistance Nucleoid Region of cytoplasm where chromosomal DNA is located. Usually a singular, circular chromosome Few or no proteins “naked DNA”; no introns Plasmid Small extra piece of chromosome/genetic material. 5 - 100 genes Not critical to everyday functions. Can provide genetic information to promote: - Antibiotic resistance - Virulence factors (molecules produced by pathogen that specifically influence host's function to allow the pathogen to thrive) - Promote conjugation (transfer of genetic material between bacteria through cell-to-cell contact) Nucleoid Plasmid STRUCTURE OF MICOBIAL CELLS

Prokaryotes Cytoplasm Also known as proto-plasm. Gel-like matrix of water, enzymes, nutrients, wastes, and gases and contains cell structures. Location of growth, metabolism, and replication. Granules Bacteria’s way of storing nutrients Staining of some granules aids in identification Cytoplasm Granules STRUCTURE OF MICOBIAL CELLS

Prokaryotes Ribosomes Found within cytoplasm or attached to plasma membrane. What are they made of? What do they do? Composed of a small (30S) subunit and a large (50S) subunit. Cell may contain thousands of ribosomes. Cytoskeleton Cellular "scaffolding" or "skeleton" within the cytoplasm. Major advance in prokaryotic cell biology in the last decade has been discovery of the prokaryotic cytoskeleton. Previously thought to be a feature only of eukaryotic cells. Eukaryotic Cells Ribosome Cytoskeleton Diagrams/Photos: Fluorescent Cell: NIH, Pub Domain

Prokaryotes - Plasma Membrane Separates the cell from its environment. Phospholipid molecules oriented so that hydrophilic phosphate heads directed outward and hydrophobic tails directed inward. Proteins embedded in two layers of lipids (lipid bilayer). Proteins allow substances to pass into and out of the cell. Water loving Water hating Semi Permiable Diagrams: Prokaryotic Cell, Mariana Ruiz Membrane: NIST

Prokaryotes – Cell Wall Peptidoglycan is a huge polymer of interlocking chains of identical peptidoglycan monomers. Backbone of peptidoglycan molecule composed of two derivatives of glucose: N-acetylglucosamine (NAG) N-acetlymuramic acid (NAM) NAG / NAM strands are connected by interpeptide bridges. Peptidoglycan - Rigid mechanical support - Freely permeable to solutes Image: Peptindoglycan Structure: NicolasGrandjean

Prokaryotes - Cell Wall From the peptidoglycan inwards all bacteria are very similar. Going further out, the bacterial world divides into two major classes (plus a couple of odd types). These are: Gram-positive Gram-negative Images: PHIL Public Health Image Library

Prokaryotes - Cell Wall: Gram-Negative & Gram-Positive Peptidoglycan makes up as much as 90% of the thick, compact cell wall. Gram-negative More chemically complex and thinner. Peptidoglycan only 5 – 20% of the cell wall. Peptidoglycan not outermost layer, between the plasma membrane and the outer membrane. Outer membrane is similar to the plasma membrane, but is less permeable and composed of lipopolysaccharides (LPS). LPS is a harmful substance classified as an endotoxin, The space between the cell wall and the plasma membrane is called the periplasm. Image: Prokaryotic Cell, Mariana Ruiz Gram +-, Julian Onions

Why are these differences in cell wall structure so important? Gram-negative bacteria: fewer interpeptide bridges but have an outer membrane made of lipopolysaccharides LPS. Penicillins and cephalosporins interfere with linking of interpeptides, but can’t easily get to in gram- bacteria. Cell walls without enough of these intact cross-links are structurally weak, and disintegrate when cells divide. This is how penicillins and cephalosporins work. Since the eukaryotic cells of humans do not have cell walls, our cells are not damaged by these drugs. Microorganisms that do not contain peptidoglycan are not susceptible to these drugs. Images: Sources unknown

Prokaryotes - Glycocalyx Some bacteria have an additional layer outside of the cell wall called the glycocalyx. This additional layer can come in one of two forms: Slime Layer Capsule Slime layer Capsule STRUCTURE OF MICOBIAL CELLS

Prokaryotes - Glycocalyx Some bacteria have an additional layer outside of the cell wall called the glycocalyx. This additional layer can come in one of two forms: 1. Slime Layer glycoproteins loosely associated with the cell wall. Slime layers cause bacteria to adhere to solid surfaces and help prevent the cell from drying out. Streptococcus The slime layer of Gram+ Streptococcus mutans allows it to accumulate on tooth enamel (yuck mouth and one of the causes of cavities). Other bacteria in the mouth become trapped in the slime and form a biofilm & eventually a buildup of plaque. Staphylococcus The slime layer of Gram+ Staphylococcus allows it to thrive in the salty, hypertonic environment of the skin. Glycocalyces are not specific to Gram+ or Gram- bacteria, sometimes only some members of a certain species (strains) have a glycocalyx, whereas others don’t. Slime layer Capsule STRUCTURE OF MICOBIAL CELLS

Prokaryotes - Glycocalyx 2. Capsules polysaccharides firmly attached to the cell wall. Capsules adhere to solid surfaces and to nutrients in the environment. Adhesive power of capsules is a major factor in the initiation of some bacterial diseases. Capsule also protect bacteria from being phagocitized by cells of the hosts immune system. Slime layer Capsule STRUCTURE OF PROKAROTIC CELLS

Prokaryotes - Endospores Dormant, tough, non-reproductive structure produced by small number of bacteria. Primary function of endospores: Allow bacteria to survive adverse conditions Resistant to radiation, desiccation, lysozyme, temperature, starvation, and chemical disinfectants. Endospores commonly found in soil and water, where they may survive for long periods of time. A stained preparation of Bacillus subtilis showing endospores as green and the vegetative cell as red Allow bacteria to survive in “suspended animation” when environmental conditions are not suitable. Kind of like a plant seed..When conditions are right the endospore will ‘sprout’ a living bacterium. Image: Stain: Jerry Keplinger, James H. Quillen College of Medicine Procedure: Source link no longer works STRUCTURE OF PROKAROTIC CELLS

Prokaryotes – Surface Appendages Some prokaryotes have distinct appendages that allow them to move about or adhere to solid surfaces. Consist of delicate stands of proteins. Flagella Long, thin extensions that allow some bacteria to move about freely in aqueous environments. Axial filaments (endoflagella) Wind around bacteria, causing movement in waves. Fimbriae Most Gram- bacteria have these short, fine appendages surrounding the cell. Gram+ bacteria don’t have. No role in motility. Help bacteria adhere to solid surfaces. Major factor in virulence. Pili Tubes that are longer than fimbriae, usually shorter than flagella. Use for movement, like grappling hooks, and also use conjugation pili (singular = pilus) to transfer plasmids. Flagella Axial filaments Fimbria Pili Images: Flagella: Mike Jones Wiki Axial Filament: Indiana USchool of Med EColi: Pub Library of Science

Endosymbiotic Theory Proposed by Lynn Margulis (1970) Explains the origin of eukaryotic cells Major evolutionary event occurred by merging two or more lineages through symbiosis (2 organisms living together)

Endosymbiosis

Endosymbiosis Mitochondria came from bacteria (probably the group that includes typhus) Chloroplast came from cyanobacteria (blue-green algae) Flagella came from spiral shaped bacteria

Evidence for Endosymbiosis Similar structure – double membrane, free ribosomes, similar DNA Mode of asexual reproduction – binary fission DNA processing is similar (RNA is translated immediately in both mitochondria and bacteria DNA sequence evidence ( Carl Woese)