MCB 100 1st Edition Lecture 13 Outline of Last Lecture I. The Gram StainII. Schaeffer-Fulton endospore stain III. Ziehl-Neelsen acid-fast stainIV. Classification of living creaturesV. Modern molecular phylogeny VI. Indentification of bacteriaVII. Media for culturing microorganisms VIII. Cell theory of life Outline of Current Lecture I. Size of typical microorganisms II. The prokaryotic cell III. Structures seen in eukaryotic cells but not in prokaryotes a. Endoplasmic reticulum b. Mitochondriac. Chloroplastsd. Nuclear membrane e. Cytoskeleton f. Phagolysosomesg. snRNPs Current LectureI. How big are typical microorganisms like protozoa, bacteria, and viruses? A. Generally, protozoa are bigger than bacteria, bacteria are bigger than viruses. There are exceptionally large bacteria and exceptionally small protozoa so there are cases where some bacteria are bigger than some protozoa II. The prokaryotic cell A. Typical cell contains capsule, cell wall, plasma membrane, cytoplasm, ribosomes, plasmid, pili, nucleoid, bacterial flagellum B. Typical bacterial cell has cell wall, cytoplasmic membrane, cytoplasm, nuclear area, ribosomes, soluble RNA, capsule, flagella C. Envelopei. Cell membrane: diffusion barrier, always present. Function: allows some substances to diffuse into/out of cell but prevents other substances from These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.entering or leaving cell. It’s the structure that defines border between living matter within the cell and nonliving matter that is outside. 1. In bacteria, enzymes and electron carriers of the respiratory chain are embedded in the cytoplasmic membrane. (In eukaryotic cells, respiratory enzymes are found in inner mitochondrial membranes. Bacterial cells don’t have mitochondria) 2. Composed of a lipid bilayer with protein molecules embedded within it- typically 50% protein and 50% lipid. Lipids found in bacterial cell membranes are phospholipids ii. Cell wall: usually present, maintains cell shape, protects from osmotic lysis by preventing excessive swelling iii. Glycocalyx: external layer of slime, protects bacterium from host immune system, freezing and dessication helps bacteria to stick together iv. Bacterial cell wall1. Function: gives a cell its shape and protects it from osmotic lysis. Cell wall is not rigid like a brick wall but rather a net-like bag that surrounds the cell and protects it from swelling up. Theres a tendency for water to diffuse into cell, except when bacteria are in a salty solution. In low salt solutions, water diffuses into cell and causes cell to swell. Cell wall prevents lysis due to osmotic pressure 2. Composition: made of a chemically complex substance called peptidoglycan, which is made of long chains of modified sugars that are cross-linked by chains of amino acids (peptides). Cross-linking peptide chains are made of amino acids linked by amide bonds like those found inprotein. But peptidoglycan contains several unusual amino acids that are never seen in proteins. 3. Gram positive cell wall- thick layers of peptidoglycan are held together by teichoic acid molecules (stains purple in gram stain)4. Gram negative cell wall- thin layer of peptidoglycan covered by an outer membrane. The OM contains lipopolysaccharide or endotoxin. Periplasmic place is the compartment b/w inner and outer membranes (stains pink in gram stain) 5. Lipopolysaccharide (LPS) --> found in gram negative outer membrane. Thelipid A portion is embedded in membrane, the O-antigen is a sugar polymer that sticks out on outer surface and R-core joins Lipid A to O-antigen. Its also known as bacterial endotoxin. 6. Teichoic acids: components of thick cell walls of gram positive bacteria. They are polymers of sugar acids. TA helps bind together the layers of peptidoglycan in thick wall. Lipoteichoic acids help anchor cell wall to the cell membrane 7. Bacterial capsule/glycocalyx: layer or organic polymers that coats the outside surface of a bacterial cell. If glycocalyx is firm, its called a capsule, if it is loose and drippy, its called a slime layer. a. Function: protect the cell from drying out or freezingb. Help the bacterium to stick to surfaces and other bacteria (protein fibers called fimbrae that also help) c. Protect cell from recognition by host's immune system and phagocytosis d. Storage of sugars/other nutrients that may be abundant when the bacterium is making the capsule but may be broken down and used for food at a later time ii. Bacterial appendages: structures found on the outside of cell; simple protein tubules1. Flagella: rotating helical fibers that act as propellers; consists of single protein fiber that is external to cell membranea. Monotrichous- 1 hairb. Lophotrichous- tuft or clump of hairc. Amphitrichous- on both sidesd. Peritrichous- all around e. Axial filaments- inside the periplasmic space 2. Fimbrae/pili: fibers that help bacteria stick to surfaces and to each other. Fibrae help some E. coli strains to stick to cells that line the urethra- important factor in urinary tract infections 3. Sex pilus: a special fimbri that is used during conjugation a. Hollow tubes of protein that stick out on the outer surface of bacteria; about same diameter as flagella but are shorter and straight; help bacteria to stick to surfaces and to each other; some are virulence factors that allow pathogenic bacteria to stick to host cells; others are important for formation of biofilms2. Chemotaxis: pruposeful movement of a microbe/cell in a chemical concentration gradient either towards source of an attractant or away from source of a repellant 3. Run and tumble motion: form of movement in a semi-random fashion. Progress in the right direction occurs when average length of a run in the correct direction is longer than the average length of a run in wrong direction ii. Ribosomes: Enzyme complexes that read mRNA and make proteins with the tRNAs iii. Cytoplasmic structures: bacterial endospore1. Endospore: tough resting state that allows bacteria to survive a period of harsh conditions such as when soil dries out or they run out of food; not areproductive structure ii. Common types of inclusion bodies (granules) found in bacterial cells1. Starch (glucose polymer)2. Protein (storage)3. Lipoid granules (globs of fat) ii. Differences b/w archaea and bacteria 1. Cell membrane lipids2. Cell wall composition3. RNA