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Chapter 3

Microbiology ch3.docx

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York University
BIOL 2905
Tanya Da Sylva

Microbiology Prokaryotic and Eukaryotic Cells: An overview All living things are composed of cells. Cells are living, growing, reproducing, responding and metabolizing. - Cells can be categorized as either prokaryotic or eukaryotic - Scientist categorize organisms onto groups called taxa ex for prokaryote’s taxa’s would be Domain Achaea and Domain Bacteria - Distinctive feature of prokaryotic is that they can make proteins simultaneously to reading the genetic code because the typical prokaryotic does not have a membrane covering its genetic material. Meaning they do not have nucleus. - Eukaryotic have a membrane surrounding their DNA and have more organelles than the prokaryotic. - Cells of algae, protozoa, fungi, animals and plants are all prokaryotes - External Structures of Bacteria Cells Many cells have special external features that enable them to respond to other cells or their environment. In bacteria these features include glycocalyces, flagella, fimbriae and pili Glycocalyces - Some cells have a sticky substance that surrounds the outside of the cell, this is called glycocalyx which means “sugar cup”. - These chemicals are produced in the inside and extruded on the outside - When the glycocalyx of a bacterium is composed of organic chemicals firmly attached to the cells surface the glycocalyx is called a capsule. - When there is a loose, water-soluble glycocalyx it is called a slime layer, they are often sticky allowing it to attach to things ex in your teeth, sticking to your teeth and causing decay - They protect the bacteria from drying out - Because these capsules are chemically alike to the ones in our body our defensive cells overlook them ex streptococcus pneumonaie and Klebsiella pneumonia found in the respiratory tract Flagella Cells mobility may enable it to flee or go towards certain environments; the organelle responsible for this is the flagella Structure - Bacteria Flagella are composed of three parts, a long thin filament, a hook and a basal body about 20nm extending out of the cells environment. - It is composed of many identical sphere like molecules of a protein called flagellin 62 - No membrane covers the flagella - The filament inserts into a curved structure, the hook which is made out of different protein, the basal body which is also made out of diff proteins it anchors the filament and hook to the cell wall and cytoplasmic membrane by means of a rod and 2 integral proteins for gram(+) and four for (-) - Together the hook, rod, and rings allow the filament to rotate at a 360 degree angle. Arrangement - Flagella that covers the surface of the cells is called peritrichous, polar flagella are at the ends ex (63) Some have tufts of polar flagella- meaning a lot are located in one area. - Some spiral shaped bacteria called spirochetes have flagella at both ends that spiral tightly around the cell instead of protruding outside of the cell these flagella are called endoflagella form an axial filament and wrap itself around the cell between its cytoplasmic membrane and outer membrane. - It moves as if it was a corkscrew, some scientist believe their shapes allow them to invade human tissue Treponema palladium agent of syphilis Function - They rotate at about 360 degrees, The flow of hydrogen ions or of sodium ions through the cytoplasmic membrane near the basal body powers the rotation, propelling it at 60 cell lengths a sec equ to a car going 670 miles per hour. - They move with a series of “runs” and “tumbles” - Counter clockwise flagellar rotation produces runs - moves forward, If more than one flagellum is present the flagella and rotate together as a bundle, Tumbles are abrupt, random changes in direction caused by clockwise flagellar rotation - Responses to stimuli is called taxis, light phototaxis and chemicals chemotaxis - Fimbriae and Pilli - Bacteria use fimbriae –sticky, bristle like projections to attach to things in its environment, may be hundreds per cell they are shorter than flagella. - Ex. Neisseria gonorrhoea causes gonorrhoea able to colonize in the mucous membrane of the reproductive tract - They use fimbriae to move across a something or toward another bacterium they use a method similar to pulling a rope. Its fimbriae attach, then the bacterium retracts pulling itself closer to the object - Fimbriae play an important role in biofilms, slimy masses of microbes adhering to something by means of fimbriae and glycocalyces. - Some fimbriae act as electrical wires conducting electrical signals within the biofilms. - 99% of all bacteria in nature are found in biofilms - Biofilms form plaque on teeth, slime on rocks bunch of microbes attached to a surface - Special type of fimbria is a pilus also called conjugation pilus, they are longer than fimbriae typically a few pili are on the bacteria and that’s if they have them - Conjugation pili mediate the transfer of DNA from one cell to the other via a process called conjugation Bacterial Cell Wall The cells of most prokaryotic are surrounded by a cell wall that provides structure and shape to the cell and helps in assistance or resistance. On most note that animal cells do not have cell walls so it helps in the treatment of bacteria cells, - Cocci can appear singly or in chains ex streptococci or in cuboidal packets - Rod-shaped cells called Bacilli appear singly or in chains Bacterial cells are composed of peptidoglycan a complex polysaccharide; it in turn is made up of sugar molecules called N-acetylglucosamine (NAD) and N-acetylmuramic acid (NAM)- structurally similar to glucose. - Millions of these two sugars are in a chain alternating this is the glycan part of the peptidoglycan , they are attached to other chains by crossbridges of four amino acids (tetrapeptides), this is the “peptido” part - Depending on the bacterium the tetrapeptides could be linked together or by short connecting chains of other amino acids. - These peptidoglycan’s surround the whole cell, they must continually insert these chains if it is to grow and divide Gram –Positive Bacterial Cell Walls Gram-positive bacterial have thick layer of peptidoglycan that contains a chemical called teichoic acid. Some are linked to lipids forming lipoteichoic acids that anchor the peptidoglycan to the cytoplasmic membrane. - Teichoic acids have a neg charge giving the surface of the gram positive a ng charge- may play a role in the passage of ions
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