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Chapter 2

BIOLOGY 2EE3 Chapter Notes - Chapter 2: Flagellum, Siderophore, Spiral Bacteria

Course Code
Turlough Finan

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Chapter 2 Bacteria: (pgs 36-71)
Morphology of bacterial cells
oBacteria can take many diferent shapes or morphologies… Spherical is coccus plural cocci, Rod
shaped is bacillus plural bacilli, comma-shaped is vibrio plural vibrios, spiral is spirillum plural
spirilla, pleiomorphic varied shapes
oBacteria can also assume multicellular organization
Hyphae (branching filaments of cells)
Mycelia (tufts of hyphae)
Trichomes (smooth, unbranched chains of cell
oSize of bacteria …
Smalled than eukaryal cells 0.5-5 um in length
Small eukaryal cells are 5 um in diameter
Exceptions to general size of bacterial cell
Thiomargaritan amibiensis up to 700 um in diameter
Epulopiscium fishelsoni 200-700 x 80 um
Some mycoplasma cells are only 0.2 um in diameter
The cytoplasm
oWhats in the cytoplasm of bacterial cells?
Largest area is nucleoid region, housing the chromosones and DNA replication machinery
The remainder of the cytoplasm is a stew of macromolecules- tRNA rRNA mRNA, proteins,
Inclusion bodies may present are large things seen through the microscope in the cytoplasm, a
separate membrane doesn't surround these bodies
Poly-hydroxybutyrate grandules: C storage
Polyphosphate: phosphorus storage
Sulfur globules: sulfer storage
Gas vesicles: buoyancy control
Carboxysomes: location of carbon fixation reactions
Magnetosomes: organelle associated with direction finding… orienting cell during
movement, composed of protein, lipid and iron
The bacterial cytoskeleton
oCytoskeleton is an internal structure that helps organize bacterial cells, it is a series of internal proteins
that assist in keeping everything in or moving it to the right lcoations in cells.
oSome cytoskeleton proteins are involved in cell wall synthesis during cell division FtsZ and MreB
(polymerizes actin like helical bands next to plasma membrane)
oOther cytoskeleton proteins are involved in moving internal items, ex plasmids and magnetosomes
The cell envelope
oAll cells have a plasma membrane that separate outer from inner membrane, its composed of a
phospholipid bilayer with embedded proteins it may have sterol molecules called “hopanoids” in it to
help with stability across temperature ranges similar to cholesterol in eukaryotes , not found in all
bacteria cells
oThings get in and out of cell by diffusion such as O2 and CO2, H2O is helped by aquaporin protein
channels, osmosis is the flow of water across it towards the side with the higher solute, it can cause
cells to swell or shrink

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oNutrients cross the plasma membrane through facilitated diffusion, moves with concentration gradient
no energy needed. Or active transport against a gradient requiring energy as ATP binding cassettes
ABC transporters or co transport mechanism such as symport and antiport
oThe plasma membrane can also be used for generating energy through the embedded ETC which can
help promote motive force PMF, can be used for synthesis and respiration and to derive energy for
motion in flagella
oPlasma membrane can also hold sensory systems, proteins In the membrane can be used to detect
environment changed, the cells can use the detected changes to alter gene expression to respond
oPM help in the making and shipping or proteins to outside of the cell which uses ATP energy, such as
toxins, siderophores, enzymes
oThe bacterial cell wall is composed of cross linked strands of peptidoglycan subunits forming a
matrix , cell wall gives the cells their shape and protection from osmotic lysis and mechanical forces
oPeptidoglycan disaccharide subunit is : N-acetylmuramic acids with a small peptide chain , and N-
acetylglucosamine ----- NAM and NAG
oThe amino acid NAM can vary from species to specis , the way the peptides are crosslinked in the cell
wall can also vary , NAMS are usually D forms which is a mirror image of the L form found in
biological proteins
oThe structure of the cell wall can be degraded by lysozyme and lysostaphin secretions, and by b-
lactam antibiotics which works by preventing peptidoglycan crosslinking, weakening the cell wall
oWhen lysosome cuts peptidoglycan thus cell wall, without an intact cell wall the rod shape is lost, and
thus in hypotonic conditions water rushes in and the cell will burts
oSome bacteria can produce an enzyme to destroy the critical b-lactam ring structure, but we can add a
second drug to inhibit that enzyme and restore the first drugs efficieny
oGram postitve cells have a thicker peptidoglycan of cell wall, narrow periplasmic space, and teichoic
acids in the peptidoglycan negatively charged
oGram negative cells have a varying width periplasmic space containing a very thin layer of
peptidoglycan, and outer membrane composed of lipopolysaccharide LPS- composed of O side chain,
core polysaccaride, and lipid A
oLPS from gram negative can be harmful, lipid A portion induced a strong inflammatory response,
Outer side chains of polysaccarides can vary dramatically and even be changed by the microbe to
evade host immune responses – endotoxins are in fact due to LPS
oNutrients getting through cell walls : gram+ peptidoglycanhas large pores throughtout its matric,
gram_ cell has posin and TonB-like proteins in its outer membrane to transfer molecules into the
periplasmic space…. Once there, active transport will move things into cytoplasm, TonB dependent
transport systems- siderphore uptake and B12 uptake
oMolcules going out of gram- cells periplasmic space then… some move from the periplasm to outside
directly “autotransporters” rare, and some use single step of never entering periplasm transport system
such as type 3 secretion systems
oAlchohol decolorization step shrinks the large pores in gram+ helps lock the purple stain in
oThe alcohol also may strip away some of the outer membrane lipids in the gram- cells making them
more likely to lose the purple stain
oGram- have a wide periplasm
The bacterial cell surface
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