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Prokaryotic Cell Arrangements & Anatomy: emphasis on Cell Wall

Prokaryotes, as mentioned earlier are cells containing NO nucleus. I will write a post on the major differences of prokaryotes and eukaryotes later.

In microbiology, there are plenty of research under bacteriology (study of bacteria). In this post, we will focus on bacteria (which is made up of eubacteria & archaebacteria).

Relative size of bacteria (measured in micrometer µm)

  • mycoplasma – bactera like (no cell wall) ~0.4 µm
  • genitalium – acts as a contaminant in labs ~0.4µm
  • Haemophilus influenza f (considered as a true bacteria)~0.2um
  • Staphylococcus aureus* ~ 0.9 µm
  • Escherichia coli* ~ 1.5 µm
  • Bacillus megaterium ~4.0 µm

*Note: both are used as controls in Gram’s stain

Based upon these numbers we can say that bacteria are really tiny!

BACTERIAL SHAPES:Image from http://bioweb.uwlax.edu/bio203/s2008/jaedike_alic/360px-Bacterial_morphology_diagram_svg.png

COCCUS (sphere)

Arrangements of Coccus

  • diplococci (2 next to each other)
  • streptococci (more than 2 in a chain)
  • tetrad (4 planar making a square)
  • sarcinae (superimposed tetrad)
  • staphylococci (grape-like arragements)

COCCOBACILLUS (semi oval)

BACILLUS (rod shaped- usually seen at 100x under oil immersion with a microscope)

Arrangements of bacilli

  • single bacillus
  • diplobacilli
  • streptobacilli
  • V shape (daughter cells remain attach making a V arrangement – spore forming)
  • palisade (side by side)

VIBRIO (tear drop)
SPIRILLUM (spiral and stiff)
SPIROCHETE (corkscrew like DNA helix)
PLEOMORPHIC (changing and varied shape

ANATOMY OF THE PROKARYOTIC CELL

CELL WALL

It is made up of protein and sugar:

Contains alternating NAG-NAM, amino acids, glycan

Peptidoglycan:

 

 

  • two alternating sugars of NAG (N- acetylglucosamine) and NAM (N-acetylmuramic acid), they make the sugar backbone of the peptidolycan, linked covalently, and is the glycan portion of the peptidoglycan
  • cross bridges made up of four amino acid (tetrapeptides) giving it its “peptido” some bacteria has either covalently bound tetrapeptides or short connecting chains of amino acid
  • Some cells have a thick peptidoglycan layer, some has thin
  • Detection of whether a thick or thin layer is determined by the Gram’s Stain


Gram’s Stain used to test Bacteria

Difference in composition of Gram negative and Gram positive cellsIn testing for an unknown bacteria, Gram’s stain are usually done first

  • to determine whether the organisms contains a thick or thin peptidoglycan
  • Note Lipid A is embedded in the outer membrane

    does it contain the lipopolysaccharide unit that contains the O antigen, Lipid A, and polysaccharide, (see image above)

  • does the bacteria have a waxy like, lipid, outer layer of mycolic acid protruding from the cell membrane preventing the proper staining of a Gram stain?
  • The most important, I think, is most likely determining whether or not the bacteria is a Gram negative since prior to treatments, a provider ought to know whether their patient may enter severe Sepsis or worsened autoimmunefunction if he/she were further treated with antibiotics.

Gram Negative Cell: Contains LPS on outer membrane, thin peptidoglycan

Not shown in these figures is the TEICHOIC ACID which is found in the GRAM POSITIVE cell wall
Not shown: MYCOLIC ACID (ID by Acid Fast Stains) associated with
GRAM POSITIVE

 

RECALL ANTIBIOTICS:

  • made from a fungus and are two kinds:bacteriostatic (stop bacterial growth) or bacteriocidal (killsbacteria
  • Of these two, bacteriostatic antibiotics are clearly more useful in treating Gram negative bacterial infections vs. bacteriocidal antibiotics simply due to degradation of the cell wall would release Lipid A(a subunit of the lipopolysaccharide molecule), a toxin that causes sepsis

CELL MEMBRANE

Phospholipid bilayer – with proteins, integral proteins, peripheral proteins, glycoproteins within, or around it. Proteins here can act as recognition proteins, enzymes, receptors, carriers, or channels for substances to enter in and out of the cell.

Function

  • selectively permeable, meaning allowing substances to cross in and out of the cell on its own by size and dependent on the concentration gradient or chemical gradient, which also is associated with an electrical gradient or voltage that exists across the membrane since the concentration of these substances are usually electrically charged

Diffusion – net movement of chemical down in its concentration gradient

Faciliated Diffusion – movements of large or electrically charged molecules are blocked and can only be permeates the membrane only if it is of the right size or of the right electrical charge. Some proteins (permease) has a binding site and is selective in allowing one substance to pass

Osmosis – is the movement of water molecules based upon the gradient of the water, to maintain isotonic environments. A net loss or gain of water will occur due to the high concentration of solutes or low concentration of solutes respectively, leading to the conditions known as hypertonic or hypotonic. Remember: tonic refers to the solute concentration; hyper means MORE and hypo means LESS.

Active Transport – is an active process that requires a transmembrane permease protein that opens or closes depending on the need of the cell. Uniports are permease transporting substances to only one direction. Antiports are permease transporting in both directions. The proteins is controlled and is open or closed. Its function is to transport substances against their electrochemical gradient. (i.e. ATPase)

Group Translocation – active process only in prokaryotes – in which substances are chemcially altered during transport

EXTERNAL STRUCTURES:

glycocalyces – also found in some eukaryotes lacking a cell wall, this gelatinous, sticky substance surrounding outside of the cell, aka sugar cup, composed of polysaccharides, polypeptides, or both. These chemicals are presented outside of the cell surface.

Capsules and slime layers are featured in harmful prokaryotes.

flagella – movement, protective and propel cell through environment, not all prokaryotes have flagella.

    • Structure: contains a filament (inserts into a structure), a hook (composed of different protein) and a basal body (composed of different proteins and achors filament and hook into cell wall using a rod and a series of 2-4 rings of integral proteins). Hook, rod, rings, allow filament to rotate 360. Differences in flagella among bacerial flagella varies by strains, serovars. Also contains globular proteins called flagellin
    • Arrangement: various arrangements have been found. peritrichous - are flagella covering the surface of the cell. polar – are flagella found at the ends of the cell Spirochete, has flagella on both ends and found around the cell’s circumference (endoflagella), which forms the axial filament that wraps around the cell membrane and an outer membrane. Since the axial filament wraps around teh cell, it’ll cause the spirochete to move in a corkscrew-like motion through the medium (i.e. Treponema pallidum, Borrelia burgdorferi)

Image taken from http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=cell&part=A3946

  • Function: bacterial flagella move is not understood but they rotate 360 rather than whipping side to side. It may travel clockwise or counterclockwise and can be reversed by the cell. Receptors may be found at surface of the cell that sends a signal to the flagella to either respond to light or chemicals, the movement for these purposes are calledphototaxis and chemotaxis, respectively.

fimbriae* – sticky, proteinaceous, bristlelike projectsions adhering to another substance in the environment, adhesions of bacteria can lead to making biofilms (masses of bacteria connected via fibriae or glycocalyces) (i.e. Neisseria gonorrhoeae)

pili*- tubules containing protein pilin. Longer than fimbriae, pili can be used to make a conjugate tube between neighboring bacteria or a substrate with transposable elements that allow the transfer of plasmid (bacterial DNA) from one cell to another (i.e. Yensenia pestis aka Bacillus Pestis)

CYTOPLASM of PROKARYOTES

Cytosol – is the liquid part of the cytoplasm, mostly water, contains dissolved and suspended materials (ions, carbohydrates, proteins, lipids, wastes) also contains cell’s DNA in a region called nucleoid (recall prokaryotes do not have nuclear membrane surrounding DNA)

Nucleoid – different from the Eukaryotic nucleus, it does not have a nuclear membrane and takes DNA and ompacts together

Inclusions – aka deposits, found in cytosol, may be reserve deposits for lipids, starch, compounds containing nitrogen, phosphate, sulfur for when there is an abundance and can be later used when cell is lacking.

  • has carbon and energy molecules stored in glycogen or as poly-beta-hydroxybutric acid (PHB)
  • cyanobacteria – an aquatic prokaryote contains inclusions called gas vesicles which stores gases in protein sacs, which allows the buoyancy of it in water
  • useful in biothech and pharmaceuticals because the compact peptides here are in linear form and thus may be easily unfolded to achieve a certain protein code and refold the inclusion body back

Endospores pg. 75- NOT reproductive spores of algae and fungi – resistant to drying, heat, radiation, lethal chemicals, can survive in really harsh conditions

  • formed under hostile environments (nutrient deficient such as lack of carbon and nitroge). and usually made of older culture, the spore is grown inside the bacterial cell (vegetative cell)
  • specific for bacillus and produced by Gram + bacteria
  • detected by endospore stain (blue in color if endospore is present)

NONMEMBRANOUS ORGANELLES

Ribosomes – protein synthesis, its size is 70s (measured by Svedbergs (S) unit)

  • Svedbergs unit is determined by centrifugation of the ribosomes and measuring the rate of which the ribosomes would reach the bottom of the test tube. A greater S unit suggest longer rate for the sedimentation of the highly packed ribosomes (in contrast 80s in Eukaryotes)
  • has 2 subunits containing ribosomal RNA: 30s subunit – has polypeptides, single rRNA and 50s unit – has polypeptides and 2 rRNA molecules

Cytoskeleton - internal network of fibers, provides shape for cell

  • nonspherical prokaryotes show simple ones vs. spherical prokaryotes lacking

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The former contents were notes taken from Professor Phil Hawkins at Foothill College Bio 41 in Winter 2010. Additional information are also taken from the textbook: Microbiology with Diseases by Taxonomy, 2nd edition, by Robert Bauman.

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2 Responses to “Prokaryotic Cell Arrangements & Anatomy: emphasis on Cell Wall”

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  1. anita

    A lot of good information I can use thanks

  2. Amy B

    Awesome… Thanks for the help. 2 nights before finals.

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