Download Chapter 4

Chapter 4
Prokaryotic organisms
Prokaryotic cell



Includes bacteria and archaea
Thousands of species of bacteria differ by
morphology (shape), chemical composition,
nutritional requirements, biochemical
activities, and sources of energy
Bacteria divide by binary fission (asexual
reproduction)
Size, shape, and arrangement




Most bacteria range in size between 0.2
micrometers (microns) to 2.0 microns
The basic shapes are cocci, bacilli, and
spirilla
Cocci may occur in pairs (diplococci), in
chains (streptococci), and in clusters
(staphylococci)
Bacilli may appear as single rods, diplobacilli,
streptobacilli, or coccobacilli
Other shapes





Spiral bacteria have one or more twists
Curved rods (comma shaped) are vibrios
Others called spirilla are corkscrew shaped and
move with whip-like appendages called flagella
Spirochetes are helical and flexible and move by
axial filaments
Most bacteria maintain a single shape and are
monomorphic, but some may have more than one
shape and are pleomorphic
Structures external to cell wall




Glycocalyx means sugar coat, and is a sticky,
gelatinous polymer that is outside the cell
wall
If the glycocalyx is firmly attached to cell wall
and is organized it is called a capsule
If the glycocalyx is unorganized and loosely
attached it is called a slime layer
Streptococcus pneumoniae, Haemophilus
influenzae, Bacillus anthracis have them
Flagella






These are long, filamentous appendages that
help bacteria move (motile)
No flagella is called atrichous
A single polar flagellum is monotrichous
A tuft of flagella at each end is amphitrichous
Two or more at one (or both) ends is
lophotrichous
Flagella all over is peritrichous
Flagella




The flagellum has 3 basic parts: filament is the long,
outermost region; a hook attaches to the filament;
the basal body, which anchors the flagellum to the
cell wall and plasma membrane
The basal body is a small central rod inserted into a
series of rings
In gram negative bacteria, there are two pair of rings
In gram positive bacteria, only the inner pair is
present
Motility





Bacteria have a ‘run and tumble’ movement
thanks to flagella
A bacterium with flagella can move quickly
toward or away from a stimulus
Bacteria moving toward chemical stimulus is
positive chemotaxis
Bacteria moving away is negative chemotaxis
Moving in response to light is phototaxis
Axial Filaments



Spirochetes are unique in structure and
motility
Treponema pallidium causes syphilis,
Borrelia burgdorferi causes Lyme disease
Spirochetes move by axial filaments, which
spiral around the cell and cause a corkscrew
like movement
Fimbriae and Pili




Many gram negative bacteria contain shorter
hairlike appendages called fimbriae and pili
These are used for attachment and transfer
of DNA
Fimbriae help cell stick to surfaces (Neisseria
gonorrhoeae)
Pili (sex pili or conjugation pili) help cells
transfer DNA in conjugation
Cell Wall





Helps maintain shape of the cell
Keeps cell from rupturing
Contributes to ability to cause disease
Is the site of action of some antibiotics
Helps tell differences in major types of
bacteria
Composition



Contains peptidoglycan which consists of
repeating disaccharides attached by
polypeptides that forms a lattice
Disaccharide portion has monosaccharides
called N-acetyl glucosamine (NAG) and Nacetylmuramic acid (NAM)
Alternating NAG and NAM are linked to form
a backbone, and adjacent rows are linked by
polypeptides
Difference between gram
positive and negative cells


Gram negative have an
outer membrane
Gram positive cells do
not have an outer
membrane, so the
peptidoglycan is
exposed and more
easily destroyed by
antibiotics like penicillin
Gram negative vs. Gram
positive




Gram positive cell wall has thick
peptidoglycan
Gram negative has a thin layer
Gram positive cell has teichoic acids which
help bind and regulate movement of cations
in/out of the cells
Teichoic acids may also provide antigenic
specificity which makes it easier to ID
bacteria
Gram negative cells



Have thin layer of peptidoglycan and an outer
membrane
The outer membrane (OM) has
lipopolysaccharide (LPS), lipoprotein, and
phospholipid
It has a negative charge which helps the
bacteria avoid phagocytosis and complement
(both are host defenses)
Gram negative OM





It also is a barrier to antibiotics, enzymes, etc.
Has porins (proteins) which allow passage of
some material in and out
LPS component has an O polysaccharide
portion and a lipid portion (lipid A)
The O polysaccharide is an antigen and is
used to help ID the bacteria
The Lipid A is a toxin (endotoxin) that can
cause fever and shock (endotoxin shock)
Atypical cells



Mycoplasma has no cell wall (causes walking
pneumonia), but do have sterols to protect
against rupture
Acid Fast Cell Walls- Mycobacterium and
Nocardia have mycolic acid in cell wall, which
causes these bacteria to clump and stick
together.
Damage to cell wall by lysozyme causes
either a spheroplast (gram negative) or a
protoplast (gram positive)
Cell or Plasma Membrane






Encloses the cytoplasm
Made of phospholipids (bilayer), proteins,
glycoprotein, glycolipid
Arrangement is phospholipid bilayer
Heads (hydrophilic), tails (hydrophobic)
Selective permeability
ATP production occurs here
Movement across membranes




Passive process-movement from high
concentration to low without using ATP
Includes simple diffusion (alka seltzer
example)
Facilitated diffusion-requires a protein
transporter to allow movement across
membrane
Osmosis-movement of water from greater
water to less water
Osmosis




Movement produces osmotic pressure-this is
the pressure needed to stop the flow of water
across the membrane
3 types of osmotic solutions: isotonic-equal
solid; no change in cell when placed in this
type of solution
Hypotonic=less solid, cell will swell
Hypertonic=greater solid; cell will shrink
Inside cell



Cytoplasm is 80% water and contains
proteins, carbohydrates, lipids, inorganic
ions, and contains the nuclear area,
ribosomes, and inclusions
Nuclear area contains loop shaped DNA
May have pieces of DNA called plasmids that
carry genes for resistance (resistance factors
or R factors)
Inside cell continued






Ribosomes-sites of protein synthesis
Contained in eukaryotic cells too, but different
because they are 80 S (Svedberg unit); 40 S + 60 S)
Prokaryotic ribosomes are 70 S (30 S + 50 S)
Inclusions are extra storage areas including gas
vacuoles, sulfur granules, land lipid inclusions
Metachromatic granules -collectively known as
volutin, represents a reserve of inorganic phosphate
Magnetosomes-inclusions of iron oxide found in
some gram negatives that act like magnets
Endospores




Form in gram positive rods when essential
nutrients are depleted
Endospores are highly durable and can survive
extremes of heat, dehydration, and exposure
to toxins and radiation
Begin sporulation when a key nutrient
becomes scarce
Endospores may remain dormant for years,
and will eventually ‘germinate’ and become a
vegetative cell again
Shapes, review
Shapes; cocci (spherical), bacilli (rods), vibrio
(comma), spirochetes (spring), spirillum
(helix)
Arrangements: Staphylo (clusters), strepto
(chains), mono (single), diplo (pairs), tetrads
(4), sarcina (8), palisade (side by side like a
picket fence)
Pleomorphism-variable shapes like
Corynebacterium