Today: Procaryotic cells (continued) and Eukaryotic cells (Ch. 4)
Procaryotic Cells
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Cytoplasm: substances inside the plasma membrane
o 80% water
o primarily proteins, carbohydrates, lipids and organic ions
o major structures
 DNA
 ribosomes
 inclusions
Procaryotic Cytoplasm
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Nuclear area (nucleoid): contains bacterial chromosome
o circular (most), double-stranded DNA which is attached to the plasma
membrane
o in replicating cell can be as much as 20% of cell volume
o segregates during division
Ribosomes: sites of protein synthesis
o composed of protein and rRNA
o thousands in cytoplasm give it grainy appearance
o prokaryotic are 70S (composed of 30S and 50S subunits)
Inclusions - generally reserve deposits
o Lipid
o Sulfur (Thiobacillus)
o Carboxysomes (include enzyme for fixing CO2)
o Gas vacuoles – used by some aquatics as buoyancy control to maintain
appropriate depth
o Magnetosomes – iron oxide (magnetic – hence name) deposits (in some
G-) in vitro can decompose hydrogen peroxide – may in vivo protect
organisms against hydrogen peroxide. INTERESTING NOTE: industrial
microbiologist developing culture techniques to grow/harvest magnetite
from bacteria for making magnetic tapes & disks for sound & data
recording.
Procaryotic Cell (continued)

Cell wall
o surrounds almost all prokaryotic cells
o structure unique – unlike eukaryoutes so this is ideal site to attack without
harming host
o gives shape, protects from osmotic lysis
o contains complex polysaccharide
 peptidoglycan (murein) for bacteria
 pseudomurien for archaea
o Peptidoglycan:
 2 alternating amino sugars, N-acetyl-glucosamine (NAG) and Nacetyl-muramic acid (NAM). See Fig. 4.11
 3 or 4 amino acids (including D-alanine and D-glutamic acid)
Peptidoglycan Crosslinks – susceptible site for some antibiotics (see fig 4.12a
arrows)
Procaryotic Cell (continued)

Cell wall (continued)
o Gram positive:
o have teichoic acids (50% of weight of cell wall)
o glycine interpeptide bridges in PG
Procaryotic Cell (continued)


Gram negative:
o have outer membrane in cell wall
o Lipopolysaccharide (LPS) - endotoxin due to lipid A portion; composed of
(1) lipid A, (2) core polysaccharide, (3) O-side chain
Periplasmic space:
o space between PG and cell membrane (also outer membrane in G-)
Procaryotic Cell (continued)

Outer structures:
o glycocalyx (capsule)– sticky sugar coating on outside of cell (outside cell
wall)
 made of sugars (extracellular polysaccharides)
 important in attachment (dental caries) and in preventing
phagocytosis (Klebsiella pneumoniae virulent strains)
o flagella - aid in movement (taxis = respond to stimuli e.g. chemo/photo)
 have only one filament, 15-20 micrometers long, filament made of
single protein, flagellin
 flagellin is self-assembling (forms filament outside of cell)
 monotrichous (single fil), amphi- (1 at opposite poles), lopho- (2+
at single pole), peri-(distributed over entire surface)
o Axial Filaments – in spirochetes (e.g. Treponema pallidum  syphilis)
 Anchored at ends of cell and spiral around – similar structure to
flagella filament rotation causes a corkscrew motion of cell
o Fimbriae & Pili
 Fimbriae – (few to hundreds) fibers for attachment to surfaces
 Sex pili – (1-2/cell) used in bacterial mating. Genetically
determined by plasmid genes
Procaryotic Cells (continued)

Specialized cell structures:
o endospore: special dormant form of cell found in some genera
 Bacillus, Clostridium
 complex life cycle
 forms inside cell
 resistant to heat, UV, and dessication
 germinates to form new cell
 not a form of reproduction
Eucaryotic Cells
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Plasma membrane: phospholipid bilayer
o contains sterols (may help prevent lysis)
o have carbohydrates (cell-cell recognition)
o attachment site for bacteria
Cell wall: in plants, algae, and fungi
Cytoplasm: area inside the plasma membrane and outside nucleus
o contains filaments (micro-, intermidiate, and microtubules) which form
cytoskeleton
o move things, cytoplasmic streaming
Eucaryotic Cell (continued)
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Organelles:
nucleus: contain DNA bound to histones and surrounded by double-membrane
(nuclear envelope) with small pores (nuclear pores)
o nucleoli - condensed regions of DNA where ribosomal RNA is being
synthesized
endoplasmic reticulum: network of membrane sacs, site of lipid synthesis and
protein storage
o rough ER (with ribosomes)
o smooth ER (no ribosomes)
ribosomes: composed of protein and rRNA
o 80S, composed of 60S and 40S subunits
o in chloroplast and mitochondria - 70S
Eucaryotic Cell (continued)

Organelles: (continued)
o Golgi complex: flattened sacs usually near nucleus, stacked
 form secretory vesicles which transport material within cell or out
of cell
o lysosomes: vesicles containing digestive enzymes (segregated to protect
cell)
 can break down molecules or destroy invading bacteria
o vacuoles: space or cavity, often temporary storage area derived from Golgi
o centrioles: consist of microtubules
 important in cell division
Eucaryotic Cell (continued)

Organelles: (continued)
o mitochondria: cell "powerhouse"
 site of ATP synthesis
 double membrane with an outer and inner membrane (folded into
cristae)
 has own DNA (circular molecule)
 replicate by binary fission
o chloroplast: site of photosynthesis
 membrane bound, contains stacked membranes called thylakoids
 contains pigments and enzymes for light harvesting
 also has circular DNA, 70S ribosomes and divides by binary
fission
o Endosymbiotic Theory