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Chapter 3:
Cellular Structure
1. Prokaryotic Cell Structure
2. Eukaryotic Cell Structure
1. Prokaryotic Cell Structure
A. Cell Shape
B. External Structures
C. Internal (Cytoplasmic) Structures
A. Cell Shape
Chapter Reading – pp. 322-325
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Prokaryotic Cell Shape
One convenient characteristic with which to
identify and classify prokaryotes is their
size and shape as seen in the microscope.
• the diameter of prokaryotic cells ranges from
~0.2 to 2.0 mm
• prokaryotes are essentially unicellular and more
or less maintain a constant shape (monomorphic)
• most prokaryotes have a spherical, rod-shaped
or spiral appearance though other shapes exist
as well…
Spherical Cells • spherical prokaryotes are
referred to as cocci(singular = coccus)
diplo- = found in pairs
• different kinds of cocci
exhibit characteristic
arrangements:
strepto- = found in chains
staphylo- = irregular clusters
tetrad = group of 4
sarcina = cube structure of 8
“Rod-Shaped”
Cells • rod-shaped prokaryotes
are referred to as bacilli(singular = bacillus)
• also found in various
arrangements:
diplo- = length-wise pairs
strepto- = length-wise chains”
cocco- = “rounded” bacilli
palisade = bacilli “side by side”
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Curved or Spiral Cells
vibrio = “curved rod”
spirillum = “twisted rod”
spirochete = “corkscrew
rod”
B. External Structures
Chapter Reading – pp. 59-71
Prokaryotic Cell Structures
Ribosome
Cytoplasm
Nucleoid
Glycocalyx
Cellwall Cell
membrane
Flagellum
Inclusions
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Head, whichcontainsphosphate (hydrophilic) Phospholipid
Tail (hydrophobic)
Phospholipidbilayer
Integral protein
Peripheralprotein
Integralglycoprotein
Cytoplasm
Integral proteins
true barrier between
“internal” & “external”
• phospholipid content is a bit different compared to eukaryotes
Plasma Membrane
Cytoplasm
Diffusionthrough thephospholipid bilayer
Facilitateddiffusion through a nonspecific channel protein
Facilitated diffusion through a permease specific for one chemical; binding of substrate causes shape change in channel protein
Osmosis, the diffusion of water through a specific channel protein or through a phospholipid bilayer
Extracellular fluid
Diffusion & Osmosis
Cell exterior (extracellular fluid)
Integralprotein
Protein
Cell interior (cytoplasm)
DNA
Cytoplasmic membrane
Na+
Cl–
Protein
Concentration Gradients
Different concentrations
of ions inside vs outside
the cell are set up &
maintained by :
Creates a net negative
charge inside vs outside.
• protein pumps
• active transport from
low to high conc.
• protein channels &
transport proteins
• facilitated diffusion
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Glucose N-acetylglucosamineNAG
N-acetylmuramic acidNAM
repeating disaccharidebackbone
tetrapeptide(amino acid)crossbridge
connecting chainsof amino acids
Bacterial Cell Wall
The bacterial cell wall provides structure & support:
• main component is a structure called peptidoglycan
• polypeptide-linked
chains of a repeating
disaccharide
(protects cell from
osmotic lysis!)
Cells without a wall
(e.g., mycoplasmas,
animal cells)
Cells with a wall
(e.g., plants, fungal
and bacterial cells)
H2O
H2O
H2O
H2O
H2OH2O
Cell
wall
Cell membrane
Cell
wall
Cell membrane
Isotonic
solution
Hypertonic
solution
Hypotonic
solution
Osmosis & Cell Lysis
Peptidoglycan layer of cell wall
Lipopolysaccharide
(LPS)
Outermembraneof cell wall
Cell membrane
n
O side chain(varies inlength andcomposition)
Gram-negative cell wall
Lipid A(embeddedin outermembrane)
Fatty acid
Porin
(sectioned)
Periplasmic space
Phospholipid layers
Integral
proteins
Corepolysaccharide
Porin
• thin layer of peptidoglycan
Gram-negative Cell Wall
• outer membrane containing
lipopolysaccharide (LPS)
• Lipid A (endotoxin) + polysaccharide
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Peptidoglycan layer(cell wall)
Cell membrane
Teichoic acid
Integralprotein
Lipoteichoic acid
Gram-positive cell wall
Gram-positive Cell Wall
• thick-layered peptidoglycan cell wall w/teichoic acids
• NO outer membrane
Bacterial Glycocalyx (“sugar cup”)
Outermost layer that surrounds the bacterium
• called a slime layer if loosely attached, water soluble
• called a capsule if compact, tightly attached to cell wall
• mediates
adhesion,
biofilm
formation
• protects from
dessication,
phagocytosis
Bacterial Flagellum
• basal body,
hook &
filament
• basal body
anchors
flagellum in
PM, cell wall,
rotates hook
& filament to
propel
bacterium
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Tumble
Run
Tumble
Run attractant
Flagella & Bacterial Motility Bacteria undergo taxis, i.e. movement in response to
something.
e.g., chemotaxis (movement in response to a chemical substance)
Involves random “runs” & “tumbles”:
• longer runs, less tumbles in direction of “good stuff”
(RUN = flagella rotate
counterclockwise)
(TUMBLE = clockwise)
Axial
Filament
Bundle of
endoflagella
found in
spirochetes
• anchored at one
end of cell and
rotate in unison
• rotates cell like
a “corkscrew” to
propel it forward
Fimbriae & Pili
FlagellumFimbria Conjugation pilus
Non-motile appendages that are chemically and
functionally different than flagella.
Fimbriae
• involved in adhesion
Pili (singular = pilus)
• used in conjugation
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C. Internal (Cytoplasmic) Structures
Chapter Reading – pp. 71-76
Prokaryotic Ribosomes
Ribosomes consist of 1 large and 1 small subunit.
Carry out protein synthesis (i.e., translation of mRNA).
• both subunits are made of rRNA & ribosomal proteins
• smaller, somewhat different from eukaryotic ribosomes
• specifically targeted by some antibiotics
Firstmembrane
Forespore
Vegetative cell
Cell wall
DNA aligns along
the cell’s long axis.
Cytoplasmic membrane
invaginates to form
forespore.
Cytoplasmic membrane
grows and engulfs
forespore within a
second membrane.
Vegetative cell’s DNA
disintegrates.
DNA is replicated.1
3
2
4
Cytoplasmic
membrane
DNA
Secondmembrane
Endospores When conditions
are bad, some
Gram+ bacteria
can form
endospores:
• inactive, dormant
cells enclosed in a
highly resistant
spore coat
• remain dormant until
conditions are good
(even 1000’s of yrs!)
• very resistant to
heating, freezing,
dessication
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Spore coat
Outerspore cost
Spore coat forms
around endospore.
Maturation of endospore;
completion of spore coat
and increase in resistance
to heat and chemicals by
unknown process.
Endospore released from
original cell.
A cortex of calcium and
dipicolinic acid is
deposited between
the membranes.
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7
6
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Cortex
Outerspore cost
Endospore
Completion of Endospore Formation
The Genetic MaterialA region called the nucleoid contains the circular
bacterial chromosome (DNA + non-histone proteins):
• usually several million
base pairs (bp) in size
e.g.the E. coli genome is
~4 mega-bp’s (4 Mbp)
• contains all bacterial
genes plus an origin
of replication (Ori)
• Ori is where DNA
replication starts,
essential to copy
the chromosome
PlasmidsSome bacteria have >1
extrachromosomal,
non-essential circular
DNA molecules called
plasmids:
• much smaller than
bacterial chromosome
• have own Ori so it is
copied when cell divides
• several kilo-base pairs
(usu. 3-6 Kb)
plasmid
map
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What’s the Role of Plasmids?Plasmids generally contain genes that confer
some sort of advantage for survival and
reproduction:
1) genes providing protection from toxic substances
2) genes enabling the metabolism of additional
sources of energy
3) genes for toxins to kill microbial competitors,
enhance pathogenicity
4) genes involved in gene transfer by conjugation
• including antibiotic resistance
Inclusions & Chromatophores
Inclusions are deposits of various materials found in
certain types of bacteria (e.g., magnetosomes).
Chromatophores are pigment-containing infoldings of
the plasma membrane in some photosynthetic bacteria.
2. Eukaryotic Cell Structure
Chapter Reading – pp. 77-86
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Eukaryotic Organelles
Nucleolus
Perinuclearspace
Cilia
Ribosomes
CytoskeletonSmooth endoplasmicreticulum
Cell membrane
Rough endoplasmicreticulum
Transportvesicles
Golgi body
Secretoryvesicle
Centriole
Mitochondrion
Lysosome
Nuclear pore
Nuclearenvelope
Nucleolus
Nucleoplasm
Chromatin
Nuclear envelope
Two phospholipidbilayers
Nuclear pores
Rough ER
Rough ER
Nucleus Storage of Genetic Material:
• DNA + histones =
Chromosomes when
condensed in M phase
Chromatin when
uncondensed
Nucleolus
• assembly of
ribosomes from
rRNA & proteins
Membrane-boundribosomes
Mitochondrion
Freeribosomes
Rough endoplasmicreticulum (RER)Smooth
endoplasmicreticulum (SER)
Endoplasmic Reticulum (ER) Rough ER (RER)
• beginning of the secretory pathway
• ribosomes on cytoplasmic face of ER membrane synthesize proteins
across ER membrane into lumen
Smooth ER (SER)
• no ribosomes
• has membrane-
associated
enzymes that
catalyze new lipid
synthesis
(also found in RER)
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Secretory vesicles
Vesiclesarriving from ER
The Golgi Complex
Proteins destined to leave ER next go to the Golgi
• transported in vesicles, next stop in “secretory pathway”
• undergo any
necessary
modifications or
processing
• then sent via vesicles
to various destinations
• e.g., plasma membrane,
exterior of cell, other
organelles
Outer membrane
Crista
Inner membrane
Ribosomes
Matrix
Mitochondrion
ATP production via cellular respiration
• Krebs cycle • e- transport • chemiosmosis
• high [H+] in the
intermembrane
space due to
e- transport
in inner membr.
*H+ gradient
fuels ATP
synthesis*
Granum
Stroma
Thylakoid
Inner bilayermembrane
Outer bilayermembrane
Chloroplast
Organelle of photosynthesis:
• “light” reactions
occur in the
thylakoids
• convert sunlight
to energy in ATP
and NADPH
• “dark” reactions
occur in stroma
• energy from ATP
& NADPH used to
make sugars from
CO2 and H2O
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Flagella & Cilia Microbial structures used for locomotion:
Flagella• long & “few”
• wave-like motion
Cilia• short & “many”
Other OrganellesLysosomes• acidic compartments for the breakdown or
“digestion” of foreign or waste material
Vacuoles• large storage compartments
Peroxisomes• metabolize fats for heat production, degrade toxins
• H2O2 byproduct is “neutralized” by catalase
Centrosomes• region containing centrioles and other proteins
• “organizing center” for mitotic spindle fibers
Key Terms for Chapter 3
• diplo-, strepto-, staphylo-, tetrad, sarcina
• glycocalyx, capsule, fimbriae, pili
• peptidoglycan, teichoic acid, LPS, endotoxin
• coccus, bacillus, vibrio, spirillum, spirochete
• chemotaxis, endospores, plasmids, nucleoid
• inclusions, chromatophores, vegetative
• periplasmic space (periplasm)
Relevant Chapter Questions MC: 1, 5, 7-10, 13-15 Matching: 1, 2
Labeling (both) SA: 1-4, 7-10, 12-16