Download 1. Prokaryotic Cell Structure A. Cell Shape 9/1/2016 1

9/1/2016
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)
• different kinds of cocci
exhibit characteristic
arrangements:
diplo- = found in pairs
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
Inclusions
Ribosome
Cytoplasm
Flagellum
Nucleoid
Glycocalyx
Cell
wall
Cell
membrane
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Plasma Membrane
Head, which
contains
phosphate
(hydrophilic)
true barrier between
“internal” & “external”
Phospholipid
Tail
(hydrophobic)
Integral proteins
Cytoplasm
Phospholipid
bilayer
Integral
glycoprotein
Integral protein
Peripheral
protein
• phospholipid content is a bit different compared to eukaryotes
Diffusion & Osmosis
Extracellular fluid
Cytoplasm
Diffusion
through the
phospholipid
bilayer
Facilitated
diffusion
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
Concentration Gradients
Na+
Cl –
Cell exterior (extracellular fluid)
Different concentrations
of ions inside vs outside
the cell are set up &
maintained by :
Cytoplasmic membrane
Integral
protein
Protein
DNA
Protein
Cell interior (cytoplasm)
• protein pumps
• active transport from
low to high conc.
• protein channels &
transport proteins
• facilitated diffusion
Creates a net negative
charge inside vs outside.
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Bacterial Cell Wall
The bacterial cell wall provides structure & support:
• main component is a structure called peptidoglycan
• polypeptide-linked
chains of a repeating
disaccharide
repeating disaccharide
backbone
Glucose
tetrapeptide
(amino acid)
crossbridge
N-acetylglucosamine N-acetylmuramic acid
NAG
NAM
(protects cell from
osmotic lysis!)
connecting chains
of amino acids
Osmosis & Cell Lysis
Cells without a wall
(e.g., mycoplasmas,
animal cells)
H 2O
H2O
H2O
Cells with a wall
(e.g., plants, fungal
and bacterial cells)
Cell
wall
Cell
wall
H2O
H2O
Cell membrane
H2O
Cell membrane
Isotonic
solution
Hypertonic
solution
Hypotonic
solution
Porin
Outer
membrane
of cell wall
Porin
(sectioned)
Peptidoglycan
layer of cell wall
Periplasmic space
Cell membrane
n
O side chain
(varies in
length and
composition)
Lipopolysaccharide
(LPS)
Phospholipid layers
Integral
proteins
Gram-negative Cell Wall
Core
polysaccharide
Lipid A
(embedded
in outer
membrane)
Gram-negative cell wall
• thin layer of peptidoglycan
Fatty acid
• outer membrane containing
lipopolysaccharide (LPS)
• Lipid A (endotoxin) + polysaccharide
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Gram-positive Cell Wall
Peptidoglycan layer
(cell wall)
Cell membrane
Lipoteichoic
acid
Teichoic acid
Integral
protein
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 capsule if compact, tightly attached to cell wall
• called a slime layer if loosely attached, water soluble
• 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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Flagella & Bacterial Motility
Bacteria undergo taxis, i.e. movement in response to
something.
e.g., chemotaxis (movement in response to a chemical substance)
Tumble
Run
attractant
(RUN = flagella rotate
counterclockwise)
Run
Tumble
(TUMBLE = clockwise)
Involves random “runs” & “tumbles”:
• longer runs, less tumbles in direction of “good stuff”
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
Non-motile appendages that are chemically and
functionally different than flagella.
Pili (singular = pilus)
Fimbriae
• involved in adhesion
Fimbria
Flagellum
• used in conjugation
Conjugation pilus
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C. Internal (Cytoplasmic) Structures
Chapter Reading – pp. 71-76
Prokaryotic Ribosomes
Carry out protein synthesis (i.e., translation of mRNA).
Ribosomes consist of 1 large and 1 small subunit.
• both subunits are made of rRNA & ribosomal proteins
• smaller, somewhat different from eukaryotic ribosomes
• specifically targeted by some antibiotics
Endospores
Cell wall
Cytoplasmic
membrane
1 DNA is replicated.
DNA
Vegetative cell
2 DNA aligns along
the cell’s long axis.
When conditions
are bad, some
Gram+ bacteria
can form
endospores:
• inactive, dormant
cells enclosed in a
highly resistant
spore coat
3 Cytoplasmic membrane
invaginates to form
forespore.
Forespore
4 Cytoplasmic membrane
grows and engulfs
forespore within a
second membrane.
Vegetative cell’s DNA
disintegrates.
First
membrane
Second
membrane
• remain dormant until
conditions are good
(even 1000’s of yrs!)
• very resistant to
heating, freezing,
dessication
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Completion of Endospore Formation
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A cortex of calcium and
dipicolinic acid is
deposited between
the membranes.
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Spore coat forms
around endospore.
Cortex
Spore coat
Outer
spore cost
7 Maturation of endospore;
completion of spore coat
and increase in resistance
to heat and chemicals by
unknown process.
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Endospore released from
original cell.
Endospore
Outer
spore cost
The Genetic Material
A 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
Plasmids
Some bacteria have >1
extrachromosomal,
non-essential circular
DNA molecules called
plasmids:
plasmid
map
• much smaller than
bacterial chromosome
• several kilo-base pairs
(usu. 3-6 Kb)
• have own Ori so it is
copied when cell divides
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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
• including antibiotic resistance
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
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
Nuclear
envelope
Nuclear pore
Lysosome
Mitochondrion
Nucleolus
Centriole
Perinuclear
space
Secretory
vesicle
Cilia
Golgi body
Transport
vesicles
Ribosomes
Rough endoplasmic
reticulum
Cell membrane
Cytoskeleton
Smooth endoplasmic
reticulum
Nucleus
Storage of Genetic Material:
• DNA + histones =
Nucleolus
Nucleoplasm
Chromatin
Nuclear envelope
Chromosomes when
condensed in M phase
Chromatin when
uncondensed
Two phospholipid
bilayers
Nuclear pores
Rough ER
Nucleolus
• assembly of
ribosomes from
rRNA & proteins
Rough ER
Endoplasmic Reticulum (ER)
Rough ER (RER)
• ribosomes on cytoplasmic face of ER membrane synthesize proteins
across ER membrane into lumen
Membrane-bound
• beginning of the secretory pathway
Smooth ER (SER)
ribosomes
Mitochondrion
Free
ribosomes
• no ribosomes
• has membraneassociated
enzymes that
catalyze new lipid
synthesis
(also found in RER)
Smooth
endoplasmic
reticulum (SER)
Rough endoplasmic
reticulum (RER)
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The Golgi Complex
Proteins destined to leave ER next go to the Golgi
• transported in vesicles, next stop in “secretory pathway”
Secretory vesicles
• undergo any
necessary
modifications or
processing
• then sent via vesicles
to various destinations
• e.g., plasma membrane,
exterior of cell, other
organelles
Vesicles
arriving
from ER
Mitochondrion
ATP production via cellular respiration
• Krebs cycle
• e- transport
• chemiosmosis
Outer membrane
• high [H+] in the
intermembrane
space due to
e- transport
in inner membr.
Inner membrane
Crista
*H+ gradient
fuels ATP
synthesis*
Matrix
Ribosomes
Chloroplast
Organelle of photosynthesis:
• “light” reactions
occur in the
thylakoids
Granum
• 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
Stroma
Thylakoid
Inner bilayer
membrane
Outer bilayer
membrane
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Flagella & Cilia
Microbial structures used for locomotion:
Flagella
• long & “few”
• wave-like motion
Cilia
• short & “many”
Other Organelles
Lysosomes
• 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
• coccus, bacillus, vibrio, spirillum, spirochete
• diplo-, strepto-, staphylo-, tetrad, sarcina
• peptidoglycan, teichoic acid, LPS, endotoxin
• glycocalyx, capsule, fimbriae, pili
• 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
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