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Chapter 4
Prokaryotic
&
Eukaryotic Cells
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Prokaryotes VS Eukaryotes
General Differences
Prokaryotes
¾generally small (0.2 - 2 microns diameter & from 2-8 microns long)
¾no nucleus or other membrane bound organelles
¾one circular chromosome (most)
¾no histone proteins associated with DNA
¾cell wall generally contains peptidoglycan (complex polysaccharide)
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¾divide by binary fission
Eukaryotes
¾large cells
¾"true nucleus" and other membrane bound organelles
¾multiple linear chromosomes
¾histone proteins always associated with DNA
¾cell wall does not contains peptidoglycan
¾divide by mitosis (complex process)
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Bacterial Shapes
Coccus = sphere shaped
Bacillus = rod shaped
Coccobacillus = very short rod (egg) shaped
Vibrio = comma shaped
Spirillium = spiral shaped & rigid
Spirochete = spiral shaped & flexible
Star-Shaped = example: Stella
Rectangular – example Haloarcula
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Bacterial Arrangements
Due to plane of division used when new cells form
Chains form when they divide in one plane only
Tetrads form when divisions occur in two planes
Cube-like structures form when division is in three planes
e.g. Sarciniae
Grape-like clusters form with irregular divisions
e.g. Staphylococcus
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Arrangement: notice the plane of division
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What is the plane of division?
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Generalized Structure of Bacterium
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Structure of a Bacterium
(outside first!)
Features outside the cell wall MAY include:
Glycocalyx (‘sugar halo’) – a protective capsule secreted by the cell.
This often has the appearance and texture of a ‘slime coating’
Pili – transfer tubes which allow movement of DNA from one
bacterium to another – horizontal evolution
Fimbriae – attachment filaments present in many G-organisms. These
are used to attach to their target host or tissue. In some cases (mutants)
when these are not present the organism is less likely to cause disease
since it cannot readily attach to its host
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Movement Structures
(we’re still outside the cell wall)
Flagella – long whip-like structures seen in some bacteria
when ‘twirled’ or beaten (snakelike) these propel bacteria
through their environment
Flagellar arrangements: how many & where are they found?
Monotrichous – single flagellum located at the pole (end)
Lophitrichous –multiple flagella located at one end
Amphitrichous –flagella located at both ends
Peritrichous – flagella scattered over entire surface
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Attachment of Flagella
Basal Body is imbedded in the cell wall and cell membrane
(protein complex – two rings in G+ and four in GMain filament is attached to basal body by the hook
Clinical note:
flagellar proteins can
be of use in identifying
particular strains of
some bacteria
e.g. E. coli 0157:H7
(Bad beef!)
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More Movement Structures…
Axial Filaments, sometimes called
endoflagella (internal flagella)
these wrap around some spiral
shaped bacteria
Contraction of these filaments
produces a corkscrew-like
motion of these bacteria
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Movement in Response to Stimuli
Chemotaxis – movement toward favorable chemicals such as nutrients
(positive chemotaxis) or away from harmful chemicals (negative
chemotaxis)
chemotaxis follows a chemical gradient – movement toward (or away
from) stronger concentration of stimulus
Phototaxis – movement toward (or away from) light
Attractant – a positive stimulus which attracts bacteria
Repellent – a negative stimulus which causes bacteria to flee
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your book discusses attractant/repellent under chemotaxis, these can
also be applied to light
Bacterial Cell Wall
Composed of a network of repeating sugar molecules and proteins
called peptidoglycan (and sometimes other molecules)
Two sugars are NAM and NAG – a repeating disaccharide
N-acetylglucosamine = NAG
N-acetylmuramic acid = NAM
Peptides lace through the NAG/NAM bundles
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Gram Positive Cell Wall Details
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Gram Negative Cell Wall Details
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Comparison of G+ and G- cell wall
G+
G-
Note large amount of
peptidoglycan and
no second (outer) layer
of plasma membrane
Note small amount of
peptidoglycan and
second (outer)layer
of plasma membrane
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Outer Membrane of GComposed of:
¾Phospholipid bilayer
¾Lipopolysaccharides
¾Lipoproteins
Functions:
¾Barrier to some antibiotics
¾barrier to attack from some chemicals (detergents, metals…)
Proteins called porins allow some useful materials to enter cell
Polysaccharide portion useful for identifying some strains
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One particular lipid, Lipid-A is an endotoxin causing fever & shock
(blood or gastrointestinal)
Cell /Plasma Membrane
Structure:
phospholipid bilayer = two layers of phospholipids
Arranged tail to tail with ‘heads’ on the extreme outer & inner edges of
the membrane and tails pointing to the inside of the membrane contains
embedded proteins
This arrangement is known as the Fluid Mosaic Model
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Cell Membrane as a Barrier
semi-permeable membrane (permits specific things to pass)
small molecules and water pass freely
charged molecules and larger ones cannot pass freely must be assisted
in some fashion
Proteins imbedded in the membrane transport substances across
the membrane either as pores or by facilitated diffusion
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Movement Across the Membrane
Some methods for moving across membrane
(descriptions to follow on later slides)
Diffusion
Osmosis
Passive Transport
Active Transport
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Diffusion – the movement of particles from region of high
concentration to low concentration
Tends to continue until evenly distributed throughout the medium
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Osmosis
diffusion of water across a semi-permeable membrane
(our cell membrane is a semi-permeable membrane)
ok backup, what is diffusion?
Movement of molecules from an area of high concentration to an area
of low concentration (often proceeds until equilibrium)
Solutions relative to cell solute concentration can be either:
isotonic: equal solute concentration
hypotonic: lower concentration of solutes
hypertonic: higher concentration of solutes
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Osmotic pressure: pressure which causes water
movement in or out of a cell
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Passive Transport
Large pores in the membrane (formed by proteins) allow some
molecules to pass through by simple diffusion
This is referred to as passive because the cell has to expend
no energy for it to occur
Successful passage through a pore often based on
¾ charge of molecule
¾ size of molecule
¾ shape of molecule
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Facilitated Diffusion
Protein carrier molecules provide access across the membrane
requires no energy from the cell
Substances flow along concentration gradient – that is to say, from high
concentration where they are plentiful to low concentration where they are scarce
(this provides the energy)
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Active Transport
(requires energy)
Protein mediated – proteins act as carrier molecules
Molecules that are needed inside the cell can be transported against the
concentration gradient
Often molecules pass through unchanged to be used in cell as is…
ALTERNATIVELY cells can perform:
Group Translocation – molecules are chemically altered during trip
across the membrane in a way that keeps it inside the cell
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Cytoplasm
The fluid portion of the cell – largely (80%) water, this
solution also contains proteins, lipids, ions, carbohydrates
and other chemicals
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‘Nuclear Area’
The DNA of a bacterium is not contained in a nucleus (i.e. not
surrounded by a separate membrane)
The bacterial chromosome is a continuous circular loop of
double-stranded DNA
The chromosome is attached to the inner surface of the cell membrane
at a spot called the origin (replication begins here)
Occasionally smaller loops of DNA occur separate from the
chromosome, these are called plasmids
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Ribosomes
These structures are composed of rRNA and protein
They are the ‘protein factories’ of the cell
Each ribosome consists of two subunits
¾30S
¾50S
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Inclusions
Often prokaryotes store nutrients of other molecules in crystals or
droplets in the cytoplasm – Some include:
Metachromatic granules – inorganic phosphate stores these often stain
red in the presence of Methylene Blue they are typical of
Cornybacterium diptheriae
Polysaccharide granules – starch or glycogen (energy!) stores stain
blue (starch) or red-brown (glycogen) in presence of iodine
Lipid Inclusions (fat/oil) – energy store – visible with fat soluble dyes
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More Types Of Inclusions
Sulfur Granules – energy for some – Thiobacillus can utilize sulfur as
an energy source
Carboxysomes – present in bacteria that can use CO2 and
photosynthesis to produce energy. These inclusions are an enzyme
that assists their metabolism
Gas Vacuoles – ‘bubbles’ these help maintain a particular depth so the
organism has access to light & nutrients
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Still More Inclusions
Magnetosomes – magnetic clusters of
iron oxide. May
provide some protection from hydrogen
peroxide (occurs in
nature, not just in a brown bottle from the
drug store).
Novel use for bacterial products!
Researchers now grow magnetosome
producing bacteria
and harvest the magnetite to produce
magnetic recording
media for tape & computer disks
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Endospores
Resting state formed by some bacteria during environmental stress.
Spores are highly resistant to drying & temperature extremes.
(can survive boiling water for hours!)
Spores can remain dormant for thousands of years!
Sporultion – the process of forming spores
Germination – spore returning to the vegetative (normal) state
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Endospores and Disease
• Dry spores are far more likely to become airborne as ‘dust’.
• Thus, when considering virulence (ability to produce disease), dry
spores are far more dangerous than wet live cultures.
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Eukaryotic Cells
Organisms with a nucleus AND… Membrane bound organelles
Plasma membrane: phospholipid bilayer (as prokaryotic cells)
Plasma membrane also contains sterols which may help
Prevent lysis (rupture)
Membrane also contains surface molecules (proteins & carbohydrates)
used in cell-cell recognition. Surface molecules may provide
attachment sites for bacteria
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Cell Wall
Cell wall: in plants, algae, and fungi (NOT PRESENT in animal cells)
Cell wall of yeast = polysaccharides
¾ chitin
¾ glucan
¾ mannan
Cell wall of plants (and some algae) also polysaccharide
¾ cellulose
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Cytoplasm
Cytoplasm: area inside the plasma membrane and outside nucleus
Consists of:
¾ cytosol
¾ organelles (‘little organs’)
Cytosol – the fluid part of the cell (excluding the organelles)
about 80% water. Includes dissolved solids such as ions,
proteins, other molecules
contains filaments (microfilaments, intermediate filaments, and
microtubules) which form cytoskeleton
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Filaments also help accomplish cytoplasmic streaming
Cytoplasmic Inclusions
‘Things inside a cell’
Oil/fat droplets – for energy storage
Glycogen grains (animal starch) for energy storage
Organelles – ‘cellular organs’
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Organelles… (so we begin)
Ribosomes – the ‘protein factories’ of the cell
Made up of rRNA and Protein
There are two subunits
¾a large 60S subunit and
¾a small 40S subunit
Together then form an 80S ribosome
S = refers to their sedimentation rate not their size so you don’t add the
numbers
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Nucleus
Nucleus: contain DNA bound to histones and surrounded by
double-membrane (nuclear envelope) with small pores (nuclear pores)
Nucleoli - condensed regions of DNA where ribosomal RNA is
being synthesized
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Mitochondria
Production of energy for the cell. Mitochondria have both an inner and
outer membrane (double membrane)
Synthesize ATP - Enzymes within the matrix (fluid) are involved in the
production of ATP
Cristae – folds in the inner membrane – site of enzymes involved in
ATP production
Mitochondria have their own DNA (circular) & ribosome (70S)
Mitochondria replicate by binary fission
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Chloroplast
Membranous inner sacs called thylakoids contain the chlorophyll and
enzymes involved in photosynthesis
Chloroplasts have their own DNA & 70S ribosomes
Chloroplasts replicate within the cell by binary fission
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Endosymbiotic Theory
Chloroplasts & Mitochondria – ‘hitchhikers’
likely to be ancient organisms living in symbiosis with eukaryotic cells
They receive safe, nutrient rich environment
they provide energy or harvest light for the host cell
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Student Reading
Review remaining organelles… know basic functions of
Endoplasmic reticulum
Golgi apparatus
Lysosomes
Peroxisomes
Flagella
Cilia
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