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Prokaryotic and Eukaryotic Cellular Structure
Prokaryotic & Eukaryotic Cells: An Overview
 Prokaryotes
 Do not have membrane surrounding
their DNA
 lack a nucleus
 Lack various internal structures bound
with phospholipid membranes
 Are small, ~1.0 µm in diameter
 Have a simple structure
 Composed of bacteria and archaea
Prokaryotic & Eukaryotic Cells: An Overview
 Eukaryotes
 Have membrane surrounding their
DNA
 Have a nucleus
 Have internal membrane-bound
organelles
 Are larger, 10-100 µm in diameter
 Have more complex structure
 Composed of algae, protozoa,
fungi, animals, and plants
Prokaryotic & Eukaryotic Cells: An Overview
[INSERT FIGURE 3.1]
Prokaryotic Cell Membrane
•
Structure
– Referred to as phospholipid
bilayer; composed of lipids and
associated proteins
– Approximately half composed of
proteins that act as recognition
proteins, enzymes, receptors,
carriers, or channels
• Integral proteins
• Peripheral proteins
• Glycoproteins
– Fluid mosaic model describes
current understanding of
membrane structure
Cell Membrane
Membranes contain a
hydrophilic and
hydrophobic side
Composed of many
different types of
proteins
Proteins in the lipid
bilayer move freely
within the membrane
Thin pliable lipid and protein envelope
that defines a cell.
Cell Membrane
Phospholipid bilayer
Functions:
•
•
•
•
•
Regulates nutrient and water
intake
Regulates waste removal
Site of prokaryotic respiration
Site of prokaryotic flagella
attachment
Involved in the distribution of
genetic material during binary
fission
Prokaryotic Cytoplasmic Membranes
•
Function
– Energy storage
– Harvest light energy in
photosynthetic prokaryotes
– Selectively permeable
– Naturally impermeable to most
substances
– Proteins allow substances to
cross membrane
• Occurs by passive or active
processes
– Maintain concentration and
electrical gradient
• Chemicals concentrated on
one side of the membrane or
the other
• Voltage exists across the
membrane
Cell Membrane
External Structures of Prokaryotic Cells
• Glycocalyces
– Gelatinous, sticky
substance surrounding
the outside of the cell
– Composed of
polysaccharides,
polypeptides, or both
External Structures of Prokaryotic Cells
•
Types of Glycocalyces
– Capsule
• Composed of organized
repeating units of organic
chemicals
• Firmly attached to cell surface
• Protects cells from drying out
• May prevent bacteria from
being recognized and
destroyed by host
Capsule
Polysaccharides or
polypeptides in composition.
Surround the cell wall in
some bacteria.
Function:
•Protection from
phagocytosis
•Osmotic barrier
•Reservoir for nutrients
•Virulence factor
Capsule Stain
Slime Layer
Consist of polysaccharide
fibers that extend form the
bacterial surface
Functions:
•Protection
•Attachment
•Associated with biofilms
External Structures of Prokaryotic Cells
•
Types of Glycocalyces
– Slime layer
• Loosely attached to cell
surface
• Water soluble
• Protects cells from drying out
• Sticky layer that allows
prokaryotes to attach to
surfaces
Bacterial
Appendages
Flagella
Axial Filaments
Pili (Fimbriae)
Bacterial Appendages
Structures of locomotion
Originate in the plasma
membrane
In bacteria rotate like a
propellar
Many different
arrangements
Flagella
External Structures of Prokaryotic Cells
• Flagella
– Are responsible for
movement
– Have long structures that
extend beyond cell surface
– Are not present on all
prokaryotes
External Structures of Prokaryotic Cells
 Flagella
 Structure
 Composed of filament, hook,
and basal body
 Flagellin protein (filament)
deposited in a helix at the
lengthening tip
 Base of filament inserts into
hook
 Basal body anchors filament
and hook to cell wall by a rod
and a series of either two or
four rings of integral proteins
 Filament capable of rotating
360º
Bacterial Appendages
A. Monotrichous
B. Lophotrichous
C. Amphitrichous
D. Peritrichous
Arrangements of Flagella
Bacterial Appendages
Axial filament (endoflagella)
Originates in the cell membrane and
transverses the length of the cell in the
periplasmic space.
As the endoflagella rotate to move the cell
the characteristic shape is formed .
Endoflagella are associated with
spirochetes.
External Structures of Prokaryotic Cells
Endoflagellum is also know as an
axial filament.
Attached to the plasma embrane
and transverses the entire cell.
Responsible for the spirochete
morphology.
External Structures of Prokaryotic Cells
•
Flagella
– Function
• Rotation propels bacterium
through environment
• Rotation reversible, can be
clockwise or counterclockwise
• Bacteria move in response to
stimuli (taxis)
– Runs
– Tumbles
Bacterial Appendages
• Fimbriae and Pili
– Rod-like proteinaceous
extensions
Bacterial
Appendages
Hollow tubes that
protrude from some
bacteria
Compose of protein
Fimbriae
External Structures of Prokaryotic Cells
• Fimbriae
• Sticky, bristlelike
projections
• Used by bacteria to
adhere to one another, to
hosts, and to substances
in environment
• Shorter than flagella
• May be hundreds per cell
• Serve an important
function in biofilms
• Virulence factor
External Structures of Prokaryotic Cells
•
Pili
– Tubules composed of pilin
– Also known as conjugation pili
– Longer than fimbriae but shorter
than flagella
– Bacteria typically only have one or
two per cell
– Mediate the transfer of DNA from
one cell to another (conjugation)
Bacterial Conjugation
Transfer of plasmid DNA
from a donor to a
recipient.
Process strengthens the
bacterial cell and alows
for survival in a
competitive environment.
Bacterial Inclusion Bodies
1. poly-Beta-hydroxybutyric acid - stores lipids for use in plasma
membrane
2. glycogen - stores starch like polymer of sugar for energy production
3. Polyphosphate granules (metachromatic granules) - storage for
phosphates for plasma membrane and the formation of ATP from
ADP.
4. Sulfur granules - stores sulfur which is necessary for the metabolic
reactions in biosynthesis.
5. Mesosome
Mesosomes - invagination of the
plasma membrane that increases
the surfaces area of the plasma
membrane during binary fission.
The mesosome also serves as a
site for the attachment and
distribution of genetic material
during binary fission.
Mesosome
In prokaryotic cell division, called
binary fission.
A diagram of the attachment of
bacterial chromosomes, indicating
the possible role of the mesosome
(an inward fold of the cell
membrane) in ensuring the
distribution of the "chromosomes"
in a dividing cell.
Upon attachment to the plasma
membrane, the DNA replicates and
reattaches at separate points.
Continued growth of the cell
gradually separates the
chromosomes and allocates
chromosome copies to the two
daughter cells.
Inclusion Bodies
6. gas vacuoles - storage of metabolic gases such as methane or hydrogen
gas. The gas vacuoles help in the buoyancy of the cell and aids in it
motility.
7. ribosomes - responsible for the synthesis of proteins.
8. nucleoid material - the genetic material of bacteria, which usually is balled
up in the cell. During binary fission the nucleoid material unravels within the
cell in order to be copied and distributed to the daughter cells.
9. Plasmid - small fragments of self-replicating extrachromosomal DNA that
codes for the resistance to antibiotics or for the productions of a specific
metabolite, i.e. toxins, pigments. These plasmids may be transferred from
one bacterial cell to another by the F-pili.
Inclusion Bodies
9. Plasmid - small fragments of self-replicating extrachromosomal DNA that
codes for the resistance to antibiotics or for the productions of a specific
metabolite, i.e. toxins, pigments. These plasmids may be transferred from
one bacterial cell to another by the F-pili.
Inclusion Bodies
These plasmids may be transferred from one bacterial cell to another by the
F-pili.
Inclusion Bodies
10. Endospores - a survival mechanism of certain genera of bacteria
such as Clostridium and Bacillus.
The endospores are composed of a complex of dipicolinc acid and
calcium and the function of the endospore is to protect the bacterial
chromosome.
The endospores are very resistant to heat, desiccation, freezing,
and other physical properties such as pesticides, antibiotics, dyes,
and acids.
Inclusion Bodies
The endospores may remain dormant for many years until the
environment becomes suitable to sustain the life of the bacteria.
The endospore will then germinate to form an exact copy of the
parent cell that produced it.
Eukaryotic Cell Walls & Cytoplasmic Membranes
•
•
Fungi, algae, plants, and some
protozoa have cell walls but no
glycocalyx
Composed of various
polysaccharides
– Cellulose found in plant cell
walls
– Fungal cell walls composed of
cellulose, chitin, and/or
glucomannan
– Algal cell walls composed of
cellulose, proteins, agar,
carrageenan, silicates, algin,
calcium carbonate, or a
combination of these
Cell Walls
Three different types of cell walls
and their compositions:
Fungal cell walls are composed of
cellulose and/or chitin.
Plant cell walls are composed of
cellulose.
Algal cell walls are composed of
cellulose, silicon, and calcium
carbonate.
Plasma Membrane
Consist of a lipid bilayer and
associated proteins. The Plasma
Membrane of Eukaryotic cells
resembles and functions in the
same manner as the prokaryotic
plasma membrane with the
following exceptions;
Contains high levels of sterols such
as cholesterol.
No respiratory enzymes are located
in the eukaryotic plasma
membrane.
Respiration occurs in the
mitochondria.
External Structure of Eukaryotic Cells
•
Glycocalyces
– Never as organized as prokaryotic
capsules
– Help anchor animal cells to each
other
– Strengthen cell surface
– Provide protection against
dehydration
– Function in cell-to-cell recognition
and communication
Eukaryotic
Appendages
Flagella
There are several different
arrangements of flagella in
eucaryotes.
This diagram represents a
biflagellated eukaryotic cell.
One of the flagella aids in
movement laterally and the other
aids in up and down movement.
The eukaryotic flagella move like a
whip.
See Flagellar handout.
Eukaryotic Appendages
• Flagella
– Function
• Do not rotate, but undulate
rhythmically
Eukaryotic
Appendages
Cilia
Similar to flagella both structurally
and functionally but are much
shorter and more numerous.
Cilia are found peritrichously to the
cell.
Move in an undulating manner and
motility by those organisms with
cilia is much more rapid than those
with flagella.
Intracellular Structures of Eukaryotic Organisms (organelles)
 Membranous Organelles
 Nucleus
 Often largest organelle in cell
 Contains most of the cell’s DNA
 Semi-liquid portion called
nucleoplasm
 One or more nucleoli present in
nucleoplasm; RNA synthesized in
nucleoli
 Nucleoplasm contains chromatin –
masses of DNA associated with
histones
 Surrounded by nuclear envelope –
double membrane composed of
two phospholipid bilayers
 Nuclear envelope contains nuclear
pores
Intracellular Structures of Eukaryotic Organisms (organelles)
Nucleus - double membraned
organelle that houses the genetic
material of cell.
Nuclear membrane contains
numerous pores through which
proteins and RNA can move.
Intracellular Structures of Eukaryotic Organisms (organelles)
 Membranous Organelles
 Endoplasmic reticulum
 Netlike arrangement of flattened,
hollow tubules continuous with
nuclear envelope
 Functions as transport system
 Two forms
 Smooth endoplasmic
reticulum (SER) – plays role
in lipid synthesis
 Rough endoplasmic
reticulum (RER) –
ribosomes attached to its
outer surface; transports
proteins produced by
ribosomes
Intracellular Structures of Eukaryotic Organisms (organelles)
Endoplasmic reticulum - network of
cytoplasmic membranes where
lipids and proteins are produced.
Smooth ER - synthesis of lipids
Rough ER - associated with
ribosomes and is responsible for
the synthesis of proteins.
.
Intracellular Structures of Eukaryotic Organisms (organelles)
 Membranous Organelles
 Golgi body
 Receives, processes, and
packages large molecules for
export from cell
 Packages molecules in
secretory vesicles that fuse
with cytoplasmic membrane
 Composed of flattened
hollow sacs surrounded by
phospholipid bilayer
 Not in all eukaryotic cells
Intracellular Structures of Eukaryotic Organisms (organelles)
Golgi apparatus (dictyosome) is
associated with the ER.
It modifies and packages the lipids
and proteins manufactured by the
ER and places them in vesicles for
cellular use.
Intracellular Structures of Eukaryotic Organisms (organelles)
•
Membranous Organelles
– Lysosomes, peroxisomes,vacuoles,
and vesicles
• Store and transfer chemicals
within cells
• May store nutrients in cell
• Lysosomes contain catabolic
enzymes
• Peroxisomes contain enzymes
that degrade poisonous wastes
Intracellular Structures of Eukaryotic Organisms (organelles)
• Membranous
Organelles
– Mitochondria
• Have two membranes
composed of phospholipid
bilayer
• Produce most of cell’s ATP
• Interior matrix contains
70S ribosomes and
circular molecule of DNA
Intracellular Structures of Eukaryotic Organisms (organelles)
mitochondria - involved in the
production of chemical energy in
the form of ATP.
Consist of convoluted inner
membrane and outer membrane.
Invaginations are called cristae and
contain enzymes used to synthesis
ATP.
All respiratory enzymes are located
in the inner membrane of the
mitochondria.
Cytoplasm of Eukaryotes
• Membranous
Organelles
– Chloroplasts
• Light-harvesting structures
found in photosynthetic
eukaryotes
• Have two phospholipid
bilayer membranes and
DNA
• Have 70S ribosomes
Cytoplasm of Eukaryotes
• Endosymbiotic Theory
– Eukaryotes formed from union of small aerobic
prokaryotes with larger anaerobic prokaryotes
– smaller prokaryotes became internal parasites
• Parasites lost ability to exist independently;
retained portion of DNA, ribosomes, and
cytoplasmic membranes
• Larger cell became dependent on parasites for
aerobic ATP production
• Aerobic prokaryotes evolved into mitochondria
• Similar scenario for origin of chloroplasts
– Not universally accepted
Cytoplasm of Eukaryotes
[INSERT TABLE 3.5]
Cytoplasm of Eukaryotes
[INSERT TABLE 3.4]
Eukaryotic Cell Walls &
Cytoplasmic Membranes
[INSERT TABLE 3.3]