Download Prokaryotic and Eukaryotic Cells


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






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
[INSERT FIGURE 3.1]

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

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.
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

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

Glycocalyces


Gelatinous, sticky
substance surrounding the
outside of the cell
Composed of
polysaccharides,
polypeptides, or both

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
Polysaccharides or
polypeptides in
composition.
Surround the cell wall in
some bacteria.
Function:
Protection
from
phagocytosis
Osmotic barrier
Reservoir for nutrients
Virulence factor
Consist of polysaccharide
fibers that extend form the
bacterial surface
Functions:
Protection
Attachment
Associated
with biofilms

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
Flagella
Axial Filaments
Pili (Fimbriae)
Flagella
Structures of locomotion
Originate in the plasma
membrane
In bacteria rotate like a
propellar
Many different
arrangements

Flagella



Are responsible for
movement
Have long structures that
extend beyond cell surface
Are not present on all
prokaryotes

Flagella

Structure
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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
Arrangements of Flagella
A.
Monotrichous
B.
Lophotrichous
C.
Amphitrichous
D.
Peritrichous
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.
Endoflagellum is also know as an
axial filament.
Attached to the plasma embrane
and transverses the entire cell.
Responsible for the spirochete
morphology.

Flagella

Function
 Rotation propels bacterium
through environment
 Rotation reversible, can be
clockwise or counterclockwise
 Bacteria move in response to
stimuli (taxis)
 Runs
 Tumbles

Fimbriae and Pili

Rod-like proteinaceous
extensions
Fimbriae
Hollow tubes that
protrude from some
bacteria
Compose of protein
•
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

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.
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.
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.
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.
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.
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.
These plasmids may be transferred from one bacterial cell to another by the
F-pili.
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.
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.

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
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.
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.

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
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.

Flagella

Function

Do not rotate, but undulate
rhythmically
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.

Membranous Organelles
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Nucleus
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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
Nucleus - double membraned
organelle that houses the genetic
material of cell.
Nuclear membrane contains
numerous pores through which
proteins and RNA can move.


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
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.
.

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
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.

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

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
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.

Membranous Organelles

Chloroplasts



Light-harvesting structures
found in photosynthetic
eukaryotes
Have two phospholipid bilayer
membranes and DNA
Have 70S ribosomes

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
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