Transcript prokaryotic cells

PROKARYOTIC CELLS
I.
II.
III.
IV.
V.
SIZE, SHAPE, AND
ARRANGEMENT
CELL WALL
CELL MEMBRANE
INTERNAL STRUCTURE
EXTERNAL STRUCTURE
CLASSIFICATION OF
PROKARYOTES
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All prokaryotes are classified to
either the domain Arehaea (ancient
bacteria) or the domain Bacteria
(true bacteria).
The two domains differences are on
the molecular level, not in the
structural level.
Most belong to the domain Bacteria.
Archaea has no pathogenic forms,
yet!
I. SIZE, SHAPE, AND
ARRANGEMENT
A. Bacteria are generally smaller than
Eukaryotes.
B. They have a large volume to
surface ratio which allows them to
move substances in and out of the
cell quickly.
C. The bacteria Epulopicium fishelsoni
can be seen with the naked eye!
I. SIZE, SHAPE, AND
ARRANGEMENT
D. Bacteria are grouped by shape
(look at figure 4.1).
1. Coccus – round and “grape like”
shape.
2. Bacillus – rodlike shape. They
can be rectangular, club shaped or
swollen.
3. Coccobacillus –between a
coccus and bacillus.
I. SIZE, SHAPE, AND
ARRANGEMENT
4. Vibrio – spiral bacteria that has a
comma shape.
5. Spirillum (Spirilla) – spiral bacteria
that has a rigid wavy-shape.
6. Spirochete – sprial bacteria that
has a corkscrew shape.
I. SIZE, SHAPE, AND
ARRANGEMENT
E. Bacteria can also have certain
arrangements (look at figure 4.2).
1. Di = pairs
2. Tetrads = groups of 4
3. Sarcina(e) = packets of 8
4. Strepto = chains
5. Staphylo = grape like clusters
6. Star shaped, Square and
Rosette(attached to a substrate)
What are the following
pictures(shape and
arrangement)?
An Overview of Structure
 Bacterial
cells have a cell
membrane, cytoplasm,
ribosomes, a nuclear
region, and external
structures.
II. CELL WALL
A. Most all bacteria have a cell wall
(Look at figure 4.3 and your
coloring sheets). It serves two
functions:
1. It helps maintain the shape of
the cell.
2. It prevents the cell from
bursting by osmosis.
II. CELL WALL
B. The rigid cell wall outside the cell
membrane is composed mainly of
the polymer peptidoglycan (most
important component in cell
walls).
C. Cell walls differ in composition
and structure. We classify them
on a staining technique a called
the gram stain. They can be
positive or negative.
II. CELL WALL
D. GRAM POSITIVE BACTERIA
1. In Gram-positive bacteria, the cell
wall consists of a thick, dense layer
of peptidoglycan, with teichoic acid
in it (Look at figure 4.6).
2. If you digest the cell wall of these
bacteria they become
PROTOPLASTS (a cell that has a
membrane but no cell wall). It also
has a small periplasmic space (area
between membrane and the cell
wall).
II. CELL WALL
E. GRAM NEGATIVE BACTERIA
1. Cell wall has a thin layer of
peptidoglycan, separated from the
cell membrane by the periplasmic
space(larger) and enclosed by an
outer membrane made of
LIPOPOLYSACCARIDE (Contains
Lipid A – Fat), or ENDOTOXIN.
2. If you digest away the cell wall they
become SPHEROPLASTS (has cell
membrane and most of the outer
membrane.
3. Lipid A can cause fever ect…Toxic!
II. CELL WALL
F. In acid-fast bacteria, the cell wall
consists mainly of lipids, some of
which are true waxes, and some of
which are glycolipids.
G. Some bacteria have no cell walls.
One species is Mycoplasma and
shows various shapes and forms.
H. Cell walls are controlled by
Penicillin (blocks formation of cell
walls) and Lysozyme (found in
tears and secretions digests
peptidoglycan).
III. CELL MEMBRANE
A. The cell membrane has a fluidmosaic structure with
phospholipids forming a bilayer and
proteins interspersed to a mosaic
pattern.
B. It regulates the movement of
materials into and out of cells.
C. It performs functions usually
carried out by organelles of
eukaryotic cells – DNA replication,
respiration, captures ATP, secretes
proteins.
IV. INTERNAL STRUCTURES
A. Cytoplasm - the semifluid
substance inside the cell
membrane. Look at coloring sheets.
B. Ribosomes - consist of RNA and
protein, serve as sites for protein
synthesis.
C. Nuclear region - usually includes
just one, large, circular
chromosome, which contains the
prokaryotic cell's DNA and some
RNA and protein. It is also possible,
but rarely, to have two circular
chromosomes.
IV. INTERNAL STRUCTURES
D. Inclusions – small bodies inside the
cytoplasm. There are two types:
1. Granules - store glycogen
(energy) or other substances.
2. Vesicles - filled with gas (to help
them float in water).
E. Endospores – helps the organism
survive in adverse conditions. May
also be part of the regular life
cycle. They are very resistant to
heat, acid, radiation. Can live up to
10,000 years at –14C at 430m!
IV. INTERNAL STRUCTURES
F. Plasmids –
smaller circular
molecules of
DNA. This
supplements
information
contained in the
chromosome.
These are also
used in genetic
engineering.
V. EXTERNAL STRUCTURES
A. Bacteria can contain flagella & pili
which extend beyond the cell wall
and can have slime layers and
capsules which surround the cell
wall.
B. Flagella - (Half of all bacteria are
motile) long thin, hairlike
projections. 5 types:
1. Monotrichous – one flagella at
one end.
V. EXTERNAL STRUCTURES
2. Amphitrichous – 2 flagella; one at
each end.
3. Lophotrichous – 2 or more at one
end or both ends.
4. Peritrichous – Flagella all over the
surface.
5. Atrichous – without flagella, cocci
rarely have them.
V. EXTERNAL STRUCTURES
C. Structure of a Flagella (Figure
4.13)
1. Made of Protein = Flagellin
2. Basal body – embedded in the
cell membrane.
3. Hook – rotates; attaches to
filament; counterclockwise =
moves straight; clockwise = moves
in a tumble.
4. Filament – Extends from cell,
causes the movement.
Flagella and
Movement
V. EXTERNAL STRUCTURES
D. Axial filaments or Endoflagella- do
not extend away from body; on
surface; found in spirochetes;
causes it to rotate like a corkscrew.
E. Much of bacterial movement is
random (see figure 4.14).
F. Chemotaxis - movement toward
attractants and away from
repellants.
G. Phototaxis - movement toward or
away from light.
V. EXTERNAL STRUCTURES
H.
Pili – help bacteria attach to a surface.
1. Conjugation pili - allow exchange of
DNA.
2. Attachment pili (fimbrae) - help
bacteria adhere to surfaces.
I. Glycocalyx - includes all
polysaccharides external to a bacteria’s
cell wall. Two types:
1. Capsules - prevent host cells from
destroying a bacterium; capsules of any
species of bacteria have a specific
chemical composition.
V. EXTERNAL STRUCTURES
2. Slime layers - protect bacterial
cells from drying, trap nutrients,
and sometimes bind cells together,
as in dental plaque.