Download Fig. 4-1 - ISpatula

Jacquelyn G. Black
Microbiology: Principles and
Explorations
Sixth Edition
Chapter 4:
Characteristics of Prokaryotic and
Eukaryotic Cells
Copyright © 2005 by John Wiley & Sons, Inc.
Basic Cell Types
• Prokaryote: single-celled organisms, and all are bacteria.
• All bacteria are Prokaryote
• Prokaryotic cell means (cells lack a nucleus and other membrane
enclosed structures)
• Bacteria don’t have a mitochondria but it has the enzymes that
carry out the functions of mitochondria in its cytoplasmic
membrane (cell wall synthesis , ATP synthesis also done by the
cytoplasmic membrane)
• Eukaryote: single-celled or multi-cellular organisms
• Ex :fungi, protozoa
• Pro = before
• Eu = true
• Karyon = nucleus
###m see table 4.1 page80
• Similarities: Plasma membrane, DNA
and cell wall (plant cells)
• Differences:
1. Eukaryotic DNA is in a nucleus
surrounded by a nuclear membrane
2. Prokaryotic DNA is in a nuclear
region not surrounded by a
membrane
Table 4.1:Similarities and Differences
Between Prokaryotic/Eukaryotic Cells
• Prokaryotic cells have a single circular
chromosome; Eukaryotic cells have paired
chromosomes
• Prokaryotic cells lack histone proteins;
Eukaryotic cells have histone proteins
• Prokaryotic cell wall has peptidoglycan; plant
and fungal cells have both cellulose and
chitin(the exoskeleton of arthropods)
Domains
•
A relatively new concept in biological
classification, domain is the highest category
• The father of Botany classification is Carl
Linnaeus
• Three domains:
1. Archaea (ancient)… Bacteria is exist in this
domain
2. Bacteria (eubacteria) eu means true
3. Eukarya
Size, Shape and Arrangement
• Prokaryotes are among the smallest of all
organisms
• The smallest bacteria is (ricketsia and
clamedia)
• Prokaryotes range from 0.5 – 2.0 µm in
diameter and from 1.0 – 60 µm in length
• (in general)
shapes of Bacteria
1. Coccus (‫ )دائري‬spherical
2. Bacillus(rod like)
3. Coccobacilli (short rod intermediate
between cocci and bacillus)
4. Spiral : 1- comma shaped (vibrio)
2- wavy shaped (spirillum)
3- cork screw (spirochete) ex:
treponema pallidum( the cause of
sypihlis)
• ‫عادة‬
ً the bacteria of the same kind has the same size if
culturized at the same condition (depending on the
nutrients) other that a contamination has occurred
• less nutrient (starvation) the bacteria get smaller and
some time the shape will be changed
• More nutrient (it becomes larger)
• Even bacteria of the same kind sometimes vary in
size and shape depending on the availability of
nutrient
• Pleomorphism (different shapes) associated with the
lack of cell wall
Ex from other organism is ameboa
Arrangements (genetically determined upon
division) of Bacteria
Cocci in pairs (diplococci): Neisseria gonorria sp.)‫(المسببة لمرض السيالن‬
Cocci in chains (streptococci): Streptococcus sp . Strepto means chains &
cocci means spherical
The first 2 developed from cutting the organism in one plane
•
See figure 4.2 p 82
•
Cocci arranged in sarcina formed by a devision in 3 planes
•
Arrangment is specially for cocci
1.
2.
4- Cocci in clusters: Staphylococcus sp.
(grape like cluster) formed by devision in many planes randomly
5- Rods in chains: Lactobacillus sp.
(trains or side by side)
6- spiral rarely has arrangement
According to the shape there are other shape of bacteria
Ex: rosette, star shape,square
An Overview of Structure
•
•
•
From inside to out side
(chromosome in nuclear region-ribosome(protein synthesis)cytoplasm-cytoplasmic membrane(phospho lipid bilayer)-cell
wall(peptidoglycan)
After the cell wall some bacteria have (Flagella – papillae
(attachment)- capsule (protection)
•
Structurally, bacterial cells consist of the following:
1.
Cell membrane, usually surrounded by a cell wall (different among
doifferent type of bacteria) ex grab (+) & gram(-)
Internal cytoplasm with ribosomes, nuclear region, and in some
cases plasmid , granules and/or vesicles
Capsules, flagella, and pili (external)
2.
3.
The Cell Wall
•
Lies outside the cell membrane in nearly all bacteria
*not all bacteria have cell wall(do not have a peptidoglycan layer)
There is a cell wall deficient bacteria ex: (mycoplasma) but instead of
the cell wall it has a chemical called sterols(give regidity)
•
1.
2.
Two important functions:
Maintains the characteristic shape
Prevents the cell from bursting when fluids flow into the cell by
osmosis so if we remove the cell wall the bacteria will dye unless
we put it in protective environment (the pressure inside is equal to
the pressure out side)
****The cell wall is so porus allow the chemical substances to inter the
cell(not work as a permeability barrier)
****it digested by the lysozymes (in tears and saliva) discovered by
flemming (lysozyme has an antimicrobial activity
• Depending on the structure of the cell wall
there are 3 types of bacteria:
• 1- gram(+)
• 2- gram(-)
• 3- nonreactive
Components of Bacterial Cell Walls
•
•
Peptidoglycan (murein): The single most
important component
This polymer is made up of two alternating sugar
units: (sugar backbone)
1. N-acetylglucosamine (NAG)
2. N-acetylmuramic acid (NAM)
for each 1 NAM there is a pentapeptide
• The sugars are joined by (cross linking) short
peptide chains that consist of four amino acids
(tetrapeptides)
PEPTIDOGLYCAN LAYER
4
3
*layers of polymers of NAM & NAG , AND then they are cross linked by enzyme trans
peptidase (exist in the cytoplasmic membrane of gram (+) and gram (-) bacteria) this
process gives a rigid cell wall so if this process does not occurs then we get a very
weak cell wall then the bacteria get bursting
*(SUGAR BACKBONE) B 1-4 glycosidic bond between the NAM & NAG
*PENTAPEPTIDE WITH PENTAPEPTIDE BEFORE THE PROCCESS OF CROSS LINKING
*WHEN DIAMINOPIMELIC ACID IN POSITION 3 THEN WE TALK ABOUT GRAM (-) BACTERIA BUT
WHEN IT IWAS L LYSINE THEN IT WAS GRAM (+)
*THE CROSS LINKING MAY BE DIRECTLY VIA PEPTIDE BOND OR VIA GLYSINE BRIDGE
Teichoic Acid & lipoteichoic Acid
•
•
•
An additional component found in cell walls
of gram-positive bacteria
Consists of glycerol, phosphates, and ribitol
(sugar alcohol)
This polymer extends beyond the rest of the
cell wall EVEN THE CAPSULES (BRANCHED FROM THE
CELL WALL)
• Two functions:
1. Attachment site for bacteriophages (virus
cause infection for bacteria)
2. Passageway for movement of ions in/out of
cell
Outer Membrane (OM)
• A bilayer membrane found in gramnegative bacteria
• It works as a permeability barrier (prevent
the passage of chemical & anti microbial
agents ) gram(-) more resistant than the
gram(+) bacteria.
• Forms the outermost layer of the cell wall; is
attached to the peptidoglycan by a
continuous layer of lipoprotein molecules
• Proteins called porins(water filled channels)
form channels through the OM
• OM has surface antigens and receptors
Lipopolysaccharide (LPS)
*The cell wall in gram (-) is thinner but has additional
layer (LPS)
*An important component of the OM
• Also called endotoxin & pirogens; used to ID gramnegative bacteria
• *pyrogen free means: does not contain LPS
• When the LPS RELEASED … IT causes indotoxic
shock (vasodilation & hypotention & fever then heart
arrest then coma & MIGHT cause death)
• LPS Released when the cell walls of bacteria are
broken down
• Consists of polysaccharides and Lipid A
LIPOPOLYSACCHARIDE
The toxicity comes from the lipid A
Periplasmic Space
• The area between the cell membrane and the cell wall in gramnegative bacteria
• Another factor that means gram(-) bacteria more resistance than
gram (+) towards the anti microbial agent (in gram (+) the
enzymes that released to out side then it will be diluted when
treating it with anti microbial agent but in gram (-) it stored in the
periplasmic space in suffecient concentration to help destroy
substances that might harm the bacterium)
• Active area of cell metabolism & as a store
• Contains the cell wall, digestive enzymes and transport proteins
• Gram-positive bacteria lack both an OM and a periplasmic space
Distinguishing Bacteria by Cell Walls
•
•
•
•
•
Bacteria that has a cell wall divided to :
1-Gram-positive Bacteria have a relatively thick layer of peptidoglycan (60-90%) or a
high protein content called (m protein exist in streptococci)
*** protoplasts : g(+) bacteria the cell wall has been digested away by the effect of
different agent such as the lysozymes and this available in the protective environment
(osmolarity controlled so as not to burst)
** upon aging the cell wall become thinner & leaky then the rxn towards the stain
becomes variable
**** retain christal violet dye
•
2-Gram-negative Bacteria have a more complex cell wall with a thin layer of
peptidoglycan (10-20%)
Do not retain the crystal violet- iodine dye because of their thin walls and partly because of
relatively large quantity of lipoproteins & LPS
•
•
3-Acid-fast Bacteria is thick, like that of gram-positive bacteria, but has much less
peptidoglycan and about 60% lipid ex: mycobacteria
**there are Bacteria that do not have a cell wall
BACTERIAL CELL WALL
Acid-Fast Bacteria
•
Found in bacteria that belong to the genus, Mycobacterium sp.( resistent
against more than one antimicrobial agent) & it has a very slow growth
rate ( may be reach 1 month to growth )and this make it difficult to
identificated….. but the dubling time for the other bacteria is 30 min
•
PCR polymerase chain rxn : rapid identification technique to culturize
the microorganism and depends on the DNA to identificate the bacteria
•
Cell wall is mainly composed of lipid (waxy layer strongly lipophilic make
it impermeable)
•
•
Lipid component is mycolic acid above the peptidoglycan layer
The lipid make impermeable to most stain protects from acid and alkyl
•
Arabinogalactan ia a sugar make binding of the waxy layer with
peptidoglycan layer (instead of glycoprotein)
•
Acid-fast bacteria stain gram-positive
Controlling Bacteria by Damaging Cell Walls
• Cell wall is an essential component of the bacteria and
we can destruct it by some chemical or antibiotics ex :
B-lactam that include penicillin, cephalosporin,
pancomycin , esterasin & pilocarbine
• 1-The antibiotic penicillin blocks the final stages of
peptidoglycan synthesis
• 2-The enzyme lysozyme, found in tears and other
human body secretions, digests peptidoglycan
• Glycopeptides such as vancomycin & ( )
• If we remove the cell wall of g(+) bacteria we called it
protoplast and if we remove the cell wall of g(-) we
called it spheroplast
Wall-Deficient Organisms
• Bacteria that belong to the genus Mycoplasma have no cell walls,
protoplast , spheroplast & L-form
• They are protected from osmotic swelling and bursting by a
strengthened cell membrane that contains sterols
• Wall deficient strains are called L-forms (named after lister institute)
They have cell wall but suddenly lose their ability to form cell wall
(naturally OR UNDER THE EFFECT OF CERTAIN CHEMICAL)
•
•
So with this type of bacteria we don’t use the B-lactams ( high selectivity &
low toxicity) we use other agents
Arachae bacteria genetically do not have cell wall
Internal Structure
•
•
Cytoplasmic membrane has enzymes that are essential for the
growth of the microorganism
Cytoplasmic membrane is dynamic , constant change that main
function is regulate movement of material in & out & it
synthesizes the cell wall component & the electrons transport
chain & releasing flagillin done by the cell membrane
•
1.
Bacterial cells typically contain (in their cytoplasm):
Ribosomes (protein synthesis)
2.
Nucleoid region (contains the genetic material)
3.
Vacuoles (storage of certain chemical)
4. Certain bacteria sometimes contain endospores
Ribosomes
• Consist of ribonucleic acid and protein; serve as sites of
protein synthesis
• Abundant in the cytoplasm of bacteria
• Often grouped in long chains called polyribosomes(
translation of massenger RNA)
• 70S in bacteria 30S & 50S; 80S in eukaryotes
• Streptomycin(amino glycoside used as anti mycobacterial)
& Erythromycin (MACROLYTE for treatment of acne) bind
specifically to 70S ribosomes and disrupt bacterial protein
synthesis
Nuclear Region (Nucleoid)
• This centrally located nuclear region
consists mainly of DNA, but also contains
RNA and protein
• DNA: Usually one large, circular
chromosome
• Vibrio cholerae: Two chromosomes, one
large and one small
• Plasmids: Extrachromosomal pieces of
smaller, circular DNA