Lecture 2
Dr. Dalia Mohsen prof. In Microbiology
Dr. Dalia M. Mohsen
CLS (311)
Prof. in Microbiolog
• Functional Anatomy of Prokaryotic and Eukaryotic
Cells
Dr. Dalia M. Mohsen
Prof. in Microbiolog
All living cells are classified into Prokaryotic and
Eukaryotic Cells, based on their structural and
functional characteristics.
Prokaryote comes from the Greek words for prenucleus.
Eukaryote comes from the Greek words for true
nucleus.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
PROKARYOTIC
CELLS
• Archaea
• Bacteria
EUKARYOTIC
CELLS
• Fungi
• protozoa,
• algae,
• plants
• animals
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Important
• Viruses -Non-cellular elements that do not fit
into any organizational scheme of living cells.
(will be discussed later)
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Bacteria are unicellular.
Most bacteria are 0.2 um in diameter and 2-8 um in
length.
Most bacteria are monomorphic – maintain a single
shape.
and few are pleomorphic – they can have many
shapes. Ex – Rhizobium and Corynebacterium.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Basic shapes of bacteria
COCCI
• Cocci may be oval, elongated, or flattened on one side.
• Cocci may remain attached after cell division. These group
characteristics are often used to help identify certain cocci.
Cocky that remain in pairs after
dividing are called diplococci.
Cocci that remain in chains
after dividing are called
streptococci.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Cocci that divide in two planes
and remain in groups of four are
called tetrads.
Cocci that divide in three planes and
remain in groups or cube like groups
of eight are called sarcinae.
Cocci that divide in multiple planes
and form grape like clusters or
sheets are called staphylococci.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Bacillus means rod shaped.
Bacilli only divide across their short axis, so there are fewer
groups.
•
Most bacilli appear as single rods. Diplobacilli appear in pairs after division.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Spiral bacteria have one or more twists.
Vibrios look like curved rods
Spirilla have a helical shape and
fairly rigid bodies.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
•Spirochetes have a helical shape and flexible bodies.
• Spirochetes move by means of axial filaments, which
look like flagella contained beneath a flexible external
sheath.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Stella are star-shaped.
Haloarcula, a genus of halophilic
archaea, are rectangular.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Streptobacilli appear in chains
after division.
Some bacilli are so short and
fat that they look like cocci and
are referred to as Coccobacilli.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
STRUCTURE OF A PROKARYOTIC CELL
virulent factor
movement
attachment
Dr. Dalia M. Mohsen
Prof. in Microbiolog
The structure is described according to the
following organization
Structures, external to cell wall
Structure of cell wall
Structures, internal to cell wall
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Dr. Dalia M. Mohsen
Prof. in Microbiolog
 Glycocalyx
 Flagella
 Axial filaments
 Fimbriae
 Pili
Dr. Dalia M. Mohsen
Prof. in Microbiolog

The glycocalyx (capsule, slime layer, or extra cellular
polysaccharide) is a gelatinous polymer.
A capsule is neatly organized
A slime layer is unorganized & loose
 External to cell wall, composed of polysaccharide, polypeptide
covering or both.
 The presence of a capsule can be determined by negative
staining.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Capsules are important in contributing to the virulence
of the bacteria.
• Protect bacteria by preventing phagocytosis.
• Allows the bacteria to adhere and colonize.
• Important components of biofilm –
 protects cell
 Facilitates communication among them
 Enable to survive by attaching to various surfaces
• Protects cell against dehydration
• Inhibit the movement of nutrients out of the cell.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Capsulated bacteria –
• Streptococcus pneumoniae
• Klebsiella pneumoniae
• Haemophilus influenzae
• Bacillus anthracis
• Streptococcus mutans
• Yersinia pestis
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Streptococcus pneumoniae
(in vivo)
Dr. Dalia M. Mohsen
Prof. in Microbiolog
K. pneumoniae
Haemophilus influenzae
Dr. Dalia M. Mohsen
Prof. in Microbiolog
• Long filamentous appendages consisting of a
filament, hook, and basal body
• Made of chains of protein (flagellin)
• Attached to a protein hook
• Anchored to the wall and membrane by the
basal body
• Semi rigid, helical structure that moves the
cell by rotating from the basal body.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Flagella are anchored by pairs of rings associated with the plasma membrane and cell
wall. Gram positive bacteria have only the inner pair of rings
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Flagella Arrangement
Peritrichous – distributed over
the entire cell
Dr. Dalia M. Mohsen
Monotrichous – single flagellum at
one pole
Prof. in Microbiolog
Lophotrichous – a tuft of flagella
coming from one pole
Dr. Dalia M. Mohsen
Amphitrichous – flagella at both
poles of cells
Prof. in Microbiolog
Dr. Dalia M. Mohsen
Prof. in Microbiolog
• Rotate flagella to run or tumble
• Move toward or away from stimuli (taxis)
• The stimuli include chemicals like oxygen, ribose, galactose –
Chemotaxis.
• Stimuli can be light – Phototaxis.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
• Flagellar (H) protein functions as an antigen.
• Flagella proteins are H - antigens - useful in distinguishing
the variants within the species of gram-negative bacteria.
• Example – 50 different H antigen for E. coli are identified.
• E. coli O157:H7 – associated with food borne epidemics.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
•Also known as Endoflagella – are bundles of fibrils that arise at
the ends of the cell beneath an outer sheath and spiral around the
cell.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
• Spiral cells that move by means of an axial
filament are called spirochetes.
• Axial filaments are similar to flagella, except
that they wrap around the cell.
• Anchored at one end of a cell
• Rotation causes cell the movement of the
outer sheath that propels the spirochetes in a
spiral motion.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
• Fimbriae and pili are short, straight, thin, hair like
appendages.
Made up of protein
called Pilin.
Arranged helically
around a central core.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
• Fimbriae –
– Occur at poles or evenly distributed.
– Number can vary from few to several hundreds
– Allow attachment to surfaces and adhere to each other
• Pili –
– Longer than Fimbriae
– Only one or two per cell
– are used to transfer DNA from one cell to another by
Conjugation – (sex Pili).
– Involved in motility called twitching motility – short jerky
intermittent movements, seen in Neisseria gonorrhoeae.
– Other type of motility is gliding motility – smooth gliding
movement of mycobacterium.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Is a complex, semi rigid structure responsible for the shape of
the cell.
Surrounds the underlying, fragile plasma membrane.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Functions:
•
Prevents osmotic lysis
•
Keep or protect the cell shape
•
Point of anchorage for flagella
•
In some species it has the ability to cause disease
and is the site of action for some antibiotics.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
• PEPTIDOGLYCAN - Main component of bacterial cell wall (also
known as murein) - a polymer consisting of disaccharide
N-acetyl glucoseamine (NAG) & N-acetyl muramic acid (NAM)
linked by polypeptides chains.
N-acetyl glucosamine (NAG) and N-acetyl
muramic acid (NAM) joined as in
peptidoglycan
Dr. Dalia M. Mohsen
Prof. in Microbiolog
• Alternating NAM and NAG molecules form a carbohydrate backbone (the glycan
portion).
• Rows of NAG and NAM are linked by polypeptides (the peptido - portion).
•The structure of the polypeptide cross-bridges may vary but they always have a
tetra peptide side chain, which consists of 4 amino acids attached to NAMs. The
amino acids occur in alternating D and L forms.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
consist of many layers of peptidoglycan and also contain teichoic acids.
Teichoic acids may:
• bind and regulate movement of cations into and out of the cell
• prevent extensive wall breakdown and possible cell lysis during cell growth
• provide much of the cell wall's antigenicity
Dr. Dalia M. Mohsen
Prof. in Microbiolog
•
Have a lipopolysaccharide-lipoprotein-phospholipid outer membrane
surrounding a thin (sometimes a single) peptidoglycan layer.
• Gram-negative cell walls have no teichoic acids.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
• Forms the periplasm between the outer membrane and the
plasma membrane.
• Protection from phagocytes, complement, antibiotics like
penicillin, lysozyme, and other chemicals. .
• O polysaccharide antigen, e.g., E. coli O157:H7.
• Lipid A is an endotoxin – causes fever and shock
• Porins (proteins) form channels through membrane
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Dr. Dalia M. Mohsen
Prof. in Microbiolog
• Like Mycobacterium tuberculosis,
Mycobacterium leprae
• Contains Mycolic acid layer (waxy layer)
instead of Peptidoglycan layer
Dr. Dalia M. Mohsen
Prof. in Microbiolog
• Mycoplasmas
– Smallest known bacteria
– Lack cell walls
– Sterols in plasma membrane protect them from lysis.
• Archaea
– Wall-less, or
– Walls of pseudomurein (lack NAM and D amino acids)
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Plasma membrane
Cytoplasm
Nucleoid
Ribosomes
Inclusions
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Cytoplasm is the aqueous solution or substances inside the plasma membrane
Consists of 80% water and primary proteins (enzymes), carbohydrates, lipids,
many low molecular weight compounds
Inorganic ions are present in higher concentration
It is thick, aqueous, semitransparent, and elastic containing DNA, ribosomes and
inclusions.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Bacteria contains negative supercoiled single covalently closed circular
chromosome (cccc) – single , long, continuous, and frequently
circularly arranged thread of double stranded DNA called Bacterial
Chromosome
Nuclear area (nucleoid), there is no nucleus
Bacteria can also contain plasmids, which are circular, extra-chromosomal
DNA molecules.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
The cytoplasm of a prokaryote contains numerous 70s ribosomes; ribosomes consist of
rRNA and protein.
Protein synthesis occurs at ribosomes; it can be inhibited by certain antibiotics.
The difference between prokaryotic (70s) and eukaryotic (80s) ribosomes allows
antibiotics to selectively target the prokaryotic ribosomes while sparing eukaryotic
ribosomes.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Endospores are resting
structures formed by
some bacteria for
survival during adverse
environmental
conditions.
•The process of endospore formation is called sporulation; the return of an
endospore to its vegetative state is called germination..
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Eukaryotic organisms include algae, protozoa,
fungi, plants and animals.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Flagella are few and long in relation to cell size; cilia are numerous
and short.
Flagella and cilia are used for motility, and cilia also move
substances along the surface of the cells.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Figure 4.23a, b
Both flagella and cilia are anchored to plasma
membrane by a basal body and consists of nine
pairs arranged in a ring, and two other single
microtubules in the center of the ring called a 9
plus 2 array.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
The cell wall of many Algae and some Fungi contain
cellulose.
The main material of Fungal cell walls is chitin (a polymer
of NAG units.
Yeast cell wall consist of glucan and mannan
(polysaccharide).
Animal cells are surrounded by a glycocalyx, which
strengthen’s the cell and provides a means of
attachment to other cells.
Dr. Dalia M. Mohsen
Prof. in Microbiolog
PLASMA MEMBRANE
Phospholipid bilayer
Peripheral proteins
Integral proteins
Transmembrane proteins
Sterols
Glycocalyx carbohydrates
Dr. Dalia M. Mohsen
Prof. in Microbiolog
Cytoplasm – encompasses substance inside the plasma
membrane and outside the cell
Cytosol - Fluid portion of cytoplasm
Cytoskeleton – provides support and shape and assists in
transporting substances through the cell
Cytoplasmic streaming - Movement of cytoplasm
throughout cells helps distribute nutrients and move
the cell over the surface
Dr. Dalia M. Mohsen
Prof. in Microbiolog