i want 30 multiple choice questions with their model answer below each question that covers different aspects of all of the following information: objectives The student should be able to:
u Determine microbiology ; meaning and major groups of microorganisms.
u Differentiate between prokaryotic and eukaryotic cells.
u Describe the typical bacterial cell based on Size, shape and grouping of bacteria.
u Determine structure and importance of structural components of bacterial cell.Pre test:
u Which of the following bacterial structures is located
outside bacterial cell wall?
u Choose the most accurate sentence describing prokaryotic
bacterial cell.
a.
b.
c.
d.
Its DNA isn’t enclosed in nuclear membrane.
It has only one chromosome.
It has peptidoglycan in its cell wall.
All of the above.
u Peptidoglycan represents the main cell wall component in
which of the following cells?
b.
a.
b.
c.
d.
Human cell.
Fungal cell.
Bacterial cell.
Viral cell.
c.
d.
a.
b.
c.
d.
Plasmids.
Cytoplasmic membrane.
Capsid.
Flagella.
u Choose the most accurate sentence describing bacterial
cell wall.
a.
Peptidoglycan represents 50% of thickness in Gram
positive cell wall and 5-10% of Gram-negative cell wall.
Peptidoglycan represents 5%of thickness in Gram positive
cell wall and 5-10% of Gram-negative cell wall.
Peptidoglycan represents 50% of thickness in Gram
positive cell wall and 60% of Gram-negative cell wall.
Peptidoglycan represents 5-10 % of thickness in Gram
positive cell wall and 50% of Gram-negative cell wall.u As regarding bacterial cell membrane function.
Which of the following is true?
a.
b.
Determines cell reaction to Gram stain.
Plays a role in cell division.
c. Maintains shape and Gram character of
bacteria.
d. Maintain a constant inner bacterial
environment.
u Which of the following best describes Gram negative cell wall?
a.
u Bacterial cytoplasmic membrane maintains
constant inner bacterial environment by which
of the following mechanisms?
a.
b.
Controlling transport mechanisms.
Determining Gram character.
c. Maintaining bacterial shape.
d.
Participating in cell division.
Choose the best sentence about medical importance of bacterial spores.
a. Sterilization by boiling at 100°c for 20-30 minutes is needed to free instruments and products from spores for medical use.
b. Sterilization by dry heat at 121°c for 20-30 minutes is needed to free instruments and products from all microorganisms except spores
for medical use.
c. Sterilization by autoclaving at 121°c for 20-30 minutes is needed to free instruments and products from spores for medical use.
d. Sterilization by autoclaving at 100°c for 5 minutes is needed to free instruments and products from only spores for medical use.
Lipopolysaccharide is extremely toxic to the human body and is called the
endotoxin.
b.
c.
d.
Lipopolysaccharide is released only when the bacterial cells are lysed, and
is responsible for the fever, hypotension and shock caused by gram negative
organisms.
Has a thin layer of peptidoglycan (2 sheets) which forms only 5-10% of the
cell wall material is located inside the outer layer of LPS.
All of the above.
u Which of the following best describes Gram negative cell wall?
a.
Contains Lipopolysaccharide (LPS) which is non toxic to the human body.
b.
c.
d.
Contains Lipopolysaccharide (LPS) which is extremely toxic to the human
body.
Contains teichoic acid which is extremely toxic to the human body.
Contains teichoic acid which is non toxic to the human body.uMicrobiology: science dealing with
invisible microbes.
uHuman infectious agents: bacteria,
fungi,
viruses,
helmenths.
protozoa
andProkaryotic cell
Eukaryotic cell
7Characteristic Prokaryotic
Eukaryotic
bacterial cells human cells
DNA within nuclear
membrane
Mitotic division
Mitotic division
DNA associated with
histones
Absent
No
No
Chromosome number One
Chromosome number
Membrane bound
organells
Size of ribosome
Size of ribosome
Cell wall containing
peptidoglycan
No
70S
Yes
Present
Yes
Yes
More than one
Yes
80S
NoShape
Arrangement
ArrangementBacterial structure
Cell wall
• Gram positive
• Gram negative
Structures inside
cell wall
• Cytoplasmic
membrane
• Nucleoid
• Ribosomes
• Intracytoplasmic
inclusions.
• plasmids
Structures
outside cell wall
• Capsule
• Flagella
• Pilicontinued
Bacterial cell wall
uThe cell wall is the outermost component of all bacteria.
uIt is a multilayered structure located external to the
cytoplasmic membrane.
uIt is composed of a layer of peptidoglycan to which the
cell owes its rigidity.continued
Bacterial cell wall
uPeptidoglycan layer 50% of thickness in
gram positive bacteria, 5-10% of thickness
in gram negative bacteria.
uNAG – NAM (back bone) , tetrapeptide side
chains and peptide cross bridges.uGood target for antibacterial drugs.
uBeside peptidoglycan additional
components in the cell wall
differentiate gram negative from
grampositivebacteria.In gram positive bacteria:
uThick peptidoglycan 40 sheets.
uResponsible for bacterial rigidity
and shape.Teichoic and lipotechoic acid:
u Major surface component.
u On both sides of peptidoglycan layer.
u Immunogenic.
u induces Tnf α and IL-1 production by
macrophages.
u Toxic shock.
u Adherence.continued
In gram negative bacteria:
Lipopolysaccharide (LPS) (endotoxin):
ü outer layer of lipopolysaccharides (LPS) which is extremely toxic to the human
body and is called the endotoxin.
ü It is released only when the bacterial cells are lysed, and is responsible for the
fever, hypotension and shock caused by gram negative organisms.
- (Lipid A ): the lipid fraction responsible for the
toxicity.
- (polysaccharide (somatic O antigen): immunogenic.u Lipoprotein molecules cross link the outer membrane and
peptidoglycan layers.
Periplasmic space:
- Is the space between outer and inner layer of cytoplasmic
membrane.
- Filled with gel solution of proteins.
- It is the site of β-lactamase enzymes in some bacteria that
degrade penicillins and other ℬ-lactam drugs.continued
Functions of cell wall:
Remember shape of bacteria
uMaintains shape of bacteria.
uOsmotically insensitive so it protects cytoplasmic
membrane against bursting in hypotonic solutions.
uDetermines the cell reaction to Gram’s stain.
uPlays a role in cell division.
RememberGram characters
of bacteriauThink about peptidoglycan layer and
antibiotics development !!!!!!!
Since peptidoglycan is present in bacteria
but not in human cells, it is a good target
for antibacterial drugs. Several of these
drugs, such as,
the penicillin and
cephalosporins, inhibit its synthesis.Cell wall deficient bacteria:
u Mycoplasma: is the only bacterial species deficient in cell wall. Hence, they are pleomorphic,
are not destroyed by penicillin which acts on the bacterial cell wall, and can not be stained
with gram stain.
u Protoplasts.
u Spheroplasts.
u L- forms.
Bacterial cell wall may be lost under the effect of certain environmental conditions e.g.
treatment with penicillin and lysozyme. If such treated cells are placed in osmotically protective
media, they liberate protoplasts from gram positive cells and spheroplasts from gram negative
cells.
ü Revert to original form!!!!!!
ü Effect on infection!!!!!!Structures inside cell wall
1- Cytoplasmic membrane
usemipermeable .
uDouble layer.
uPhospholipid and protein.Function of cytoplasmic membrane
Main function is maintaining constant environment inside the cell by controlling
transport mechanisms
Active
transport
Selective
permeability
hydrophobic
barrier
against
hydrophilic
molecules
of ions (H ,
Na , K ,
etc..) and
nutrients
to achieve
osmotic
balance
and a pool
of
nutrients.
Energy
production
(respiration
site) supplies
the cell with
energy
through
electron
transport and
oxidative
phosphorylati
on, i.e. site
of
respiration.
Hydrolytic
enzymes
(degrades
nutrients)
degrade the
different
nutrients
into subunits
small enough
to penetrate
the
cytoplasmic
membrane.
Excretion
of
pathogenicity
proteins e.g.
IgA
protease
and some
exotoxins.
Enzymes
and
carrier
molecules
Function
in DNA ,
cell wall
and lipid
membrane
layer
synthesis
Receptors
and
proteins
for
chemotactic
and other
sensory
transduction
systemsMesosomes
u Invaginations of cytoplasmic membrane.
u play a role in respiration and cell division.
u They function:
u Origin of the transverse septum that divides the cell in half.
u Binding site of the cell DNA which duplicates to provide the
genetic material of each daughter cell.continued
Intracytoplasmic structure
1- Nucleoid:
u DNA in the cytoplasm with no nuclear membrane or
nucleolus.
u (Chromosome) single circular packed bundle of
double stranded DNA.
u Carries the genetic material to daughter cells.
u It duplicates before cell division.continued
2- Ribosome
- Tightly packed spherical particles in the
cytoplasm.
- 40% protein, 60% RNA.
- 70 S with 30 S and 50 S subunits.
- Site of protein synthesis.3- Intracytoplasmic inclusions
- Accumulation of food reserve.
- Rich in lipids or carbohydrates.
- volutin granules rich in metaphosphate are found in the
genus Corynebacterium.4- Plasmids
- Extrachromosomal double stranded
circular DNA.
- Replicates independent of the
bacterial chromosome.continued
Structures outside cell wall
1- capsule
- Gelatinous polysaccharide layer.
- In anthrax bacillus it is polypeptide.
- Best formed in vivo.
- Appears as unstained halo around
- organism.Capsular function:
1- Antiphagocytic:
The slimy capsule makes it difficult to phagocytes
to hold firmly on bacterial cells.
The capsule masks bacterial cell wall components as
complement receptors.
2- Facilitates adherence to human cells.continued
Role in bacterial classification
u Variation of sugar components of the polysaccharide
is responsible for presence of different serological
types within one species.
u 85 Strept. pneumoniae types.Importance of capsule in medicine:
- Identification of an organism can be made by adding anti-
capsular antibodies to the organism, if the antibody is
specific, the capsule swells and can be seen by the
microscope, this is called the quellung reaction.
Acts as immunogen in certain vaccines like, meningococcal,
pneumococcal and H. influenza type b.• Glycocalyx (slime layer)
what?
is a loose polysaccharide meshwork of fibrils
extending outward from the cell of some
bacteria.
Action?
It allows the bacteria to adhere firmly to
various structures e.g. skin, heart valves,
and catheters.
Example?
It mediates adherence of Strept. mutans to
the surface of the teeth leading to the
formation of dental plaque which is the
precursor of dental caries.2- Flagella
- Long thin filamentous appendages
attached to cell wall and cytoplasmic
membrane with basal body.
- Composed of single protein (flagellin).
- Seen only By electron microscope.Function of flagella:
Organ of motility, they move bacteria
towards nutrients and other attractants.
Importance in medicine:
Specific antisera can be prepared against
flagellar H antigen and are used to
determine the serologic type of strain in
certain flagellated species.3-Pili
-Hair like filaments.
-Shorter and thinner than flagella.
- Composed of protein pilin.
- Found mainly in gram negative organisms.
- They are 2 types.A- Ordinary pili (colonization antigens):
ü Also known as "colonization antigens",
ü these mediate adherence of bacteria to specific receptors on human cell
surface which is a necessary step in the initiation of infection for some
organisms. Mutants of N. gonorrhoeae that do not have pili are non-
pathogenic.
ü Pili are also antiphagocytic, so they are virulence factors in some species of
bacteria.
B- Sex pili:
ü These are responsible for attachment between the male (F+ donor) and the
female (F- recipient) bacteria during conjugation.Bacterial endospores
uHighly resistant resting form of
some gram positive bacteria.
uFormed due to exposure to
unfavorable conditions like ,
heat or dryness.Sporulation:
- Ingrowth of the cytoplasmic membrane.
- Separating part of the cytoplasm and nuclear material, ribosomes, glycolytic
enzymes and little water.
- Thick cortex of peptidoglycan and tough keratin like spore coat are formed
around.
Marked resistance results from:
- Thick spore cortex and tough spore coat.
- The large amounts of calcium dipicolinate which is found only in the core of spores.
- Dehydrated state.
- Very low metabolic and enzymatic activity.Medical importance of spores: Sterilization by autoclaving at 121°c for 20-30 minutes is needed to free instruments and products from spores for medical use.