External structures and drug targets in prokaryotic cells
Session 5: External structures and drug targets in prokaryotic cells
Total Session Time: 120 minutes
Pre-requisites
Students Learning Tasks
By the end of this session students are expected to be able to:
Resources Needed:
SESSION OVERVIEW
|Step |Time |Activity/ |Content |
| | |Method | |
|1 |5 minutes |Presentation |Introduction, Learning Tasks |
|2 |50 minutes |Presentation |External structures of prokaryotic|
| | | |cells |
|3 |25 minutes |Presentation |Drug Targets in Bacterial Cell |
| | | |Wall |
|4 |30 minutes |Presentation |Acid fast Bacilli |
|5 |5 minutes |Presentation |Key Points |
| 6|5 minutes |Presentation |Evaluation |
SESSION CONTENTS
STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)
READ or ASK students to read the learning tasks and clarify
ASK students if they have any questions before continuing
STEP 2: Bacterial External Structures and Drug Targets (50 minutes)
o External structures include the cell wall and structures external
to it
o A cell wall is a layer located outside the cell membrane found in
plants, fungi, bacteria, algae, and archaea.
o The bacterial cell wall is a rigid structure outside the cell
membrane (and inner to the capsule for capsulated bacteria)
composed of peptidoglycan layers making up a cell envelope around
the cell
o Peptidoglycan is composed of disaccharides and amino acids which
gives structural support to the bacteria
o Peptidoglycan is unique to bacteria
Figure 5.1: Structure of Peptidogycan
[pic]
[pic]
o Bacteria are classified as being either Gram-positive or Gram-
negative based in differences in the structure of their
peptidoglycan cell wall
o Gram-positive bacteria are stained dark blue or violet by Gram
staining
o In Gram-positive bacteria, the cell wall is thick and consists of
several layers of peptidoglycan
o Gram negative bacteria lack the outer membrane envelope found in
Gram-negative bacteria
polyribitol substituted with phosphates and a few amino
acids and sugars
o Functions of the bacterial cell wall;
are responsible for cell motility
o Monotrichous –Single polar flagellum e.g. Vibrio
cholerae
o Amphitrichous –Single flagellum on both sides e.g.
Alkaligens faecalis
o Lophotrichous –Tufts of flagella at one or both sides
e.g. Spirillum
o Peritrichous–Numerous flagella all over the bacterial
body
the surface of some bacteria. They are made up of proteins
called pilins
according to their morphology, distribution, and function
bacteria and some gram-negative bacteria
attachment
deposited outside the cell wall
definite boundaries
protect a bacterial cell from ingestion and destruction by
white blood cells (phagocytosis)
•
centrifugation), unorganized layer of extracellular
material that surrounds bacteria cells
can be easily washed off
it may serve to trap nutrients, to aid in cell motility, to
bind cells together or to adhere to smooth surfaces
STEP 3: Drug Targets in Bacterial Cell Wall (25 minutes)
o Fosfomycin
o Cycloserin
o Bacitracin
o Vancomycin
(Transpeptidases)
o Penicillins
o Cephalosporins
o Carbapenems
o Monobactams
STEP 4: Acid-fast Bacteria (30 minutes)
from both gram negative and gram positive bacteria
composed primarily of the fatty acid "Mycolic Acid"
arabinogalactan which in turn invest the inner lipid membrane common
to all bacteria
resistant to gram stain.
decolorization with acid alcohol, thus their name "Acid-Fast”
o A thin layer of peptidoglycan
[pic]
o The peptidoglycan prevents osmotic lysis
o The arabinogalactan layer is linked to both the peptidoglycan and
to the mycolic acid outer membrane and probably provides additional
strength to the cell wall
o The mycolic acids and other glycolipids also impede the entry of
chemicals causing the organisms to grow slowly and be more
resistant to chemical agents and lysosomal components of phagocytes
than most bacteria
to the gram-negative cell wall and the pores are much longer
strain and species, carry out a variety of activities, including
functioning as enzymes and serving as adhesins, which enable the
bacterium to adhere intimately to host cells and other surfaces in
order to colonize and resist flushing
STEP 4: Key Points (5 minutes)
cell wall composed of varying layers of peptidoglycan.
imbalance of electrolytes that trigger cell death.
building blocks leading to cell lysis and death
from both gram negative and gram positive bacteria
peptidoglycan linked to a layer of arabinogalactin, which in turn is
linked to an outer membrane containing mycolic acids and overlaid with
a variety of polypeptides and glycolipids.
STEP 4: Evaluation (5 minutes)
References
Hugo and Russell (2011), Pharmaceutical Microbiology 8th Edition, Willey-
Blackwel publications
Karen C. Carroll et al (2013); Jawetz, Melnick and Adelberg’s Medical
Microbiology 26th Ed. McGraw Hill Co. Inc.
Greenwood et al (2012); Medical Microbiology, 18th edition Churchill
Livingstone
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