Mentors Mente power point presentation for medical students.

1. SISTER NIVEDITA UNIVERSITY
• NAME ::- MD SAQLAIN UMAR
• ENROLLEMENT ID:- 2311225005028
• STREAM:- Bsc(h) IN BOTT
• SUBJECT:-MICRO BIOLOGY
• REGESTERATIN NO:-230050281771
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2. BACTERIAL CHEMOTAXIS
AND APPLICATION

3. CONTENTS
• Introduction
• Biological example
• References
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4. INTRODUCTION
. Chemotaxis - Composed of two words "chemo + taxis".
. Chemo means a "chemical substance" is a form of matter that has constant chemical
composition and characteristic properties.
. Taxis means "arrangement" is the movement of an organism in response to a stimulus
such as light or the presence of food.
. Chemotaxis is the movement of an organism/bacteria in response to a chemical stimulus i.e.,
move away or towards substances that are present in the environment through a non-random
process.
.This movement is often directed either
. Positive chemotaxis - movement towards attractants (nutrients) or
. Negative chemotaxis - movement away from the repellents (toxin).

5. .Chemoattractants - Chemicals that attract bacteria.
. e.g., for E.coli amino acids (serine and aspartic acid), sugars (maltose, ribose, galactose, glucose),
dipeptides,
pyrimidines and electron acceptors (oxygen, nitrate, fumarate).
. Chemorepellents - Chemicals that drive bacteria away.
. e.g., for E.coli amino acid (leucine), metal ion (Ni), pH, potentially noxious chemicals
(alcohols and fatty acids).
. E. coli uses temporal gradients to guide Its motion.
. Uses a biased-random-walk strategy to sample space and convert spatial gradients to
temporal ones.
. In liquid environments, E. coli swims in a pattern than resembles a random

6. CHEMOTAXIS BEHAVIOR
. E. coli moves up a gradient of attractant –
. Detects a net positive change in attractant concentration,
. Reduces the probability of a tumble and tends to continue going up the
gradient.
. Swim/Runs - the cell keeps a rather constant direction which produce
Counter clockwise rotation.
. The runs last about 1 sec on average.
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7. . E. coli detects a concentration of repellent increases with time –
. The cell increases tumbling frequency,
. Tends to change direction and avoid swimming toward repellents.
. Tumbles - the bacterium stops and randomly changes direction which
produce
Clockwise rotation.
. The tumbles about 0.1 sec on average.
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8. Fig. Bacterial runs and tumbles are related to the rotation direction of the flagella
motors. When all motors spin counter-clockwise (CCW), the flagella turn in a bundle
and cell is propelled forward. When one or more motors turn clockwise (CW), the
cell tumbles and randomizes its orientation. The switching dynamics of a single
motor from CCW to CW and back can be seen by tethering a cell to a surface by
means of its flagellum, so that the motor spins the entire cell body (at frequencies of
a few hertz due to the large viscous drag of the body).
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9. RESPONSE & EXACT ADAPTATION
. Addition of an attractant in space, increasing the attractant concentration from 0 to 1, but no
spatial gradients are formed.
. The cells sense an increase in attractant levels and suppress the tumbles: the tumbling frequency
of the cells plummets within about 0.1 sec.
. After a while, the tumbling frequency of the cells begins to increase, even though attractant is. still
present. This process is called adaptation.
. Bacterial chemotaxis shows exact adaptation:
"The steady-state tumbling frequency is
independent of attractant levels."
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10. CHEMOTAXIS SYSTEM OF E. COLI
Chemoreceptors form complexes with the CheA (kinase proein) and
CheW (adaptor protein)
CheA phosphorylates itself & transfers phosphoryl (P) groups to CheY
(diffusible messenger protein)
phosphorylated CheY interacts with the flagellar motors to induce
tumbles.
Rate of CheY dephosphorylation is greatly enhanced by
CheZ (phosphate activator)
Binding of attractants to the receptors decreases the rate of CheY
phosphorylation and tumbling is reduced
Note: Adaptation is provided by changes in the level of methylation of the
chemoreceptors: methylation increases the rate of CheY phosphorylation.
Pair of enzymes, CheR (methyl transferase) and CheB (methyl esterase),
add and remove methyl (m) groups.
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12. REFERENCES
• There are many informative webpages on your own department's site. Here are a few
highlights - Check it out!
• Department of Microbiology homepage
• Faculty Research Groups - areas your professors are investigating
• Research Facilities - available to UMass researchers
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13. THANK YOU
MD SAQLAIN UMAR
7564948731
mdsaqlainumar@gmail.com