MICROBIOLOGY GOOD REVISION
QUESTIONS AND THEIR
EXPECTED ANSWERS
Peptidoglycan is a polymer of millions of N-acetylglucosamine
(NAG) and N-acetylmuramic acid (NAM) sugars based on
glucose molecules linked together in long chains cross-braced
with four amino acids that link individual polymer chains
together in a chain-link fence pattern. Layers of cross-braced
NAG and NAM sheets are stacked vertically and held together
by proteins with lipid anchors attached to the cell's
cytoplasmic membrane to form a scaffold of sugars and
proteins that is able to hold the bacterial cell's shape, even in
response to extreme osmotic pressures. How would you
expect a microbiology student to be able to describe the
composition of peptidoglycan?
What is the composition of the peptidoglycan layers found in
the cell wall of bacteria?
Short amino acid chains, NAG, NAM, and some lipid proteins
Gram-positive bacterial cell wall
Teichoic acids
Single lipid bilayer membrane
Thick layer of peptidoglycan
Gram-negative bacterial cell wall
,Lipopolysaccharides
Dual lipid bilayer membrane
Thin layer of peptidoglycan
Periplasmic space
At this point in writing your tutorial, you have to find a way to
get across to the students the importance of a cell wall to a
bacterium. How do you convey that the bacterial cell will be at
the mercy of its environment? The cell wall will need to act as
a support mechanism to neutralize the inflow or outflow of
water that would alter the shape of the cell. The cell cannot
search out for a better place in the environment that has more
available water; or if there is water that it has a high enough
solute concentration that the cell will not gain water. Because
that's the problem for a bacterial cell, it cannot control the
tonicity due to solute concentrations in the surrounding water.
Water will flow in or out depending on solute concentrations
and the only thing a bacterial cell can do to keep from
collapsing due to water loss or rupturing due to too much
water coming in is to have a strong cell wall that will hold its
shape regardless of the osmotic pressures. The rigidity of the
cell wall will maintain a set shape regardless of water flow.
The proteins and lipids that anchor the cytoplasmic membrane
to the cell wall will tether the membrane to the peptidoglycan
layer so that when environmental conditions result in the loss
of water from the cell, the membrane will not collapse in on
itself. Similarly, changes in environmental conditions that
would result in the inflow of water would expand the volume
, of the cell to the limits of the cell wall and no more.
The composition of the cell wall allows for the expansion and
contraction of the cell wall in response to the gain or loss of
water from the cell.
False
Since the bacterial cell is at the mercy of the environment, it
requires a rigid structure to maintain its shape when osmotic
pressure would cause a cell to shrink or expand.
The cell wall
The cell wall peptidoglycan layer is flexible but still rigid enough
to maintain its shape; the cytoplasmic membrane is attached to
the cell wall through the use of proteins and lipids
A cell wall is a requirement for all living bacteria
False
With the description of the different cell walls, membranes,
and associated proteins set in the students' minds, you now
need to introduce them to the idea that the cell wall can also
act as a foundation to build things upon. Bacterial appendages
require a strong foundation that will offer the support needed
to move and function in a dynamic world. For example,
flagella are long, whiplike protein structures that are used by
many Gram-positive and Gram-negative bacteria for
locomotion. In order to function effectively, a flagellum must
be firmly anchored to the cell wall. How will you be able to get
across the idea that the peptidoglycan cell wall is strong
enough to support such a mechanism? With a protein rod that
QUESTIONS AND THEIR
EXPECTED ANSWERS
Peptidoglycan is a polymer of millions of N-acetylglucosamine
(NAG) and N-acetylmuramic acid (NAM) sugars based on
glucose molecules linked together in long chains cross-braced
with four amino acids that link individual polymer chains
together in a chain-link fence pattern. Layers of cross-braced
NAG and NAM sheets are stacked vertically and held together
by proteins with lipid anchors attached to the cell's
cytoplasmic membrane to form a scaffold of sugars and
proteins that is able to hold the bacterial cell's shape, even in
response to extreme osmotic pressures. How would you
expect a microbiology student to be able to describe the
composition of peptidoglycan?
What is the composition of the peptidoglycan layers found in
the cell wall of bacteria?
Short amino acid chains, NAG, NAM, and some lipid proteins
Gram-positive bacterial cell wall
Teichoic acids
Single lipid bilayer membrane
Thick layer of peptidoglycan
Gram-negative bacterial cell wall
,Lipopolysaccharides
Dual lipid bilayer membrane
Thin layer of peptidoglycan
Periplasmic space
At this point in writing your tutorial, you have to find a way to
get across to the students the importance of a cell wall to a
bacterium. How do you convey that the bacterial cell will be at
the mercy of its environment? The cell wall will need to act as
a support mechanism to neutralize the inflow or outflow of
water that would alter the shape of the cell. The cell cannot
search out for a better place in the environment that has more
available water; or if there is water that it has a high enough
solute concentration that the cell will not gain water. Because
that's the problem for a bacterial cell, it cannot control the
tonicity due to solute concentrations in the surrounding water.
Water will flow in or out depending on solute concentrations
and the only thing a bacterial cell can do to keep from
collapsing due to water loss or rupturing due to too much
water coming in is to have a strong cell wall that will hold its
shape regardless of the osmotic pressures. The rigidity of the
cell wall will maintain a set shape regardless of water flow.
The proteins and lipids that anchor the cytoplasmic membrane
to the cell wall will tether the membrane to the peptidoglycan
layer so that when environmental conditions result in the loss
of water from the cell, the membrane will not collapse in on
itself. Similarly, changes in environmental conditions that
would result in the inflow of water would expand the volume
, of the cell to the limits of the cell wall and no more.
The composition of the cell wall allows for the expansion and
contraction of the cell wall in response to the gain or loss of
water from the cell.
False
Since the bacterial cell is at the mercy of the environment, it
requires a rigid structure to maintain its shape when osmotic
pressure would cause a cell to shrink or expand.
The cell wall
The cell wall peptidoglycan layer is flexible but still rigid enough
to maintain its shape; the cytoplasmic membrane is attached to
the cell wall through the use of proteins and lipids
A cell wall is a requirement for all living bacteria
False
With the description of the different cell walls, membranes,
and associated proteins set in the students' minds, you now
need to introduce them to the idea that the cell wall can also
act as a foundation to build things upon. Bacterial appendages
require a strong foundation that will offer the support needed
to move and function in a dynamic world. For example,
flagella are long, whiplike protein structures that are used by
many Gram-positive and Gram-negative bacteria for
locomotion. In order to function effectively, a flagellum must
be firmly anchored to the cell wall. How will you be able to get
across the idea that the peptidoglycan cell wall is strong
enough to support such a mechanism? With a protein rod that
