MICR4423 EXAM 2 QUESTIONS AND ANSWERS
Why is the bacterial cell wall a good target for antibiotic action? There are 2 criteria it
meets. - Answers - 1. it is crucial for bacterial shape and division
2. crucial for viability
-different between eukaryotic and prokaryotic cells
How do gram-positive and gram-negative cells typically differ with respect to their cell
envelope? - Answers - Gram pos: inner membrane and a thick cell wall of peptidoglycan
gram neg: inner membrane, cell wall, and outer membrane (LPS)
Why are gram-negative organisms typically more resistant to antibiotics? - Answers -
outer membrane acts as a barrier and is harder to get through as they are even harder
for large molecules.
Why do bacterial cells have to have carefully coordinated enzymatic activities on the cell
wall in order to grow? - Answers - The cell wall is always under mechanical stress but
also must be enlarged for the cell to grow. Hence, bonds must be broken so that the cell
wall can grow but without compromising its structural integrity. Adding exactly where
you are cutting in order to grow without rupturing
For a rod-shaped bacterial cell, cell wall growth can be divided into two distinct phases.
What are they? Which of these is the only phase for a spherical cell? - Answers -
Elongation and division. In a spherical cell, division only.
Describe a peptidoglycan precursor molecule in terms of the number and types of
smaller molecular groups that it is made from. You can draw a diagram. - Answers -
Nag and Nam connected to each other (disaccharides) and 5 in peptide chain branching
of the Nam, final two in chain are D-ala D-ala. It is a disaccharide (NAG-NAM) with a
pentapeptide extending from the NAM saccharide.
Which part of a PG precursor is used to build glycan strands? - Answers - NAG and
NAM
PG precursor is used to build peptide cross-bridges? - Answers - pentapeptide
What are the names of the enzymes that polymerize glycan strands and peptide cross-
bridges, respectively? - Answers - Transglycosylase (TGase) and transpeptidase
(TPase)
What part of a PG precursor is used to link it to the existing PG wall structure? -
Answers - The pentapeptide
, Where are PG precursors located when they are used by enzymes to build new cell wall
material? What is the whole precursor-carrier molecule called? - Answers - On the outer
face of the cytoplasmic membrane. Lipid II
What is the name of the lipid carrier upon which PG precursors are built and
transported? - Answers - Bactoprenol.
Describe the structure of peptidoglycan. Which parts are relatively flexible and which
parts are not? - Answers - made up of glycan strands that are made of alternating NAG
and NAM
-also has peptide & peptide cross-links
-connects 3 to 4 on the peptide crosslinks
-peptide cross-bridges: flexible, extensible
-glycan strands: rigid, inextensible
What is the function of the bacterial cell wall? - Answers - 1. gives cell its shape
2. resists turgor pressure
How many molecules compose the cell wall surrounding an individual bacterium? -
Answers - One—the cell wall is a single, giant, covalently linked macromolecule
Which positions on pentapeptides are typically linked together to form peptide cross-
bridges in PG? - Answers - 3 to 4, 3.DAP to 4.D-ala.
Why might rod shape be favorable to a bacterial cell? - Answers - rod is favorable due
to it preserving the surface area to volume ratio
What type of fabric resembles the PG meshwork? - Answers - Spandex
What would happen if a bacterial cell had a shortage of precursor molecules? - Answers
- it would not grow because it could not expand the wall with a lack of precursors
Name/draw the steps involved in PG synthesis, beginning with GlcNAc and ending with
Lipid IIon the extracellular face of the membrane. - Answers -
Name the enzymes that are involved in each step of PG synthesis, beginning with
GlcNAc and ending with Lipid II on the extracellular face of the membrane. - Answers -
1. MurAB
2. Mur CDE
3. Mur F
4. MraY
5. MurG
6. MurJ
Why is the bacterial cell wall a good target for antibiotic action? There are 2 criteria it
meets. - Answers - 1. it is crucial for bacterial shape and division
2. crucial for viability
-different between eukaryotic and prokaryotic cells
How do gram-positive and gram-negative cells typically differ with respect to their cell
envelope? - Answers - Gram pos: inner membrane and a thick cell wall of peptidoglycan
gram neg: inner membrane, cell wall, and outer membrane (LPS)
Why are gram-negative organisms typically more resistant to antibiotics? - Answers -
outer membrane acts as a barrier and is harder to get through as they are even harder
for large molecules.
Why do bacterial cells have to have carefully coordinated enzymatic activities on the cell
wall in order to grow? - Answers - The cell wall is always under mechanical stress but
also must be enlarged for the cell to grow. Hence, bonds must be broken so that the cell
wall can grow but without compromising its structural integrity. Adding exactly where
you are cutting in order to grow without rupturing
For a rod-shaped bacterial cell, cell wall growth can be divided into two distinct phases.
What are they? Which of these is the only phase for a spherical cell? - Answers -
Elongation and division. In a spherical cell, division only.
Describe a peptidoglycan precursor molecule in terms of the number and types of
smaller molecular groups that it is made from. You can draw a diagram. - Answers -
Nag and Nam connected to each other (disaccharides) and 5 in peptide chain branching
of the Nam, final two in chain are D-ala D-ala. It is a disaccharide (NAG-NAM) with a
pentapeptide extending from the NAM saccharide.
Which part of a PG precursor is used to build glycan strands? - Answers - NAG and
NAM
PG precursor is used to build peptide cross-bridges? - Answers - pentapeptide
What are the names of the enzymes that polymerize glycan strands and peptide cross-
bridges, respectively? - Answers - Transglycosylase (TGase) and transpeptidase
(TPase)
What part of a PG precursor is used to link it to the existing PG wall structure? -
Answers - The pentapeptide
, Where are PG precursors located when they are used by enzymes to build new cell wall
material? What is the whole precursor-carrier molecule called? - Answers - On the outer
face of the cytoplasmic membrane. Lipid II
What is the name of the lipid carrier upon which PG precursors are built and
transported? - Answers - Bactoprenol.
Describe the structure of peptidoglycan. Which parts are relatively flexible and which
parts are not? - Answers - made up of glycan strands that are made of alternating NAG
and NAM
-also has peptide & peptide cross-links
-connects 3 to 4 on the peptide crosslinks
-peptide cross-bridges: flexible, extensible
-glycan strands: rigid, inextensible
What is the function of the bacterial cell wall? - Answers - 1. gives cell its shape
2. resists turgor pressure
How many molecules compose the cell wall surrounding an individual bacterium? -
Answers - One—the cell wall is a single, giant, covalently linked macromolecule
Which positions on pentapeptides are typically linked together to form peptide cross-
bridges in PG? - Answers - 3 to 4, 3.DAP to 4.D-ala.
Why might rod shape be favorable to a bacterial cell? - Answers - rod is favorable due
to it preserving the surface area to volume ratio
What type of fabric resembles the PG meshwork? - Answers - Spandex
What would happen if a bacterial cell had a shortage of precursor molecules? - Answers
- it would not grow because it could not expand the wall with a lack of precursors
Name/draw the steps involved in PG synthesis, beginning with GlcNAc and ending with
Lipid IIon the extracellular face of the membrane. - Answers -
Name the enzymes that are involved in each step of PG synthesis, beginning with
GlcNAc and ending with Lipid II on the extracellular face of the membrane. - Answers -
1. MurAB
2. Mur CDE
3. Mur F
4. MraY
5. MurG
6. MurJ
