MICR 4423 EXAM #2 QUESTIONS AND ANSWERS
Why is the bacterial cell wall a good target for antibiotic action? - Answers - bacterium
specifically target and all bacteria are specific to microbes and its essential for bacteria
growth or life
How do gram-positive and gram-negative cells typically differ with respect to their cell
envelope? - Answers - Gram-positive cells have no outer membrane and a thick
peptidoglycan wall
Gram-negative cells have an outer membrane and a thin peptidoglycan wall
Why are gram-negative organisms typically more resistant to antibiotics? - Answers -
The outer membrane acts as a barrier or especially large antibiotics with a higher
molecular weight
Describe the structure of peptidoglycan - Answers - it's a meshwork of long glycan
strands which are relatively inflexible and do not stretch and the peptide cross bridges
are flexible and stretch
Which parts of the peptidoglycan are relatively flexible and which parts are not? -
Answers - Peptide cross bridges are flexible
Glycan strands are inflexible
What is the function of the bacterial cell wall? - Answers - - prevent rupturing
- help maintain shape
- contributes to the ability to cause disease
The primary function of the peptidoglycan mesh bag is to restrain pressure and to keep
cells from bursting
How many molecules compose the cell wall surrounding an individual bacterium? -
Answers - it is one giant covalently linked micro-molecule
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
because of the osmotic pressure and the cells are under pressure so for cells to grow
they have to add new material to the cell wall while under pressure and into the
meshwork by breaking bonds and immediately adding material to balance.
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 - The
two phases are elongation and division. For a spherical cell the only phase is division,
for one cell to become tw it has to make two new hemispheres that become the two new
haves of the two new daughter cells
,Describe a peptidoglycan precursor molecule in terms of the number and types of
smaller molecular groups that it is made from - Answers - A disaccharide made up of
NAG and NAM and coming from the NAM is a pentapeptide.
Which part of a PG precursor is used to build glycan strands? - Answers - The
disaccharide, a long repeating NAM-NAG chain that makes this up
Which part of a PG precursor is used to build Peptide cross-bridges? - Answers - The
pentapeptide side chain make this up
What are the names of the enzymes that polymerize glycan strands and peptide cross-
bridges, respectively? - Answers - Transglycosylase making repeating NAM-NAG
Transpeptidase is an enzyme that cross links two glycan strands together making the
peptide cross bridges
What part of a PG precursor is used to link it to the existing PG wall structure? -
Answers - The pentapeptide.
When new glycan strands are polymerized they have to be connected to the cell wall by
transpeptidation making new peptide cross bridges ana that action forms
transpeptidase.
Where are PG precursors located when they are used by enzymes to build new cell wall
material? - Answers - The cell wall is on the outside of the outer membrane so the
precursors also have to be located on the outside of the cytoplasmic membrane
What is the whole precursor-carrier molecule called? - Answers - Lipid II its the
disaccharide and pentapeptide connected to the bactoprenol carrier which is in the
cytoplasmic membrane.
What is the name of the lipid carrier upon which PG precursors are built and
transported? - Answers - Bactoprenol
Which positions on pentapeptides are typically linked together to form peptide cross-
bridges in PG? - Answers - Usually position 3 or 4 so diaminopimelic acid to D-alanine
DAP to D-ala
Why might rod shape be favorable to a bacterial cell? - Answers - IN A ROD, it can
make it as long as needed and the surface area scales linearly with the volume. The rod
shape may be twice as long but have twice the volume and twice the surface area.
Another reason a cell might want to be rod shaped is because it also allows orientation
of subcellular components.
, But, a sphere gets bigger and bigger and its volume scales different from its surface
area and the volume grows fast than the surface area. Because bacteria need to eat
and secrete waste products through the surface of the cell quickly the cell becomes to
large.
What type of fabric resembles the PG network? - Answers - Spandex
What would happen if a bacterial cell had a shortage of precursor molecules? - Answers
- If a cell wants to grow it has to put in new cell wall material so if it doesn't have enough
precursors it cannot grow the cell wall so the cell itself cannot grow.
Name the steps involved in PG synthesis, beginning with GlcNAc and ending with Lipid
II on the extracellular face of the membrane. - Answers - NAG gets converted to NAM,
first 3 amino acids of the pentapeptide are added and the last two D-ala-D-ala are
added to the bactoprenol carrier to form Lipid I and then NAG is added on to Lipid II.
Then Lipid II is flipped across the membrane
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. MurCDE
3. Mur F
4. MraY
5. MurG
6. MurJ
How is the phosphorylation state of the bactoprenol carrier important for its role? -
Answers - Only the bactoprenol monophosphate with one phosphate group can be
connected to the NAM pentapeptide to form Lipid I. When Lipid I is added it has two
phosphates cause Lipid I is the peptidoglycan precursor is connected to uridine
diphosphate and 1 phosphate comes along
Whenever the precursor is removed by a transglycosylase to form a glycan strand it
leaves behind to bactoprenol carrier and both phosphates. In order to use the
bactoprenol again to make Lipid I that second phosphate group has to be removed by a
phosphatase enzyme, and now back to bactoprenol monophosphate.
Name two antibiotics that take advantage of the phosphorylation requirements of the
bactoprenol cycle. How do they work? - Answers - Bacitracin: binds bactoprenol
diphosphate and prevents dephosphorylation so it cannot be converted back to the
bactoprenol monophosphate, it cannot be used to make a fresh/new Lipid I molecule.
Frenolicin B: binds to the bactoprenol and prevents reloading of that monophosphate
and a precursor to make Lipid I.
Why is the bacterial cell wall a good target for antibiotic action? - Answers - bacterium
specifically target and all bacteria are specific to microbes and its essential for bacteria
growth or life
How do gram-positive and gram-negative cells typically differ with respect to their cell
envelope? - Answers - Gram-positive cells have no outer membrane and a thick
peptidoglycan wall
Gram-negative cells have an outer membrane and a thin peptidoglycan wall
Why are gram-negative organisms typically more resistant to antibiotics? - Answers -
The outer membrane acts as a barrier or especially large antibiotics with a higher
molecular weight
Describe the structure of peptidoglycan - Answers - it's a meshwork of long glycan
strands which are relatively inflexible and do not stretch and the peptide cross bridges
are flexible and stretch
Which parts of the peptidoglycan are relatively flexible and which parts are not? -
Answers - Peptide cross bridges are flexible
Glycan strands are inflexible
What is the function of the bacterial cell wall? - Answers - - prevent rupturing
- help maintain shape
- contributes to the ability to cause disease
The primary function of the peptidoglycan mesh bag is to restrain pressure and to keep
cells from bursting
How many molecules compose the cell wall surrounding an individual bacterium? -
Answers - it is one giant covalently linked micro-molecule
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
because of the osmotic pressure and the cells are under pressure so for cells to grow
they have to add new material to the cell wall while under pressure and into the
meshwork by breaking bonds and immediately adding material to balance.
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 - The
two phases are elongation and division. For a spherical cell the only phase is division,
for one cell to become tw it has to make two new hemispheres that become the two new
haves of the two new daughter cells
,Describe a peptidoglycan precursor molecule in terms of the number and types of
smaller molecular groups that it is made from - Answers - A disaccharide made up of
NAG and NAM and coming from the NAM is a pentapeptide.
Which part of a PG precursor is used to build glycan strands? - Answers - The
disaccharide, a long repeating NAM-NAG chain that makes this up
Which part of a PG precursor is used to build Peptide cross-bridges? - Answers - The
pentapeptide side chain make this up
What are the names of the enzymes that polymerize glycan strands and peptide cross-
bridges, respectively? - Answers - Transglycosylase making repeating NAM-NAG
Transpeptidase is an enzyme that cross links two glycan strands together making the
peptide cross bridges
What part of a PG precursor is used to link it to the existing PG wall structure? -
Answers - The pentapeptide.
When new glycan strands are polymerized they have to be connected to the cell wall by
transpeptidation making new peptide cross bridges ana that action forms
transpeptidase.
Where are PG precursors located when they are used by enzymes to build new cell wall
material? - Answers - The cell wall is on the outside of the outer membrane so the
precursors also have to be located on the outside of the cytoplasmic membrane
What is the whole precursor-carrier molecule called? - Answers - Lipid II its the
disaccharide and pentapeptide connected to the bactoprenol carrier which is in the
cytoplasmic membrane.
What is the name of the lipid carrier upon which PG precursors are built and
transported? - Answers - Bactoprenol
Which positions on pentapeptides are typically linked together to form peptide cross-
bridges in PG? - Answers - Usually position 3 or 4 so diaminopimelic acid to D-alanine
DAP to D-ala
Why might rod shape be favorable to a bacterial cell? - Answers - IN A ROD, it can
make it as long as needed and the surface area scales linearly with the volume. The rod
shape may be twice as long but have twice the volume and twice the surface area.
Another reason a cell might want to be rod shaped is because it also allows orientation
of subcellular components.
, But, a sphere gets bigger and bigger and its volume scales different from its surface
area and the volume grows fast than the surface area. Because bacteria need to eat
and secrete waste products through the surface of the cell quickly the cell becomes to
large.
What type of fabric resembles the PG network? - Answers - Spandex
What would happen if a bacterial cell had a shortage of precursor molecules? - Answers
- If a cell wants to grow it has to put in new cell wall material so if it doesn't have enough
precursors it cannot grow the cell wall so the cell itself cannot grow.
Name the steps involved in PG synthesis, beginning with GlcNAc and ending with Lipid
II on the extracellular face of the membrane. - Answers - NAG gets converted to NAM,
first 3 amino acids of the pentapeptide are added and the last two D-ala-D-ala are
added to the bactoprenol carrier to form Lipid I and then NAG is added on to Lipid II.
Then Lipid II is flipped across the membrane
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. MurCDE
3. Mur F
4. MraY
5. MurG
6. MurJ
How is the phosphorylation state of the bactoprenol carrier important for its role? -
Answers - Only the bactoprenol monophosphate with one phosphate group can be
connected to the NAM pentapeptide to form Lipid I. When Lipid I is added it has two
phosphates cause Lipid I is the peptidoglycan precursor is connected to uridine
diphosphate and 1 phosphate comes along
Whenever the precursor is removed by a transglycosylase to form a glycan strand it
leaves behind to bactoprenol carrier and both phosphates. In order to use the
bactoprenol again to make Lipid I that second phosphate group has to be removed by a
phosphatase enzyme, and now back to bactoprenol monophosphate.
Name two antibiotics that take advantage of the phosphorylation requirements of the
bactoprenol cycle. How do they work? - Answers - Bacitracin: binds bactoprenol
diphosphate and prevents dephosphorylation so it cannot be converted back to the
bactoprenol monophosphate, it cannot be used to make a fresh/new Lipid I molecule.
Frenolicin B: binds to the bactoprenol and prevents reloading of that monophosphate
and a precursor to make Lipid I.
