MICR 4423 2025 EXAM QUESTIONS AND
CORRECT ANSWERS!!
peptide cross-link cleavage, nascent glycan strand insertion, cross-link formation
what is essential for enlargement of the PG sacculus?
a. The cell wall is a good target because it is different between bacteria and eukaryotes (1)
and it targets something (at minimum) important for biology
1. Why is the bacterial cell wall a good target for antibiotic action? There are 2 criteria it meets.
a. Gram positive cells have an outer cell wall and inner cell membrane. Gram negative cells
have three layers in their envelope: an outer membrane, cell wall, and inner membrane
1. How do gram-positive and gram-negative cells typically differ with respect to their cell
envelope?
a. Gram negative is typically more resistant because the three-layer cell envelope makes it
harder to penetrate
Why are gram-negative organisms typically more resistant to antibiotics?
a. Peptidoglycan is one giant covalently-linked macromolecule
b. It consists of glycan chains (inextensible) connected by stretchy peptide cross-links
1. Describe the structure of peptidoglycan. Which parts are relatively flexible and which parts are
not?
a. The cell wall helps shape the cell and protects it from osmotic lysis (turgor pressure)
i. Cytoplasm has a lot of solutes, so water rushes in. the cell doesn't burst because of the
mesh bag effect that the cell wall has
1. What is the function of the bacterial cell wall?
a. One giant covalently-linked macromolecule
How many molecules compose the cell wall surrounding an individual bacterium?
, a. To grow, the cell has to expand its cell wall. Thus, it has to break the right bonds at the
right place and add new ones quickly to enable to protective aspect of the cell wall. If the
coordination is weak, the cell could burst from turgor pressure
1. Why do bacterial cells have to have carefully coordinated enzymatic activities on the cell wall
in order to grow?
a. First is elongation, next is division. Spherical cells only have to go through division
1. 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?
i. NAG: also called Glcnac, short for N-acetyl glucosamine
ii. NAM: also called Murnac, short for N-acetyl muramic acid
iii. DAP: Di-aminopimelic acid
iv. The cross link will occur between 3 DAP on NAM and 4 D-Ala on NAM
order: L-Ala, D-glu, DAP, D-ala, D-ala
1. 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.
a. NAG and NAM form the glycan strands
b. DAP and D-Ala form the peptide cross bridges
c. Glycan strands: Tgase/ transglycosylase
d. Peptide cross bridge: Tpase/transpeptidase
Which part of a PG precursor is used to build glycan strands? Peptide cross-bridges? What are
the names of the enzymes that polymerize glycan strands and peptide cross-bridges,
respectively?
a. It's the pentapeptide via transpeptidation
What part of a PG precursor is used to link it to the existing PG wall structure?
a. It starts in the cytoplasm then moves to the outer face of the cell membrane
b. Lipid II
CORRECT ANSWERS!!
peptide cross-link cleavage, nascent glycan strand insertion, cross-link formation
what is essential for enlargement of the PG sacculus?
a. The cell wall is a good target because it is different between bacteria and eukaryotes (1)
and it targets something (at minimum) important for biology
1. Why is the bacterial cell wall a good target for antibiotic action? There are 2 criteria it meets.
a. Gram positive cells have an outer cell wall and inner cell membrane. Gram negative cells
have three layers in their envelope: an outer membrane, cell wall, and inner membrane
1. How do gram-positive and gram-negative cells typically differ with respect to their cell
envelope?
a. Gram negative is typically more resistant because the three-layer cell envelope makes it
harder to penetrate
Why are gram-negative organisms typically more resistant to antibiotics?
a. Peptidoglycan is one giant covalently-linked macromolecule
b. It consists of glycan chains (inextensible) connected by stretchy peptide cross-links
1. Describe the structure of peptidoglycan. Which parts are relatively flexible and which parts are
not?
a. The cell wall helps shape the cell and protects it from osmotic lysis (turgor pressure)
i. Cytoplasm has a lot of solutes, so water rushes in. the cell doesn't burst because of the
mesh bag effect that the cell wall has
1. What is the function of the bacterial cell wall?
a. One giant covalently-linked macromolecule
How many molecules compose the cell wall surrounding an individual bacterium?
, a. To grow, the cell has to expand its cell wall. Thus, it has to break the right bonds at the
right place and add new ones quickly to enable to protective aspect of the cell wall. If the
coordination is weak, the cell could burst from turgor pressure
1. Why do bacterial cells have to have carefully coordinated enzymatic activities on the cell wall
in order to grow?
a. First is elongation, next is division. Spherical cells only have to go through division
1. 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?
i. NAG: also called Glcnac, short for N-acetyl glucosamine
ii. NAM: also called Murnac, short for N-acetyl muramic acid
iii. DAP: Di-aminopimelic acid
iv. The cross link will occur between 3 DAP on NAM and 4 D-Ala on NAM
order: L-Ala, D-glu, DAP, D-ala, D-ala
1. 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.
a. NAG and NAM form the glycan strands
b. DAP and D-Ala form the peptide cross bridges
c. Glycan strands: Tgase/ transglycosylase
d. Peptide cross bridge: Tpase/transpeptidase
Which part of a PG precursor is used to build glycan strands? Peptide cross-bridges? What are
the names of the enzymes that polymerize glycan strands and peptide cross-bridges,
respectively?
a. It's the pentapeptide via transpeptidation
What part of a PG precursor is used to link it to the existing PG wall structure?
a. It starts in the cytoplasm then moves to the outer face of the cell membrane
b. Lipid II
