MCB 301 Exam III Questions and Answers 2024
In the enrichment portion of the Experiment, how many nutrient agar plates will be
inoculated from your vegetation sample? ** Answ** Incorrect 5
Incorrect 3
Incorrect 4
Correct: 2
In the isolation portion of the Experiment, wet mounts will be made from potential spore-
forming cells that grew on the plates that were ** Answ** Incorrect incubated
anaerobically.
Incorrect incubated aerobically and anaerobically.
Correct: incubated aerobically.
In the post-enrichment portion of the Experiment, your spore-forming isolate will be
inoculated into how many tubes and flasks of medium? ** Answ** Incorrect 4
Correct: 5
Incorrect 2
Incorrect 3
Incorrect 1
What should be the Gram reaction of the spore-formers we isolate? ** Answ**
Correct: Gram-positive rods
Incorrect Gram-positive cocci
Incorrect Gram-negative rods
Incorrect Gram-negative cocci
What are the two most common genera of bacteria that can make endospores, and
describe some common characteristics between the two genera (unrelated to spore
formation)? (2 pts) ** Answ** Bacillus and Clostridium (1 pt)
Both are Gram-positive bacteria, rod-shaped and most are motile (1 pt)
Is sporulation a form of reproduction? Why or why not? ** Answ** No, because
sporulation involves a single vegetative cell forming into a single spore (1 pt), instead of
a single cell forming two viable cells as in reproduction (1 pt).
During sporulation, an inner forespore membrane and an outer forespore membrane
are formed (although one of them is degraded later). Where did each membrane come
from, and structurally how do the two membranes in the forespore differ from each
other? (2 pts ** Answ** The inner forespore membrane came from the original
daughter cell membrane, and the outer forespore membrane came from the mother cell
membrane. (1 pt)
, The outer forespore membrane is actually inside out compared to the inner forespore
membrane. (1 pt)
Suring sporulation, the membrane of the mother cell grows around the membrane of the
daughter cell. As a result, the daughter cell is engulfed inside the mother cell and is
surrounded by two membranes : the inner foreshore membrane, which arises from it's
own cytoplasmic membrane, and the outer foreshore membrane which arises from the
inside-out cytoplasmic membrane of the mother cell
In the sporeformer post-enrichment exercise, PYE medium was supplemented with
glucose. How many milliliters (mL) of a 25% glucose stock solution must be added to 20
mL of PYE medium to make 0.4% glucose? (2 pts) ** Answ** 0.32 ml (2 pts)
Note: (25%)(x mL) = (0.4%)(20 mL) = 0.32 mL
C1V1=C2V2, (25% glu) X = (0.4% final glu) (20 mL PYE), X = 0.32 mL
Why are cysteine residues important in the spore coat protein? (2 pts) ** Answ**
Cysteine residues contain sulfhydryl groups so two residues can covalently link to each
other by forming a disulfide bond. This allows the coat proteins to interact more strongly
with one another to strengthen the spore coat. Also, intramolecular disulfide bonds
might form to strengthen the individual coat protein. (2 its)
Cysteine residue can form covalent bonds with one another through the sulfhydryl group
on their side chains resulting in a disulfide bond. This bond provides additional stability
to the spore coat protein because the two cysteine in the primary structure can form a
cross-link between two parts of the polypeptide chain, and may join the spore coat
proteins together.
During the butanediol fermentation pathway, two pyruvate molecules interact and are
metabolized further. What eventually happens to the carbon atoms in those pyruvate
molecules? (2 pts) ** Answ** Two carbon atoms are each released as a carbon
dioxide gas molecule (1 pt) and the other four carbon atoms are eventually excreted as
butanediol (1 pt).
In the MIC Determination Experiment, serial dilutions of chloramphenicol are made in
several tubes as described in the Lab Manual. An MCB301 student accidentally used a
chloramphenicol stock solution that had a concentration of 5 mg/mL instead of the
proper concentration of 3 mg/mL. Assuming the student did not make any other
mistakes while making the dilutions, what should be the concentration of antibiotic in
Tube #3 (in μg/mL) made by this student? (Please just supply the numerical answer
without units.) ** Answ** 625
In the enrichment portion of the Experiment, how many nutrient agar plates will be
inoculated from your vegetation sample? ** Answ** Incorrect 5
Incorrect 3
Incorrect 4
Correct: 2
In the isolation portion of the Experiment, wet mounts will be made from potential spore-
forming cells that grew on the plates that were ** Answ** Incorrect incubated
anaerobically.
Incorrect incubated aerobically and anaerobically.
Correct: incubated aerobically.
In the post-enrichment portion of the Experiment, your spore-forming isolate will be
inoculated into how many tubes and flasks of medium? ** Answ** Incorrect 4
Correct: 5
Incorrect 2
Incorrect 3
Incorrect 1
What should be the Gram reaction of the spore-formers we isolate? ** Answ**
Correct: Gram-positive rods
Incorrect Gram-positive cocci
Incorrect Gram-negative rods
Incorrect Gram-negative cocci
What are the two most common genera of bacteria that can make endospores, and
describe some common characteristics between the two genera (unrelated to spore
formation)? (2 pts) ** Answ** Bacillus and Clostridium (1 pt)
Both are Gram-positive bacteria, rod-shaped and most are motile (1 pt)
Is sporulation a form of reproduction? Why or why not? ** Answ** No, because
sporulation involves a single vegetative cell forming into a single spore (1 pt), instead of
a single cell forming two viable cells as in reproduction (1 pt).
During sporulation, an inner forespore membrane and an outer forespore membrane
are formed (although one of them is degraded later). Where did each membrane come
from, and structurally how do the two membranes in the forespore differ from each
other? (2 pts ** Answ** The inner forespore membrane came from the original
daughter cell membrane, and the outer forespore membrane came from the mother cell
membrane. (1 pt)
, The outer forespore membrane is actually inside out compared to the inner forespore
membrane. (1 pt)
Suring sporulation, the membrane of the mother cell grows around the membrane of the
daughter cell. As a result, the daughter cell is engulfed inside the mother cell and is
surrounded by two membranes : the inner foreshore membrane, which arises from it's
own cytoplasmic membrane, and the outer foreshore membrane which arises from the
inside-out cytoplasmic membrane of the mother cell
In the sporeformer post-enrichment exercise, PYE medium was supplemented with
glucose. How many milliliters (mL) of a 25% glucose stock solution must be added to 20
mL of PYE medium to make 0.4% glucose? (2 pts) ** Answ** 0.32 ml (2 pts)
Note: (25%)(x mL) = (0.4%)(20 mL) = 0.32 mL
C1V1=C2V2, (25% glu) X = (0.4% final glu) (20 mL PYE), X = 0.32 mL
Why are cysteine residues important in the spore coat protein? (2 pts) ** Answ**
Cysteine residues contain sulfhydryl groups so two residues can covalently link to each
other by forming a disulfide bond. This allows the coat proteins to interact more strongly
with one another to strengthen the spore coat. Also, intramolecular disulfide bonds
might form to strengthen the individual coat protein. (2 its)
Cysteine residue can form covalent bonds with one another through the sulfhydryl group
on their side chains resulting in a disulfide bond. This bond provides additional stability
to the spore coat protein because the two cysteine in the primary structure can form a
cross-link between two parts of the polypeptide chain, and may join the spore coat
proteins together.
During the butanediol fermentation pathway, two pyruvate molecules interact and are
metabolized further. What eventually happens to the carbon atoms in those pyruvate
molecules? (2 pts) ** Answ** Two carbon atoms are each released as a carbon
dioxide gas molecule (1 pt) and the other four carbon atoms are eventually excreted as
butanediol (1 pt).
In the MIC Determination Experiment, serial dilutions of chloramphenicol are made in
several tubes as described in the Lab Manual. An MCB301 student accidentally used a
chloramphenicol stock solution that had a concentration of 5 mg/mL instead of the
proper concentration of 3 mg/mL. Assuming the student did not make any other
mistakes while making the dilutions, what should be the concentration of antibiotic in
Tube #3 (in μg/mL) made by this student? (Please just supply the numerical answer
without units.) ** Answ** 625
