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Here is a sample Biology passage for those of you studying for the MCAT. The solutions will be posted next week.
Auxotrophy is the inability of an organism to synthesize a particular organic molecule required for growth. An auxotroph is an organism that demonstrates auxotrophy (adj. auxotrophic). The opposite of auxotrophy is prototrophy. Prototrophy is characterized by the ability to synthesize all the compounds needed for growth. An auxotroph is not able to grow on minimal media. Instead, an auxotroph will only be able to group on media supplemented with the organic molecule they’re unable to synthesize.
Escherichia coli strain 679-680 will only grow on minimal media if it is supplemented with threonine and leucine. Escherichia coli strain Y44 will only grow on minimal media if it is supplemented with arginine and methionine.
In the first of three experiments, when the two strains are grown together in liquid culture supplemented with threonine, leucine, arginine, and methionine and then subsequently plated on unsupplemented minimal media, colonies of E. coli grow.
In a second experiment, strain 679-680 and Y44 were grown in a U-tube (strains are kept separate from each other by a fine-pored filter) containing liquid culture supplemented with threonine, leucine, arginine, and methionine. After incubation in the U-tube, when the strains are plated on unsupplemented minimal media colonies do not grow.
A third experiment involved an additional strain of E. coli, strain III. Strain III did not require supplementation to grow on minimal media. When this third strain was grown in a U-tube with Y44, after incubation, Y44 cells plated on minimal media with arginine would grow. When plated on minimal media supplemented with methionine, Y44 cells from the U-tube culture did not grow.
Questions
1) Which is the most likely explanation for the survival of bacteria grown on minimal media after 679-680 and Y44 strains were combined?
A. Cell fusion occurred.
B. Conjugation occurred
C. Transduction occurred
D. Transformation occurred.
2) Of the structures listed, which is most likely be present for 679-680 and Y44 strains to exchange DNA with each other?
A. Pili
B. Porin proteins
C. Cytoskeleton
D. Capsid proteins
3) Of the following, which is a likely explanation for the survival of strain Y44 grown on minimal media supplemented with arginine?
I. Y44 could synthesize its own methionine
II. Arginine was no longer toxic to Y44
III. Strain III secreted proteins that allowed Y44 to survive
A. I only
B. II only
C. III only
D. I, II, and III
4) In prokaryotes, genetic transfer is characterized by ___.
I. Being unidirectional
II. The inability to form true diploids
A. I only
B. II only.
C. I and II
D. Neither I nor II
Auxotrophy is the inability of an organism to synthesize a particular organic molecule required for growth. An auxotroph is an organism that demonstrates auxotrophy (adj. auxotrophic). The opposite of auxotrophy is prototrophy. Prototrophy is characterized by the ability to synthesize all the compounds needed for growth. An auxotroph is not able to grow on minimal media. Instead, an auxotroph will only be able to group on media supplemented with the organic molecule they’re unable to synthesize.
Escherichia coli strain 679-680 will only grow on minimal media if it is supplemented with threonine and leucine. Escherichia coli strain Y44 will only grow on minimal media if it is supplemented with arginine and methionine.
In the first of three experiments, when the two strains are grown together in liquid culture supplemented with threonine, leucine, arginine, and methionine and then subsequently plated on unsupplemented minimal media, colonies of E. coli grow.
In a second experiment, strain 679-680 and Y44 were grown in a U-tube (strains are kept separate from each other by a fine-pored filter) containing liquid culture supplemented with threonine, leucine, arginine, and methionine. After incubation in the U-tube, when the strains are plated on unsupplemented minimal media colonies do not grow.
A third experiment involved an additional strain of E. coli, strain III. Strain III did not require supplementation to grow on minimal media. When this third strain was grown in a U-tube with Y44, after incubation, Y44 cells plated on minimal media with arginine would grow. When plated on minimal media supplemented with methionine, Y44 cells from the U-tube culture did not grow.
Questions
1) Which is the most likely explanation for the survival of bacteria grown on minimal media after 679-680 and Y44 strains were combined?
A. Cell fusion occurred.
B. Conjugation occurred
C. Transduction occurred
D. Transformation occurred.
2) Of the structures listed, which is most likely be present for 679-680 and Y44 strains to exchange DNA with each other?
A. Pili
B. Porin proteins
C. Cytoskeleton
D. Capsid proteins
3) Of the following, which is a likely explanation for the survival of strain Y44 grown on minimal media supplemented with arginine?
I. Y44 could synthesize its own methionine
II. Arginine was no longer toxic to Y44
III. Strain III secreted proteins that allowed Y44 to survive
A. I only
B. II only
C. III only
D. I, II, and III
4) In prokaryotes, genetic transfer is characterized by ___.
I. Being unidirectional
II. The inability to form true diploids
A. I only
B. II only.
C. I and II
D. Neither I nor II