Question at position 1 For the E. Coli strains containing the lac operon listed below, LacZ and LacY are inducible, constitutive, or unable to make β-galactosidase and permease?I- o+ Z- Y+ / I+ oc Z+ Y- no expression of lacZ; lacY is constitutive.no expression of lacZ; lacY is constitutive.lacZ is constitutive; lacY is constitutive.lacY is constitutive; lacZ is induciblelacZ is constitutive; lacY is inducible.单项选择题
A
no expression of lacZ; lacY is constitutive.
B
no expression of lacZ; lacY is constitutive.
C
lacZ is constitutive; lacY is constitutive.
D
lacY is constitutive; lacZ is inducible
E
lacZ is constitutive; lacY is inducible.

Question

Question at position 1 For the E. Coli strains containing the lac operon listed below, LacZ and LacY are inducible, constitutive, or unable to make β-galactosidase and permease?I- o+ Z- Y+ / I+ oc Z+ Y- no expression of lacZ; lacY is constitutive.no expression of lacZ; lacY is constitutive.lacZ is constitutive; lacY is constitutive.lacY is constitutive; lacZ is induciblelacZ is constitutive; lacY is inducible.单项选择题

A

no expression of lacZ; lacY is constitutive.

B

no expression of lacZ; lacY is constitutive.

C

lacZ is constitutive; lacY is constitutive.

D

lacY is constitutive; lacZ is inducible

E

lacZ is constitutive; lacY is inducible.

BlackTom AI · Accepted Answer

Question restatement: For the E. coli strains containing the lac operon listed, determine whether LacZ and LacY are inducible, constitutive, or unable to make β-galactosidase and permease. The specific genotype combination given is I- o+ Z- Y+ / I+ oc Z+ Y-.

Option 1: 'no expression of lacZ; lacY is constitutive.'
- This option posits that β-galactosidase (LacZ) is not produced, while permease (LacY) is produced constitutively. Given Z- on one chromosome, that allele cannot yield functional LacZ, which would explain the lack of β-galactosidase from that chromosome. The other chromosome has Z+ but the configuration I+ oc Z+ Y- places an operator-constitutive element (oc) that can drive continuous expression of the operon’s genes irrespective of the usual repressor, potentially resulting in ongoing LacY production; however, the Y- on that chromosome indicates no LacY production from that chromosome. Overall, the observed phenotype aligns with LacZ being nonfunctional due to the Z- allele on one chromosome and LacY being produced constitutively from the appropriate regulatory configuration on the other chromosome, yielding constitutive permease activity. This matches the stated option’s assertion.

Option 2: 'no expression of lacZ; lacY is constitutive.'
- This option is identical in wording to Option 1. If taken literally, it would imply the same phenotype as Option 1. Since the details of the genotype can yield a single consistent interpretation, duplicating the exact same outcome doesn’t introduce a new, distinct mechanism. In a well-constructed multiple-choice item, a duplicate option would usually be considered redundant or could indicate a test construction issue. The reasoning about the genotype in Option 2 would mirror Option 1, but its redundancy does not provide additional explanatory value beyond Option 1.

Option 3: 'lacZ is constitutive; lacY is constitutive.'
- This option states both LacZ and LacY are produced constitutively. Given the Z- allele on one chromosome (nonfunctional LacZ) and the Y- allele on the other chromosome (nonfunctional LacY), constitutive expression of both is inconsistent with the provided genotypes. The presence of a Z- allele prevents LacZ from being produced from that chromosome, and a Y- allele prevents LacY production from the other, so simultaneous constitutive production of both enzymes would require both functional alleles and regulatory elements enabling constant expression, which the genotype does not support. Therefore, this option contradicts the specific alleles present.

Option 4: 'lacY is constitutive; lacZ is inducible'
- Here, LacY would be produced constantly, but LacZ would only be produced upon induction. The Z- allele on one chromosome already disables LacZ production from that chromosome, and even with induction, a functional Z across the diploid may still be limited by regulatory context; however, the explicit Z- allele makes inducible LacZ unlikely to yield functional LacZ expression in this genetic arrangement. Additionally, the oc element on the other chromosome may complicate induction patterns. In short, this option assigns conflicting or improbable regulatory states to LacZ given Z- and oc contexts and to LacY given Y- and constitutive expectations, making it an inconsistent interpretation of the genotype.

Option 5: 'lacZ is constitutive; lacY is inducible.'
- This option suggests LacZ is always on while LacY is inducible. The Z- allele on one chromosome precludes constitutive LacZ expression, and the presence of Z+ on the other chromosome with the oc element does not guarantee universal constitutive LacZ activity. Moreover, lacY being inducible contradicts the Y- allele on the second chromosome, which would limit LacY production. Taken together, this combination does not coherently reflect the genotype described and introduces a mismatch between the described alleles and the proposed regulation.

Summary of analysis across options:
- Option 1 (and the essentially identical Option 2) fits the genotype by placing nonfunctional LacZ (Z-) on one chromosome and a regulatory context that yields constitutive LacY expression on the other, yielding no LacZ activity and constitutive LacY activity. The reasoning hinges on the Z- allele disabling LacZ and the regulatory arrangement allowing continuous LacY activity from the remaining, permissive chromosome.
- Options 3, 4, and 5 assign impossible or inconsistent regulatory states to LacZ and LacY given the specific alleles (Z-, oc, I+ etc. with Y-), or propose mutually exclusive patterns that do not align with the genotype, making them incorrect explanations.

Note on wording and interpretation: This analysis works through how the specific alleles (Z-, Y-, oc, I-, I+) influence expression of LacZ and LacY in a diploid arrangement, considering dominant/recessive effects, operator mutations, and constitutive regulation. The key takeaway is that a Z- allele blocks LacZ production, while the oc (operator constitutive) plus the other regulatory arrangement can lead to constitutive LacY expression, which supports Option 1 as the accurate characterization of the given genotype.

类似问题

How does the catabolite repression mechanism, involving the cAMP-CAP complex, modulate the expression of the lac operon when both glucose and lactose are present?

In the presence of lactose but absence of glucose, what happens to cAMP levels and the lac operon?

A researcher grows E. coli in minimal medium containing both glucose and lactose and observes that the lac operon is not highly expressed. Which explanation best accounts for this observation?

A mutation in the lacZ gene alters β-galactosidase so it makes more allolactose compared with a normal β-galactosidase enzyme. How would this mutation affect the expression of the lac operon?

The binding of ___________ to the lac repressor disables the lac repressor to bind to the site, thereby transcription.

On the chromosome, CAP is mutated such that it no longer produces a functional CAP protein, and the operator is mutated such that it no longer binds to the repressor. On the plasmid, lacI is mutated so that it no longer produces a functional repressor protein. Lactose and glucose are both absent.

Match the following states of nutrient availability with the corresponding state of the lac operon during gene expression regulation: 1: High glucose present, no lactose present 2: High glucose present, lactose also present 3: Low glucose present, high lactose present

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