Some operons have both positive and negative control mechanisms encoded …

Biology Questions
Short Answer
Step by Step Solution
Biology Questions

Some operons have both a positive and negative control mechanism built into the DNA sequence of the operon. That means both an activator protein and a repressor protein are present simultaneously. Consider a system that has both positive and repressible negative controls. a. Describe the four combinations of active or inactive regulatory proteins that could be present at any time in the cell. b. Draw diagrams similar to those in Models 1√¢¬Ä¬ì3 to show each of the combinations in part a. (Divide the work among group members so that each member is drawing one diagram.) c. Label each of the combinations in part b as “operon on” or “operon off.” d. Describe in complete sentences the cellular environment(s) that would turn the operon “on.”

Short Answer

The operation of an operon is governed by four combinations of regulatory proteins: (1) active activator and inactive repressor turns the operon ON, while (2) inactive activator and active repressor, and (3) active activator and active repressor turn it OFF, and (4) inactive activator and inactive repressor also turns it ON. Environmental conditions influence these states, with the presence or absence of specific molecules affecting the activator and repressor’s statuses.

Step-by-Step Solution

Step 1: Understand the Combinations

There are four possible combinations of regulatory proteins that determine whether an operon is turned “on” or “off.” These combinations are:

  • Active activatorinactive repressor: Operon ON
  • Inactive activatoractive repressor: Operon OFF
  • Active activatoractive repressor: Operon OFF
  • Inactive activatorinactive repressor: Operon ON

Step 2: Visual Representation of Combinations

Each combination can be represented visually to better understand the relationship between the activator, repressor, and operon. The diagrams illustrate:

  • Active activator and inactive repressor: Operon ON
  • Inactive activator and active repressor: Operon OFF
  • Active activator and active repressor: Operon OFF
  • Inactive activator and inactive repressor: Operon ON

Step 3: Activation and Deactivation Triggers

The operon’s activation depends on the environment and can change based on specific conditions. It turns “on” when:

  • The activator protein is active and the repressor protein is inactive, often due to the presence of a necessary molecule.
  • The operon will turn “off” when the repressor protein is active, which can occur from the absence of required signals or nutrients.

Related Concepts

Regulatory Proteins

Proteins that influence the expression of a gene by controlling the operation of an operon, specifically acting as activators or repressors.

Operon

A cluster of genes under the control of a single regulatory signal, which can be turned “on” or “off” depending on the presence or absence of regulatory proteins.

Activator And Repressor

An activator is a protein that increases gene expression, while a repressor is a protein that decreases or halts gene expression, together determining the state of the operon.

Table Of Contents
  1. Some operons have both a positive and negative control mechanism built into the DNA sequence of the operon. That means both an activator protein and a repressor protein are present simultaneously. Consider a system that has both positive and repressible negative controls. a. Describe the four combinations of active or inactive regulatory proteins that could be present at any time in the cell. b. Draw diagrams similar to those in Models 1–3 to show each of the combinations in part a. (Divide the work among group members so that each member is drawing one diagram.) c. Label each of the combinations in part b as "operon on" or "operon off." d. Describe in complete sentences the cellular environment(s) that would turn the operon "on."

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