Question

The transcription of a gene is controlled by a transcription factor binding either glucose or lactose. When there is \(0.2 \mathrm{mM}\) of either glucose or lactose in the cell, the gene is transcribed at about \(10 \%\) of the maximum. When there is more than \(2 \mathrm{mM}\) glucose in the cell, the gene is fully induced. However, when there is \(2 \mathrm{mM}\) lactose in the cell, the amount of transcription is approximately half of the maximum. At \(40 \mathrm{mM}\) of either glucose or lactose in the cell, the gene is fully induced. The transcriptional regulation is likely: a. Ultrasensitive with respect to both glucose and lactose. b. Ultrasensitive with respect to lactose but not glucose. c. Graded with respect to glucose. d. Ultrasensitive with respect to glucose but not lactose. e. Hyperbolic with respect to glucose but not lactose.

Short answer

The transcriptional regulation is ultrasensitive with respect to glucose but not lactose (d).

Step-by-step solution

Understanding Ultrasensitivity

'Ultrasensitive' refers to a system where the output (transcription rate) changes in a much steeper manner compared to a simple graded response. An ultrasensitive response implies that small changes in the concentration of a molecule can lead to large changes in transcription.

Analyze Glucose Effect

The problem states that the transcription factor fully induces transcription at over 2 mM glucose and starts at 10% duty at 0.2 mM. This indicates a sharp transition in transcription across a small range of glucose concentration, suggesting an ultrasensitive response.

Analyze Lactose Effect

For lactose, the transcription increases from 10% at 0.2 mM to 50% at 2 mM and becomes fully induced only at 40 mM. This indicates a more gradual increase compared to glucose, suggesting a graded response rather than an ultrasensitive one.

Conclusion Based on Analysis

According to the definitions and our analyzations, glucose shows an ultrasensitive response while lactose displays a graded response.

Key concepts

Ultrasensitivity

Ultrasensitivity in gene expression is akin to flipping a switch. It's when a small change in the concentration of a molecule causes a rapid and large change in transcription levels. Imagine a light dimmer that only needs a slight turn to go from dim to bright instantly—that's ultrasensitivity!
In biological systems, this is particularly important because cells need to respond swiftly to changes in their environment to ensure survival and proper function.
For example, in the given exercise, the system displays ultrasensitivity regarding glucose. A small change in glucose concentration—from 0.2 mM to over 2 mM—drastically increases transcription from 10% to full induction. This sharp transition implies that cells prioritize responding quickly to glucose availability, enabling them to adjust their metabolism efficiently. This feature is crucial in processes like cellular signaling, where precise and rapid responses are essential for proper cell function.
In summary, ultrasensitivity is like having a rapid-response team in the cell that ensures quick and decisive shifts in gene expression based on minute environmental changes.

Gene Expression

Gene expression is the process by which information from a gene is used to synthesize functional products like proteins. It's as if the cell translates the genetic code into a 'recipe' to create proteins.
Transcription, the first step of gene expression, involves making a "copy" of a gene's DNA sequence to RNA. This RNA acts as a template for protein synthesis. The expression of genes is tightly regulated to ensure that the right proteins are produced at the right time and in the right amounts.
Factors like transcription factors, hormone levels, and environmental cues, such as glucose and lactose concentrations, play a crucial role. In the exercise example, changes in glucose or lactose concentration regulate the transcription of a particular gene. When the transcription factor binds glucose or lactose, it either enhances or diminishes the transcription, thereby adjusting the amount of protein product formed.
Proper regulation of gene expression is vital for cellular processes like metabolism, growth, and adaptation to environmental changes. It ensures that genes are turned on or off as needed, like managing different appliances on a smart home system based on daily needs.

Transcription Factors

Transcription factors are proteins that help turn specific genes "on" or "off" by binding to nearby DNA. They work like master switches that control the flow of genetic information from DNA to RNA. By attaching to the promoter or enhancer regions, they can increase or decrease the rate of transcription.
Think of transcription factors as keys that open locks on the genetic code, allowing the cell to express genes as needed. Different transcription factors respond to diverse signals such as chemical signals in the cell, physical signals from the environment, or hormonal signals.
In the example exercise, transcription factors modulate gene expression by interacting with glucose or lactose. When these sugars are present, the right transcription factors bind to a gene's DNA, effectively adjusting the transcription rate according to the sugar concentration.
This process highlights how transcription factors are central to gene regulation, ensuring cells respond appropriately to internal and external stimuli. They play a pivotal role in cellular differentiation, development, and adaptation, orchestrating a symphony of genetic activity perfectly attuned to the cell’s needs.