Question

Long-term adaptation to changes in the nutritional state can be regulated by the change in synthesis of enzymes, regulated by the rate of gene transcription. All of the following statements concerning transcription are correct except A. insulin increases a sterol-response-element-binding protein (SREBP), which increases transcription of lipogenic genes. B. glucose increases a carbohydrate-response-clement-binding protein (ChREBP), which decreases the transcription of lipogenic genes. C. glucagon promotes the transcription of genes encoding gluconeogenic enzymes via activation of adenylate cyclase. D. a SRBEP regulates cholesterol synthesis. E. energy deficiency activates AMPK and reduces the ability of SREBP to transcribe genes for fat and cholesterol synthesis.

Short answer

Answer: B. Glucose increases a carbohydrate-response-element-binding protein (ChREBP), which decreases the transcription of lipogenic genes.

Step-by-step solution

Analyze Statement A

Insulin is known to increase a sterol-response-element-binding protein (SREBP), which in turn increases the transcription of lipogenic genes. This statement is true, so it is not the correct answer.

Analyze Statement B

Glucose is known to increase a carbohydrate-response-element-binding protein (ChREBP). However, instead of decreasing the transcription of lipogenic genes, ChREBP actually increases the transcription of lipogenic genes. Therefore, this statement is incorrect, and it is the correct answer.

Analyze Statements C, D, and E (for completeness)

For completeness, let's analyze the remaining statements: - Statement C: Glucagon does promote the transcription of genes encoding gluconeogenic enzymes via activation of adenylate cyclase, making this statement true. - Statement D: An SREBP (sterol response element-binding protein) indeed regulates cholesterol synthesis, so this statement is also true. - Statement E: Energy deficiency does activate AMPK, which then reduces the ability of SREBP to transcribe genes for fat and cholesterol synthesis. This statement is true as well. The correct answer is B.

Key concepts

Enzyme Synthesis

Enzymes are biological molecules that significantly speed up the rate of virtually all of the chemical reactions that take place within cells. The synthesis of enzymes is a vital process that is carefully regulated by the cells in response to various stimuli, including changes in the nutritional state of the organism.

For example, in the presence of high levels of glucose, the body may increase the synthesis of insulin, which in turn can stimulate the production of enzymes involved in fat storage. Conversely, during times of fasting or low carbohydrate intake, glucagon is produced to encourage the synthesis of gluconeogenic enzymes, helping the body to produce glucose from non-carbohydrate sources.

Regulating enzyme synthesis according to the body's metabolic needs ensures efficient utilization of nutrients, and improper regulation can lead to metabolic disorders. Therefore, understanding the mechanisms that control enzyme production, such as gene transcription, is crucial for elucidating many aspects of cellular metabolism and health.

Nutritional State Adaptation

The ability of an organism to adapt to its nutritional state is a remarkable process that involves tight regulation of metabolic pathways. At a molecular level, this adaptation is often controlled by regulating the transcription of genes involved in metabolism. Hormones like insulin and glucagon play a significant role in this adaptation by influencing gene transcription related to carbohydrate and fat metabolism.

When the body has excess nutrients, insulin promotes the transcription of genes for lipogenic enzymes, leading to fat storage. On the other hand, during nutrient scarcity, AMPK (AMP-activated protein kinase) is activated, which can inhibit the activity of sterol-response-element-binding protein (SREBP), a key transcription factor. This results in reduced transcription of genes involved in fat and cholesterol synthesis, conserving energy for essential functions.

Similarly, glucagon acts in opposition to insulin, promoting the generation of glucose through gluconeogenesis in times of energy deficiency. Such precise control mechanisms allow the body to maintain homeostasis despite fluctuations in nutrient availability.

Gene Transcription Elements

Gene transcription is a complex process governed by various molecular components known as gene transcription elements. These elements include promoters, enhancers, response elements, and transcription factors. Together, they work to precisely regulate when and how much gene product is made.

Promoters are DNA sequences located upstream of the gene that provide a binding site for RNA polymerase, the enzyme that synthesizes RNA. Enhancers are regulatory DNA sequences that can be located far away from the actual gene and can increase transcription rates when bound by specific proteins. Response elements, such as the sterol-response element and carbohydrate-response element, are specific DNA sequences within promoters or enhancers that bind to particular transcription factors and regulate gene expression in response to cellular signals.

In the context of nutrient metabolism, factors like SREBP and ChREBP are essential transcription factors that bind to their respective response elements to adjust the rate of transcription of metabolic genes. These elements and their interactions introduce a level of precision and adaptability to metabolic regulation, which is necessary for the organism's survival amid varying nutritional states.