14. Cell Signaling

Intracellular messnegers: Hormones and Nitric Oxide

14. Cell Signaling

Intracellular messnegers: Hormones and Nitric Oxide: Videos & Practice Problems

Topic summary

Intra-cellular receptor signaling involves hormones and nitric oxide (NO). Steroid hormones easily cross the plasma membrane and bind to nuclear receptors, which then translocate to the nucleus to regulate gene expression. This binding triggers a conformational change, activating specific DNA regulatory sites. Similarly, NO diffuses across membranes and binds to guanylyl cyclase, producing cyclic GMP, which mediates various physiological effects, including muscle relaxation and the action of Viagra. Understanding these pathways is crucial for grasping cellular communication and hormonal regulation.

concept

Hormones and NO

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Hormones and NO Video Summary

Intracellular receptor signaling plays a crucial role in how hormones and nitric oxide communicate within cells. Hormones, particularly steroid hormones, can easily cross the plasma membrane without any special transport mechanisms. Once inside the cell, they bind to specific intracellular receptors, often referred to as nuclear receptors. Although these receptors can be found in the cytosol, their activation by hormone binding triggers a conformational change that facilitates their transfer into the nucleus. In the nucleus, these receptors function as transcriptional regulators, influencing gene expression by binding to specific DNA regulatory sites. This specificity ensures that each hormone activates only certain pathways, leading to precise cellular responses.

For example, when a steroid hormone diffuses across the plasma membrane and binds to its nuclear receptor, this interaction initiates a cascade that ultimately affects transcription, translation, and gene expression. The process highlights the importance of these receptors in mediating the effects of hormones on cellular functions.

Similarly, nitric oxide (NO) also diffuses across the plasma membrane without requiring special transport. Once inside, it binds to intracellular signaling proteins, such as guanylate cyclase. This binding catalyzes the conversion of GTP to cyclic GMP (cGMP), a secondary messenger that plays a significant role in various physiological processes. One notable function of nitric oxide is its ability to induce muscle relaxation in blood vessels, which is essential for regulating blood flow. Additionally, nitric oxide is involved in the mechanism of action for medications like Viagra, which enhances its effects by increasing cGMP levels, leading to improved erectile function.

In summary, both hormones and nitric oxide utilize intracellular signaling pathways to exert their effects, with hormones primarily acting through nuclear receptors to regulate gene expression, while nitric oxide influences various pathways through its interaction with intracellular proteins. Understanding these mechanisms is vital for comprehending how cellular communication and regulation occur in response to different stimuli.

Problem

Steroid hormones signaling through binding….

GTPases

Nuclear receptors

Kinases

Phosphatases

Problem

Nitric Oxide signals by binding to which of the following molecules?

GTPases

Nuclear Receptors

Adenyl cyclase

Guanyl cyclase

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Here’s what students ask on this topic:

How do steroid hormones cross the plasma membrane and what happens once they are inside the cell?

Steroid hormones can easily cross the plasma membrane without the need for any special transport mechanisms because they are lipophilic. Once inside the cell, they bind to intracellular receptors known as nuclear receptors. These receptors can be located in the cytoplasm or the nucleus. Upon binding to the hormone, the nuclear receptor undergoes a conformational change and translocates to the nucleus. In the nucleus, the activated receptor acts as a transcriptional regulator, binding to specific DNA regulatory sites to influence gene expression. This process ultimately affects transcription and translation, leading to changes in cellular function.

What role does nitric oxide play in intracellular signaling?

Nitric oxide (NO) is a small, diffusible gas that plays a crucial role in intracellular signaling. It easily crosses the plasma membrane and binds to intracellular signaling proteins. One of its primary targets is guanylyl cyclase, an enzyme that converts GTP to cyclic GMP (cGMP). The production of cGMP mediates various physiological effects, such as muscle relaxation and vasodilation. For example, NO is released by endothelial cells in blood vessels to stimulate smooth muscle relaxation, leading to vasodilation. Additionally, NO is involved in the mechanism of action of drugs like Viagra, which enhances the effects of cGMP to promote blood flow.

What is the mechanism of action of nuclear receptors in gene regulation?

Nuclear receptors are a class of intracellular receptors that regulate gene expression. When a hormone binds to a nuclear receptor, it triggers a conformational change in the receptor. This activated receptor then translocates to the nucleus, where it binds to specific DNA regulatory sites known as hormone response elements (HREs). By binding to these HREs, the nuclear receptor acts as a transcriptional regulator, either promoting or inhibiting the transcription of target genes. This regulation of gene expression ultimately affects various cellular processes, including growth, metabolism, and differentiation.

How does nitric oxide contribute to the physiological effects of Viagra?

Nitric oxide (NO) contributes to the physiological effects of Viagra by enhancing the production of cyclic GMP (cGMP). NO diffuses across the plasma membrane and binds to guanylyl cyclase, an enzyme that catalyzes the conversion of GTP to cGMP. Increased levels of cGMP lead to smooth muscle relaxation and vasodilation, particularly in the blood vessels of the penis. This vasodilation increases blood flow, facilitating an erection. Viagra works by inhibiting the enzyme phosphodiesterase type 5 (PDE5), which breaks down cGMP. By preventing the degradation of cGMP, Viagra prolongs its effects, thereby enhancing erectile function.

What are the similarities and differences between hormone and nitric oxide signaling pathways?

Both hormone and nitric oxide (NO) signaling pathways involve the diffusion of signaling molecules across the plasma membrane and their interaction with intracellular targets. Hormones, particularly steroid hormones, bind to nuclear receptors, which then translocate to the nucleus to regulate gene expression. NO, on the other hand, binds to guanylyl cyclase, leading to the production of cyclic GMP (cGMP) and subsequent physiological effects like muscle relaxation. The key difference lies in their targets and outcomes: hormones primarily affect gene transcription, while NO influences enzymatic activity and second messenger systems. Despite these differences, both pathways are crucial for cellular communication and regulation.

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