Content Writer-SME
Key Highlights
- Hormone receptors are complex molecules that are used to trigger a cellular response.
- These receptors are found in cell membranes, cytoplasm, or nucleus.
- There are two types of hormone receptors, namely intracellular hormones and cell surface hormone receptors.
- The receptors play an important role in regulating the growth and differentiation of cells in breast cancer treatment.
- Peptide hormones bind with the cell receptors, whereas steroid hormones are ligands for nuclear receptors.
Hormone receptors are receptor proteins that bind certain hormones, initiating changes in physiology and/or behavior.
- These receptors involve the activation or triggering of genes and generating a cellular response.
- Hormones are a form of chemical messenger that carries signals from the bloodstream to different regions of the body.
| Table of Content |
Key Terms: Hormone Receptors, Hormones, Peptide Hormones, Steroid Hormones, Types of Hormone Receptors, Regulation of Hormone Receptors
What are Hormone Receptors?
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Hormone receptors belong to the family of proteins, including retinoids, folic acid, thyroid hormones, and steroids.
- It also includes additional receptors that recognize ligands like prostaglandins and fatty acids.
- Hormones induce changes in the targeted cells by attaching to particular hormone receptors.
- These receptors play an important role in the treatment of breast cancer by influencing the growth of cells.
- The presence of one or more hormones triggers a receptor response, which starts a chain reaction of signaling pathways.
- Some common examples of hormone receptors include Glucagon receptors, Androgen receptors, Insulin receptors, and Progesterone receptors.
Location of Hormone Receptors
Hormone receptors are located in three places, which are as follows:
- Cell Membrane: The cell membrane contains adrenal medullary hormones and protein hormones.
- Cytoplasm: Cytoplasm of target cells consists of steroid hormone receptors.
- Nucleus: The nucleus of the cell contains thyroid hormone receptors.
Types of Hormone Receptors
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The capacity of a hormone to associate with the target cell's receptor determines the efficiency of a particular hormone. Hormone receptors can be broadly classified into two types based on their target site, namely Intracellular Hormone Receptors and Cell Surface Receptors, which are discussed in detail below:
Intracellular Hormone Receptors
Intracellular hormone receptors are receptors that bind glucocorticoids, corticosteroids, androgens, estrogens, and progestogens.
- It is also known as steroid hormones or nuclear receptors.
- These types of hormone receptors are found in proteins with globular structures that are found inside the cells.
- Both steroid and non-steroid hormones are included in this type of receptor.
- These types of hormone receptors are activated by hydrophobic ligands that pass through the cellular membrane.
Intracellular hormone receptors are further divided into two categories based on the location of the target:
- Nuclear Receptors: Nuclear receptors are proteins located inside the cytoplasm. They regulate homeostasis, gene expression, and metabolism of the organism. The most common examples of nuclear receptors include thyroid hormone receptors.
- InsP3 Receptor: InsP3 Receptors, also known as Inositol triphosphate receptors, are found in the endoplasmic reticulum. They are used for tissue distribution and control of several physiological and cellular processes.
Intracellular Hormone Receptors
Cell Surface Receptors
Cell surface hormone receptors are other types of hormone receptors located on the cells of the plasma membrane.
- It is also known as peptide hormone, transmembrane, or membrane receptor.
- After binding to extracellular substances, they participate in cell signaling.
- Cell surface receptors increase the interaction between the cell and the extracellular space.
- There are two main types of cell surface receptors, which are as follows:
G Protein-coupled Receptors
G-protein-coupled membrane receptors (GPCR) are a major class of peptide receptors. They are a large group of proteins that can detect molecules present outside the cell and activate further cellular responses.
- It involves GDP/GTP binding, GTP hydrolysis, and guanosine nucleotide exchange.
- They possess seven transmembrane helices that can activate a G-protein upon binding.
- The most common example of G-protein-coupled Receptors is the thyrotropin receptor.
Enzyme-linked Receptors
It is a type of hormone receptors that possesses both receptor and catalytic functions. These receptors include extracellular ligands that will initiate an enzymatic action on the intracellular side. The most common examples include receptor tyrosine kinase.
Classification based on the solubility of HormonesHormone receptors are classified into two categories based on the solubility of Hormones: Lipid Soluble Hormones Lipid soluble hormones are a type of hormone receptors in which thyroid and steroids can pass through cell and nuclear membranes.
Water Soluble Hormones Water soluble hormones, also called hydrophilic hormones, are derived from amino acids and remain stored in endocrine cells until required.
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Regulation of Hormone Receptors
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In almost every target tissue, hormones initiate biological reactions by associating with particular receptors.
- They can control how proteins function as well as induce levels of gene expression either directly or by the action of secondary messengers.
- When an excess amount of hormones is released, the number of hormone receptors decreases, causing hormones to bind, which is called downregulation.
- The number of receptors that arise during a deficit of hormones is called upregulation.
- During hormone receptor regulation, hormones enter the target cell through endocytosis, a process called internalization.
- The hormone level increases when the number of receptors decreases.
Mechanism of Hormone Action
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The cell membrane of the target organ contains receptors for each hormone, which in turn produce secondary messengers inside the cell.
- Information that needs to reach the nucleus or other organelles must go through a secondary messenger.
- An adenylyl cyclase enzyme is produced as soon as the protein hormone attaches to the receptor, triggering a sequence of events.
- The synthesis of cyclic AMP, or cAMP, the secondary messenger, is facilitated by this enzyme.
- It's now possible for this cAMP to reach the cell and have its desired effect.
Sample Questions
Ques. How do intracellular hormone receptors perform functions? (2 marks)
Ans. The expression of genes is usually altered by the action of intracellular receptors. Gene expression is a biological process by which genes are switched on to make RNA and proteins in response to DNA sequence and further express genes.
Ques. What are the differences between protein and steroid hormones? (5 marks)
Ans. The differences between protein and steroid hormones are as follows:
| Protein Hormones | Steroid Hormones |
|---|---|
| A type of hormone that is soluble in water due to the presence of polar bonds in the structure is called protein hormone. | Steroid hormones are another category of hormones that are not soluble in water. |
| Due to their water-soluble nature, they can not enter into the cells. | These types of hormones can easily penetrate the membrane of the cell. |
| It is characterized by the presence of membrane-bound hormone receptors. | It is characterized by the absence of intracellular hormone receptors. |
| Examples of protein hormones are Adrenaline and non-adrenaline. | Examples of steroid hormones are Thyroid hormone, and FSH. |
Ques. What are ligands? (2 marks)
Ans. A cell can communicate with another cell or with itself by releasing a chemical messenger called a ligand. The cellular response of the interaction could result in different modifications in that cell, such as alterations in gene expression or translation or modifications in the shape of the cell.
Ques. Is it possible for a hormone to have more than one receptor? (2 marks)
Ans. Hormone receptor diversity is common in cells however many cells possess multiple receptors for a single hormone. A cell's sensitivity to a hormone and the subsequent cellular reaction is determined by the overall number of receptors that are bound to it.
Ques. What are the roles of receptors? (2 marks)
Ans. Receptors are proteins that are present throughout the body. They play an important role in hormonal regulation in the following ways:
- It facilitates the transmission of signals.
- Moreover, immunotherapy and immunological responses are regulated by it.
- Receptors present in the body trigger growth, cellular metabolism, and apoptosis of cells.
Ques. Which type of hormone usually binds with GPCR? (2 marks)
Ans. Peptide hormones such as glucagon, adrenaline, parathyroid hormone, and calcitonin are responsive to G-protein-coupled receptors (GPCRs). These receptors have a broad range of physiological functions, including the growth and development of the skeletal system as well as governing the processes of metabolism and stress.
Ques. What are the mechanisms of hormonal action? (4 marks)
Ans. Target cells are activated by hormones either by binding a particular receptor protein in the targeted cell membrane or by diffusing through the target cell's plasma membrane (lipid-soluble hormones) to attach to a receptor protein inside the cell's cytoplasm. It involves the following functions:
- Altering the permeability of the cell membrane.
- Inducing the activation of intracellular enzymes.
- Acting on genes in the target cells.
Ques. Do plants also have hormone receptors? (3 marks)
Ans. Yes, like animals plants also have receptors to which their hormones bind. Hormones in plants are composed of small organic compounds, peptides, and small protein molecules. Similar to hormones in mammals, these chemicals act as ligands that bind to receptor proteins and result in transcellular transcriptional modifications and long-term biological responses.
Ques. What organ in the body regulates hormones? (2 marks)
Ans. The endocrine system, or hormonal system, is controlled by the hypothalamus. The hypothalamus sends signals to the pituitary gland. The anterior and posterior lobes are the two lobes of this gland. Hormones produced by the hypothalamus are secreted by the posterior lobe.
Ques. What is the location and function of receptors in plants? (2 marks)
Ans. Cellular signaling is initiated in a significant way by cell surface receptors that are found in the plasma membrane of plant cells. Plant cells may have cell surface receptors with inherent protein kinase activity.
Ques. Which of the thyroid hormones released by the thyroid gland binds more strongly to its receptor? (2 marks)
Ans. Thyroxine (T4) released into the bloodstream by the thyroid is converted to triiodothyronine (T3) by particular cells in the body through a process known as de-iodination. This occurs because T3 shows greater affinity for receptors as compared to T4.
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