Speaker A
A very good morning friends, today's topic of discussion is important LAQ.
Detailed explanation of hormone mechanisms of action, differentiating group one and group two hormones by receptor type and second messenger systems.
Key Takeaways
- Hormones are classified based on receptor location and mechanism of action into two main groups.
- Group one hormones are lipophilic and act via intracellular receptors affecting gene transcription.
- Group two hormones are hydrophilic and use second messenger systems to elicit cellular responses.
- Second messenger systems include cyclic AMP, cyclic GMP, calcium/phosphatidyl inositol, and kinase cascades.
- Understanding hormone mechanisms is crucial for grasping endocrine system functions and hormone-related therapies.
Summary
- Hormones are chemical substances secreted by ductless endocrine glands acting on target tissues.
- Hormones are classified into group one (intracellular receptors) and group two (cell membrane receptors with second messengers).
- Group one hormones are lipophilic, have long half-lives, require transport molecules, and act via hormone-receptor complexes inside cells.
- Group two hormones are hydrophilic, have short half-lives, do not require transport molecules, and act through second messenger systems.
- Group two hormones are further divided into A (cyclic AMP), B (cyclic GMP), C (calcium/phosphatidyl inositol), and D (kinase/phosphatase cascade) subgroups.
- Examples of group one hormones include steroid hormones, thyroid hormones, calcitriol, and retinoic acid.
- Examples of group two hormones include adrenaline, glucagon, FSH, LH, nitric oxide, oxytocin, growth hormone, insulin, among others.
- Mechanism of group one hormones involves hormone-receptor complex formation, binding to hormone responsive elements, and activation of gene transcription.
- Group two hormone action involves binding to cell surface receptors, activation of G proteins, protein kinases, and formation of phosphoproteins leading to cellular response.
- The video provides a clear classification and sequence of events for hormone action mechanisms essential for understanding endocrine physiology.
Full Transcript — Download SRT & Markdown
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That is mechanism of hormone action.
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Okay, all of you know the definition of hormone.
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Yes.
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Hormones, these hormones are they are chemical secreted by endocrine glands.
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Generally these glands they are ductless glands, endocrine gland and it has action on target tissues.
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Target tissues.
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This type of chemicals or substances they are known as hormones.
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These hormones they are classified on the basis of their mechanism of action.
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There are two main classification.
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The first one is the group one hormone.
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And second class is the group two hormone.
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Okay, it is based on their receptors.
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Okay.
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It is based on their receptors.
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If receptors are present intracellularly.
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Intracellular receptors.
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They are known as group one hormones.
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And if receptors they are present on cell membrane and mechanism is through second messenger.
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Hormone is a first messenger.
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And if the receptors they are present on cell membrane and mechanism of action is through the second messenger.
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These hormones belongs to group two.
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These group two hormones.
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They are again divided into group A.
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B, C and D.
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Group A, B, C and D.
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If second messenger is cyclic AMP, it is group A.
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If it is cyclic GMP, it is group B.
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If it is calcium or inositol.
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It is group three.
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That is group C.
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And if it is through kinase and phosphatase cascade.
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Phosphatase cascade, it is group D.
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Okay, group two A, B, C, D, cyclic AMP, cyclic GMP, calcium, phosphatidyl inositol and kinase cascade pathway.
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Okay, the hormone acting through this second messengers they belongs to group two.
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Now we'll see the basic difference between group one and group two hormones.
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These group one hormones.
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They are lipophilic in nature.
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And it is very very important.
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They are lipophilic.
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In nature.
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All of you know that cell membrane.
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It is a bilayer lipid.
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Layer.
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So this hormones that is group one hormones they can easily traverse or easily pass through a cell membrane.
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Okay, they are lipid soluble.
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Lipophilic.
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In nature.
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Then they have long half life.
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Long half life.
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In hours to days.
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In hours, days.
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Then they require transport molecule.
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Transport.
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They require transport molecule.
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In group two hormones they are hydrophilic.
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They are hydrophilic.
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They cannot travel through a cell membrane.
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Hence their receptors they are present on the cell membrane then they send a message which causes a cellular response.
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They are hydrophilic in nature.
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The short half life.
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Short half life.
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In minutes.
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Then they do not require transport molecule.
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No transport molecule is required.
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Then receptors.
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Next difference is mediator.
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The group one hormone they act by forming hormone receptor complex.
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And these hormones they act through second messenger.
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So this is a basic difference between these two.
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As they are hydrophilic, lipophilic.
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They can pass through a membrane.
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And they act on intracellular receptor.
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They are hydrophilic they cannot pass through a membrane.
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By attaching to the cell surface receptor, surface receptor they activate the second messenger that causes the cellular response.
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Now coming to the examples.
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Of group one and group two hormones.
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Group one hormone.
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It includes steroid hormones.
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It is glucocorticoids.
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Mineralocorticoids.
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Androgens.
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Progestin.
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Estrogen.
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Then calcitriol.
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Vitamin D.
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It is calcitriol.
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Thyroid hormone T3, T4.
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And retinoic acid.
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Retinoic acid.
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Which is a mechanism of action of steroid hormone.
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Through a intracellular receptor by forming hormone receptor complex.
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Steroid hormones.
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Group one hormones includes steroid hormones then it includes calcitriol, thyroid hormones and retinoic acid.
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Steroid hormones includes.
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These are the steroid hormones.
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Glucocorticoids, mineralocorticoids, androgens, progestin and estrogen.
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Then other compounds that is vitamin D.
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Thyroid hormone and retinoic acid.
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They act also act through.
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Intracellular receptors.
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Of these these two thyroid hormones and retinoic acid.
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They act on intranuclear receptors.
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Intranuclear receptors.
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This is a MCQ.
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Intranuclear thyroid hormones and retinoic acid.
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Okay.
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This is about group one hormones.
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Now coming to the examples of group two hormones.
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Group two.
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First is the second messenger is through cyclic AMP.
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Through cyclic AMP.
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It includes mainly it is a group two A.
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Okay.
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A for adrenaline.
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Then second one is the glucagon.
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Adrenaline, glucagon.
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Then FSH, LH, MSH, ACTH.
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Parathyroid hormone, calcitonin.
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Somatostatin.
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And etc.
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So these are the some examples of hormones which act through second messenger cyclic AMP.
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Group two A.
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Now coming to group two B.
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It is very easy to remember group two B.
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Through cyclic GMP.
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It includes nitric oxide.
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And atrial natriuretic factor.
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Nitric oxide and atrial natriuretic factor.
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They act through cyclic GMP.
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Then group two C.
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When the second messenger is calcium or phosphatidyl inositol.
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Calcium or phosphatidyl inositol.
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It includes oxytocin.
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Gonadotropin releasing hormone.
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Gastrin.
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Cholecystokinin.
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Thyrotropin releasing hormone.
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Platelet derived growth factor.
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Substance P.
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Muscarinic ACTH.
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And alpha one adrenergic catecholamines.
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These are the examples of group two C that is through calcium and phosphatidyl inositol.
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Oxytocin, gonadotropin releasing hormone, gastrin, cholecystokinin, thyrotropin releasing hormone, platelet derived growth factor, substance P, muscarinic ACTH.
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And alpha one adrenergic catecholamines.
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They act through.
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Calcium and phosphatidyl inositol.
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This alpha two adrenergic they belongs to cyclic AMP.
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That is alpha two adrenergic catecholamines.
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And beta adrenergic catecholamines.
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They belongs to cyclic AMP.
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Group two A.
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Now the last one that is group four.
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Sorry.
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It is group two D.
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Group two D through kinase and phosphatase cascade.
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It includes growth hormone.
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Epidermal growth factor.
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Then prolactin.
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And important one insulin.
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Important one insulin.
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So you can take a snapshot here.
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These are the group two hormones A, B, C and D.
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This one is the A.
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A, B, C and D.
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A through cyclic AMP, B through cyclic GMP, C through calcium and phosphatidyl inositol.
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And D it is through kinase cascade pathway.
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So these are the important examples of group two hormones.
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Now we'll see the sequence of events in the group one and group two hormones.
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Okay, in the hormone action.
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Sequence of events.
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In group one hormones.
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First this hormone it it travels through a cell membrane.
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And it binds with the intracellular receptor.
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So first one is the hormone receptor complex formation.
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Complex formation.
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Intracellular complex formation of hormone receptor complex.
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Okay, second.
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Binding of this hormone receptor complex to hormone responsive element.
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Okay, binding of hormone receptor complex to hormone responsive element.
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Third point is the.
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Activation, transcription and synthesis of protein.
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Which is responsible for expression.
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Expression and biochemical response.
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Biochemical response.
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So this is the events first they traverse through a cell membrane.
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Enters a intracellular enters intracellularly.
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Binds to the receptor, intracellular receptor.
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Then binding of hormone receptor complex to hormone responsive element.
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Activation of this responsive element lead to the transcription, production of MRNA which leads to the production of appropriate protein.
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And expression of this appropriate protein leads to the biochemical response.
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This is a event, these are the events.
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In the mechanism of action of group one hormones.
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While in group two hormone.
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Group two hormones.
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The first they binds to the cell surface receptors.
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Okay.
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Which leads to the activation of G protein.
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Activation of G protein.
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This activation of G protein leads to the activation of.
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Protein kinases.
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And activation of protein kinases leads to the formation of phosphoprotein.
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Phosphoprotein which is responsible for biochemical response.
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Biochemical response.
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So these are the events in group two.
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Hormone mechanism of action.
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Okay, bind to cell surface receptor.
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Activation of G protein.
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Activation of protein kinase.
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Phosphoprotein formation.
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And biochemical response.
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So this is group one hormone and group two hormone.
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Now of this now G protein.
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What what do you mean by G protein?
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G protein it is a hetero.
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Trimeric protein.
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Okay, now coming to a explanation of G protein coupled receptor.
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It has seven transmembrane domain.
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Okay.
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It has seven transmembrane domain.
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And there is attachment of gamma subunit.
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Beta subunit and alpha subunit.
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Which is GDP bound.
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GDP bound.
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This is a G protein.
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This is a receptor G protein.
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Receptor.
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And this is a effector molecule.
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Effector molecule can be cyclic AMP.
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It can be phospholypase C.
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It can be calcium and so on.
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Okay.
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Got it.
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This is receptor, this is G protein, this is effector molecule.
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Effector molecule can be cyclic AMP.
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It can be phospholypase C.
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It can be calcium, it can be sodium etc.
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Okay.
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On binding of hormone to the receptor causes activation.
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In the form of tilting of this seven transmembrane domain.
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The tilting occurs and as there is tilting occurs there is.
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Due to this GTPase activity.
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There is separation of this alpha from beta gamma subunit.
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Now this becomes active.
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It is GTP bound.
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And it becomes active.
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This active subunit will causes changes in the effector molecule.
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And that's that causes biochemical response.
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Got it.
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This is G protein coupled receptor in short.
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Now coming to the mechanism of action of group two A hormone.
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Group two hormones the mechanism is through G protein coupled receptor.
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Group two hormones they binds with the cell surface receptor.
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Okay.
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After binding with cell surface receptor.
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They causes activation of G protein.
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And G protein will activate phospholypase C.
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Phospholypase C this is a effector molecule.
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Phospholypase C.
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This is a membrane.
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Okay.
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This is a membrane.
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Attachment of hormone to receptor activates G protein which activates phospholypase C.
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This phospholypase C causes conversion of phosphatidyl inositol bisphosphate.
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To diacylglycerol and inositol triphosphate.
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Okay.
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Diacylglycerol and inositol triphosphate.
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This G protein also increases the movement of calcium ions.
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Okay.
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Now this DAG will activate protein kinase.
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It will activate protein kinase.
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IP3 causes release of calcium from endoplasmic reticulum.
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It causes release of calcium from endoplasmic reticulum.
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Now this calcium attached with the calmodulin to form calcium calmodulin complex.
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Calmodulin complex.
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This calcium calmodulin complex activates various calmodulin dependent kinases.
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Okay, they activates various specific kinases.
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And these kinases will causes conversion of protein into phosphoprotein.
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And will show its effect.
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This protein kinases they can directly through diacylglycerol.
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They can directly convert this protein into phosphoprotein and will show effect.
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This calcium and calmodulin complex can directly convert this protein into phosphoprotein and will show effect.
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This is a mechanism of action of group two C hormones.
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Which includes oxytocin, vasopressin.
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Substance P.
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Cholecystokinin.
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Gastrin.
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Muscarinic ACTH.
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And alpha one adrenergic catecholamines.
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So these are included into group two C.
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And this is the mechanism of action.
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Now coming to the group two D and it is a very very important.
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For post graduate student.
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But we will see this topic.
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That is mechanism of action of group two D.
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For UG students.
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Okay, group two D means through kinases.
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Kinase phosphatase cascade.
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So it includes mainly insulin.
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Insulin.
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Growth hormone.
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Then prolactin.
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They act through group two D.
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Means through kinase phosphatase cascade.
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On binding of insulin to receptor.
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Causes activation of tyrosine molecule.
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Intrinsic tyrosine molecule.
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Which activates the insulin receptor substrate one to four by phosphorylation.
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Again by the phosphorylation.
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And due to this phosphorylation of insulin receptor substrate it causes activation of various protein kinases.
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Which includes.
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That is PI3 kinases and PTEN.
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And they will show their response.
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In the form of protein translocation.
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Activation of enzyme, transcription.
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Gene expression, DNA synthesis, cell growth.
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And early response.
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Through various proteins.
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Okay, so this is all about mechanism of hormone action.
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This is a very very important topic.
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Read this topic from Harper's Illustrated Biochemistry.
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It is the best book for this topic.
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Okay.
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Keep watching.
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Thank you.
Topics:hormonesmechanism of hormone actionendocrine systemgroup one hormonesgroup two hormonessecond messengerintracellular receptorscyclic AMPcyclic GMPprotein kinase cascade
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