Insulin structure, Insulin synthesis, Insulin types, Insulin Secretion, Insulin mechanism of Action

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Insulin structure, Insulin synthesis, Insulin types, Insulin Secretion, Insulin mechanism of Action
Insulin is a protein composed of two chains, an A chain (with 21 amino acids) and a B chain (with 30 amino acids), which are linked together by sulfur atoms. Insulin is derived from a 74-amino-acid prohormone molecule called proinsulin. Proinsulin is relatively inactive, and under normal conditions only a small amount of it is secreted. In the endoplasmic reticulum of beta cells the proinsulin molecule is cleaved in two places, yielding the A and B chains of insulin and an intervening, biologically inactive C peptide. The A and B chains become linked together by two sulfur-sulfur (disulfide) bonds. Proinsulin, insulin, and C peptide are stored in granules in the beta cells, from which they are released into the capillaries of the islets in response to appropriate stimuli. These capillaries empty into the portal vein, which carries blood from the stomach, intestines, and pancreas to the liver. The pancreas of a normal adult contains approximately 200 units of insulin, and the average daily secretion of insulin into the circulation in healthy individuals ranges from 30 to 50 units.
Secretion
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A rise in glucose levels in extra-cellular fluid (ECF) is the stimulus for insulin release.
Glucose is transported into the beta cell by facilitated diffusion through GLUT2 channels. Therefore, a rise in glucose concentration in ECF causes a rise in glucose concentration in beta cells. This leads to membrane depolarisation of ATP-sensitive K+ channels, opening Ca2+ channels. This triggers an influx of calcium.
An increase in intracellular Ca2+ triggers insulin release by a two stage process:
Margination: the process by which insulin storage vesicles move to the cell surface.
Exocytosis: This is fusion of the vesicle membrane with the plasma membrane, with release of the vesicle’s entire contents
Secretion of insulin follows a biphasic pattern - i.e. occurs in two phases:
Pulsatile release (rapid onset): Short term blood glucose control: clearing absorbed nutrients from the blood following a meal.
Protracted release (longer): Long term insulin release for glucose uptake e.g. for cell growth, cell division, stimulating protein synthesis and DNA replication.
Mechanism of Action
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Insulin binds to a highly specific insulin receptor on cell surfaces.
The receptor is a dimer: 2 identical sub-units spanning the cell membrane. The 2 subunits are made of:
One alpha chain (on the exterior of the cell membrane)
One beta chain (spans cell membrane in a single segment)
These are connected by a single disulfide bond.
When insulin is detected, the alpha chains move together and fold around the insulin. This moves the beta chains together making them an active tyrosine kinase. This initiates a phosphorylation cascade which results in an increase of GLUT4 expression - a protein channel to allow glucose uptake. The result is an increase of glucose uptake by cells.
Overall effects
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Overall, Insulin can be considered the “anabolic” or building hormone - it assists processes that build compounds for storage and decrease processes that break down those storage reserves.
In muscle and liver, insulin increases glycogenesis and decreases glycogenolysis.
Decreased gluconeogenesis in the liver
Increased glycolysis in liver and adipose tissue.
Decreased the breakdown of amino acids in the liver.
Increased amino acid uptake and protein synthesis in muscle, liver, and adipose tissue.
Decreased lipolysis
Increased lipogenesis and esterification of fatty acids in the liver and adipose tissue.
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[@uma674]

Great information and well explained thank you so much sir !
Waiting for more vedios ♥️!

[@doctorbhanuprakash]

Always welcome

[@vivekanandaramavtar8025]

Sir.
Very easy explanation of insulin
Thanks.
See you in your next video

[@doctorbhanuprakash]

Keep watching

[@dhirajsakat9378]

Awesome ❤❤❤

[@vishalnatwadia7597]

Sir please carbohydrates topic also cover thank you

[@rupaliyadav5710]

Nice to see you sir ..after osh 😃

[@doctorbhanuprakash]

thank u

[@youtubemonarch007]

Sir insulin tertiary level protein ha ya phir quaternary level protein???

[@sasankasekharpradhan1838]

Relationship between C peptide and insulin what sir

[@osamashekh155]

Awesome 👏 lecture sir

[@doctorbhanuprakash]

Thanks and welcome

[@hellohellogoodbye9327]

I want to see more videos of sir.. He is awesome 🤧

[@doctorbhanuprakash]

Very soon

[@rishiraj2548]

🙏💯

[@amolkelkar7231]

Nice video

[@doctorbhanuprakash]

So nice