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Questions and Answers
If a researcher aims to study the paracrine effects within the islets of Langerhans, which cellular interaction would be the most relevant to investigate?
If a researcher aims to study the paracrine effects within the islets of Langerhans, which cellular interaction would be the most relevant to investigate?
- The direct effect of blood glucose levels on beta cell function, irrespective of alpha cells.
- The influence of pancreatic acinar cells on beta cell insulin secretion.
- The impact of alpha cell glucagon secretion on neighboring beta cells. (correct)
- The autocrine signaling within individual beta cells affecting their own insulin production.
During insulin synthesis, what would be the MOST immediate consequence if the ribosome is unable to bind to the endoplasmic reticulum?
During insulin synthesis, what would be the MOST immediate consequence if the ribosome is unable to bind to the endoplasmic reticulum?
- The signal sequence will not be able to penetrate the rough endoplasmic reticulum. (correct)
- mRNA will not be translated into a sequence of amino acids.
- The transcription process in the nucleus will be halted due to lack of feedback.
- Pre-pro-insulin will be directly converted into pro-insulin in the cytosol.
An experimental drug inhibits endopeptidase activity within the rough endoplasmic reticulum. What direct effect would this drug have on insulin synthesis?
An experimental drug inhibits endopeptidase activity within the rough endoplasmic reticulum. What direct effect would this drug have on insulin synthesis?
- Block the conversion of pre-pro-insulin to pro-insulin. (correct)
- Inhibit the transcription of the insulin gene in the nucleus.
- Prevent the formation of disulfide bonds in pro-insulin.
- Halt the packaging of insulin and C-peptide into secretory vesicles.
In a patient with a genetic mutation affecting the Golgi's endopeptidase, which step of insulin processing would be directly impaired?
In a patient with a genetic mutation affecting the Golgi's endopeptidase, which step of insulin processing would be directly impaired?
If a researcher discovers a new drug that selectively disrupts the function of alpha cells in the pancreatic islets, what downstream effect on beta cell activity might be observed?
If a researcher discovers a new drug that selectively disrupts the function of alpha cells in the pancreatic islets, what downstream effect on beta cell activity might be observed?
A scientist is studying the effects of a novel compound on insulin production. The compound is found to prevent the formation of the initial signal sequence during translation. What is the MOST likely outcome of this?
A scientist is studying the effects of a novel compound on insulin production. The compound is found to prevent the formation of the initial signal sequence during translation. What is the MOST likely outcome of this?
A researcher is investigating a mutation that prevents pre-pro-insulin from folding correctly within the rough endoplasmic reticulum (RER). What is the likely consequence of this mutation?
A researcher is investigating a mutation that prevents pre-pro-insulin from folding correctly within the rough endoplasmic reticulum (RER). What is the likely consequence of this mutation?
A pharmaceutical company is designing a drug that will enhance the storage capacity of insulin in beta cells. Which cellular component should the drug target to achieve this effect?
A pharmaceutical company is designing a drug that will enhance the storage capacity of insulin in beta cells. Which cellular component should the drug target to achieve this effect?
If a patient has a condition where their beta cells release insulin but cannot release C-peptide, what is the MOST likely problem in their insulin production pathway?
If a patient has a condition where their beta cells release insulin but cannot release C-peptide, what is the MOST likely problem in their insulin production pathway?
Consider a scenario where a researcher introduces a compound that inhibits the formation of secretory granules in beta cells. What direct impact would this have on insulin secretion?
Consider a scenario where a researcher introduces a compound that inhibits the formation of secretory granules in beta cells. What direct impact would this have on insulin secretion?
Flashcards
Pancreatic Cells
Pancreatic Cells
Cells in the pancreas that secrete peptide hormones; beta cells are most abundant and located in the center of the islets, alpha cells are found at the periphery.
Beta Cells
Beta Cells
The most abundant cells in the islets of Langerhans, located centrally, that produce insulin.
Alpha Cells
Alpha Cells
Cells located at the periphery of the islets of Langerhans that produce glucagon.
Paracrine Regulation
Paracrine Regulation
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Gene Transcription
Gene Transcription
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Signal Sequence
Signal Sequence
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Endopeptidase
Endopeptidase
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Cleavage in Golgi
Cleavage in Golgi
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Equal Packaging
Equal Packaging
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Insulin Storage and Release
Insulin Storage and Release
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Study Notes
- The pancreas contains cells that secrete peptide hormones.
- Beta cells, located in the center of the islets of Langerhans, are the predominantly found.
- Alpha cells are found at the periphery of the islets surrounding the beta cells.
Paracrine Regulation
- Blood supply to the Islets of Langerhans goes through the center because they are pervaded by fenestrated capillaries.
- Beta cells are located in the center and discharge insulin that enters fenestrated capillaries.
- Alpha cells in the periphery are exposed to elevated levels of insulin.
- Insulin suppresses glucagon release from alpha cells.
- Paracrine regulation is when one group of cells releases a product affecting nearby cell activity.
Synthesis and Storage of Insulin
- Gene transcription occurs for insulin production on chromosome 11 on the short arm.
- The gene responsible for insulin is activated, and the DNA sequence unwinds.
- Transcription starts to form messenger RNA (mRNA).
- Mature mRNA molecules move to the cytosol.
- In the cytosol, mRNA binds to ribosomes and translates into an amino acid sequence.
- The initial chain part made during translation is the signal sequence, with hydrophobic amino acids.
Translation of Preproinsulin
- The initial signal sequence moves the ribosome and mRNA to the endoplasmic reticulum.
- The signal sequence penetrates the rough endoplasmic reticulum (RER).
- Ribosomes attach to the RER, continuously producing peptide chains while attached to the endoplasmic reticulum.
- As translation proceeds, more peptide chains are formed and pushed by the signal sequence into the rough endoplasmic reticulum.
- Peptide chains inside the RER fold and form pre-pro-insulin.
Processing to Proinsulin
- Endopeptidase is an enzyme is located inside the lumen of the rough endoplasmic reticulum where it digests the peptide chain.
- Its main function is to convert pre-pro-insulin into pro-insulin.
- Pro-insulin molecules then form disulfide bonds, and are packaged into vesicles formed by the endoplasmic reticulum.
Packaging and Cleavage in the Golgi Apparatus
- Vesicles with pro-insulin molecules bud off and move toward the Golgi complex.
- Once the vesicles fuse with the Golgi complex, they release the pro-insulin inside.
- Inside the Golgi complex, an endopeptidase enzyme works on pro-insulin, cleaving the C-peptide to form insulin molecules and C-peptide fragments.
- Endopeptidase converts pro-insulin into insulin within the secretory vesicles.
- A mature insulin molecule consists of two chains, the A chain (30 amino acids) and the B chain (21 amino acids).
- Insulin and C-peptide molecules are packaged equally with zinc ions inside the secretory vesicles.
Storage and Release
- Insulin and C-peptide are stored in secretory granules within the beta cells.
- Stimuli such as high blood glucose levels cause granules to undergo exocytosis, releasing insulin and C-peptide into the bloodstream in equimolar amounts.
Key points
- Endocrine function of the pancreas is done by the Islets of Langerhans.
- Islets of Langerhans account for 1% of the pancreas mass.
- Beta cells produce insulin, amylin, C-peptide, and pro-insulin, and are stored with Zn molecules in secretory vesicles.
- Alpha cells produce glucagon.
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