Peroxisomes Overview and Function
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Questions and Answers

What happens to a peroxisome after it accumulates more proteins and expands?

  • It fuses with another organelle.
  • It breaks down into smaller molecules.
  • It undergoes fission. (correct)
  • It undergoes apoptosis.

    • Which condition is primarily caused by mutations in peroxin genes?

  • Zellweger syndrome (correct)
  • Cystic fibrosis
  • Mitochondrial myopathy
  • Hunter syndrome

    • What can accumulate in tissues due to impaired peroxisome function?

  • Very long-chain fatty acids and branched chain fatty acids (correct)
  • Short-chain fatty acids
  • Glucose
  • Ketone bodies

    • Which of the following is associated with Zellweger syndrome?

    <p>Deficient levels of plasmalogens</p> Signup and view all the answers

    What type of genetic mutation primarily causes Zellweger syndrome?

    <p>Recessive mutations</p> Signup and view all the answers

    Which factor is NOT associated with the peroxin genes implicated in Zellweger syndrome?

    <p>PEX25</p> Signup and view all the answers

    What role do peroxins play in the cell?

    <p>Assembly of peroxisomes</p> Signup and view all the answers

    What is an effect of accumulating long-chain fatty acids in cells?

    <p>Impaired function of multiple organ systems</p> Signup and view all the answers

    What is a common facial characteristic associated with peroxisomal disorders?

    <p>High forehead</p> Signup and view all the answers

    Which is a typical symptom experienced by infants with peroxisomal disorders?

    <p>Hypotonia</p> Signup and view all the answers

    What long-term developmental issues are common in patients with peroxisomal disorders?

    <p>Developmental delay and mental retardation</p> Signup and view all the answers

    What effect does Zellweger syndrome have on the central nervous system's myelin?

    <p>Hypomyelination</p> Signup and view all the answers

    How do patients with peroxisomal disorders typically engage in feeding?

    <p>Difficult to feed</p> Signup and view all the answers

    Which animal model was used to investigate direct insulin signaling in the liver?

    <p>All of the above</p> Signup and view all the answers

    What procedure was performed on the mice to assess glucose tolerance?

    <p>Intraperitoneal glucose injection</p> Signup and view all the answers

    What is indicated by a reduction in serum insulin concentrations in the experiment?

    <p>Insulin resistance</p> Signup and view all the answers

    What is the primary function of enzymes found in peroxisomes?

    <p>To detoxify harmful substances including hydrogen peroxide</p> Signup and view all the answers

    How do peroxisomes differ from lysosomes regarding their origin?

    <p>Peroxisomes self-replicate, while lysosomes are formed in the Golgi complex</p> Signup and view all the answers

    What essential process occurs in liver cell peroxisomes?

    <p>Detoxification of alcohol and harmful compounds</p> Signup and view all the answers

    What is the fate of hydrogen peroxide in peroxisomes?

    <p>It is broken down into water, making it safe</p> Signup and view all the answers

    Which of the following accurately describes the genetic makeup of peroxisomes?

    <p>They contain no internal DNA and thus must import proteins</p> Signup and view all the answers

    What role do peroxisomal targeting signals play in the function of peroxisomes?

    <p>They facilitate the import of proteins into the peroxisome</p> Signup and view all the answers

    How does the role of peroxisomes in membrane formation contrast with their detoxifying functions?

    <p>Phospholipid production is unrelated to their detoxifying abilities</p> Signup and view all the answers

    Which of the following substances do peroxisomes primarily convert to water?

    <p>Hydrogen peroxide</p> Signup and view all the answers

    What technique was used to study the mice's hepatic glucose production?

    <p>Euglycemic, hyperinsulinemic clamp technique</p> Signup and view all the answers

    What was the mean blood glucose concentration maintained during the insulin clamp procedure?

    <p>125 mg/dl</p> Signup and view all the answers

    What is the function of phosphorylase activated by glucagon signaling?

    <p>Activating glycogen phosphorylase</p> Signup and view all the answers

    Which of the following enzymes was not mentioned in relation to the metabolic profiling of the liver?

    <p>Fructose-1,6-bisphosphatase</p> Signup and view all the answers

    What type of animal model was used in the described experiments?

    <p>Male WT, IR(lox/lox), and LIRKO mice</p> Signup and view all the answers

    What role does cAMP play in glucagon signaling?

    <p>It activates various proteins through PKA</p> Signup and view all the answers

    What does lactate provide for gluconeogenesis?

    <p>Building blocks</p> Signup and view all the answers

    What is the purpose of the Northern blotting technique in the context of the experiments?

    <p>To analyze RNA levels of specific enzymes</p> Signup and view all the answers

    Study Notes

    Peroxisomes

    • Peroxisomes are organelles that contain enzymes to rid cells of toxic substances, specifically hydrogen peroxide.
    • Hydrogen peroxide is a byproduct of cellular metabolism.
    • They convert hydrogen peroxide into water, making the toxic substance safe.
    • Some peroxisomes, like those in liver cells, detoxify alcohol and other harmful substances by transferring hydrogen from toxins to oxygen molecules (oxidation).
    • Others are crucial for phospholipid production, which is vital for membrane formation.

    Peroxisome Structure and Function

    • Peroxisomes have a single membrane.
    • The core contains enzymes involved in specific metabolic pathways.
    • They self-replicate, unlike mitochondria.
    • Peroxisomes obtain needed proteins from the surrounding cytosol. This process of obtaining proteins from the cytosol isn't fully understood but requires specific targeting signals found in amino acid sequences.
    • These signals attach to receptor proteins in the cytosol and docking proteins in the peroxisome membrane.

    Peroxisomal Disorders

    • Zellweger syndrome is an autosomal recessive disorder caused by mutations in genes encoding peroxins, proteins essential for normal peroxisome assembly.
    • Mutations in related PEX genes often cause deficiencies in peroxisome function.
    • Affected individuals often have characteristic facial abnormalities (e.g., high forehead, frontal bossing, small face, low-set ears, and slanted eyes).
    • They commonly present with hypotonia (floppy muscles), developmental delays, and mental retardation.
    • Peroxisomal disorders can lead to an accumulation of very long-chain fatty acids (VLCFAs) and branched-chain fatty acids (BCFAs) within tissues and cells, potentially impairing multiple organ systems.
    • Reduced levels of plasmalogens (ether-phospholipids) in brain and lung tissue are often seen.

    Oral Glucose Tolerance Test (OGTT)

    • The OGTT measures blood glucose levels after consuming glucose. The test gauges how well the body regulates blood glucose after glucose consumption.
    • Blood glucose levels are measured at various time points after glucose ingestion.
    • Corresponding insulin levels are measured at the same time points to see the immediate response of the body's endocrine system.
    • A graph of blood glucose versus time is plotted, and normal/abnormal results can be noted.

    Glucose Homeostasis

    • Glucose homeostasis is regulated primarily through the actions of insulin and glucagon.
    • Insulin, released from the pancreas’ beta cells, reduces blood glucose levels. It aids glucose uptake into cells and encourages glycogen storage.
    • Glucagon, released from alpha cells in the pancreas, increases circulating glucose. It stimulates glycogen breakdown in the liver, enhancing gluconeogenesis.

    Type 1 Diabetes

    • Type 1 diabetes results from an autoimmune attack of insulin producing beta cells in the pancreas. Beta cells no longer produce sufficient insulin.
    • In type 1 diabetes, the body cannot appropriately regulate blood sugar or utilize glucose for energy.

    Insulin Secretion

    • The release of insulin into the blood is a complex process in response to elevated blood glucose levels.
    • The glucose uptake into beta cells leads to metabolic pathways. The result leads to membrane depolarization, which prompts the opening of calcium channels.
    • The influx of calcium ions triggers the release of insulin granules into the blood stream.

    GLUT4 Translocation

    • Insulin promotes glucose uptake by activating the translocation of glucose transporters (e.g., GLUT4) to the cell membrane.
    • Muscle cells and adipocytes require insulin for glucose uptake, meaning the proper function and release of insulin is necessary for these cells to respond to glucose.
    • The absence of insulin prevents the recruitment of GLUT4 to the membrane impeding the ability of these cells to use glucose for energy.

    Glucagon Regulation

    • Glucagon, produced by alpha cells in the pancreas, is fundamental in regulating the homeostasis of glucose levels.
    • Glucagon is triggered by hypoglycemia (low blood glucose) and acts on the liver in response to lower than normal blood glucose levels.
    • Glucagon increases blood glucose through stimulating glycogenolysis (glycogen breakdown) and gluconeogenesis (formation of glucose).
    • Increased glucagon results in increased glucose in the blood.

    Glucagon Signaling in the Liver

    • Glucagon signaling in the liver mainly occurs through a G-protein coupled receptor (GPCR) pathway which utilizes protein kinases (e.g., PKA).
    • Glucagon binds to the liver receptor causing a cascade of intracellular events.
    • The subsequent actions decrease glycogen stores and increase glycogen production (gluconeogenesis), increasing glucose in the blood.
    • Pyruvate and lactate are crucial substrates for gluconeogenesis, offering vital building blocks for sugar production.

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    Week 8 Lecture 13 PDF

    Description

    This quiz explores the structure and function of peroxisomes, essential organelles in cellular metabolism. Learn about their role in detoxifying harmful substances like hydrogen peroxide and their importance in phospholipid production. Test your understanding of these vital cellular components.

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