Lipid Transport and Lipoprotein Structure
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Questions and Answers

What is the primary function of apolipoprotein A-I?

  • Activates lipoprotein lipase
  • Regulates uptake via the HDL receptor (correct)
  • Facilitates the transport of chylomicrons
  • Inhibits lecithin: cholesterol acyltransferase

    • Which apolipoprotein is specifically associated with the LDL receptor?

  • Apo A-I
  • Apo C-II
  • Apo B-100 (correct)
  • Apo E

    • What characterizes the metabolism of very low-density lipoproteins (VLDL)?

  • They mainly transport dietary lipids
  • They have a half-life of about 1 hour
  • They are synthesized in the intestine
  • They contain 10% protein including apo B-100 (correct)

    • Which of the following components is NOT a characteristic of chylomicrons?

    <p>They are formed in the liver (D)</p> Signup and view all the answers

    What is the primary result of lipoprotein lipase (LPL) action on IDL?

    <p>Decrease in TAG and loss of apo C but retention of apo E (A)</p> Signup and view all the answers

    What portion of lipoproteins is predominantly made up of protein?

    <p>HDL with up to 60% protein (B)</p> Signup and view all the answers

    Which lipoprotein type typically contains the most triacylglycerol (TAG)?

    <p>Chylomicrons (A)</p> Signup and view all the answers

    Which of the following lipoproteins is primarily synthesized in the liver and competes with plasminogen?

    <p>Lipoprotein (a) [Lpa] (D)</p> Signup and view all the answers

    What percentage of total plasma lipids does cholesterol typically account for?

    <p>40% (B)</p> Signup and view all the answers

    Which lipoprotein has the lowest density due to its high lipid content?

    <p>Chylomicrons (C)</p> Signup and view all the answers

    Which of the following statements about apolipoproteins is correct?

    <p>Apo (a) has high carbohydrate content and is found in Lp(a). (C)</p> Signup and view all the answers

    Which method is NOT used to separate lipoproteins?

    <p>Filtration (B)</p> Signup and view all the answers

    Flashcards

    Apolipoprotein

    A protein component of lipoproteins that helps them interact with receptors on cells, enabling the uptake of lipids into tissues.

    Chylomicron

    A type of lipoprotein that transports dietary lipids (mainly triglycerides) from the intestines to the liver and other tissues.

    Lipoprotein lipase (LpL)

    An enzyme that breaks down triglycerides in chylomicrons and VLDL, releasing fatty acids for energy.

    Very low-density lipoprotein (VLDL)

    A lipoprotein that transports lipids synthesized by the liver to the peripheral tissues.

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    Intermediate density lipoprotein (IDL)

    A type of lipoprotein that forms from VLDL after it loses most of its triglycerides (through LpL activity).

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    Why are lipids packaged with proteins?

    Lipids are insoluble in water, so they need to be packaged with proteins for transport in the bloodstream.

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    What are lipoproteins?

    Lipoproteins are particles that transport lipids in the blood, made up of a lipid core and a protein coat.

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    What are apolipoproteins?

    Apolipoproteins are the protein portion of lipoproteins. They help stabilize the lipoprotein structure and promote lipid solubility.

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    How is lipoprotein density determined?

    The density of a lipoprotein is determined by the ratio of protein to lipid. More protein means higher density.

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    What are chylomicrons?

    Chylomicrons are the largest and least dense lipoproteins, responsible for transporting dietary fats from the intestines to tissues.

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    What are VLDLs?

    Very low-density lipoproteins (VLDL) are produced by the liver and transport triglycerides to tissues.

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    What are LDLs?

    Low-density lipoproteins (LDL) are known as the 'bad cholesterol' because high levels can contribute to heart disease. LDL carries cholesterol from the liver to tissues.

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    What are HDLs?

    High-density lipoproteins (HDL) are considered the 'good cholesterol' as they transport cholesterol back to the liver for processing.

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    Study Notes

    Lipid Transport

    • Lipids are insoluble in water, thus associated with proteins to form lipoproteins, which are water-soluble.
    • The protein component of lipoproteins is called apolipoprotein.
    • Lipoproteins facilitate lipid transport between tissues.
    • Total plasma lipids range from 400-600 mg/dL, comprising triacylglycerol (20%), phospholipids (30%), cholesterol (40%), and free fatty acids.

    Lipoprotein Structure

    • Lipoproteins consist of a lipid core (triacylglycerol and cholesterol esters) and a protein shell (apolipoproteins).
    • Apolipoproteins are categorized as integral or peripheral. The percentages vary from 1% (chylomicrons) to 60% (some HDLs).

    Lipoprotein Classification

    • Lipoprotein density increases with the protein component.
    • Lipoproteins are classified using ultracentrifugation and electrophoresis.
      • Chylomicrons
      • Very-low-density lipoproteins (VLDL)
      • Intermediate-density lipoproteins (IDL)
      • Low-density lipoproteins (LDL)
      • High-density lipoproteins (HDL)
      • Lipoprotein (a) (Lp(a)): similar lipid composition to LDL, but also competing with plasminogen to tissue plasminogen receptors.
    • The predominant lipid component varies among types. For example: Triacylglycerol (TAG) is predominant in chylomicrons and VLDL. Cholesterol is predominant in LDL, and phospholipids are abundant in HDL.

    Apolipoproteins

    • Apolipoproteins are the protein components of lipoproteins.
    • Five major classes (A-E) are known.
    • Apo B exists in two forms (apo B-100 and apo B-48). Apo B-100 is in LDL, while apo B-48 is in chylomicrons.
    • Apo (a) is present in lipoprotein (a), with apo B-100 and has a high carbohydrate content.
    • Apolipoproteins:
      • Enhance lipid solubility in plasma.
      • Maintain lipoprotein stability.
      • Act as ligands for lipoprotein receptors, facilitating tissue uptake.
      • Specific apolipoproteins bind to specific receptors (apo B-100 and apo E for LDL receptors, etc.).

    Apolipoprotein Enzyme Activity

    • Some apolipoproteins are enzyme activators:
      • Apo C-II for lipoprotein lipase.
      • Apo A-I for lecithin:cholesterol acyltransferase (LCAT).
    • Some apolipoproteins are enzyme inhibitors:
      • Apo A-II and apo C-III for lipoprotein lipase.
      • Apo C-I for cholesteryl ester transfer protein.

    Metabolism of Chylomicrons

    • Site of synthesis: Intestinal mucosa.
    • Function: Transport of dietary lipids to peripheral tissues.
    • Structure: Mostly triacylglycerol (98%), proteins (1-2%, including apo B-48, apo E, and apo C-II).
    • Half-life: Approximately 1 hour.

    Metabolism of Very-Low-Density Lipoproteins (VLDL)

    • Site of synthesis: Liver.
    • Function: Transport of endogenously synthesized lipids to peripheral tissues.
    • Structure: Mostly triacylglycerol, proteins (10%, including apo B-100, apo E, and apo C-II).
    • Half-life: 1-3 hours.

    Formation of Intermediate-Density Lipoproteins (IDL)

    • The action of lipoprotein lipase results in the loss of 70-90% of triacylglycerol and apo C.
    • This leads to VLDL remnants, which are called IDL (intermediate-density lipoproteins).
    • IDL has less triacylglycerol and more cholesterol.
    • IDL is either: taken up by liver cells via LDL receptors, or converted to LDL.

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    Related Documents

    Lipid Transport Lecture 4 PDF

    Description

    This quiz covers the important concepts of lipid transport and the structure of lipoproteins. You'll learn about the composition of lipoproteins, the role of apolipoproteins, and the classification of lipoproteins based on density. Understand how lipids are transported in the body and their significance in health.

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