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Related Concept Videos

Cholesterol: Significance and Regulation01:29

Cholesterol: Significance and Regulation

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Although not a source of energy, cholesterol plays a significant role as a foundational structure for bile salts, steroid hormones, and vitamin D, as well as being a crucial component of plasma membranes. Approximately 15% of blood cholesterol is derived from our diet, with the remainder synthesized from acetyl CoA by the liver and intestines. Cholesterol is eliminated from the body through its conversion into bile salts, which are eventually discarded in the feces.
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Cell membranes are composed of phospholipids, proteins, and carbohydrates loosely attached to one another through chemical interactions. Molecules are generally able to move about in the plane of the membrane, giving the membrane its flexible nature called fluidity. Two other features of the membrane contribute to membrane fluidity: the chemical structure of the phospholipids and the presence of cholesterol in the membrane.
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Membrane fluidity is explained by the fluid mosaic model of the cell membrane, which describes the plasma membrane structure as a mosaic of components—including phospholipids, cholesterol, proteins, and carbohydrates—that gives the membrane a fluid character.
Mosaic nature of the membrane
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The ER synthesizes lipids for building cell membranes and performing cellular functions such as energy storage and signaling. The lipid synthesis machinery embedded in the ER membrane primarily collects all reactants from the cytosol. Following synthesis, the secretory pathway and the ER contact sites distribute these lipids to other cellular organelles. Additionally, the energy-rich triacylglycerides are transported from the ER via lipid droplets.
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Lipids are an essential component of all biological membranes. The average lipid content in mammalian membranes is 50%, though it can be as low as 20% in the inner mitochondrial membrane or as high as 80% in the myelin sheath present around the nerve cells.
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Biological membranes show uneven distribution of different types of lipids in the inner and outer layers, resulting in transverse asymmetric membranes. The treatment of the erythrocyte membrane with the enzyme phospholipase confirmed the asymmetric nature of the lipid bilayer. The enzyme hydrolyzes lipids into fatty acids and hydrophilic groups. The phospholipase acts only on the outer layer of the membrane, while the inner layer remains intact. The phospholipase treatment resulted in 80%...
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Enrichment of Mammalian Tissues and Xenopus Oocytes with Cholesterol
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Active membrane cholesterol as a physiological effector.

Yvonne Lange1, Theodore L Steck2

  • 1Department of Pathology, Rush University Medical Center, 1653 W. Congress Parkway, Chicago, IL 60612, USA.

Chemistry and Physics of Lipids
|February 14, 2016
PubMed
Summary
This summary is machine-generated.

Active cholesterol, a highly accessible fraction, regulates cellular sterol balance by moving to organelles and influencing protein activity. This dynamic cholesterol pool impacts various membrane proteins, suggesting a broader biological role.

Keywords:
Active cholesterolChannelsHomeostasisReceptorsTransporters

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Area of Science:

  • Biochemistry
  • Cell Biology
  • Membrane Biophysics

Background:

  • Sterols, particularly cholesterol, form complexes with specific membrane lipids.
  • A fraction of cholesterol, termed 'active cholesterol,' exhibits high accessibility and fugacity.
  • Understanding cholesterol's distinct roles beyond bulk lipid pools is crucial for cell function.

Purpose of the Study:

  • To review the role of active cholesterol in cellular sterol homeostasis.
  • To investigate the involvement of active cholesterol in the function of diverse membrane proteins.
  • To highlight the significance of active cholesterol in cellular signaling and transport.

Main Methods:

  • Literature review of sterol-lipid interactions and cellular cholesterol regulation.
  • Analysis of studies investigating active cholesterol's effects on membrane protein activity.
  • Synthesis of evidence implicating active cholesterol in various cellular processes.

Main Results:

  • Active cholesterol acts as an upstream regulator of sterol homeostasis.
  • It redistributes to the endoplasmic reticulum and mitochondria, modulating effector feedback.
  • Evidence suggests active cholesterol influences caveolin-1, ABC transporters, solute transporters, receptors, and ion channels.

Conclusions:

  • Active cholesterol plays a significant, previously underestimated role in cellular regulation.
  • Its dynamic distribution and interaction with membrane proteins warrant further investigation.
  • The proposed functions of active cholesterol are readily testable in experimental systems.