lipid

Examples of lipid in the following topics:

• Connecting Lipids to Glucose Metabolism

  • Lipids can be both made and broken down through parts of the glucose catabolism pathways.
  • Like sugars and amino acids, the catabolic pathways of lipids are also connected to the glucose catabolism pathways.
  • The lipids that are connected to the glucose pathways are cholesterol and triglycerides.

• Lipid-Derived, Amino Acid-Derived, and Peptide Hormones

  • All hormones in the human body can be divided into lipid-derived, amino acid-derived, and peptide hormones.
  • One of the key, distinguishing features of lipid-derived hormones is that they can diffuse across plasma membranes whereas the amino acid-derived and peptide hormones cannot.
  • Most lipid hormones are derived from cholesterol, so they are structurally similar to it .
  • The primary class of lipid hormones in humans is the steroid hormones.
  • Amino acid-derived and polypeptide hormones are water-soluble and insoluble in lipids.

• Lipid Biosynthesis

  • Many of the immune activating abilities of lipopolysaccharide can be attributed to the lipid A unit.
  • Lipids may be broadly defined as hydrophobic or amphiphilic small molecules.
  • Using this approach, lipids may be divided into eight categories: fatty acids, glycerolipids, glycerophospholipids, sphingolipids, saccharolipids, and polyketides (derived from condensation of ketoacyl subunits); and sterol lipids and prenol lipids (derived from condensation of isoprene subunits ).
  • Although humans and other mammals use various biosynthetic pathways to both break down and synthesize lipids, some essential lipids cannot be made this way and must be obtained from the diet.
  • Outline the characteristics and processes of lipid biosynthesis, including:; lipogenesis and fatty acid biosynthesis

• Digestion and Absorption

  • Emulsification is a process in which large lipid globules are broken down into several small lipid globules.
  • Lipids are hydrophobic substances.
  • The bile salts' hydrophilic side can interface with water, while the hydrophobic side interfaces with lipids, thereby emulsifying large lipid globules into small lipid globules.
  • Vitamins can be either water-soluble or lipid-soluble.
  • It is important to consume some amount of dietary lipid to aid the absorption of lipid-soluble vitamins.

• Lipid Soluble Vitamins

  • The lipid soluble vitamins, shown in the diagram below, are not as easily eliminated and may accumulate to toxic levels if consumed in large quantity.
  • From the structures shown here, it should be clear that these compounds have more than a solubility connection with lipids.

• Lipid Metabolism

  • Lipids are universal biological molecules.
  • Among these, lipids can be metabolized by microbes for use as a primary energy source.
  • Fatty acids are the building blocks of lipids.
  • Lipids are an energy and carbon source.
  • Before complex lipids can be used to produce energy, they must first be hydrolyzed.

• Fatty Acids

  • The lipids are a large and diverse group of naturally occurring organic compounds that are related by their solubility in nonpolar organic solvents (e.g. ether, chloroform, acetone & benzene) and general insolubility in water.
  • There is great structural variety among the lipids, as will be demonstrated in the following sections.
  • The common feature of these lipids is that they are all esters of moderate to long chain fatty acids.
  • Acid or base-catalyzed hydrolysis yields the component fatty acid, some examples of which are given in the following table, together with the alcohol component of the lipid.
  • These acids are also precursors to the prostaglandins, a family of physiologically potent lipids present in minute amounts in most body tissues.

• Chemical Digestion of Carbohydrates, Proteins, Lipids, and Nucleic Acids

  • Digestion of certain fats begins in the mouth, where lingual lipase breaks down short chain lipids into diglycerides.
  • Lipid digestion involves the formation of micelles in the presence of bile salts, and the passage of micelles and fatty acids through the unstirred layer.

• Mechanisms of Hormone Action

  • Hormones activate target cells by diffusing through the plasma membrane of target cells (lipid-soluble hormones) to bind a receptor protein within the cytoplasm of the cell or by binding a specific receptor protein in the cell membrane of the target cell (water-soluble proteins) .
  • 4. eicosanoids: hormones containing lipids synthesized from the fatty acid chains of phospholipids found in the plasma membrane.
  • Nuclear hormone receptors are activated by a lipid-soluble hormone such as Estrogen, binding to them inside the cell.
  • Lipid-soluble hormones can cross the plasma membrane.

• Intracellular Hormone Receptors

  • Lipid-soluble hormones diffuse across the plasma membrane of cells, binding to receptors inside the cells where they alter gene expression.
  • Lipid-derived (soluble) hormones such as steroid hormones diffuse across the lipid bilayer membranes of the endocrine cell.
  • At the target cell, the hormones are released from the carrier protein and diffuse across the lipid bilayer of the plasma membrane of the target cells.
  • Other lipid-soluble hormones that are not steroid hormones, such as vitamin D and thyroxine, have receptors located in the nucleus.