Biology Lipids Overview

Lipids

• Lipids are a diverse group of organic molecules that don't dissolve in water (hydrophobic).
• They are extracted from tissue using nonpolar solvents and are transported in the blood bound to proteins within lipoprotein particles.

Biological Functions of Lipids

• Cell Membrane Structure: Lipids are key components of cell membranes.
• Energy Storage: They store energy efficiently for the body.
• Insulation: Lipids provide insulation from the environment.
• Water Repellent: They help repel water.
• Signaling Molecules: Lipids act as signaling molecules for cells, including paracrine hormones and steroid hormones.
• Pigments: Some lipids are pigments that contribute to color. Examples include the red color of tomatoes and the orange color of carrots.
• Antioxidants: Lipids like Vitamin E act as antioxidants.
• Cofactors for Enzymes: They are cofactors for enzymes, such as Vitamin K.

Deficiencies or Imbalances of Lipid Metabolism

• Obesity and atherosclerosis are examples of major health problems that can arise from imbalances in lipid metabolism.

Fatty Acids

• Fatty acids are aliphatic, single carboxylic acid chains with a general structure of R-(CH2)n-COOH.
• The "n" in the formula represents an even number of carbon atoms ranging from 4 to 36.
• Fatty acids with chains longer than 22 carbons are found in the brain.

Classification of Fatty Acids

• Saturated Fatty Acids: Do not contain any double bonds.

  • Short Chain Saturated Fatty Acids: Contain 2-10 carbon atoms. Examples include acetic acid with 2 carbons (CH3-COOH).
  • Long Chain Saturated Fatty Acids: Have more than 10 carbon atoms. Example is palmitic acid with 16 carbons, CH3-(CH2)14-COOH.

• Unsaturated Fatty Acids: Contain one or more double bonds.

  • Monounsaturated: Contains one double bond. Example is palmitoleic acid: CH3-(CH2)5CH=CH-(CH2)7 –COOH.
  • Polyunsaturated (EssentialFatty Acids): Contain multiple double bonds. The body cannot synthesize these fatty acids, so they are essential for normal growth and metabolism. Deficiencies are rare, but can cause dry skin due to issues with synthesizing molecules needed for skin's water barrier. Examples include:
    • Linoleic acid: 18 carbons with two double bonds. Structure: CH3-(CH2)4-CH = CH-CH2-CH=CH-(CH2)7-COOH.

Nomenclature

• IUPAC Nomenclature: Uses the carboxyl carbon as C-1.
• Common Nomenclature: Uses Greek letters to label carbons starting from C-1 (α, β, γ, δ, ε, etc.). The carbon furthest from the carboxyl group is designated ω.
• Shortened Notation: C18:1Δ9 indicates an 18-carbon fatty acid with a double bond located between carbons 9 and 10. This would be oleic acid. This notation can also be written as C18:1(9).
• Trans Fats: Have a trans configuration across the double bond. They are found in dairy products, meat, and are produced during the hydrogenation of vegetable oils or fish oils. Trans fats are linked to increased LDL (bad cholesterol) and decreased HDL (good cholesterol) levels.

Melting Points

• At room temperature, saturated fatty acids have a waxy consistency.
• Unsaturated fatty acids of similar chain lengths are oily liquids.

Specific Gravity of Lipids

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Simple Lipids: Fats and Oils

• Simple lipids include fats and oils.
• Types of Triglycerides:
  • Simple Triglycerides: Contain three identical fatty acid molecules.
  • Mixed Triglycerides: Contain three different fatty acid molecules.

Triacylglycerols

• They are a primary form of stored energy, found in fat cells under the skin, mammary glands, and in the abdominal cavity.

Triglycerides vs. Polysaccharides as Storage Fuel

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Triacylglycerols as Insulation

• Triglycerides provide insulation, protecting the body from temperature changes.

Structural Lipids in Membranes

• Membrane lipids are amphipathic, meaning they have both hydrophilic (water-loving) and hydrophobic (water-fearing) regions.

Metabolism of Lipids

• Lipogenesis: The process of synthesizing fats.
• Synthesis of TAG: The process of making triglycerides.
• Catabolism of TAG: The breakdown of triglycerides.
• Fatty Acid Beta Oxidation: The process of breaking down fatty acids to generate energy.
• Ketogenesis and Ketone Bodies Formation: The production of ketone bodies from fatty acids.

Catabolism of TAG:

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Fate of Glycerol

• Details about the metabolic fate of glycerol, likely involving its conversion into glucose or other metabolic intermediates, are expected in this section.

Fatty Acid Beta Oxidation

• Free fatty acids bind to albumin in the blood.
• Activation of Fatty Acids: Fatty acids are activated by an esterification reaction with coenzyme A (CoA).
• Membrane Transport: The resulting fatty acyl-CoA ester is transported across the mitochondrial membrane.
• Carbon Backbone Reaction Sequence:
  • Dehydrogenation: Removal of hydrogen atoms.
  • Hydration: Addition of a water molecule.
  • Dehydrogenation: Removal of hydrogen atoms.
  • Thiolase Reaction: Cleavage of a bond between the fatty acid and CoA.
• Activation of Fatty Acids: Steps of the fatty acid activation process may be discussed in this section.

Transport into the Mitochondrial Matrix

• Carnitine Palmitoyltransferase I: An enzyme on the outer mitochondrial membrane that transfers an acyl group from CoA to carnitine, forming acylcarnitine and regenerating free CoA.
• Translocase: A protein that transports acylcarnitine into the mitochondrial matrix in exchange for free carnitine.
• Carnitine Palmitoyltransferase II: An enzyme on the inner mitochondrial membrane that transfers the acyl group from carnitine back to CoA in the mitochondrial matrix.

Fatty Acid Beta Oxidation: Step 1

• Details on the first step of beta oxidation, including the enzyme involved and the products formed.

Fatty Acid Beta Oxidation: Step 2

• Details on the second step of beta oxidation, including the enzyme involved and the products formed.

Fatty Acid Beta Oxidation: Step 3

• Details on the third step of beta oxidation, including the enzyme involved and the products formed.

Fatty Acid Beta Oxidation: Step 4

• Details on the final step of beta oxidation, including the enzyme involved and the products formed.

Beta Oxidation and ATP

• Activation of a fatty acid requires two ATP molecules.
• Each cycle of beta oxidation produces:
  • 1 NADH (which generates 3 ATP)
  • 1 FADH2 (which generates 2 ATP)
• Acetyl CoA produced from beta oxidation entering the Citric Acid Cycle generates 12 ATP molecules.

This quiz explores the diverse group of lipids, their unique characteristics, and essential biological functions in living organisms. It covers their roles in cell membrane structure, energy storage, insulation, and more, providing a comprehensive understanding of lipids in biology.