In-Depth Notes on Lipids and Building the Hydrophobic Barrier

  • Lipids and Building the Hydrophobic Barrier

    • Overview of Lipids

    • Diverse group of hydrophobic molecules; characteristic of low or no affinity for water.

    • Composed mainly of hydrocarbons (nonpolar covalent bonds).

    • Major types of lipids:

      1. Neutral lipids (fats)

      2. Phospholipids

      3. Steroids

  • Neutral Lipids

    • Predominantly consist of triacylglycerides (fats).

    • Composition: One glycerol molecule (three carbon compound with three hydroxyl groups).

    • Three fatty acids (hydrocarbon chains with terminal carboxylic acid groups).

  • Functional Groups and Their Reactions

    • Hydroxyl groups are polar and facilitate the dissolution of organic compounds ( glucose, Glyceral, and serine).

    • Carboxylic acids (e.g., acetic acid) release hydrogen ions, contributing to acidity.

    • Carboxyl groups convert to carboxylate ions in cellular contexts.

  • Fat Synthesis

    • Lipid synthesis occurs via dehydration reactions forming ester linkages between glycerol and fatty acids.

    • The general reaction produces water as a byproduct.

  • Saturated vs Unsaturated Fats

    • Fats are semi-solid at room temperature, while unsaturated fats remain liquid due to the presence of double bonds that create kinks in the fatty acid chains.

    • Saturated fats:

    • All C-C bonds are single; and solid at room temperature.

    • Stearic acid CH3(CH2) 16COOH is a common saturated fatty acid found in animal fats and is known for its role in energy storage.

    • Van der Waals Forces play a crucial role in the stabilization of lipid structures, as they contribute to the hydrophobic interactions that allow lipids to form membranes and barriers.

    • 14-22 carbons long

    • Contains only a single bond between carbons

    • Unsaturated fats:

    • Contain one or more double bonds; liquid at room temperature(Oil).

    • Fewer hydrogen bonds

    • Cis configuration results in chain bending, whereas trans configuration keeps the chain straight.

    • Oleic acid CH3(CH2)7CH=CH(CH2)7COOH

  • Nutrition and Essential Fatty Acids

    • Humans can synthesize nearly all fats from carbohydrates; however, three essential fatty acids must be acquired through diet:

    1. Linoleic acid (omega-6)

    2. Linolenic acid (omega-3)

    3. Arachidonic acid

    • Essential for hormone production (e.g., prostaglandins).

  • Roles of Neutral Fats

    • In Mammals and Birds:

    • Store energy efficiently, act as insulation.

    • In Insects and Plants:

    • Form waxes for waterproofing (e.g., beeswax).

  • Steroids

    • Characterized by four fused carbon rings made up of carbon skeleton, side groups modify functionality and solubility (ex. Cyclohexane C6H12)

    • Example of steroids include cholesterol, important for membrane structure and fluidity.

    • Estradiol, estrogen for females and testosterone for males

  • Solubility

  • Hydrophilic molecules soluble in water,

  • Hydrophobic molecules insoluble in water

  • Amphipathic regions of a molcules are hydropholic whereas other regions are hydrophobic

  • Emulsification the process of disrupting lipid interacts and makind lipids soulble in an aqueous soulution, which is crucial for digestion and absorption of dietary fats in the gastrointestinal tract.

  • Bile salts are essential for human survival

  • Phospholipids

    • Comprise two fatty acids and a phosphate group attached to glycerol.

    • Amphipathic: hydrophobic tails face inward, hydrophilic heads face outward.

    • Essential for forming cell membranes through bilayer arrangement.

    • Cholesterol is for animals and humans

    • Phytosterols are for plants and characteristics in membrane

    • The monolayer of phospholipids provides the outer shell,

  • Fluidity of Membranes

    • Lipid bilayers are fluid, resembling salad oil characteristics.

    • Cholesterol maintains fluidity by preventing tight packing of fatty acid chains at varying temperatures (supports function in cold environments).

  • Selective Permeability of the Bilayer

    • Nonpolar molecules (e.g., O2, N2, hydrocarbons-CH3(CH2)CH3 bein channels for transport; charged ions require facilitated diffusion.

    • Passive Diffusion occurs when molecules spread out into an event space, likely being a random, directional movement from high to low concentration that has a concentration gradient

  • Defining Life

    • Life can be defined as a self-replicating system existing in an aqueous environment, enclosed by a semi-permeable membrane, utilizing external energy sources to sustain internal order.