Lipids Overview and Composition

Lipids

• Lipids are a diverse group of biological molecules, including fats, oils, waxes, and steroids
• Lipids store long-term energy, 2x more than carbohydrates/proteins
• They cushion and protect vital organs
• They are a major component of cell membranes
• Lipids are used as hormones (chemical signals)
• Lipids insulate the body against heat loss (e.g., whale blubber)
• They provide a waterproof coating for fur, feathers, and leaves

Lipid Composition

• Lipids contain carbon (C), hydrogen (H), and oxygen (O)
• Lipids have more non-polar C-H bonds and fewer polar hydroxyl (O-H) bonds
• This characteristic makes them hydrophobic, meaning they are insoluble in water but soluble in oils.

Major Lipid Types

• Triglycerides/Fats: Composed of a glycerol molecule and three fatty acids.
• Phospholipids: Major components of cell membranes, having both hydrophilic (water-loving) heads and hydrophobic (water-fearing) tails. Phospholipids form a bilayer in cell membranes.
• Steroids: Include cholesterol, testosterone, estrogen, and cortisol. Composed of four fused carbon rings. Important for hormones, membrane structure, and bile production.
• Waxes: Long fatty acid chains linked to alcohols or carbon rings, providing a hydrophobic, water-resistant layer. Examples include earwax, beeswax and cutin on leaves.

Triglycerides/Fats

• Triglycerides are formed by bonding glycerol to three fatty acids
• Fatty acids are chains of carbon atoms with a carboxyl group (COOH) at one end and a methyl group (CH3) at the other end
• Fatty acids can be saturated, unsaturated, or polyunsaturated

Saturated/Unsaturated Fats

• Saturated Fats: Have no double bonds between carbon atoms; solid at room temperature; mostly from animal sources (e.g., butter, lard).
• Unsaturated Fats: Have one or more double bonds between carbon atoms; cause kinks in the fatty acid chain; liquid at room temperature; mostly from plant sources (e.g., olive oil, vegetable oils). Unsaturated fats include both monounsaturated, having one double bond, and polyunsaturated fats, containing more than one double bond.
• Polyunsaturated are generally better for you than saturated fats because polyunsaturated fats help maintain the fluidity of cell membranes.

Cis and Trans Fats

• Cis Fats: Hydrogen atoms are on the same side of the double bond. These are generally considered part of the unsaturated fat category
• Trans Fats: Hydrogen atoms are on opposite sides of the double bond. Trans fats are created by a process called hydrogenation. Hydrogenation is a process that changes the molecular structure and can raise the melting point of liquid oils, resulting in a solid, shelf-stable fat.

Phospholipids in Cell Membranes

• Phospholipids are amphipathic, meaning they have both hydrophilic (water-loving) and hydrophobic (water-fearing) regions
• The hydrophilic heads face the water inside and outside of the cell
• The hydrophobic tails face each other, forming a barrier keeping water out. Phospholipids are crucial for the structure and function of cell membranes.

Polyunsaturated Omega-3s

• Essential fatty acids found in fish
• Include EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid)
• ALA (alpha-linolenic acid) is plant-based omega-3
• Crucial for brain development, reduce inflammation, and lower cardiovascular disease risk. Omega-3s are important for maintaining overall health.

Lipid Synthesis and Breakdown

• Lipids are synthesized by bonding fatty acids to glycerol
• Lipids are broken down by enzymes called lipases

Steroids

• Steroids are made from four linked carbon rings
• Cholesterol is a precursor to other steroids like cortisol, progesterone, estrogens, testosterone, and bile acids
• Cholesterol is important for cell membrane structure and is a precursor to several hormones. Cholesterol is essential for maintaining cell membrane fluidity and integrity.
• Cholesterol can contribute to heart disease if present in excess. Excessive cholesterol levels can lead to plaque buildup in arteries.

Eicosanoids

• Derived from arachidonic acid, a fatty acid
• Act as chemical messengers, impacting inflammation, blood clotting, hormone action, labor contractions, regulating blood vessel diameter. Important signaling molecules.

Side Effects of Steroid Abuse

• Excessive steroid use can lead to various health problems (acne, baldness, blood clots, high blood pressure, heart disease, mood swings, joint pain, etc.)
• Problematic for men and women.
• Important to note, these effects are usually observed with excessive use of steroids beyond the recommended doses and are not typical effects for proper use of these compounds.

Waxes

• Long fatty acid chains linked to alcohols or carbon rings
• Hydrophobic, firm consistency, pliable
• Produced by animals (e.g., earwax, beeswax) and plants (e.g., cutin)

Diagrams of Lipids

• Diagrams illustrate the structures of glycerol, fatty acids, saturated/unsaturated fats, phospholipids, steroids, and waxes