Lipids Flashcards

Lipids

Overview

• Lipids are a diverse group of organic molecules.
• Include fats, oils, waxes, steroids, and phospholipids.

Composition

• Composed of carbon (C) and hydrogen (H) with very few oxygen (O) atoms.
• Example: C12H24O2

Hydrophobicity

• Lipids are hydrophobic because they do not have many OH bonds.
• They are non-polar and cannot form hydrogen bonds with water.

Functions

• High-density energy storage:
  • 1 gram of carbohydrate = 4 calories
  • 1 gram of fat = 9 calories
  • Fats are better for long-term energy storage.
• Absorption of fat-soluble nutrients (e.g., vitamins A, D, E).
• Padding and insulation.
• Hormone production.
• Membrane structure.
• Protection and waterproofing.

Waxes

• Sticky rather than oily.
• Solid at room temperature due to high melting point.
• Provide a protective layer:
  • Prevent water loss in plants.
  • Protect eardrums from dust, dirt, and insects.

Steroids

• Four-carbon ring structure.
• Different functional groups attached to the four-ringed carbon backbone determine the steroid's function.
• Examples: Cholesterol, Testosterone, Estrogen, Aldosterone.

Cholesterol

• Found in the plasma membrane.
• Precursor for other steroids like estrogen and progesterone.
• Important but excessive amounts can lead to health issues, such as arterial clogging and heart failure.

Phospholipids

• Lipids with a phosphate group.
• Composed of two fatty acids and a phosphate group.
• Main component of cellular membranes (plasma and organelle membranes).

Phospholipid Bilayer

• Comprises the plasma membrane.
• Has a hydrophilic head and hydrophobic core.
• Amphipathic nature: having both hydrophilic and hydrophobic components.
• Outside cell: water; inside cell: water.

Micelles & Liposomes

• Due to their amphipathic nature, phospholipids can form a ring called a micelle, important for cellular organelles like liposomes.
• The mechanism of how soap cleans grease and food off plates.
• Hydrophobic core and hydrophilic outside.

Fats

• Long-term energy storage in animals.
• Stored within adipocytes (fat cells) of adipose tissue.
• Holds 9 calories of energy per gram.
• Functions:
  • Insulation to keep body temperature constant.
  • Protection by cushioning organs.

Oils

• Used by plants as energy storage.
• Elaioplasts, a type of plastid within plant cells, house oil bodies.

Fats and Oils Composition

• Composed of:
  • One glycerol: a 3-carbon molecule with 3 hydroxyl groups.
  • Three fatty acids: contain a carboxyl functional group that can release H+.

Triglycerides (Fats and Oils)

• Formed through dehydration synthesis.
• 3 Fatty Acids + Glycerol → Triglyceride + 3H2O

Hydrolysis of Triglycerides

• Requires 3 hydrolysis reactions to break down a triglyceride back into glycerol and fatty acids.

Fatty Acids: Hydrophilic vs Hydrophobic

• Fatty usually implies hydrophobic.
• Acids release H+, making them ionic and usually hydrophilic.
  • Most of the molecule is hydrocarbon and hydrophobic, so that character dominates.

Saturated vs Unsaturated Fatty Acids

• Fatty acids are classified based on the presence or absence of C=C (carbon-carbon double bonds).
  • Saturated Fats: no C=C bonds.
  • Unsaturated Fats: have C=C bonds.

Hydrogen Count

• Saturated fats have the maximum number of hydrogens (e.g., C{12}H{24}O_2).
• Unsaturated fats have fewer hydrogens (e.g., C{12}H{18}O_2).

Monounsaturated vs Polyunsaturated Fats

• Monounsaturated: one double bond in the hydrocarbon chain.
• Polyunsaturated: more than one double bond in the hydrocarbon chain.

Physical Properties

• Saturated fats are more solid.
• Unsaturated fats are more liquid.
• Straight chains pack together tightly in saturated fats.
• "Kinked" chains in unsaturated fats tend to slide past each other, preventing tight packing.

Identification

• Ask: Is it liquid or solid at room temperature?

Hydrogenation

• Oils can be converted to solids by adding hydrogen gas to break the double bonds between carbons.
• This process is called hydrogenation, resulting in flat, stackable chains.
  Hydrogenation can produce transfats.

Trans Fats

• Carbon backbone cannot rotate around C=C.
• Cis: Hydrogens on the same side.
• Trans: Hydrogens on different sides.

Implications of Hydrogenation

• When an oil is hydrogenated, most double bonds will become single, but some may become trans.

Harmful Effects of Trans Fats

• Used in fast food, snack food, fried food, and baked goods to increase shelf life and allow repeated heating.
• More harmful than naturally occurring oils:
  • Increase "bad" cholesterol (LDL).
  • Lower "good" cholesterol (HDL).
  • Increase risk for cardiovascular problems like heart disease, stroke, and diabetes.