Fatty Acids and Lipids Quiz

Biomolecules: Lipids

• Lipids are essential components of all living organisms
• They are organic molecules composed mainly of carbon, hydrogen, and oxygen
• Lipids are found in plants, animals, and microorganisms
• They are used for cell membrane components, energy storage, insulation, and hormones
• Lipids are a diverse group, insoluble in water but soluble in nonpolar organic solvents
• Lipids are hydrophobic (nonpolar) or amphipathic (both nonpolar and polar regions)

Classification of Lipids

• Lipids aren't polymers; they lack a repeating monomeric unit
• They are classified based on molecular structures
• Simple lipids:
  • Fats and oils: yield fatty acids and glycerol upon hydrolysis
  • Waxes: yield fatty acids and long-chain alcohols upon hydrolysis
• Compound lipids:
  • Phospholipids: yield fatty acids, glycerol, phosphoric acid, and a nitrogen-containing alcohol upon hydrolysis
  • Glycolipids: yield fatty acids, sphingosine or glycerol, and a carbohydrate upon hydrolysis
  • Sphingolipids: yield fatty acids, sphingosine, phosphoric acid, and an alcohol component upon hydrolysis
• Steroids:
  • Compounds containing a phenanthrene structure
  • Differ from lipids made of fatty acids
  • Characterized by a four-fused carbon skeleton

Classification of Lipids (Continued)

• Fatty Acids: in the carboxylic acid family
• Waxes: fatty acids + alcohols
• Triglycerides: 3 fatty acids + glycerol
• Phospholipids and glycolipids: 2 fatty acids + glycerol + phosphate + X
• Steroids: Derivatives of cholesterol
• Eicosanoids: Derivatives of the fatty acid arachidonic acid
• Membranes: Formed from phospholipids and glycolipids

Physical Properties of Lipids

• Lipids can be liquids or solids at room temperature
• Unlike popular belief, pure fats and oils are usually colorless, odorless, and tasteless
• Colors, odors, and flavors in lipids come from foreign substances absorbed
• Fats and oils are usually lighter than water
• They are poor conductors of heat and electricity, acting as insulators in the body

Key Principles of Fatty Acids

• Fatty acids (FAs) are water-insoluble hydrocarbons used for cellular energy storage
• FAs are highly reduced, providing a rich source of stored chemical energy in cells
• Storage of hydrophobic fats as triacylglycerols is very efficient
• Water is not needed to hydrate the stored fat

Fatty Acids

• Carboxylic acids with hydrocarbon chains (4 to 36 carbons long, typically 12-20)
• Contain a carboxylic acid group (polar) and a hydrocarbon tail (nonpolar)
• This makes them overall nonpolar

Fatty Acids: Saturation

• Some chains are fully saturated (no double bonds)
• Others have one or more double bonds (unsaturated)
• Some contain three-carbon rings, hydroxyl groups, or methyl-group branches

Fatty Acid Nomenclature

• Standard nomenclature: numbers carbon atoms and positions of double bonds (omega-3 and omega-6)

Fatty Acids: Physical Properties

• Structure influences melting point: Fully saturated FAs have higher melting points, while unsaturated FAs have lower (due to kinks)
• Unsaturated fats are generally liquid at room temperature, while saturated fats are solid

Common Saturated Fatty Acids

• Different types of saturated fatty acid with varying carbon skeletons (12 to 24 carbons)
• Varying melting points.

Common Unsaturated Fatty Acids

• Include linoleic and linolenic acids (essential fatty acids) and arachidonic acids.
• Many are cis-unsaturated (kinked)
• These often have lower melting points than saturated fatty acids.

Simple Lipids (Fats and Oils)

• Fats and oils are the most abundant lipids in nature.
• Esters composed of fatty acids linked to glycerol
• Classification based on physical state at room temperature (solid fat, liquid oil).

Structure of Triacylglycerols

• Simplest lipids constructed from fatty acids
• Composed of three fatty acids in ester linkage with a single glycerol molecule, these are also known as triglycerides
• Predominantly nonpolar, making them highly insoluble in water.

Esters

• Chemically synthesized by reacting a carboxylic acid with and alcohol
• Distinguished by a functional group with oxygen.

Fatty Acid Compositions of Food Fats

• Natural fats (vegetable oils, dairy, animal fat) are complex mixtures of triacylglycerols
• Containing different lengths and degrees of saturation.
• Melting points are direct functions of compositions.
• Olive oil has more unsaturated fats, leading to its liquid state.
• Butter has more saturated fats, with a higher melting point.
• Beef fat, higher in saturated fats, is a hard solid

Trans Fatty Acids in Foods

• Formed when unsaturated fats are exposed to oxygen, or during processes like partial hydrogenation (to increase shelf life and stability)
• Conversion of cis- to trans-bonds leads to changes in properties and health implications
• Commercial hydrogenation partially converts cis-double bonds into trans-double bonds, increasing the melting point

Lipoproteins

• Transport water-insoluble lipids like triglycerides, phospholipids, and cholesterol in the blood.
• Contain lipids and proteins; categorized by density
• Chylomicrons: transport triglycerides, from digestive tract.
• LDLs (low-density lipoproteins): transport cholesterol and phospholipids to other tissues
• HDLs (high-density lipoproteins): transport cholesterol and phospholipids back to the liver

Triglycerides

• Storage form of fatty acids in mammals.
• Can be measured through blood tests.
• High levels may indicate a risk for atherosclerosis.

Fat Stores in Cells

• Found in cells and tissues as microscopic oily droplets
• Triacylglycerols are stored in adipocytes in vertebrates or seeds of many plants.
• Adipocytes contain enzymes (lipases) that breakdown stored triacylglycerols
• Triacylglycerols provide more energy than carbohydrates.
• Serve as insulation in some animals

Adipose Tissue - Fat

• Cushions major organs
• Provides insulation
• Carries flavors and vitamins from food

Fat - Essential Energy

• Long-term energy storage and metabolism is through body fat (triglycerides).
• Short-term energy is stored as glycogen.

Waxes

• Esters of long-chain (C14-C36) saturated/unsaturated fatty acids and alcohols (C16-C30)
• Function as protective, water-proof coatings in plants and animals.
• Some are used commercially (beeswax, carnauba wax).

Membrane Lipids

• Backbone of glycerol or sphingosine
• Attached to long-chain alkyl groups (yellow) and polar head groups (blue).

Phospholipids and Glycolipids

• Building blocks of biological membranes
• Highly amphipathic, leading to their spontaneous formation of lipid bilayers

Phospholipids

• Two types of phospholipids: Glycerophospholipids and sphingolipids
• Glycerophospholipids: Have a glycerol backbone with two fatty acids and a phosphate group attached.
• Sphingolipids: Have a sphingosine backbone instead of glycerol.

Glycerophospholipids

• Similar to triglycerides, but with one fatty acid replaced with a phosphate group

Sphingolipids

• Similar to glycerophospholipids, but have a sphingosine backbone instead of glycerol.

Glycolipids

• Sphingolipids with sugars attached to the alcohol portion
• Include important cellular markers and components of the myelin sheath

Sterols - Cholesterol

• Structural lipids in membranes of most eukaryotic cells
• Rigid steroid nucleus with an alkyl side chain and a hydroxyl group
• Packs well with other membrane lipids, maintaining membrane fluidity
• Cholesterol is only found in animal cells

Sterols and Their Roles

• Act as precursors for steroid hormones and vitamins
• Also help regulate cell membrane fluidity
• Bile salts are involved in the digestion of fats.

Steroids

• Cyclic organic compounds with 17 carbons in a four-ring structure
• Subtypes are distinguished by substituent groups.
• Sterols/hormones/vitamin D/bile acids all related to this structure.

Saponifiable vs. Non-Saponifiable Lipids

• Saponifiable lipids have ester linkages and can be hydrolyzed by acids, bases, or enzymes
• Non-saponifiable lipids don't have ester linkages and can't be hydrolyzed in the same way.

Lipid Classification

• Lipids can be categorized as Simple, Complex, and Derived

Lipids (- Review)

• Heterogeneous group of compounds, including fats, oils, steroids, waxes, and related compounds
• Related by their physical properties like insolubility in water, and solubility in nonpolar solvents
• Important in biological systems because they form cell membranes, provide energy, and are components of vitamins
• Can be categorized into saponifiable (hydrolyzed by acids/bases) and nonsaponifiable (cannot be hydrolyzed)