lipids 1 foundtaion

Introduction & Classification of Lipids

• Lipids are organic compounds that are relatively insoluble in water but soluble in organic solvents like chloroform, ether, and benzene.
• Lipids serve various functions, including energy storage, insulation, and structural components of cell membranes.
• Lipids are classified into simple, complex, and derived lipids.

Learning Objectives

• Students will learn about lipids, their classification, and biochemical functions.

Lipid Chemistry

• Lipids are organic substances relatively insoluble in water, yet soluble in organic solvents like chloroform, ether, and benzene.

Functions of Lipids

• Lipids perform various functions, including flavor and taste in food, energy storage, insulation, and metabolic regulation.
• They aid in the absorption of vitamins and are involved in various other bodily functions.
• Lipids are also precursors for bile acids, steroid hormones, vitamin D, and eicosinoids.
• Lipids provide thermal and electrical insulation.
• They contribute to the structural integrity of internal organs, shielding them from physical shocks.
• Lipids contribute to protecting the body from water and electrolyte loss.
• Lipids aid in the transport of fat-soluble vitamins and safeguarding against the harmful effects of water-soluble substances.
• Cell structures like neural tissue, especially the brain, contain substantial amounts of lipids.

Functions

• Lipids are precursors for bile acids, steroid hormones, vitamin D, and eicosinoids.

• Lipids provide thermal insulation to the nervous system, protecting it from temperature extremes.

• Lipids are integral to the anatomical stability of internal organs, safeguarding them from physical shock.

• Lipids, particularly those beneath the skin, help prevent excessive water and electrolyte loss from the body.

Function

• Lipids facilitate the transport of fat-soluble vitamins.
• They help shield the body from the detrimental effects of water-soluble substances.
• Lipids are crucial components in metabolic processes and cell signaling.
• Neuronal tissue (including the brain) contains relatively high amounts of lipids.

Classification of Lipids

• Lipids are broadly categorized into simple, complex, and derived lipids.

Simple Lipids

• Simple lipids are esters of fatty acids with various alcohols.
• These are subclassified into neutral fats (or oils) and waxes. -Neutral fats (or oils) have glycerol as the alcohol component. -Waxes have an alcohol component other than glycerol.
• Natural fats and waxes are included under simple lipids.
• Triglycerides are composed of glycerol and three fatty acid chains.

Simple Lipids: Mono, Di and Triacylglycerol

• The number of hydroxyl groups in glycerol distinguishes these acyl-glycerols into mono, di and triacylglycerols.

Simple Fats

• Simple fats act as neutral lipids, primarily storing energy in adipose tissues.
• They are crucial for body contouring and insulation.
• Simple fats are essential for energy storage.

Mono and diacylglycerols

• Mono and diacylglycerols play roles in digestion and are involved in metabolic intermediary processes.
• Triglycerides (TAGs) are significant for storing and transporting lipids.
• TAGs with varying fatty acid compositions are categorized as mixed TAGs.

Physical Properties of TAGs

• Triglycerides (TAGs) can exist as liquids or non-crystalline solids at room temperature.
• Pure fats and oils are typically colorless, odorless, and tasteless.
• Impurities (e.g. color) in fats (e.g. butter) are usually due to coloring pigments (carotene) or flavor compounds (e.g. diacetyl and 3-hydroxy-2-butanone).

Waxes (Simple Lipids)

• Waxes are esters of fatty acids with higher-molecular weight, monohydric alcohols. Examples of waxes include lanolin, beeswax, and whale sperm oil.

• Waxes are not hydrolyzed and lack nutritional value.

• Waxes have diverse functions in plants and animals, serving to protect skin and hair and acting as lubricants.

• Waxes are water-repellent and contribute to the structural integrity of surfaces and tissues.

Complex Lipids

• Complex lipids are fatty acid esters with alcohols containing added prosthetic groups.
• Subdivisions include phospholipids, glycolipids, and lipoproteins.

Compound Lipids

• In addition to fatty acids and alcohols, compound lipids contain other components.
  • This is further classified to glycerophospholipids (which include phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol), glycolipids (which include cerebrosides and gangliosides), and sphingolipids (which include ceramides and sphingomyelin)
• Different classes of compound lipids play different roles, such as forming cell membranes and facilitating intercellular communication.

Derived Lipids

• Derived lipids are products of the hydrolysis of simple and compound lipids.
• They retain the characteristics of lipids.
• Examples include fatty acids, steroids, lipid-soluble vitamins, and hormones, keton bodies.
• Derived lipids are involved in a broad range of biological processes.

Functions of Lipids

• Lipids serve as energy stores, structural components of cells, precursors to hormones and vitamins, and insulators.

Lipid Peroxidation

• Lipid peroxidation is the oxidative degradation of lipids in cell membranes.
• Free radicals steal electrons from lipid molecules, damaging cellular components.
• This process occurs through a free radical chain reaction, primarily affecting polyunsaturated fatty acids.
• Byproducts of lipid peroxidation can be mutagenic and carcinogenic.

Free Radicals

• Free radicals are highly reactive atoms possessing an unpaired electron.
• Free radicals target various cellular components (including lipids, proteins, and DNA).
• Free radical-induced damage can trigger harmful mutations.
• Sources of free radicals are both exogenous (environmental) and endogenous (internal).

Free Radical Sources

• Exogenous sources: foods, air pollutants, radiation, cigarette smoke.
• Endogenous sources: cellular metabolism, detoxification processes, and immune responses.

Mechanisms of Lipid Peroxidation

• Photoxidation, involving singlet oxygen and sensitizers, triggers the process.
• Enzymatic oxidation, facilitated by enzymes like cyclooxygenase and lipoxygenase, leads to the oxidation of fatty acids.
• Autoxidation, in which free radicals initiate a chain reaction, is another important mechanism.

Reactive Oxygen Species (ROS)

• Reactive oxygen species (ROS), including superoxide, hydroxyl, and peroxyl radicals, are involved in lipid peroxidation.
• Hydroperoxyl and alkoxyl radicals are other types of ROS.
• ROS are generated as byproducts of metabolism but are also found in environmental sources.

Oxidative Stress

• Oxidative stress arises from a disruption of the balance between prooxidants and antioxidants.
• This imbalance can lead to cellular and tissue damage.
• Oxidative stress occurs naturally and plays a role in aging.

Consequences of Lipid Peroxidation

• Lipid peroxidation leads to structural changes in cell membranes by altering fluidity, ion channels, and membrane-bound proteins.
• It can decrease the permeability of cell membranes and compromise their integrity.

Pathological Conditions Associated with Oxidative Stress

• Lipid peroxidation is associated with inflammation, atherosclerosis, ischemia/reperfusion injury, cancer, and the aging process.

Inflammation and Lipid Peroxidation

• Immune cells migrate to sites of inflammation, generating oxidants to combat pathogens.
• However, these oxidants can also damage healthy tissue.
• Lipid peroxidation and oxidative stress form a damaging cycle in inflammation.

How to Reduce Free Radicals

• Consume foods rich in antioxidants to counteract free radical damage.

Antioxidants

• Antioxidants oppose oxidation by neutralizing free radicals.
• Common antioxidants include vitamins A, C, and E, selenium, and various plant-derived compounds.

How Antioxidants Reduce Free Radicals

• Antioxidants neutralize free radicals by accepting or donating electrons.
• This action diminishes the free radicals' reactivity and prevents cellular damage.

Ideal Antioxidants

• Ideal antioxidants are safe for consumption, do not negatively affect product quality, and are effective in low concentrations.
• Ideally they are fat soluble, and are not deteriorated by processing.

Antioxidant Defenses

• The body's antioxidant defense mechanisms include fat-soluble antioxidants like vitamins E and beta-carotene and water-soluble scavengers like vitamin C, glutathione peroxidase, superoxide dismutase, and catalase.