Lipids: Basics and Function

Lipids Basics

• Lipids serve various functions in the body
• Lipids are hydrophobic biomolecules
• Lipids do not dissolve in water
• Synthesized by the body
• Essential for biological processes
• Lipase enzymes breakdown fats
• Lipoprotein lipase enzymes breakdown triglycerides
• Acetyl CoA - carboxylase is involved in lipid metabolism

Primary Function of Lipids

• Energy storage
• Protection
• Insulation
• Lubrication
• Hormone precursors

Structural Components of Lipids

• Glycerol: Three-carbon alcohol that serves as the structural backbone of lipids
• Fatty Acids: Organic compounds with three main components
  • Hydrocarbon chain
  • Carboxyl group at the front end
  • Methyl group at the other end
  • Building blocks, play essential biological roles

Types of Fatty Acids

• Saturated: Contain only single bonds between carbon atoms, fully saturated with hydrogen, and prevent the formation of double bonds
• Unsaturated: Contain one or more double bonds within the hydrocarbon chain Monounsaturated (MUFA): Contains one double bond in the hydrocarbon chain Polyunsaturated (PUFA): Contains two or more double bonds in the hydrocarbon chain
• Triacylglycerol (Triglyceride): A major form of lipid, consists of a glycerol molecule bonded to three fatty acid chains through ester linkages

Biological Role of Lipids

• Energy Storage: Lipids are a significant source of energy storage
  • 30-70% of energy used during rest comes from fat
  • Lipids primarily function as long-term energy reserves stored in adipocytes, unlike glycogen
• Signaling Molecules: Act as signaling molecules by transmitting information
  • Bind to specific receptors to trigger cellular responses
  • Steroid hormones (e.g., testosterone and estrogen) derived from cholesterol
• Phospholipids: Break down into second messengers, initiating signaling cascades
• Inflammation Regulation: Play a role by serving as signaling molecules that trigger inflammatory responses
  • Vasodilation
  • Pain sensation
  • Recruitment of immune cells to injury sites
  • Mediates inflammatory response to tissue damage or infection
• Insulation and Protection: Contribute to cholesterol formation, a crucial component
• Cholesterol: A type of lipid synthesized in the liver and intestines
  • Used as a building block to create cell membranes, hormones, and Vitamin D
  • Subcutaneous fat is located under the skin, provides insulation and protection from the cold, and cushions hands and buttocks
  • Visceral fat surrounds vital organs like the heart, kidneys, and liver
• Digestion and Nutrient Absorption Dietary fats aid in digestion by combining with fat-soluble nutrients

Classes of Lipids

• Simple Lipids: Composed of esters of fatty acids and alcohol such as triglycerides or natural waxes Triglycerides (fats & oils) Found in blood and fat cells Excess calories convert into triglycerides that release energy when fasting Excessive intake can lead to hypertriglyceridemia, which can increase heart disease risk Prevention: Regular exercise and reduce intake of refined foods Natural Waxes Derived from plants and insects, made from esters of fatty acids

Functions of Lipids

• Glycerophospholipids contain a glycerol backbone and are found in brain tissue
• Sphingophospholipids contain sphingosine instead of glycerol such as sphingomyelin
• Glycolipids are composed of fatty acids, alcohols, and carbohydrates Cerebrosides aid in neuron communication Gangliosides contain sialic acid, crucial for neurodevelopment and immune response
• Lipoproteins are fat and protein complexes in the bloodstream to help transport cholesterol and triglycerides
• Derived lipids can be sphingosine.

Fatty acids

• Functions include metabolism, signaling, and structural integrity.
• No double bonds in saturated fatty acids
• Steroids derived from a sterol backbone, help to reduce inflammation
• Fat-soluble vitamin A helps with vision and immunity

Fatty Acids: Composition and Classification

• Consist of a hydrocarbon chain attached to a methyl and a carboxyl group
• Building blocks for larger lipid compounds and function as substrates for bioactive molecules
• Serve as major energy sources and membrane constituents based on chain length or degree of unsaturation.
  • Classified as saturated or unsaturated

Fatty Acid Chains

• Short Chain Fatty Acids (SCFA) have fewer than 6 carbon atoms, exist as liquids at room temperature, such as Butyric acid (C-4).
• Medium Chain Fatty Acids (MCFA) have 6-12 carbon atoms, for example Caproic acid (C-6) and Caprylic acid (C-8).
• Long Chain Fatty Acids (LCFA) contain 16-20 carbon atoms, found in some vegetable oils, ex: Myristic acid (C-14) and Palmitic acid (C-16)
• Very Long Chain Fatty Acids (VLCFA) contain more than 22 carbon atoms, metabolized by peroxisomes, and poses health risks, such as Erucic acid (C-22).

Saturated vs Unsaturated Fatty Acids

• Saturated Fatty Acids contain only single bonds and are fully bonded to hydrogen
  • Found in animal products (e.g., beef, milk, cheese) and include Butyric acid and Caproic acid.
• Unsaturated Fatty Acids contain at least one double or triple bond with a weaker structure,
  • Considered healthier because they lower health risks.

Unsaturated Fatty Acids Types and Configuration

• Monounsaturated Fatty Acids (MUFA) have one double bond, found in olive oil, avocados, nuts, and seeds
• Liquid at room temperature
• May solidify when chilled
• Polyunsaturated Fatty Acids (PUFA) Contain two or more double bonds that can be found in nuts, seeds, soybeans, and fish
  • They provide essential nutrients like Vitamin E help lower cholesterol and lower the risk of heart disease
• Cis-Fatty Acids: Hydrogen atoms are on the same side of the double bond Create a slight curve to its structure, found in natural products like olive oil
• Trans-Fatty Acids: Found in at least one double bond in the trans configuration, naturally occurring animal versions won't harm you but hydrogenated vegetable oils will

Fatty Acid Types and Key Differences

• Fatty Acids have differences between types
  • Saturated have single bonds, and are considered bad fats
  • Monounsaturated have one double bond, and are considered good fats
  • Polyunsaturated have two or more double bonds, and are considered good fats

Lipid Deficiency Disorders - Fatty Acids

• Essential Fatty Acid Deficiency (EFAD) can occur with a lack of essential fatty acids in the diet
  • Key EFAs are Omega-3 (Alpha-linolenic acid) and Omega-6 (Linoleic acid.
  • Serve as precursors to eicosanoids, help regulate inflammation and immunity, and help support brain and retinal development via DHA
• EFAD Causes: Inadequate dietary intake, malabsorption disorders, or increased physiological demand
• Can also cause metabolic disorders
• Sufferers generally exhibit dry, scaly rash, stunted growth, increased susceptibility to infections, delayed wound healing, and vision problems

Lipid Deficiency Disorders - MTTP

• Abetalipoproteinemia (Bassen-Kornzweig Syndrome) is a genetic mutation in the MTTP gene
  • Key symptoms are fatty, foul-smelling stool, diarrhea, abdominal swelling, and muscle weakness
• Hypoalphalipoproteinemia occurs when levels of high-density lipoprotein cholesterol (HDL-C) are low
  • Genetic conditions can be risk factors such as Tangier Disease and Lipoprotein Lipase (LPL) Deficiency
• Hypolipidemia will result in orange-colored tonsils/anemia and is when lipid levels are lower than normal

Lipid Excess Disorders

• Farber's Disease cause: Mutation in the ASAH1 gene leading to ceramide accumulation
• Hypocholesterolemia cause: Genetic predisposition (Familial Hyperlipidemia) or lifestyle factors.
• Atherosclerosis cause: Genetic predisposition (Familial Hyperlipidemia) or lifestyle factors.