Lipid Overview and Classification

LIPID Overview

• Lipids are synonymous with "fat"
• They are insoluble in water but soluble in organic solvents
• Fats are solid at room temperature, while oils are liquid
• The chemical structure of lipids is glycerol + fatty acids
• Triglycerides are the primary component of both fats and oils

Lipid Classification

• Simple lipids: Fatty acids (FAs) are esterified with glycerol
• Compound lipids: Similar to simple lipids, but with additional compounds attached besides glycerol
• Phospholipids: Fats containing phosphoric acid and nitrogen (e.g., lecithin)
• Glycolipids: FAs compounded with carbohydrates (CHO) but no nitrogen
• Derived lipids: Substances produced from the prior types through hydrolysis
• Sterols: Large molecular weight alcohols found in nature combined with fatty acids (e.g., Cholesterol)

Saturated Fats

• All chemical bonds between carbons are single bonds
• No double bonds
• Fully "saturated" with hydrogen atoms
• Solid at room temperature
• Examples include butter, shortening, lard, coconut oil, palm oil, and fully hydrogenated vegetable oils, poultry skin, and whole milk

Mono-Unsaturated Fatty Acids

• Contain only one double bond
• Liquid at room temperature
• Examples include olive oil, canola oil, peanut oil, and various nuts and seeds (avocado, almonds, cashews, pecans, sesame seeds)

Poly-Unsaturated Fatty Acids

• Contain two or more double bonds
• Include Omega-3 and Omega-6 fatty acids (essential fatty acids)
• Examples include linolenic acid (omega-3), linoleic acid (omega-6), and oils like corn, sunflower, safflower, and cotton seed oils

Fatty Acids

• Key components are carbon groups and a carboxyl group (COOH)
• Fatty acid chain lengths vary
• Short chain: 2-6 carbons
• Medium chain: 8-12 carbons
• Long chain: 14-24 carbons
• Plants and animals synthesize fatty acids with an even number of carbons
• 16C to 18C fatty acids are common

Fatty Acid Chain Length

• Melting points increase with chain length
• Fatty acids tend to have even numbers of carbons
• Longer chains, generally, are more prevalent

Fatty Acid Specific Examples and Information

• Different fatty acids have specific sources (e.g., Acetic Acid- bacterial metabolism).

Essential Fatty Acids

• Required for body functions but cannot be produced by humans
• Must be absorbed from the diet
• Examples include linoleic acid (18:2 n-6), linolenic acid (18:3 n-3), arachidonic acid (20:4 n-6), eicosapentaenoic acid (20:5 n-3), and docosahexaenoic acid (22:6 n-3)

Functions of Essential Fatty Acids

• Component of cell membranes and phospholipids
• Precursor for prostaglandins (i.e. arachidonic acid)
• Important metabolic regulator, influencing smooth muscle contractions, platelet aggregation, and inflammation

Arachidonic Acid

• Precursor to prostaglandins, thromboxanes, prostacyclins, and leukotrienes
• Important in neurotransmission and synthesized in the liver, elongation of linoleic acid

Triglycerides

• Triglycerides are formed from glycerol and three fatty acids
• An important form in which lipids are stored, and utilized for energy
• Crucial for energy reserves

Complex Lipids - Phospholipids

• Two main types of phospholipids, Glycerophosphatides and Sphingophosphatides
• Glycerophosphatides core structure is glycerol, integral parts of cell membranes, chylomicrons, and lipoproteins
• Sphingophosphatides core structure is sphingosine, part of sphingomyelins

Complex Lipids - Glycolipids

• Contain a carbohydrate component in their structure
• Cerebrosides and gangliosides are examples, part of the myelin sheath of nerves

Derived Lipids

• Prostaglandins: Derived from arachidonic acid, key in multiple metabolic functions.
• Steroids: Examples include cholesterol, ergosterol, and bile acids
• Terpenes: Produced by plants; examples include carotenoids and xanthophylls

Sterols

• Have a multi-ring structure
• Insoluble in water
• Present in both plants and animal foods
• Cholesterol is the major sterol in animal products, manufactured by the liver
• High cholesterol content found in organ meats and egg yolks

Functions and Properties of Lipids

• Concentrated energy source (9 kcal/g)
• Key energy reserves, stored as triglycerides in adipose tissue
• Provide insulation for the body
• Help maintain body temperature (mechanical insulation)
• Protect vital organs
• Essential for electrical insulation (myelin sheath)
• Supply essential fatty acids (EFAs)
• Contribute to cell membrane formation (phospholipids)
• Involved in hormone synthesis
• Important for the transport of fat-soluble vitamins
• Influence palatability and aroma of foods
• Regulate satiety (fullness) levels through hormones like CCK and GIP

Lipid Metabolism

• Hydrolysis: Breaking down lipids using water and enzymes
• Hydrogenation: Adding hydrogen to unsaturated fatty acids
• De Novo synthesis: Creating new fats from other substances, mostly in the cytoplasm
• Beta-oxidation: Breaking down fatty acids into acetyl-CoA in mitochondria (aerobic process)
• Ketogenesis: Formation of ketone bodies from acetyl-CoA under conditions of low carbohydrate availability

Cholesterol Synthesis and Excretion

• Cholesterol occurs as free and esterified forms in the adrenal cortex and brain, integral part of plasma membranes and lipoproteins
• Synthesized by healthy adults at a rate of ~1 gram/day
• Serum cholesterol levels (150-200 mg/dL) are regulated by managing de-novo synthesis
• Utilized in constructing cell membranes, steroid hormones, and bile acids (greatest proportion)

Cholesterol Biosynthesis

• Complex multi-step process involving numerous enzymes and intermediates with key regulatory steps, starting with Acetyl CoA and ending with Cholesterol.

This quiz covers the fundamental concepts of lipids, including their chemical structure, classification, and types of fats. Explore the differences between simple and compound lipids, as well as saturated fats and their properties. Test your knowledge on the various categories of lipids and their roles in biology.