BIOCHEM LIPIDS

Structure and Classification of Lipids

  • Definition of Lipids

    • Organic compounds in living organisms

    • Insoluble in water but soluble in non-polar organic solvents

    • Lack common structural features for classification

  • Classification of Lipids

    • Based on solubility, not functional groups

    • Insoluble or sparingly soluble in water

    • Soluble in non-polar organic solvents

Five Categories of Lipids

  • Categories

    • Energy-storage lipids (triacylglycerols)

    • Membrane lipids (phospholipids, sphingoglycolipids, cholesterol)

    • Emulsification lipids (bile acids)

    • Chemical messenger lipids (steroid hormones, eicosanoids)

    • Protective-coating lipids (biological waxes)

Structural Formulas of Lipids

  • Diversity

    • Lipids exhibit structural diversity

    • Include esters, amides, alcohols (acyclic and cyclic), and polycyclic compounds

Types of Fatty Acids

  • Saturated and Unsaturated Fatty Acids

    • Fatty acids are monocarboxylic acids with linear carbon chains

    • Classified into saturated (single C-C bonds) and unsaturated (mono- and polyunsaturated) types

    • Different chain lengths and numbering systems for fatty acids

  • Unsaturated Fatty Acids

    • Monounsaturated fatty acids have one carbon-carbon double bond

    • Polyunsaturated fatty acids have two or more double bonds

    • Omega-3 and Omega-6 fatty acids are biochemically important

Omega Acids and Essential Fatty Acids

  • Nutritional Importance

    • Essential fatty acids like Omega-3 and Omega-6 must be part of the diet

    • Imbalance in Omega-3 and Omega-6 linked to health issues

    • Ideal ratio of Omega 6 : Omega 3 is 4 - 10 g : 1g

Physical Properties of Fatty Acids

  • Melting Point

    • Depends on carbon chain length and degree of unsaturation

    • More double bonds lead to lower melting points

    • Short chain fatty acids have some solubility, while long chain fatty acids are insoluble

Energy-Storage Lipids: Triacylglycerols

  • Storage Materials

    • Triacylglycerols are primary energy storage materials in cells

    • Stored in adipocytes and nearly filled with the material

    • Simple and mixed triacylglycerols with different fatty acid compositions

Dietary Considerations and Triacylglycerols

  • "Good Fats" Versus "Bad Fats"

    • Importance of type and amount of dietary fats for a balanced diet

    • Saturated fats considered "bad fats," while monounsaturated fats are "good fats"

    • Trans-monounsaturated fats are considered "bad fats"

    • Polyunsaturated fats can be both "good fats" and "bad fats"

    • Omega-3 and Omega-6 fatty acids are essential "good fats" in the diet

Essential Fatty Acids

  • Fatty acids must be obtained from dietary sources as they are not synthesized in the body.

    • Linoleic acid (omega 6) and Linolenic acid (omega 3) are the two most important essential fatty acids.

    • Needed for proper membrane structure and production of other important fatty acids.

  • Deficiencies in these acids can lead to skin issues, infections, dehydration, and liver abnormalities.

Fat and Fatty Acid Composition of Nuts

  • Eating nuts can protect against coronary heart disease.

    • Nuts have low saturated fatty acids and contain antioxidants, vitamins, minerals, and plant fiber protein.

Chemical Reactions of Triacylglycerols

Partial Hydrolysis

  • Triacylglycerols undergo partial hydrolysis by breaking ester bonds.

  • Enzymes from the pancreas carry out this process.

Saponification

  • Saponification in basic solution produces salt of fatty acid and glycerol.

  • It involves the hydrolysis of ester bonds.

Hydrogenation

  • Hydrogenation increases saturation by adding hydrogen across double bonds.

  • Common in producing food products like peanut butter and margarine.

Oxidation

  • Oxidation of double bonds in triacylglycerols can lead to rancidity.

  • Antioxidants like Vitamin C and E are added to prevent oxidation.

Membrane Lipids: Phospholipids

  • Cell membranes are mainly composed of lipids, with up to 80% being phospholipids.

  • Phospholipids contain fatty acids, phosphate group, glycerol/sphingosine, and an alcohol.

  • Glycerophospholipids have two fatty acids and a phosphate group esterified to glycerol.

Membrane Lipids: Sphingoglycolipids

  • Sphingoglycolipids contain both fatty acids and carbohydrates.

  • Cerebrosides are simple sphingoglycolipids found in the brain.

  • Gangliosides are complex sphingoglycolipids with a branched chain of monosaccharide residues.

Membrane Lipids: Cholesterol

  • Cholesterol is a C27 steroid molecule important in cell membranes, nerve tissue, and brain tissue.

  • It plays a role in chemical synthesis of hormones and essential vitamins.

Page 34: Cholesterol in Food

  • Liver synthesizes cholesterol at about 1g daily

    • Not necessary to consume through diet

  • Ingested cholesterol decreases synthesis but not enough

    • Leads to cardiovascular disease

  • Animal food contains a lot of cholesterol

  • Plant food does not contain cholesterol

Page 35: Cell Membranes

  • Plasma membranes surround cells

    • Separates cell interior from surroundings

    • Up to 80% of membrane is lipid material

  • Membranes are lipid bilayers of phospholipids

    • Nonpolar tails in the middle, polar heads on the surface

  • Membrane is liquid-like due to unsaturation in lipid tails

Page 36: Cholesterol in Cell Membranes

  • Cholesterol regulates membrane fluidity

    • Makes membrane rigid by fitting between fatty acid chains

  • Cholesterol acts as a membrane plasticizer

Page 37: Proteins in Cell Membranes

  • Membranes contain proteins

    • Responsible for moving substances across the membrane

    • Act as receptors for hormones and neurotransmitters

  • Proteins and lipids react with carbohydrate molecules

    • Act as markers for cell recognition

Page 38: Passive Transport

  • Transport across cell membranes

    • Three types: passive, facilitated, active

  • Passive transport: molecules move by diffusion

    • Includes O2, N2, H2O, urea, and ethanol

Page 39: Facilitated Transport

  • Facilitated transport: substances move with membrane protein aid

    • Specific protein carriers are involved

Page 40: Active Transport

  • Active transport: substances move against concentration gradient

    • Requires cellular energy, ATP supplies energy

  • Proteins involved in active transport are called "pumps"

Page 41: Emulsification Lipids: Bile Acids

  • Emulsifiers disperse water-insoluble substances in aqueous solution

  • Bile acids function as emulsifying agents

    • Convert cholesterol to bile acids for lipid solubility

Page 42: Bile Acids

  • Bile acids are cholesterol derivatives

    • Side chain oxidized to carboxylic acid

    • Bonded to amino acid through amide linkage

  • Bile is a fluid containing emulsifying agents secreted by the liver

Page 43: Messenger Lipids: Steroid Hormones

  • Hormones are biochemical substances produced by glands

  • Steroid hormones and eicosanoids are lipid messengers

  • Steroid hormones are derivatives of cholesterol

Page 44: Sex Hormones

  • Steroid hormones classified into estrogens, androgens, progestins

Page 45: Adrenocorticoid Hormones

  • Produced by adrenal glands

  • Two types: mineralocorticoids and glucocorticoids

Page 46: Eicosanoids

  • Derivatives of arachidonic acid with physiological effects

  • Act as hormone-like molecules in tissues

Page 47: Types of Eicosanoids

  • Prostaglandins: involved in various physiological functions

  • Thromboxanes: promote platelet aggregation

  • Leukotrienes: promote inflammatory and hypersensitivity responses

Page 49: Biological Waxes

  • Biological wax is a monoester of long-chain fatty acid and alcohol

  • Fatty acids in waxes are saturated and contain 14-36 carbon atoms

  • Alcohols in waxes may be saturated or unsaturated, with 16-30 carbon atoms

Page 50: Section 19.14 Protective-Coating Lipids: Biological Waxes

  • Properties of Biological Waxes:

    • Water-insoluble and water-repellent due to long nonpolar hydrocarbon chains.

    • Humans and animals secrete biological waxes from skin glands.

  • Function of Biological Waxes:

    • Protect hair and skin, keeping it pliable and lubricated.

    • Impart water repellency to animal fur.

    • Birds use waxes to keep feathers water repellent and minimize heat loss.

    • Plants use waxes on leaves to prevent excessive water evaporation