Lipids: Structures and Functions
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Questions and Answers

What property primarily contributes to lipids being insoluble in water?

  • Presence of nitrogen bonds
  • High molecular weight
  • Long chains of hydrocarbon (C-H) bonds (correct)
  • Presence of polar groups
  • Which of the following is a characteristic of saturated fatty acids?

  • All C-C bonds are single bonds (correct)
  • Have a branched structure
  • Are always found in liquid state
  • Contain one or more double bonds
  • Which lipid type is classified as a glyceride?

  • Steroids
  • Waxes
  • Triglycerides (correct)
  • Phospholipids
  • What defines unsaturated fatty acids?

    <p>They can have one or more double bonds</p> Signup and view all the answers

    Lipids serve multiple functions in biological systems, but which of the following is NOT a function of lipids?

    <p>Information processing</p> Signup and view all the answers

    Which type of lipids is characterized by having structures like micelles when mixed with water?

    <p>Phospholipids</p> Signup and view all the answers

    Which statement accurately describes complex lipids?

    <p>They may contain protein components.</p> Signup and view all the answers

    Which of the following descriptions of fatty acids is true?

    <p>They are classified by the number of carbon atoms.</p> Signup and view all the answers

    Which fatty acid is classified as Omega-3?

    <p>Alpha Linolenic Acid</p> Signup and view all the answers

    What is the primary characteristic of monoglycerides and diglycerides?

    <p>They act as emulsifying agents.</p> Signup and view all the answers

    Which of the following properties is affected by the degree of unsaturation in fatty acids?

    <p>Melting point</p> Signup and view all the answers

    What type of fatty acid deficiency can lead to skin irritation and liver abnormalities?

    <p>Linoleic Acid</p> Signup and view all the answers

    Which fatty acid is produced by microalgae and commonly found in marine sources?

    <p>DHA</p> Signup and view all the answers

    Which characteristic describes long-chain fatty acids compared to short-chain fatty acids?

    <p>Higher melting points</p> Signup and view all the answers

    What is the main function of triglycerides in the body?

    <p>Storing energy</p> Signup and view all the answers

    What type of lipids are biological waxes primarily composed of?

    <p>Esters of long-chain carboxylic acids and alcohols</p> Signup and view all the answers

    What is the main difference between fats and oils?

    <p>Fats have a high percentage of saturated fatty acids, oils have a high degree of unsaturation.</p> Signup and view all the answers

    What process involves the reaction of fatty acids with glycerol to produce triglycerides?

    <p>Esterification</p> Signup and view all the answers

    Which of the following statements about hydrogenation is true?

    <p>It is used to increase the saturation level of unsaturated fatty acids.</p> Signup and view all the answers

    What is the primary purpose of saponification?

    <p>To convert triglycerides into fatty acid salts.</p> Signup and view all the answers

    Which of the following best describes phospholipids?

    <p>They contain a polar head and a nonpolar tail, making them amphipathic.</p> Signup and view all the answers

    What is generated during the acid hydrolysis of waxes or triglycerides?

    <p>Alcohol and fatty acids</p> Signup and view all the answers

    Phosphoglycerides are a type of which lipid?

    <p>Phospholipids</p> Signup and view all the answers

    What effect does the presence of unsaturated fatty acids have on the physical state of fats and oils?

    <p>It allows fats to remain liquid at lower temperatures.</p> Signup and view all the answers

    What is the primary chemical event of vision in rod cells?

    <p>Absorption of light by rhodopsin</p> Signup and view all the answers

    Which of the following vitamins plays an important role in the blood-clotting process?

    <p>Vitamin K</p> Signup and view all the answers

    Which vitamin requires the hydrolysis of ATP for its transport mechanism?

    <p>Vitamin D</p> Signup and view all the answers

    What is the primary function of vitamin E in biological systems?

    <p>Antioxidant activity</p> Signup and view all the answers

    How is vitamin A formed from its provitamin precursor?

    <p>Cleavage of beta-carotene</p> Signup and view all the answers

    What distinguishes primary active transport from secondary active transport?

    <p>Primary is directly linked to ATP hydrolysis</p> Signup and view all the answers

    Rhodopsin is formed when retinal combines with which type of protein?

    <p>Peripheral proteins</p> Signup and view all the answers

    Which type of transport is facilitated by channel proteins?

    <p>Facilitated diffusion</p> Signup and view all the answers

    What is the primary function of glucocorticoids?

    <p>Control glucose metabolism and counteract inflammation</p> Signup and view all the answers

    Which eicosanoid promotes platelet aggregation?

    <p>Thromboxane A2</p> Signup and view all the answers

    Where are estrogens predominantly synthesized in the body?

    <p>Ovaries</p> Signup and view all the answers

    What is the effect of prostaglandins on the gastrointestinal tract?

    <p>Increase protective mucus secretion</p> Signup and view all the answers

    Which mineralocorticoid is primarily responsible for regulating sodium and potassium ion balance?

    <p>Aldosterone</p> Signup and view all the answers

    Which of the following statements about leukotrienes is true?

    <p>They contain three conjugated double bonds.</p> Signup and view all the answers

    What is the role of bile acids in the digestive process?

    <p>Emulsify dietary fats</p> Signup and view all the answers

    What is primarily synthesized from arachidonic acid?

    <p>Eicosanoids</p> Signup and view all the answers

    Study Notes

    Lipids

    • A heterogeneous class of naturally occurring organic compounds
    • Classified based on their solubility with nonpolar solvents
    • Insoluble in water due to long chains of hydrocarbon (C-H) bonds
    • Amphipathic in nature.

    Functions of Lipids

    • Energy source and storage
    • Protection and insulation
    • Cell membrane structural component
    • Vitamins and vitamin absorption
    • Chemical messengers (hormones)

    Types of Lipids

    • Fatty acids
      • Saturated
      • Unsaturated
    • Glycerides
      • Glycerol-containing lipids
        • Monoglycerides
        • Diglycerides
        • Triglycerides
    • Non-glyceride lipids
      • Sphingolipids
      • Steroids
      • Waxes
    • Complex lipids (lipoproteins)

    Fatty Acids

    • Unbranched-chain carboxyl acid, commonly 12-20 carbons long
    • Derived from hydrolysis of animal fats, vegetable oils, or phosphodiacylglycerols of biological membranes.
    • Two types:
      • Saturated: all C-C bonds are single bonds
      • Unsaturated:
        • Monounsaturated: one C=C bond
        • Polyunsaturated: 2 or more C=C bonds

    Properties of Fatty Acids

    • Water solubility: short-chain fatty acids are sparingly soluble, while long-chain fatty acids are insoluble
    • Melting point depends on:
      • Length of the carbon chain
      • Degree of unsaturation (number of double bonds in a molecule)
    • Space-filling molecules:
      • The number of bends in a fatty acid chain increases as the number of double bonds increases.
      • Less packing occurs, resulting in a lower melting point and a tendency to be liquids at room temperature.

    Essential Fatty Acids

    • Alpha Linolenic Acid (ALA): found in plants (flaxseed, walnuts, canola, and soybean)
    • Linoleic Acid: found in safflower, corn, and soybean oils
    • Arachidonic Acid: found in fish, meat, and eggs
      • Precursor of eicosanoids.

    Omega Fatty Acids

    • Nutritionally important Omega-3 and Omega-6 fatty acids
      • Linolenic Acid - Omega-3
      • Linoleic Acid - Omega-6

    Linoleic Acid Deficiency

    • Skin redness and irritation
    • Infections and dehydration
    • Liver abnormalities
    • Children need it the most

    Glycerides

    • Lipid esters of glycerol and fatty acids
    • Two classes:
      • Neutral glycerides (nonionic and nonpolar)
      • Phosphoglycerides (amphipathic)

    Triglycerides (Triacylglycerols)

    • Esters of 1 molecule of glycerol with three fatty acids (TAGs)
    • Called neutral fats
    • Serve as energy storage in the fat cells of adipose tissue
    • Fats (solid): derived from animals (beef, pork, and chicken), mixture of high percentage of long-chain saturated fatty acids and less degree of unsaturation
    • Oils (liquid): derived from plants and marine animals (essential oils and fish oil), mixture of a high degree of unsaturated fatty acids and less of saturated fatty acids.

    Reactions of Fatty Acids and Glycerides

    • Esterification:
      • Fatty acids react with long chain alcohols to produce water and esters (biological waxes).
      • 3 molecules of fatty acids react with glycerol to produce water and triglyceride.
    • Hydrogenation:
      • An addition reaction when unsaturated fatty acids are converted to saturated fatty acids.
      • Commonly used in the food industry.
    • Acid hydrolysis:
      • Waxes or triglycerides may be hydrolyzed in the presence of acid or biological enzymes to form alcohol and fatty acids.
    • Saponification (Base Hydrolysis):
      • Natural soaps (fatty acid salts) are prepared by boiling triglycerides (animal fats or vegetable oils) with NaOH or KOH.

    Phospholipids

    • Phosphate ester lipids derived from phosphoric acid
    • Polar head (the phosphoryl group) and a nonpolar tail (the alkyl chain of the fatty acid)
    • Dominate up to 80% of the mass of a cell membrane.
    • Two types:
      • Phosphoglycerides (Phosphoacylglycerides)
      • Sphingolipids (Sphingomyelin)

    Steroids

    • Cyclic lipids composed of four fused rings
    • Four major classes:
      • Cholesterol
      • Bile Acids
      • Steroid Hormones
      • Vitamin D

    Cholesterol

    • Most abundant steroid in animals
    • Precursor of steroid hormones
    • Inserted into cell membranes
    • Component of bile
    • Atherosclerosis: buildup of plaque in arteries

    Bile Acids

    • Polar derivatives of cholesterol made in the liver
    • Act as detergents in the intestine
    • Emulsify dietary fats to make them accessible to digestive enzymes.

    Steroid Hormones

    • Function as signaling molecules
    • Synthesized from cholesterol
    • Three main classes:
      • Adrenocorticoid hormones
      • Sex hormones
      • Vitamin D

    Adrenocorticoid Hormones

    • Produced by adrenal glands
    • Mineralocorticoids: control balance of Na and K ions in cells
    • Glucocorticoid: control glucose metabolism and counteract inflammation

    Steroid Sex Hormones

    • Androgen: male sex hormones
      • Synthesized in the testes
      • Responsible for the development of male secondary sex characteristics
      • Testosterone
    • Estrogens: female sex hormones
      • Synthesized in the ovaries
      • Responsible for the development of female secondary sex characteristics and control of the menstrual cycle

    Eicosanoids

    • Arachidonic acid (20:4) derivatives
    • Have profound physiological effects at extremely low concentrations
    • Short-lived hormone-like molecules
    • Names are based on ring substituents and number of side-chain double bonds.

    Eicosanoids Types

    • Thromboxanes: cyclic ether ring and oxygen-containing functional groups, promote platelet aggregation
    • Leukotrienes: derivative containing three conjugated double bonds and hydroxyl groups, promote inflammatory and hypersensitivity (allergy) responses
    • Prostaglandins: synthesized from arachidonic acid by COX-1 or COX-2, maintain homeostasis in many body tissues.

    Physiological Effects of Eicosanoids

    • Blood clotting:
      • Thromboxane A2 stimulates constriction of blood vessels and platelet aggregation.
      • Prostacyclin (PGI2) dilates blood vessels and inhibits platelet aggregation.
    • Inflammatory response:
      • Prostaglandins mediate aspects of the inflammatory response.
    • Reproductive system:
      • Stimulation of smooth muscle by PGE2.
    • Gastrointestinal tract:
      • Prostaglandins inhibit gastric secretion.
      • Prostaglandins increase the secretion of protective mucus.
      • Inhibition of hormone-sensitive lipases.
    • Kidneys:
      • Prostaglandins dilate renal blood vessels, resulting in increased water and electrolyte excretion.
    • Respiratory tract:
      • Leukotrienes promote bronchoconstriction.
      • Prostaglandins promote bronchodilation.

    Biological Membranes

    • Thin, flexible barriers that enclose cells and organelles.
    • Composed primarily of phospholipids arranged in a lipid bilayer
    • Responsible for:
      • Regulating what enters and exits the cell
      • Providing a structural framework
      • Facilitating cell signaling

    Membrane Proteins

    • Embedded within the lipid bilayer.
    • Responsible for:
      • Transport of molecules across the membrane
      • Cell signaling
      • Enzymatic activity.
    • Two types:
      • Integral proteins:
        • Span the entire membrane
        • Involved in transport and signaling
      • Peripheral proteins:
        • Loosely bound to the surface of the membrane.
        • Have polar or electrostatic interactions
        • Ex. Cytochrome C

    Membrane Transport

    • Movement of substances across the membrane
    • Two types:
      • Passive transport:
        • Driven by a concentration gradient
        • Simple diffusion: a molecule or ion moves through an opening.
        • Facilitated diffusion: a molecule or ion is carried across a membrane by a carrier/channel protein.
      • Active transport:
        • A substance is moved against a concentration gradient
        • Primary active transport: transport is linked to the hydrolysis of ATP or other high-energy molecules.
        • Secondary active transport: driven by H+ gradient

    Lipid-Soluble Vitamins

    • Vitamins are divided into two classes: lipid-soluble and water-soluble.
    • Fat-soluble vitamins:
      • A (retinol)
      • D (calciferol)
      • E (tocopherol)
      • K (phylloquinone and menaquinone)

    Vitamin A (Retinol)

    • Occurs only in animal products.
    • Extensively unsaturated hydrocarbon (-carotene).
    • Found in the plant world in the form of a provitamin in a group of pigments called carotenes.
    • Enzyme-catalyzed cleavage of -carotene followed by reduction gives two molecules of vitamin A.
    • Participates in the visual cycle in rod cells.
    • The active molecule is retinal (vitamin A aldehyde).
    • Retinal forms an imine with an -NH2 group of the protein opsin to form the visual pigment called rhodopsin.
    • The primary chemical event of vision in rod cells is absorption of light by rhodopsin followed by isomerization of the 11-cis double bond to the 11-trans double bond.

    Vitamin D (Calciferol)

    • Group of structurally related compounds involved in the regulation of calcium and phosphorus metabolism.
    • Most abundant form in the circulatory system is vitamin D3.

    Vitamin E (tocopherols)

    • The most active form of vitamin E is tocopherol.
    • Vitamin E is an antioxidant, trapping HOO and ROO radicals formed as a result of oxidation by O2 of unsaturated hydrocarbon chains in membrane phospholipids.

    Vitamin K (Phylloquinone and Menaquinone)

    • Important role in the blood-clotting process.
    • Long unsaturated hydrocarbon side consists of repeating isoprene units.
    • Required to modify prothrombin and other proteins involved in the clotting process.

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