Biochem (Midterm) PDF Study Guide

Carbohydrates (CHAPTER 16) produce these enzymes; instead, they rely on symbiotic microorganisms that live within their gut to facilitate the hydroly...

Carbohydrates (CHAPTER 16) produce these enzymes; instead, they rely on symbiotic microorganisms that live within their gut to facilitate the hydrolysis of cellulose. WHY are some carbohydrates indigestible? Of the major molecular building blocks of cells nucleotides, amino acids, lipids, Carbohydrates and carbohydrates- carbohydrates are the most abundant. Virtually all the foods we Carbohydrate: a polyhydroxyaldehyde or polyhydroxyketone, or a substance that eat contain carbohydrates. Yet there are subtle chemical differences in the way small gives these compounds on hydrolysis sugars are connected to form large molecules, which means that not all Monosaccharide: a carbohydrate that cannot be hydrolyzed to a simpler carbohydrates occur in forms that can be readily broken down. As a result, we carbohydrate cannot digest and use all the carbohydrates we eat. Building blocks of all carbohydrates They have the general formula CnH2nOn, where n varies from 3 to 8 Notes: Aldose: a monosaccharide containing an aldehyde group Carbohydrates as Energy Sources Ketose: a monosaccharide containing a ketone group Carbohydrates are well-known as food sources of energy. Although they are often thought of as hydrates of carbon, carbohydrates are actually classified as The term "saccharide" means sugar. polyhydroxy compounds. This means they contain multiple hydroxyl (–OH) groups, "Monosaccharide" refers to a simple sugar. which influence their properties and functions. ➔ Compounds that contain a single carbonyl group and two or more hydroxyl groups Digestibility of Carbohydrates Monosaccharides: Not all carbohydrates are digestible. Carbohydrates are among the four major Definition: Carbohydrates that cannot be hydrolyzed into simpler carbohydrates. molecular building blocks of cells, along with nucleotides, amino acids, and lipids. Function: Serve as the building blocks of all carbohydrates. They are the most abundant biomolecules, found in virtually all foods we consume. Examples: Despite their prevalence, there are subtle chemical differences in how small sugars Glucose: A primary energy source for cells. connect to form larger molecules. These differences lead to varying biochemical Mannose: Important in various metabolic processes. characteristics and physiological functions. Galactose: A component of lactose, the sugar found in milk. Combination: As a result, not all carbohydrates are in forms that can be easily broken down by Monosaccharides can combine to form more complex the human digestive system. This means that we cannot digest and utilize all carbohydrates, such as disaccharides and polysaccharides. carbohydrates efficiently. Monosaccharides Starch and Cellulose Monosaccharides are classified by their number of carbon Starch and cellulose are both composed of the same basic building blocks, which atoms are glucose units. However, they differ significantly in their structure and function. Trioses are simplest carbohydrate monosaccharides Starch is commonly found in many plant foods, such as cassava and other starchy Glyceraldehyde contains a stereocenter and exists as a pair of vegetables. On the other hand, cellulose is a structural component of plant cell walls enantiomers and is the material that gives wood its rigidity. Mirror-images stereoisomers are called enantiomers Interestingly, some organisms, such as termites, can digest cellulose. Termites can Simplest Carbohydrates damage wooden structures because they possess enzymes called cellulases that can Glyceraldehyde: break down cellulose into glucose. However, it is not the termites themselves that Simplest carbohydrate (monosaccharide).  Contains three carbon atoms. the carbon atom at the intersection of the horizontal and vertical lines is Example of an aldose due to the presence of an aldehyde functional group. not shown ( but it is understood or it is implied to be carbon atoms ) Dihydroxyacetone: Example of a ketose (contains a ketone functional group). Also has three carbon atoms, making it a triose. Summary: Both glyceraldehyde and dihydroxyacetone are examples of trioses, the simplest forms of carbohydrate monosaccharides. Stereoisomerism: Chiral Carbon: A carbon atom bonded to four different substituents is called a chiral or stereogenic center. Carbon atoms are the usual source of optical isomerism, as was the case with amino acids. Enantiomers: Glucose: When a molecule has a chiral center, it can give rise to two substances Aldose (a sugar with an aldehyde functional group). that are mirror images of each other but are not superimposable. Contains six carbon atoms. These substances are known as enantiomers, a specific type of A primary energy source for cells. stereoisomer Fructose: Notes: Ketose (a sugar with a ketone functional group). Stereoisomer (optical isomers) molecules that differ from each other only in their Also contains six carbon atoms. configuration (three dimensional shape) Found in many fruits; it is sweeter than glucose. Enantiomers - mirror image, non superimposable stereoisomer Configuration - the three dimensional arrangements of groups around a chiral Notes: carbon atom In some instances, carbon atoms are explicitly written in structural formulas (e.g., Oligosaccharides - sugars linked by glycosidic bonds carbon-carbon-carbon). - are formed when a few monosaccharides are bonded together In other instances, carbon atoms may not be written out. The simplest monosaccharides contain three carbon atoms called trioses It is understood that these are carbon atoms located at the intersections of Glyceraldehyde is the aldose with three carbons (aldotriose) horizontal and vertical lines in structural diagrams. Dihydroxyacetone - is the ketone with three carbon atoms (ketotriose) The intersections in these diagrams represent stereogenic centers (or chiral centers). Fischer projection: A stereogenic center is a carbon atom bonded to four different substituents, ➔ bonds are written in a two dimensional representation showing the contributing to the molecule's chirality. configuration of tetrahedral stereocenters horizontal lines represent bonds projecting forward (towards) D,L Monosaccharides vertical lines represent bonds projecting to the rear (directed away) ❖ According to the conventions proposed by Fischer  D-monosaccharide: a monosaccharide that, when written as a Fischer Aldoses that have four carbon atoms (tetra means four). projection, has the -OH on its penultimate carbon on the right Example: Aldotetroses. L-monosaccharide: a monosaccharide that, when written as a Fischer projection, has the -OH on its penultimate carbon on the left D- and L-Sugars Ultimate: Means "last" or "final" in a sequence. D-Erythrose: Penultimate: Means "second to the last." Hydroxy group on the penultimate carbon (second to the last carbon) is D-Monosaccharides: located on the right, which classifies it as a D-sugar. A monosaccharide is classified as a D-monosaccharide if the hydroxy group (-OH) L-Erythrose: on its penultimate carbon (the second to the last carbon) is located on the right side The mirror image of D-erythrose; the hydroxy group on the penultimate in a Fischer projection. carbon is found on the left. Example: D-Glucose: Mirror Images: 1, 2, 3, 4, 5, 6 (six carbon atoms total). D-erythrose and L-erythrose are non-superimposable mirror images, The penultimate carbon is carbon number 5 (the second to the last carbon). classified as enantiomers. Hydroxy group on penultimate carbon: Located on the right side, confirming that D-Threosevs. L-Threose: D-glucose is a D-sugar. Similar to D- and L-erythrose, they are non-superimposable mirror images, thus classified as enantiomers. Aldotetroses D-Erythrose vs. D-Threose: Enantiomers: stereoisomers that are mirror images Not enantiomers since they are not mirror images. example: D-erythrose and L-erythrose are enantiomers Classified as stereoisomers due to different arrangements of hydroxyl Diastereomers: stereoisomers that are not mirror images groups and hydrogen around the chiral centers (stereogenic centers). example: D-erythrose and D-threose are diastereomers Types of Stereoisomers: Stereoisomers that are not mirror images are called diastereomers. Stereoisomers of Aldotetroses Notes: D-glyceraldehyde and l-glyceraldehyde are enantiomers of each other. Configuration - is the three dimensional arrangement of groups around a chiral carbon atom and stereoisomers differ from each other in configuration. What Happens if a Sugar Forms a Cyclic Molecule? Cyclization of sugars takes place due to interaction between functional groups on distant carbons, C1 to C5, to make a cyclic hemiacetal Cyclization using C2 to C5 results in hemiketal formation. In both cases, the carbonyl carbon is new chiral center and becomes an anomeric carbon Aldoses: Formation of Cyclic Molecules in Sugars: Sugars that contain an aldehyde functional group. Sugars can form cyclic molecules, which is a common occurrence, especially in Tetroses: aqueous solutions.  The prevalent form of glucose, for example, in solution is a cyclic compound. They are not enantiomers; that is, they are not non-superimposable mirror images. Diastereomers have different spatial arrangements of atoms but differ from one Formation of a Cyclic Hemiacetal another in at least one but not all of their stereocenters. They exhibit different physical and chemical properties. Haworth Projections five- and six-membered hemiacetals are represented as planar pentagons or hexagons, as the case may be, viewed through the edge most commonly written with the anomeric carbon on the right and the hemiacetal oxygen to the back right the designation ẞ- means that -OH on the anomeric carbon is cis to the terminal -CH2OH; α- means that it is trans Pentagon (5-membered ring): A cyclic structure with five carbon atoms forms a pentagonal shape. Example: Furanose forms of sugars. Hexagon (6-membered ring): Alpha Anomer (α): A cyclic structure with six carbon atoms forms a hexagonal shape. An anomer where the hydroxyl group (-OH) on the anomeric carbon (carbon 1) is Example: Pyranose forms of sugars, such as glucose. found below the plane of the ring. Beta Anomer (β): Haworth Projections (Cont'd) An anomer where the hydroxyl group (-OH) on the anomeric carbon is found A six-membered hemiacetal ring is shown by the infix -pyran- (pyranose) above the plane of the ring. A five-membered hemiacetal ring is shown by the infix -furan- (furanose) Five-membered rings are so close to being planar that Haworth projections are ➔ The term "peroses" is used to describe these cyclic forms of sugars due to adequate to represent furanoses their structural resemblance to pyran (a six-membered ring compound). For pyranoses, the six-membered ring is more accurately represented as a strain-free chair conformation Cyclic Structure Monosaccharides have -OH and C=O groups in the same molecule and exist almost entirely as five- and six-membered cyclic hemiacetals anomeric carbon: the new stereocenter resulting from cyclic hemiacetal formation anomers: carbohydrates that differ in configuration only at their anomeric carbons Cyclic Structures: Cyclic structures of sugars are more stable than their open-chain forms. This stability is attributed to the formation of cyclic hemiacetals in solution. Comparison of the Fischer and Haworth Representations Diastereomers: are a type of stereoisomer.  Benedict's Reagent: A chemical reagent commonly used to test for the presence of reducing sugars. It has a blue color due to the presence of copper(II) ions (Cu²⁺). Chemical Reaction: When a reducing sugar is present, the copper(II) ions in Benedict's reagent are reduced to copper(I) ions (Cu⁺). This reaction forms copper(I) oxide (Cu₂O), which appears as a brick red precipitate. Test Interpretation: A positive result (brick red precipitate) indicates the presence of a reducing sugar in the sample. Examples of reducing sugars include glucose, fructose, and lactose. Reaction of Monosaccharides (Cont'd) The carbonyl group of a monosaccharide can be reduced to an hydroxyl group by a variety of reducing agents, such as NaBH4 Alpha Anomer (α): reduction of the C=O group of a monosaccharide gives a polyhydroxy compound In the Fischer projection, the hydroxyl group (-OH) on carbon number one is called an alditol located on the right side. Beta Anomer (β): In the Fischer projection, the hydroxyl group (-OH) on carbon number one is located on the left side. Reaction of Monosaccharides Oxidation Process: Reducing sugar: one that reduces an oxidizing agent In monosaccharides, Oxidation of a cyclic hemiacetal form gives a lactone the carbonyl group When the oxidizing agent is Tollens solution, silver precipitates as a (C=O) can undergo silver mirror oxidation, transforming from an aldehyde (–CHO) or ketone (C=O) to a carbonyl If anomeric carbons are involved in glycosidic linkage, there will be a negative compound. Tollens reagent test Reduction Process: If another anomeric carbon is not bonded and is free, there will be a positive The carbonyl group can also be reduced, which involves adding hydrogen to Tollens reagent test convert the carbonyl into an alcohol (–OH). Catalytic Hydrogenation: This reduction is achieved through catalytic hydrogenation using hydrogen gas (H₂) in the presence of a catalyst, such as: Platinum (Pt) Palladium (Pd) Nickel (Ni) Aldose Reduction:  An aldose (an aldehyde sugar) can be reduced to form an alcohol, specifically Glycosidic Bond Formation (Cont’d) called an alditol. Phosphoric Esters Phosphoric esters are particularly important in the metabolism of sugars to provide energy phosphoric esters are frequently formed by transfer of a phosphate group from ATP Two Different Disaccharides of a-D-Glucose Glycosidic linkages can take various forms; the anomeric carbon of one sugar to any of the -OH groups of another sugar to forma an a- or ẞ- glycosidic linkage Glycosidic Bond Formation Glycoside: a carbohydrate in which the -OH of the anomeric carbon is replaced by -OR those derived from furanoses are furanosides; those derived from Disaccharides from Alpha-D-Glucose: pyranoses are pyranosides There are two different disaccharides that can be formed from alpha-D-glucose. glycosidic bond: the bond from the anomeric carbon to the -OR group Glycosidic Linkages: This is the basis for the formation polysaccharides/oligosaccharides Glycosidic linkages can take various forms, which contribute to the diversity of carbohydrates. Glycoside: All glycosidic linkages involve the formation of bonds between monosaccharides. A glycoside is formed when the hydroxyl group (-OH) at the anomeric carbon of a Variability in Linkages: monosaccharide is replaced by an alkoxy group (-O-R). The variability arises from: Types of Glycosides: Different Carbons: The specific carbon atoms involved in the linkage can vary. Furanoside: If the glycoside is derived from a furanose (5-membered ring), it is Different Atoms: Other atoms may also be involved in the bond formation. called a furanoside. Orientation in Space: The orientation of the linkage can be either: Pyranoside: If the glycoside is derived from a pyranose (6-membered ring), it is Alpha Glycoside: The hydroxyl group (-OH) on the anomeric carbon is oriented called a pyranoside. downwards. Formation of Larger Carbohydrates: Beta Glycoside: The hydroxyl group (-OH) on the anomeric carbon is oriented Glycosides serve as the building blocks for larger carbohydrates, including: upwards. Disaccharides: Formed by the linkage of two monosaccharides. Diversity in Structure: Trisaccharides: Formed by the linkage of three monosaccharides. The ability of carbohydrates to form various glycosidic linkages is a key factor in Polysaccharides: Formed by the linkage of many monosaccharides. their structural diversity. Identification of Glucose Molecules: Table sugar; obtained from the juice of sugar cane and sugar beet Consider two molecules of glucose: One unit of D-glucose and one unit of D-fructose joined by an a-1,2-glycosidic bond Left Glucose: Lactose Carbon numbering starts from the anomeric carbon. Made up of D-galactose and one unit of D-glucose joined by a ẞ-1,4-glycosidic This is carbon number 1. bond Right Glucose: Galactose is a C-4 epimer of glucose Carbon numbering begins from its anomeric carbon. Maltose This is also carbon number 1, followed by carbon 2, 3, 4. Two units of D-glucose joined by an a-1,4-glycosidic bond Glycosidic Linkage Type: Formed from the hydrolysis of starch Differs from cellobiose by the conformation of The linkage between these two glucose molecules is called an alpha glycosidic the glycosidic linkage linkage. This designation is due to the orientation of the hydroxyl group (-OH) on the Some Important Disaccharides anomeric carbon of the left glucose, which is positioned opposite to the CH₂ group of the right glucose. Specific Linkage: The linkage is described as a 1-4 alpha glycosidic linkage: The "1" refers to the anomeric carbon (carbon number 1) of the left glucose. The "4" refers to the fourth carbon (carbon number 4) of the right glucose. Glycosidic Bond: This linkage is specifically referred to as a glycosidic bond since it involves glucose residues. ➔ Alpha 1-4 and Alpha 1-6 glycosidic linkages are found in starch. Amino Sugars Reducing Sugars: The substances crucial for determining blood types are found on the surface of Reducing sugars have a free –OH group at the anomeric carbon. cells in the form of glycolipids or glycoproteins. To be classified as a reducing sugar, there must be at least one reducing end It is the type and sequence of polysaccharides attached to these molecules that present. determine the various blood types. For example, maltose is considered a reducing sugar because it possesses a free anomeric carbon. Summary Sugars can and undergo oxidation reactions, as well as, forming esters Sucrose: Glycosidic linkages are responsible for the bonding of monosaccharides to form In sucrose, there is no free –OH group at carbon number one because it is already oligosaccharides and polysaccharides involved in a glycosidic bond. The –OH group at this position has been replaced by an O atom, forming a Disaccharides glycosidic linkage. Sucrose Fructose and Sucrose: Fructose does not have a free anomeric –OH group, making it not a reducing sugar. Consequently, sucrose, which is composed of fructose and glucose, does not reduce Tollens reagent, Benedict's reagent, or Fehling's reagent. Lactose: Lactose is composed of D-galactose and D-glucose, joined by a β-1,4 glycosidic linkage. The reason it is called β is that the oxygen in the glycosidic bond is on the same side as the –CH₂ group of galactose. This structure can be referred to as β-galactopyranosyl-1,4-glucose. Since lactose has a free anomeric carbon, it is classified as a reducing sugar. Cellulose: The repeating disaccharide in cellulose is called cellobiose. Summary Cellobiose is composed of two β-D-glucose units linked by a β-1,4-glycosidic bond. The disaccharide sucrose is a common table sugar. It consists of glucose and This structure contributes to the rigidity and strength of the cellulose fibers in plant fructose linked by a glycosidic bond cell walls. Lactose, found in milk, and maltose, obtained from starch, are two other common disaccharides Polysaccharides (Cont'd) Starch is used for energy storage in plants Structures and Function of Polysaccharides a polymers of a-D-glucose units Polysaccharide- When many monosaccharides are linked together amylose: continuous, unbranched chains of up to 4000 α-D- glucose units joined Cellulose: the major structural component of plants, especially wood and plant by a-1,4-glycosidic bonds fibers amylopectin: a highly branched polymer consisting of 24-30 units of D-glucose a linear polymer of approximately 2800 D-glucose units per molecule joined by joined by a-1,4-glycosidic bonds and branches created by a-1,6-glycosidic bonds ẞ-1,4-glycosidic bonds amylases catalyze hydrolysis of a-1,4-glycosidic bonds fully extended conformation with alternating 180° flips of glucose units ẞ-amylase is an exoglycosidase and cleaves from the nonreducing end of the extensive intra- and intermolecular hydrogen bonding between chains polymer a-amylase is an endoglycosidase and hydrolyzes glycosidic linkages anywhere Polymeric Structure of Cellulose along the chain to produce glucose and maltose debranching enzymes catalyze the hydrolysis of a-1,6- glycosidic bonds Starch: Composed of α-D-glucose units. Linked primarily by α-1,4-glycosidic bonds. Cellulose: Composed of β-D-glucose units. Linked by β-1,4-glycosidic bonds. Salivary Amylase:  An enzyme that breaks down α-1,4-glycosidic bonds in starch. Enables the digestion of starch, a polysaccharide composed of α-D-glucose units. Digestive Process: Salivary amylase hydrolyzes starch into smaller sugars (dextrins and maltose) during the initial phase of digestion in the mouth. Since starch has α-1,4-glycosidic linkages, salivary amylase can effectively digest it. Cellulose: Composed of β-D-glucose units linked by β-1,4-glycosidic bonds. Humans lack the enzyme (cellulase) necessary to break down these β-glycosidic bonds, which is why cellulose (found in wood and plant cell walls) cannot be digested. Alpha Amylase is classified as an endoglycosidase. It cleaves glycosidic bonds within the polysaccharide chain rather than at the ends. This means it breaks down starch into smaller oligosaccharides or disaccharides, Formation of Starch-Iodine Complex such as maltose, by targeting the internal α-1,4-glycosidic bonds. Blue Complex Formation: When iodine (I₂) is added to a starch sample, a blue This internal cleavage facilitates the digestion of starch, allowing the resulting solution is formed due to the creation of a starch-iodine complex. smaller sugars to be further broken down by other enzymes. Mechanism: The iodine molecules fit into the helical structure of amylose, a component of starch. This interaction leads to the characteristic blue color. Amylose and Amylopectin Analytical Chemistry Application: The starch-iodine complex is commonly used in iodometry, a quantitative analytical technique to determine the concentration of iodine or related compounds. Chitin Chitin: the major structural component of the exoskeletons of invertebrates, such as insects and crustaceans; also occurs in cell walls of algae, fungi, and yeasts composed of units of N-acetyl-ẞ-D-glucosamine joined by ẞ-1,4-glycosidic bonds Examples: Chitin is found in the exoskeletons of insects (e.g., beetles) and Starch is composed of two main polymers: crustaceans (e.g., crabs, shrimp). Amylose: A linear polymer made up of α-1,4-glycosidic bonds. Amylopectin: A branched polymer that consists of both α-1,4-glycosidic bonds and α-1,6-glycosidic bonds at the branch points. Iodine can Fit Inside Amylose to Form Starch Iodine Complex  Have thinner peptidoglycan layers and an outer membrane containing lipopolysaccharides. Do not retain the crystal violet stain and are stained pink by safranin in Gram staining. Glycosaminoglycans Glycosaminoglycans: polysaccharides based on a repeating disaccharide where one of the monomers is an amino sugar and the other has a negative charge due to a sulfate or carboxylate group Heparin: natural anticoagulant Hyaluronic acid: a component of the vitreous humor of the eye and the lubricating fluid of joints Polysaccharides (Cont'd) Bacterial cell walls: prokaryotic cell walls are constructed on the framework of ➔ As people age, joint issues become more common, often due to a decrease the repeating unit NAM-NAG joined by ẞ-1,4-glycosidic bonds in hyaluronic acid levels. Hyaluronic acid is a natural component of the lubricating fluid in joints, which helps reduce friction and maintain smooth joint movement. In older individuals, the body produces less hyaluronic acid, leading to reduced joint lubrication. This decrease often results in discomfort or pain in the joints, as there’s less cushioning to protect the bones during movement. This reduction in hyaluronic acid is one reason why joint pain is more prevalent in the elderly. Chondroitin sulfate and keratan sulfate: components of connective tissue (ex. ligaments and bones) Summary Polysaccharides are formed by linking monomeric sugars through glycosidic linkages Starch and glycogen are energy-storage polymers or sugars Cellulose and chitin are structural polymers Polysaccharides are important components of cell walls in bacteria and plants Polysaccharides in Bacterial Cell Walls Location: Polysaccharides are found in the cell walls of bacteria. Glycoproteins Types of Bacteria: Glycoproteins contain carbohydrate units covalently bonded to a polypeptide chain Gram-Positive Bacteria: antibodies are glycoproteins Have thick peptidoglycan layers composed mainly of polysaccharides. Oligosaccharide portion of glycoproteins act as antigenic determinants Retain the crystal violet stain used in Gram staining. Among the first antigenic determinants discovered were the blood group Gram-Negative Bacteria: substances  In the ABO system, individuals are classified according to four blood types: A, B, AB, and O At the cellular level, the biochemical basis for this classification is a group of relatively small membrane- bound carbohydrates Summary Sugars can be found in specific bonding arrangements in some proteins ➔ and are presented on cell membranes. In the case of blood, these sugar structures determine the blood type by acting as antigens on red blood cells. Glycoproteins frequently play a role in the immune response because antibodies The types of blood (A, B, AB, and O) are determined by specific carbohydrate are actually glycoproteins. structures on the surface of red blood cells, which form unique glycoproteins or glycolipids. Each blood type has a distinct arrangement of carbohydrate residues: LIPIDS AND MEMBRANES Type O: This type has a base structure with galactose (circle), N-acetylglucosamine (square), and fucose (triangle). It lacks an additional residue, LIPIDS AND PROTEINS ARE ASSOCIATED IN BIOLOGICAL which distinguishes it from other blood types. MEMBRANES (CHAPTER EIGHT) Type A: This type has the same base structure as type O, but with an extra N-acetylgalactosamine (square with added structure) attached to the galactose Cell membrane - its the structure that separates the interior of the cell from its residue. This additional residue gives Type A its unique antigenic properties. environment. It is primarily comprised of lipid by layer Type B: While it shares the base structure with type O, Type B has an extra galactose instead of N-acetylgalactosamine bonded to the base galactose residue, What is a Lipid? differing from Type A in just one carbohydrate addition. Lipids: a heterogeneous class of naturally occurring organic compounds classified together on the basis of common solubility properties Structures of Blood-Group Antigenic Determinants ➔ Heterogeneous meaning they have different structures and only common to them is their solubility properties. insoluble in water, but soluble in aprotic organic solvents including diethyl ether, chloroform, methylene chloride, and acetone ➔ in other words they tend to dissolve in substances that are either insoluble in water or that dissolve to a lesser extent in water called this substances hydrophobic Amphipathic in nature  - Amphipathic means that molecules of lipids naturally not all but some of the molecules of lipids have polar heads and nonpolar tails whenever a substance has such characteristic it call that amphiphatic that is able to interact with polar molecules like water also able to interact with nonpolar molecules like oil like hexane Lipids include: Open Chain forms fatty acids, triacylglycerols, sphingolipids, phosphoacylglycerols, glycolipids, ➔ Glycolipids, along with sphingolipids, are important components of the cell membrane. lipid-soluble vitamins ➔ Many familiar vitamins include vitamins A, D, E, and K. ➔ These vitamins are classified as fat-soluble vitamins. ➔ They are referred to as lipid-soluble vitamins due to their ability to Notes: dissolve in fats and oils. A 16-carbon fatty acid is known as palmitic acid. ➔ Their solubility in lipids allows them to be stored in the body's fatty - A 18-carbon fatty acid is known as stearic acid. tissues and the liver. - Oleic acid is an 18-carbon unsaturated fatty acid that contains one double prostaglandins, leukotrienes, and thromboxanes bond. ➔ Cyclooxygenase (COX) is an enzyme involved in the production of - The presence of a double bond in oleic acid creates a kink in the fatty acid prostaglandins, which are lipid compounds that act as pain mediators. chain, affecting its physical properties, such as melting point and fluidity. ➔ Prostaglandins contribute to the sensation of pain and inflammation. These substances share similar structural features: ➔ To minimize pain, it's important to lower the production of prostaglandins - They have hydrocarbon tails. in the body. - They possess a carboxylic acid head (polar head). ➔ Prostaglandins, along with leukotrienes and thromboxanes, are classified - They have a nonpolar tail. as lipid compounds. They differ primarily in: Cyclic forms - The length and number of carbons in the chain. cholesterol, steroid hormones, and bile acids - The presence or absence of double bonds in the fatty acid chains ➔ Steroid hormones, such as testosterone, estrogen, and progesterone, are Most naturally occurring fatty acids contain even numbers of carbon atoms and classified as lipids. that the double bonds are nearly always cis and rarely conjugated. Fatty Acids Fatty Acids (Cont'd) Fatty acid: an unbranched-chain carboxylic acid, most commonly of 12 - Length of fatty acid plays a role in its chemical character 20 carbons, derived from hydrolysis of animal fats, vegetable oils, or Usually contain even numbers of carbons (can contain odd, depending on how they phosphodiacylglycerols of biological membranes are biosynthesized) In the shorthand notation for fatty acids FA that contain C=C, are unsaturated: If contain only C-C bonds, they are saturated the number of carbons and the number of double bonds in the chain are shown by two numbers, separated by a colon  Unsaturated fatty acids have lower melting points than their saturated counterparts; the greater the degree of unsaturation, the lower the melting point Remember: Unsaturated Fatty Acids: Notes: Contain multiple double bonds (carbon-carbon double bonds). Effect of Double Bonds on Fatty Acids: Saturated Fatty Acids: Double bonds introduce kinks or bends in the structure of unsaturated fatty acids. Contain only single carbon-carbon bonds. This prevents the molecules from packing closely together, resulting in lower If there are no double bonds present, they are classified as saturated. packing efficiency. As a result, the melting point of unsaturated fatty acids is lower Melting Points of Fatty Acids: compared to their corresponding saturated fatty acids, which can pack more tightly - The melting points of fatty acids increase as the number of carbon atoms due to their straight chains. increases, ranging from approximately 44°C to 77°C. - The more double bonds a fatty acid has, the weaker and less effective the - Reason: As the size of the molecule increases, the strength of packing of the molecules becomes. This leads to weaker interactions intermolecular forces, such as London dispersion forces, also increases, between the molecules, resulting in a lower melting temperature for the leading to higher melting points. substance. Consequently, unsaturated fatty acids, with multiple double Molecular Interactions: bonds, will melt at lower temperatures compared to saturated fatty acids. - Interactions between molecules increase as the size of the molecules increases. Triacylglycerols London Dispersion Forces: Triacylglycerol (triglyceride): an ester of glycerol with three fatty acids - These forces are a type of intermolecular force. natural soaps are prepared by boiling triglycerides (animal fats or - They depend on the size of the molecule: larger molecules have stronger vegetable oils) with NaOH, in a reaction called saponification (Latin, London dispersion forces due to an increased number of electrons and sapo, soap) greater polarizability. Melting Point of Palmitic Acid: - The melting point of palmitic acid is 63°C. This indicates that palmitic acid is a solid at room temperature. Remember: Familiarize with acid and number of carbon atoms in table 8.1 Fatty Acids (Cont'd) In most unsaturated fatty acids, the cis isomer predominates; the trans isomer is rare Notes:  Glycerol - a three-carbon compound that contains three hydroxyl groups, one Effects of Hard Water on Soap: bound to each carbon In areas with hard water where minerals like calcium, magnesium, and iron are Triacylglycerol - a lipid formed by esterification of three fatty acids to glycerol; present—these ions can react with the carboxylates in soap to form insoluble salts. also called a triglyceride This reaction reduces the effectiveness of soap because, instead of dissolving and cleaning, it precipitates out of solution. As a result, using soap in hard water can lead Soaps to decreased lathering and cleaning ability, as the soap is consumed in the formation Soaps form water-insoluble salts when used in water containing Ca(II), Mg(II), and of these insoluble salts. Fe(III) ions (hard water) The salt rinses off Phosphoacylglycerols (Phospholipids) Reactions with acids/bases as catalysts When one alcohol group of glycerol is esterified by a phosphoric acid rather than Salts formed by Saponification by a carboxylic acid, phosphatidic acid produced Base-catalyzed hydrolysis with salts formed Phosphoacylglycerols (phosphoglycerides) are the second most abundant group of naturally occurring lipids, and they are found in plant and animal membranes Notes: phospholipids are important components of a cell membrane Phospholipids: Phospholipids, often referred to as glycerol phospholipids, are crucial components of cell membranes. They consist of a glycerol backbone, two fatty acid tails, and a phosphate group. The unique structure of phospholipids allows them to form bilayers, which create a semi-permeable membrane that is essential for cellular function. Their hydrophilic (water-attracting) "head" and hydrophobic (water-repelling) "tails" enable them to organize into membranes, which serve as barriers and play a vital role in the cell's interactions with its environment. In phospholipids, the two carbon atoms of glycerol are each bonded to a fatty acid chain. The only difference in the structure is that the terminal carbon of glycerol is bonded to a phosphate group instead of a fatty acid. This phosphate group forms a phosphoric acid ester linkage. Consequently, in the case of a phospholipid, one of the hydroxyl (–OH) groups of glycerol is replaced by a phosphate group, which is crucial for the formation of the phospholipid bilayer in cell membranes. Notes: Saponification Process: When fats are saponified using sodium hydroxide (NaOH), the result is the hydrolysis of triglycerides, producing glycerol and fatty acid salts (soaps). Under basic conditions, the fatty acids form carboxylates, specifically the sodium salt of the fatty acid, which is what we commonly refer to as soap.  Sphingolipids Contain sphingosine, a long- chain amino alcohol ➔ Sphingolipids are also components of the cell membrane, similar to phospholipids. Found in plants and animals Abundant in nervous system Has structural similarity to phospholipids Ceramide tells cells to undergo apoptosis Sphingosine tells cells to grow, divide and migrate Waxes A complex mixture of esters of long-chain carboxylic acids and alcohols Found as protective coatings for plants and animals Notes: They are highly hydrophobic, making them effective as protective coatings. Plants utilize waxes to create a protective layer on their surfaces, which helps reduce water loss and protect against environmental damage. Similarly, many animals also have waxy coatings that serve to protect their skin and fur. Remember: Fix on mind the structure of a ceremide Glycolipids The common feature of these two examples of waxes is that they are esters of Glycolipid: a compound in which a carbohydrate is bound to an -OH of the lipid long-chain fatty acids and long-chain alcohols, which contributes to their high In most cases, sugar is either glucose or galactose hydrophobicity. many glycolipids are derived from ceramides Glycolipids with complex carbohydrate moiety that contains more than 3 sugars are known as gangliosides (Fig. 8.8, p. 207) Notes: This is a glucocerebroside. A glucocerebroside is related to a ceramide. A cerebroside is a ceramide that has a sugar molecule attached—in this case, a glucose molecule. This is why we say that many glycolipids are derived from ceramides.  Gangliosides are typically found in cell membranes and play a crucial role in intercellular communication, which is the process by which cells communicate with each other. This communication is vital for the normal development of tissues. For example, a cell knows to stop dividing when it senses that there are too many cells in a particular area of the tissue. Cells recognize this by detecting the presence of neighboring cells through the interaction of glycolipids and glycoproteins on their membranes. If the glycolipids or glycoproteins on the cell membranes are dysfunctional, it can lead to diseases such as cancer. In such cases, cells may fail to recognize that there are adjacent cells, leading them to believe there is still ample space to grow. As a result, these cells may continue to reproduce uncontrollably, resulting in malignancy or tumor formation. Notes: Cholesterol is an example of a steroid and is an important component of cell membranes. While cholesterol has a bad reputation, often associated with heart attacks and other health issues, it plays a crucial role in maintaining membrane fluidity. In the right amounts, cholesterol is essential for ensuring that cell membranes remain fluid enough to allow the entry and exit of materials. For instance, nutrients must be transported into the cell, while waste products need to be excreted. If the membrane becomes too rigid, these exchanges cannot occur, leading to the accumulation of waste and deprivation of essential nutrients, which can ultimately harm the cell. Thus, cholesterol is vital for maintaining the fluidity of cell membranes, facilitating the necessary exchange of materials. However, excessive cholesterol can lead to health complications, emphasizing the importance of balance in its levels. Steroids Steroids: a group of lipids that have fused-ring structure of 3 six- membered rings, Sex Hormones and 1 five- membered ring. Androgens: 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 Cholesterol  The steroid of most interest in our discussion of biological membranes is Polar heads come into contact with the aqueous environment. Remember, cells in cholesterol living systems exist in an aqueous environment. Micelles are formed when fatty acids create spherical aggregates, where their non-polar tails are buried within the structure while their polar heads are exposed to the aqueous environment. In contrast, a lipid bilayer has a different structure. Lipid Bilayers The polar surface of the bilayer contains charged groups The hydrophobic tails lie in the interior of the bilayer Notes: The molecule cholesterol is primarily nonpolar. Biological Membranes Every cell has a cell membrane (plasma membrane) Eukaryotic cells also have membrane-enclosed organelles (nuclei, mitochondria...etc) Molecular basis of membrane structure is in lipid component(s): polar head groups are in contact with the aqueous environment nonpolar tails are buried within the bilayer the major force driving the formation of lipid bilayers is hydrophobic interaction the arrangement of hydrocarbon tails in the interior can be rigid (if rich in saturated fatty acids) or fluid (if rich in unsaturated fatty acids) ➔ In other words, a cell membrane can be very rigid and inflexible if it contains a high proportion of saturated fatty acids. Conversely, it can be fluid if it is rich in unsaturated fatty acids. ➔ You do not want a structure that is too rigid because that would result in a cell that cannot move. Remember, a cell is not a static structure; it is not a Notes: solid block. Cells are capable of movement, expansion, and contraction, so Inner aqueous compartment: the inside of the cell, where water is abundant. they must maintain a certain degree of fluidity or flexibility. Extracellular matrix: the outside of the cell, which also contains water. ➔ Having too many saturated fatty acids would make the cell membrane too Lipid bilayer orientation: rigid, while having too many unsaturated fatty acids would make it Polar heads face both the cell interior and the extracellular matrix, interacting with excessively fluid, lacking the necessary rigidity. It’s like having a skeleton surrounding water. that is too weak to support you. Hydrophobic tails are buried within the bilayer's interior, creating a stable, ➔ Thus, cells must strike a balance between rigidity and fluidity to ensure nonpolar core. proper function and adaptability. This structure allows the membrane to interact with aqueous environments on Notes: either side while maintaining structural integrity and selective permeability. Biological Membranes The second layer has polar heads oriented toward the inside of the cell. Plant membranes have a higher percentage of unsaturated fatty acids than animal This bilayer arrangement allows hydrophilic (polar) heads to interact with the membranes aqueous environments both outside and inside the cell, while the hydrophobic tails The presence of cholesterol is characteristic of animal rather than plant membranes face inward, away from water, creating a stable membrane barrier. Animal membranes are less fluid (more rigid) than plant membranes The membranes of prokaryotes, which contain no appreciable amounts of steroids, Here is an example of phospholipids with different types of fatty acid are the most fluid chains: Notes: One phospholipid has a double bond in one fatty acid, indicating an Plant cell membranes are generally more fluid due to a higher proportion of unsaturated fatty acid, while the other fatty acid chain has no double bond, unsaturated fatty acids in their lipid bilayer. making it saturated. Unsaturated fatty acids have double bonds that introduce kinks, preventing tight Another phospholipid has two saturated fatty acids, with no double packing of molecules. bonds present. This fluidity supports processes like photosynthesis and nutrient exchange by Polar head groups also vary among these phospholipids: facilitating movement and flexibility in the membrane structure. The green head group represents a cerebroside. The blue-green head group corresponds to a phosphatidylglycerol. Membrane Layers The purple head group represents a ganglioside.\ Both inner and outer layers of bilayer contain mixtures of lipids The crimson (red) head group corresponds to a sphingomyelin. Compositions on inside and outside of lipid bilayer can be different This is what distinguishes the layers Effect of Double Bonds on the Conformations of Fatty Acids Kink in hydrocarbon chain Causes disorder in packing against other chains This disorder causes greater fluidity in membranes with cis- double bonds vs...... saturated FA chains Notes: The presence of a double bond in fatty acids weakens the interactions between Notes: molecules of fats and oils. This is because double bonds introduce kinks in the fatty This structure consists of a phospholipid bilayer, with one layer of phospholipids acid chains, preventing them from packing closely together. This reduced packing having their polar heads facing the outside of the cell. efficiency leads to weaker intermolecular forces, lowering the melting point and Mobility of the lipid chains increases dramatically with increasing temperature. making these substances more liquid (oils) at room temperature compared to Notes: saturated fats, which remain more solid. A membrane with a high concentration of saturated fatty acid tails requires a higher temperature to weaken, as it is more rigid due to tight packing. In contrast, The presence of a double bond introduces a kink—a bend in the structure—that a membrane with more unsaturated fatty acid tails is more fluid at lower prevents effective packing of molecules, weakening the interactions between them. temperatures because the kinks in the unsaturated chains prevent close packing, This reduction in packing efficiency lowers the melting point of the substance, or, resulting in weaker interactions. Consequently, the transition temperature—the in the case of a lipid bilayer, increases its fluidity. With more double bonds, more point at which a membrane changes from a rigid to a fluid state—is higher for kinks form, leading to greater disorder in the packing of fatty acid chains. This membranes rich in saturated fatty acids than for those rich in unsaturated fatty acids. disorder increases the fluidity of membranes that contain unsaturated (cis double-bonded) fatty acids compared to those with saturated fatty acid chains. When you heat a lipid bilayer membrane from a gel-like state, it transitions into a liquid crystal state at a specific transition temperature. It's crucial for cellular Cholesterol reduces Fluidity function that membranes do not remain in a rigid crystalline state, as this would Presence of cholesterol reduces fluidity by stabilizing extended chain hinder their ability to facilitate the entry and exit of nutrients and other essential conformations of hydrocarbon tails of FA molecules. Due to hydrophobic interactions If a cell’s membrane becomes too rigid, it could compromise the cell's viability, leading to serious consequences for its overall function and survival. Therefore, maintaining the right balance of fluidity is essential for cellular health. Membrane Proteins Functions: transport substances across membranes; act as receptor sites, and sites of enzyme catalysis Notes: Peripheral proteins (Protein 3 in figure below) For example, with three saturated fatty acid chains, they interact closely and strongly bound by electrostatic interactions due to their straight, orderly structure. However, if a cholesterol molecule is inserted can be removed by raising the ionic strength between them, it disrupts this close interaction, weakening the bonds between the ➔ Peripheral Membrane Proteins: Located at the periphery of the bilayer components. This disruption in packing lowers the rigidity of the bilayer, cell membrane. making it more fluid. Thus, cholesterol can effectively decrease the ordered packing ➔ Weak Binding: Bound to the membrane primarily through weak of fatty acid chains in the bilayer, enhancing membrane fluidity instead of causing it electrostatic interactions. to behave like a rigid structure. ➔ Easily Removable: Can be detached from the membrane by increasing ionic strength. Temperature Transition in Lipid Bilayer Integral proteins (Proteins 1, 2 and 4 in figure below) With heat, membranes become more disordered; the transition temperature is bound tightly to the interior of the membrane higher for more rigid membranes; it is lower for less rigid membranes can be removed by treatment with detergents or ultrasonification  removal generally denatures them Notes: Example of Integral Membrane Protein: ROP (Rho of Plants) protein is an example of an integral membrane protein that spans the lipid bilayer. Peripheral Protein Example: G-protein is identified as a peripheral protein because it is located on the inner leaflet of the membrane and does not span the entire width of the lipid bilayer. Notes: Proteins Can be Anchored to Membranes Lipid Bilayer Composition: Includes phospholipids, glycosphingolipids, N-myristoyl- and S- palmitoyl anchoring motifs cerebrosides, and various proteins. Anchors can be: Functions of Membrane Proteins: N-terminal Gly Transport: Act as channels for substances to cross the membrane. Thioester linkage with Cys Receptors: Receive signals from the environment, enabling cellular responses. Enzymatic Activity: Facilitate biochemical reactions (e.g., succinate dehydrogenase in the mitochondrial membrane). Integral membrane proteins are difficult to study due to their complex structure and environment. Globular proteins are soluble in the cytosol or mitochondrial matrix, making them easier to study than integral membrane proteins. When integral membrane proteins are extracted from the membrane, they often denature, which can lead to irrelevant conclusions that do not reflect their functional state in the cell membrane. Notes: Fluid Mosaic Model: The lipid bilayer is a dynamic structure, not static. Single-Molecule Fluorescence is Useful in Examining Proteins in Membranes Transverse Motion: Phospholipids can flip from one leaflet to another, a process known as transverse motion. Lateral Movement: Lipid molecules can also move laterally within their leaflet, demonstrating their mobility. The fluid mosaic model emphasizes the fluidity and flexibility of the lipid bilayer, allowing for essential cellular functions and interactions. Generally, polar molecules cannot pass through the lipid bilayer easily. The lipid bilayer is hydrophobic, preventing polar molecules from penetrating it. Molecules with both nonpolar and polar groups can pass through because:  The nonpolar group interacts with the hydrophobic region of the bilayer. Notes: The polar group interacts with the aqueous environment on either side of the Fluid Mosaic Model of Membrane Structure: membrane. The interior of the membrane contains various components, including integral Examples: membrane proteins. Polar Molecules (e.g., glucose): Cannot penetrate the membrane directly and One side of the membrane faces the interior of the cell, while the other side is require transporters or channels. oriented toward the extracellular matrix. Ions (e.g., sodium, potassium): Also cannot cross the membrane directly and must This model illustrates the dynamic nature of the membrane, where proteins and use transporter proteins for movement in and out of the cell. lipids can move freely within the lipid bilayer. Membrane Function: Membrane Transport Fluid Mosaic Model Passive transport Fluid: there is lateral motion of components in the membrane; driven by a concentration gradient proteins, for example, "float" in the membrane and can move along its plane Simple Diffusion: Mosaic: components in the membrane exist side-by-side as separate entities ➔ Molecules move from a region of high concentration to a region of low the structure is that of a lipid bilayer with proteins, glycolipids, and steroids such concentration. as cholesterol embedded in it simple diffusion: a molecule or ion moves through an opening no complexes, as for example, lipid-protein complexes, are formed facilitated diffusion: a molecule or ion is carried across a membrane by a Notes: carrier/channel protein Lateral Movement: Refers to the movement of phospholipids within the same layer Active transport of the lipid bilayer, where a phospholipid can shift from one position to another a substance is moved AGAINST a concentration gradient within that layer. primary active transport: transport is linked to the hydrolysis of ATP or other high-energy molecule; for example, the Na+/K+ ion pump Proteins can float and move within the lipid bilayer alongside phospholipids. secondary active transport: driven by H+ gradient Although they are larger, they can still shift positions freely within the membrane's Notes: plane. Passive Transport: Similar to proteins, oligosaccharides and other membrane components can also Movement of molecules occurs due to a concentration gradient. move within the membrane structure without restriction. Molecules move from an area of higher concentration to an area of lower concentration. Fluid Mosaic Model of Membrane Structure Examples include: Simple Diffusion: Molecules or ions pass through a membrane opening without assistance. Facilitated Diffusion: Molecules or ions are transported across the membrane by a specific carrier or channel protein. Active Transport: Movement of molecules occurs against the concentration gradient. For example, moving sodium ions from inside the cell to the outside, despite a higher concentration of sodium outside. Requires the expenditure of energy to move substances against the gradient. Coupled Transport: Involves transporting a substance from inside the cell to the outside. This process is coupled with the transport of another substance from the outside to the inside. The transport of the second substance is spontaneous, naturally releasing energy. The energy released from the spontaneous transport is used to drive the nonspontaneous transport of the first substance from inside to outside the cell. This mechanism allows for the movement of substances against their concentration gradient by utilizing the energy from a favorable transport process. Passive Transport Passive diffusion of species (uncharged) across membrane dependent on concentration and the presence of carrier protein 1° Active transport Movement of molecules against a gradient directly linked to hydrolysis of high-energy yielding molecule (e.g. ATP) Notes: Notes: Example of Active Transport: Example of Glucose Transport: The transport of potassium (K⁺) and sodium (Na⁺) is facilitated by an integral The concentration of glucose in the blood is approximately 5 mM. membrane protein, often referred to as an ATPase. Inside a red blood cell, the concentration of glucose is less than 5 mM. The transport process requires energy in the form of ATP. A glucose transporter (glucose permease) is present in the red blood cell In this process, ATP is converted to ADP, releasing energy necessary for transport. membrane. This type of transport is known as primary active transport because it directly uses This transporter is specific and dedicated to glucose. energy from ATP to move ions against their concentration gradients. Glucose moves from an area of high concentration (blood) to an area of low concentration (inside the cell). This process is an example of facilitated diffusion because it utilizes a dedicated protein for the transport of glucose across the membrane.  Notes: Vitamin E: Functions as a powerful antioxidant. Commonly associated with products like Myer E, which markets its benefits, especially for women. Helps prevent visible signs of aging by scavenging free radicals, which can contribute to skin damage and aging. Membrane Receptors Antioxidants, including Vitamin E, are known for their role in promoting skin Membrane receptors health and reducing the appearance of aging. generally oligomeric proteins binding of a biologically active substance to a receptor initiates an action within Vitamin A the cell Vitamin A (retinol) occurs only in the animal world Extensively unsaturated hydrocarbon (ẞ-carotene) Vitamin A is found in the plant world in the form of a provitamin in a group of pigments called carotenes enzyme-catalyzed cleavage of ẞ-carotene followed by reduction gives two molecules of vitamin A Notes: Membrane receptors are specific to particular substrates. Upon binding of the substrate, these receptors undergo a structural change. This change in structure can initiate various cellular responses or signaling pathways. Notes: The enzyme in the liver acts on beta-carotene (or beta-chotin), converting it into Lipid-Soluble Vitamins retinol, which is also known as vitamin A. Vitamins are divided into two classes: This process is essential for the body as vitamin A plays a crucial role in vision, lipid-soluble and water-soluble immune function, and skin health. Vitamin A The best understood role of Vitamin A is its participation 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 Notes: (Biochemical Connections, p. 217) These three radicals contribute to the visible signs of aging by causing oxidative damage to cells and tissues. Vitamin D The radicals can lead to skin issues such as wrinkles, fine lines, and loss of A group of structurally related compounds that are involved in the regulation of elasticity, ultimately accelerating the aging process. calcium and phosphorus metabolism the most abundant form in the circulatory system is vitamin D3 Vitamin K Vitamin K has an important role in the blood-clotting process Long unsaturated hydrocarbon side consists of repeating isoprene units Vitamin E The most active of vitamin E is a-tocopherol Vitamin E is an antioxidant; traps HOO and ROO. radicals formed as a result of oxidation by O2 of unsaturated hydrocarbon chains in membrane phospholipids Prostaglandins Prostaglandins: a family of compounds that have the 20- carbon skeleton of prostanoic acid First detected in seminal fluid...from prostate The metabolic precursor is arachidonic acid (20 carbon atoms: 4 double bonds) Production of prostaglandins from arachidonic acid occurs in several steps. Notes:  Prostaglandins are chemicals involved in pain signaling in the body. Ibuprofen and other painkillers work by inhibiting enzymes that produce prostaglandins, specifically cyclooxygenases (COX). These enzymes convert arachidonic acid into prostaglandins, which are responsible for mediating pain and inflammation. By blocking the action of cyclooxygenases, painkillers reduce the formation of prostaglandins, thereby alleviating pain. Arachodonic Acid and Some Prostoglandins Notes: Lipids are primarily categorized based on their insolubility in water and solubility in organic solvents. They exhibit a diverse structure with no coherent pattern; their only common characteristic is their solubility properties. Despite their diversity, lipids play important roles in various biological processes: Vision: For example, vitamin A is crucial for eyesight. Cell Membrane Integrity: They help maintain the fluidity and structure of cell membranes. Notes: Production of Pain Chemicals: Lipids are involved in the synthesis of Arachidonic acid is oxidized into prostaglandins. pain mediators. The term "oxidized" refers to the introduction of double bonds and functional Immune Function: They are important for the action of leukocytes (white groups, such as carbonyl (C=O) and hydroxyl (–OH) groups. blood cells). This oxidation process is catalyzed by cyclooxygenases (COX). Nutritional Source: Lipids serve as es