1 Composición Química de los alimentos
Introduction to Biological Chemistry in Food Composition
Overview of the Seminar
- Lorena Balance introduces herself as a lecturer in biological chemistry, outlining the seminar's focus on food composition.
- The recommended readings include Antonio Blanco's "Biological Chemistry" and Feduchi's "Essential Biochemistry Concepts," emphasizing that the provided material is supplementary.
Composition of Foods
- Foods consist of proteins, carbohydrates, lipids, vitamins, and minerals; the seminar will detail their chemical composition and digestion processes.
- Discussion includes intestinal villi and enterocytes (absorptive cells), crucial for nutrient absorption at the intestinal mucosa.
Understanding Carbohydrates
Chemical Structure of Carbohydrates
- Carbohydrates are defined chemically by their composition of carbon, hydrogen, and oxygen; they can be classified as aldehydes or ketones based on functional groups.
- These compounds provide 50% to 60% of total caloric intake in humans; they are categorized into monosaccharides, oligosaccharides, and polysaccharides.
Classification of Carbohydrates
- Monosaccharides consist of single sugar units; oligosaccharides contain 2 to 10 monosaccharide units; polysaccharides are larger chains formed from many monosaccharides.
- Monosaccharide naming conventions involve suffixes indicating their structure (e.g., "-ose" for sugars).
Isomerism in Sugars
Types of Monosaccharides
- Monosaccharides can be classified based on carbon count and functional group: aldoses have an aldehyde group while ketoses have a ketone group.
- Examples include aldohexoses (six carbons with an aldehyde group) and ketohexoses (six carbons with a ketone group).
Optical Isomerism
- Glucose is presented as an example with three carbon atoms featuring a chiral center that leads to two optical isomers: D-glucose (right-handed rotation) and L-glucose (left-handed rotation).
- Both isomers are mirror images but differ in how they rotate polarized light.
Functional Groups in Carbohydrates
Formation of Glycosidic Bonds
- The presence of hydroxyl (-OH) groups allows carbohydrates to form glycosidic bonds through condensation reactions between sugars.
Understanding Glucose and Its Derivatives
Structure of Glucose
- Glucose has an anomeric carbon at position 1, which can have a hydroxyl group oriented either upwards (beta form) or downwards (alpha form).
- The anomeric carbon also possesses potential aldehyde functionality, contributing to the reducing capacity of certain sugars.
- In its linear structure, glucose consists of six carbon atoms with an aldehyde group at carbon 1 and a hydroxyl group at carbon 3 positioned to the left.
Cyclic Forms of Monosaccharides
- The cyclic forms include alpha-glucose (hydroxyl down) and beta-glucose (hydroxyl up), both derived from the reaction between carbon 1 and carbon 5.
- Other monosaccharides like mannose differ in configuration at specific carbons; for instance, mannose has hydroxyl groups on carbons 2 and 3 oriented upwards.
Variations Among Sugars
- Galactose is another derivative differing from glucose by its configuration at carbon 4, affecting how it forms cyclic structures.
- Fructose is classified as a ketohexose with a ketone group on carbon 2, leading to a pentagonal ring structure known as furanose.
Disaccharides: Key Examples
- Maltose is formed from two glucose units linked by an alpha(1→4) glycosidic bond after losing a water molecule during formation.
- Lactose consists of galactose and glucose connected via a beta(1→4) glycosidic bond, making it a reducing sugar due to its free aldehyde group.
Complex Carbohydrates: Polysaccharides
- Sucrose comprises one glucose and one fructose unit linked through an alpha(1→2) bond; this linkage prevents it from exhibiting reducing properties.
Understanding Starch and Its Components
Structure of Starch: Amylose and Amylopectin
- Both amylose and amylopectin are glucose polymers, differing in structure and properties. Starch typically consists of 20% amylose and 80% amylopectin.
- Amylose is composed of glucose units (1000 to 5000) linked by alpha-1,4 glycosidic bonds, forming a helical structure.
- Amylopectin has a larger molecular size (approximately 600,000 glucose units), featuring branched structures with both alpha-1,4 and alpha-1,6 linkages.
Comparison with Glycogen
- Glycogen serves as the primary storage polysaccharide in animal cells, resembling amylopectin but with more frequent branching due to closer proximity of branches (less than 10 glucose units apart).
- The compactness of glycogen's structure results from its numerous branches compared to amylopectin.
Cellulose: Structural Differences
- Cellulose primarily serves structural functions in plants; it comprises glucose units linked by beta-1,4 glycosidic bonds.
- Unlike starch or glycogen, cellulose forms linear structures that cannot be digested by human enzymes due to the type of bond present.
Digestion Process of Carbohydrates
- In the mouth, starch is initially broken down by salivary amylase which cleaves alpha-1,4 bonds. No significant changes occur in the stomach regarding carbohydrates.
Absorption Mechanism
Understanding Lipids and Fatty Acids
Transport Mechanisms of Nutrients
- The transport of nutrients, including lipids, is facilitated by specific proteins at the apical membrane level, particularly through a protein known as blood 5.
- Lipids are essential components of living organisms, playing critical roles in cellular membranes and serving as significant energy reserves.
Importance of Lipids
- They are crucial for nutrition due to their high caloric content and involvement in various physiological activities such as hormones, vitamins, and bile acids.
- Lipids can be categorized into simple (e.g., triglycerides) and complex types (e.g., phospholipids), with fatty acids being fundamental structures within all lipid categories.
Structure of Fatty Acids
- Fatty acids are linear carboxylic acid chains that typically contain an even number of carbon atoms ranging from 4 to 26. They can be saturated or unsaturated.
- Saturated fatty acids have carbon molecules fully saturated with hydrogen atoms, while unsaturated fatty acids contain double bonds indicating a lack of hydrogen saturation.
Classification of Unsaturated Fatty Acids
- Unsaturated fatty acids are classified based on the number of double bonds: mono-unsaturated (one double bond) or polyunsaturated (multiple double bonds).
- The numbering system for fatty acids starts from the carboxyl carbon (carbon 1), with subsequent carbons designated using Greek letters for clarity.
Characteristics and Properties
- The solubility of fatty acids is influenced by chain length; longer chains tend to be less soluble in water.
- Melting points increase with chain length; saturated fats become solid at higher temperatures compared to unsaturated fats which remain liquid due to their structure.
Geometric Isomerism in Fatty Acids
- Saturated fatty acids exhibit a linear conformation while unsaturated ones can present geometric isomerism (cis or trans forms). Most natural unsaturated fats exist in the cis configuration.
Understanding Fatty Acids and Their Structures
Configuration of Fatty Acids
- The configuration of fatty acids can lead to a bend in the molecule; for example, trans-configured fatty acids do not form this bend due to their double bond structure.
Saturated vs. Unsaturated Fatty Acids
- Saturated fatty acids pack neatly in a crystalline order, influenced by carboxyl groups oriented towards the hydrophilic region.
- The presence of one or more double bonds in unsaturated fatty acids results in less stable packing compared to saturated ones.
Properties Influenced by Carboxyl Group
- The properties of fatty acids depend on the carboxyl group, which imparts acidic characteristics; as carbon chain length increases, solubility and acidity decrease.
- Salts (soaps) are formed when hydrogen from the carboxyl group is replaced by a metal; esters form through reactions with alcohol.
Oxidation and Hydrogenation
- Unsaturated fatty acids are more easily oxidized than saturated ones; however, saturated fats are more useful industrially due to hydrogenation processes that add hydrogen to double bonds.
Glycerol and Its Role in Lipid Formation
Glycerol Structure and Functionality
- Glycerol combines with fatty acids through hydroxyl groups forming ester linkages; if all fatty acids are identical, they create simple triglycerides (triglycerides).
Types of Triglycerides
- Different combinations of glycerol and varying fatty acids result in mixed triglycerides; these can be mono-, di-, or tri-glycerides based on the number of attached fatty acid chains.
Cholesterol: Structure and Importance
Cholesterol Characteristics
- Cholesterol is a prevalent sterol in animal tissues, crucial for physiological functions; its structure includes specific methyl groups and a hydroxyl group at designated carbons.
Digestion of Lipids
- Total hydrolysis isn't essential for fat absorption; most dietary fats degrade into monoglycerides before entering intestinal cells.
Lipid Absorption Mechanisms
Digestive Process Overview
- Lipid digestion primarily occurs in the intestines facilitated by bile salts and pancreatic lipase, breaking down triglycerides into monoglycerides and free fatty acids.
Enzymatic Action on Lipids
- Complete hydrolysis requires an isomerase enzyme converting monoglycerides into diglycerides for further degradation by lipases.
Final Steps in Lipid Absorption
Membrane Transport and Fatty Acid Processing
Mechanisms of Fatty Acid Absorption
- Some products can cross membranes via simple diffusion, while specific transport systems exist at the apical membrane for long-chain fatty acids.
- Small amounts of free fatty acids (10 carbons or less) can be released into the intestinal lumen through digestion but diffuse passively into capillaries without incorporation.
Synthesis of Triacylglycerols and Lipids
- Fatty acids must be activated by coenzyme A through acyl-CoA synthetase in the presence of ATP to synthesize triacylglycerols.
- Newly formed lipids, including cholesterol and phospholipids, aggregate into chylomicrons that enter lymphatic vessels; over 70% of lipids absorbed by intestinal mucosa follow this pathway.
Overview of Protein Structure
Amino Acids: Building Blocks of Proteins
- Proteins consist of structural subunits called amino acids, which contain a carbon atom bonded to various groups: hydrogen, carboxyl group, amino group, and a unique side chain (R).
- Amino acids are classified as essential (not synthesized by the body and must be obtained from diet) or non-essential (can be synthesized).
Essential vs. Non-Essential Amino Acids
- Essential amino acids are crucial during periods of rapid growth such as childhood or pregnancy; arginine is conditionally essential under certain circumstances.
- The remaining essential amino acids include leucine, isoleucine, valine, tryptophan, phenylalanine, and methionine.
Classification Based on Chemical Structure
Types of Amino Acids
- Amino acids can be categorized based on their chemical structure; glycine has a unique structure with only one hydrogen atom in its side chain.
- Aliphatic amino acids have non-polar carbon chains; examples include alanine and leucine.
Polar vs. Nonpolar Characteristics
- Neutral aliphatic amino acids may possess hydroxyl groups that confer polar characteristics; serine is an example with such properties.
Aromatic and Sulfur-containing Amino Acids
Properties of Aromatic Amino Acids
- Aromatic amino acids like tryptophan contain cyclic structures; phenylalanine is also included in this category due to its aromatic ring.
Basic Amino Acids
Amino Acids and Protein Structure
Overview of Acidic Amino Acids
- The group of acidic amino acids includes glutamic acid and aspartic acid, which possess a carboxyl group that allows them to release protons and acquire a negative charge in biological fluids.
- Derivatives of these amino acids include asparagine and glutamine, which play significant roles at the distal carbon from the alpha carbon.
Unique Amino Acids
- Proline is highlighted as an amino acid with a unique structure involving nitrogen within its ring, along with hydroxyproline, which some authors classify differently due to its hydroxyl group.
- Choline is also mentioned as an amino acid due to its structural characteristics.
Peptide Bond Formation
- Amino acids can form covalent bonds between the carboxyl group of one and the amine group of another, resulting in peptide bonds through dehydration synthesis (water molecule removal).
- The union of two amino acids forms a dipeptide; multiple such unions create polypeptides, defined as chains longer than ten amino acids.
Proteins: Definition and Examples
- Polypeptides with molecular weights over 6000 Da are classified as proteins. Examples include enzymes, hormones, hemoglobin, antibodies, actin, myosin, and collagen.
- Proteins consist primarily of carbon, hydrogen, oxygen, nitrogen atoms; many also contain sulfur. They serve critical physiological functions including nerve transmission and enzymatic catalysis.
Functions of Proteins
- Proteins have diverse roles such as mechanical support for cells/tissues, immune protection mechanisms, hormonal regulation (as receptors or channels), muscle contraction/motility regulation.
Protein Structure Levels
Primary to Quaternary Structures
- The primary structure refers to the sequence of amino acids; secondary structures involve specific spatial arrangements like alpha helices or beta sheets.
- Tertiary structures arise from interactions stabilizing protein shape while quaternary structures involve multiple subunits interacting weakly.
Stabilizing Interactions in Protein Structure
- Hydrogen bonds are crucial for maintaining helical conformations in proteins. These occur between donor hydrogen molecules and acceptor groups.
Types of Interactions in Tertiary Structure
Hydrophobic vs. Hydrophilic Interactions
- Tertiary structure stabilization involves hydrophobic interactions (nonpolar side chains clustering inward), van der Waals forces, and electrostatic interactions among polar groups on protein surfaces.
Examples: Globular vs. Fibrous Proteins
Structural Differences
- Comparison between globular proteins (e.g., lysozyme with a compact shape) versus fibrous proteins (e.g., collagen exhibiting elongated fibers). These differences stem from their tertiary structures.
Protein Digestion Process
Enzymatic Breakdown
Understanding Protein Digestion and Vitamin Absorption
Protein Digestion Process
- The pancreatic carboxypeptidase and intestinal enzymes work together to hydrolyze dietary proteins into their constituent amino acids. Some proteins, like elastin, are resistant to digestion.
- Approximately 40% of ingested proteins are broken down into free amino acids by gastric and pancreatic proteases, while the remaining 70% is converted into oligopeptides that further interact with brush border peptidases.
- After protein degradation, small peptides and free amino acids are transported through specific transporters in the enterocytes' apical membrane for absorption.
- Other transporters on the microvilli membranes facilitate the absorption of small peptides and intracellular degradation of amino acids before they enter blood capillaries.
Vitamins: Essential Nutrients
Overview of Vitamins
- Vitamins are organic compounds found in natural foods in small amounts; they cannot be synthesized by the body. Deficiencies lead to avitaminosis.
- Vitamins can be categorized as fat-soluble (A, D, E, K) or water-soluble (B complex and C).
Vitamin A Details
- Vitamin A exists in two natural forms (A1 and A2), sourced from foods like spinach, carrots, tomatoes, etc., requiring emulsification by bile salts for absorption.
- Retinol must be degraded by esterases to release fatty acids for absorption at the enterocyte level. It binds with retinol-binding protein for transport in blood.
Vitamin D Metabolism
- The synthesis of vitamin D involves hepatic and renal processes for activation. Its role in intestinal absorption is crucial alongside its extra-classical effects on health.
Vitamin E Properties
- Vitamin E sources include oils from corn, peanuts, soybeans, etc. Like other fat-soluble vitamins, it requires bile presence for proper digestion and absorption.
Functions of Fat-Soluble Vitamins
Immunomodulatory Effects of Vitamin E
- Vitamin E has immunomodulatory properties affecting macrophages and various immune cells.
Importance of Vitamin K
Vitamin K and Its Role in Coagulation
Importance of Vitamin K
- Vitamin K is essential for the synthesis of coagulation factors, including prothrombin (factor 2), factor 7, factor 9, and factor 10, which are crucial for blood coagulation.
- These proteins are synthesized in the liver as inactive precursors and require post-translational modifications to become active.
- One key modification involves the carboxylation of glutamic acid residues, converting them into gamma-carboxyglutamate, necessary for normal coagulation cascade function.
- A deficiency in vitamin K leads to increased bleeding tendencies and slower clotting times.
B Vitamins Overview
Key B Vitamins
- The B vitamin complex includes thiamine (B1), riboflavin (B2), pantothenic acid (B5), pyridoxine (B6), biotin, folic acid, and cobalamin (B12).
Thiamine (Vitamin B1)
- Thiamine is water-soluble and widely distributed in natural sources; it plays a critical role in carbohydrate metabolism through its conversion to thiamine pyrophosphate.
Cobalamin (Vitamin B12)
- Cobalamin is vital for converting homocysteine to methionine; deficiencies can lead to elevated homocysteine levels and megaloblastic anemia due to impaired folate metabolism.
Absorption and Storage of Vitamins
Mechanisms of Absorption
- Vitamin B12 requires intrinsic factor from gastric parietal cells for absorption at the ileum; it is stored primarily in the liver before distribution throughout the body.
- Unlike other water-soluble vitamins, some can be stored in the liver.
Role of Vitamin C
Functions of Vitamin C
- Vitamin C is crucial for maintaining capillary integrity and plays a significant role in cartilage metabolism through hydroxylation reactions.
Minerals: Functions and Regulation
Essential Minerals Overview
- Various minerals have specific functions within the body; their dietary intake must be balanced with hormonal regulation affecting their absorption and elimination.
Calcium Metabolism
- Calcium and phosphorus metabolism are regulated by hormones such as parathyroid hormone and vitamin D, impacting bone health.
Sodium's Role
- Sodium regulates total body water content and central nervous system function; its levels are controlled mainly by renal excretion influenced by systems like renin-angiotensin.
Potassium Regulation
Importance of Hormonal Regulation and Trace Elements
Hormonal Regulation and Vitamins
- The significance of hormonal regulation is emphasized, particularly in relation to physiological balance within the organism.
- Vitamins play a crucial role in achieving this physiological equilibrium, highlighting their importance for overall health.
Role of Trace Elements
- Trace elements such as copper and molybdenum are identified as essential components in various metalloproteins and enzymes.