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Digestion and Absorption of the Food Nutrients Chapter 3 Nutrient Digestion and Absorption Hydrolysis reactions • Catabolic Breakdown Split of chemical bonds • • Separates water molecules into • H+ - hydrogen ions • OH- - hydroxyl ions These ions then added to by-products of reaction Hydrolysis Nutrient Digestion and Absorption Hydrolysis reactions • Examples: Polysaccharides (starches) to disaccharides to monosaccharides Proteins to amino acids Lipids to glycerol and fatty acids Nutrient Digestion and Absorption Condensation reactions • • • Anabolic (building up) Join H+ and OH- to form a water molecule Source of metabolic water Condensation Enzymes Accelerate chemical reactions Reusable Specific protein catalyst Reduce activation energy (energy input) Enzymes don’t get changed during the reaction Substrate Any substance acted upon by an enzyme Lock and Key Mechanism Coenzymes Coenzymes Facilitate enzyme action Nonprotein Additional ions (minerals) Smaller organic molecules (like B-vitamins) Coenzymes Coenzymes Temporary carrier NAD+ NADH Carry electrons and H+ This carrier allows the enzymes of the electron transport chain to extract the electrons and H+ Passive Transport Cell membranes Selectively permeable Maintain consistency in chemical composition Passive Transport (4 types-does not require energy input) Simple diffusion Facilitated diffusion Osmosis Filtration Simple Diffusion Continuous molecular movement Higher to lower concentration Until they are evenly dispersed Examples Almost all gases Ex. Oxygen, Carbon dioxide Concentration gradients allow movement of gases Facilitated Diffusion Membrane proteins Channels in cell membrane Open under specific conditions Chemical messenger Ions ( + or - ) Neurotransmitter Voltage gated channels Thus, they facilitate the movement of molecules Facilitated Diffusion Examples Glucose Lipid insoluble Uncharged Binds to site on membrane Structural change Osmosis Water moves based on differences in solute concentration It can move freely between these compartments Intracellular Extracellular Plasma Osmosis Osmolality Concentration of dissolved particles in a solution • Isotonic solution • Hypertonic • No gain or loss of water between cells and fluid surrounding them Higher solute concentration outside cell than inside (causes cell to shrink) Hypotonic Higher water concentration outside cell than inside (causes cell to swell) Osmolality Filtration Hydrostatic pressure Pressure in blood stream is higher than surrounding tissues Causes flow of fluid from capillaries to interstitial space Higher protein content in plasma Osmotic pressure causes absorption of interstitial fluid back into capillaries Filtration Active Transport Requires energy (ATP) Ex. Sodium-Potassium Pump Moves ions against electrochemical gradients Sodium-potassium ATPase Sodium-Potassium Pump Na+ leak into cell Action potential Depolarization K+ moves out to reestablish charge Sodium-potassium pump “resets” cell to resting gradients Coupled Transport Linked, simultaneous transport Two substances Across cell membrane Same direction – symport Opposite directions – antiport Coupled Transport Bulk Transport Movement of large particles and molecules Exocytosis Hormones, Neurotransmitters, Secretions, wastes ICF to ECF Stages Enclosed in pouch Pouch migrates to membrane Contents ejected into ECF Bulk Transport Endocytosis Water, lipids Plasma membrane of cell surrounds substance Pinches away Moves into cytoplasm http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437 316/120068/bio02.swf::Endocytosis%20and%20Exocytosis Acid-Base Concentrations Acid: any substance that dissociates (ionizes) in solution and releases hydrogen ions (H+) Base: any substance that picks up or accepts H+ to form hydroxide ions (OH) in water solutions pH: provides a quantitative measure of the acidity or alkalinity (basicity) of a liquid solution Acid-Base Concentrations pH 1.0 to 14.0 Examples HCl – 1.0 (acid) Blood – 7.4 Lye – 14.0 (base) Acid-Base Concentrations Enzymes Activated/inactivated by pH Example Salivary amylase Mouth Inactivated by stomach pH Denatured Acid-Base Concentrations Chemical buffers • Use a base to “neutralize” an acid Acid + base → weaker acid → dissociates into harmless or less harmful products Acid-Base Concentrations Ventilatory buffer • Increases or decreases in pulmonary ventilation Lactic acid (Hla) • • • H+ + LaH+ + HCO3- → H2CO3 → CO2 + H2O Tissues → Lungs Acid-Base Concentrations Renal buffer • Kidneys excrete or conserve H+ to maintain acid–base stability of body fluids