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  Specific protein catalyst  Reduce activation energy (energy input)  Reusable  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

 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  Neurotransmitter Ions ( + or - )  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 No gain or loss of water between cells and fluid surrounding them Hypertonic 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 re- establish 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  hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/ /120068/bio02.swf::Endocytosis%20and%20Exocytosis hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/ /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 + + La - H + + HCO 3 - → H 2 CO 3 → CO 2 + H 2 O Tissues → Lungs

Acid-Base Concentrations  Renal buffer Kidneys excrete or conserve H + to maintain acid–base stability of body fluids