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BIOL 103 Lecture Notes Jan 7

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BIOL 103
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Biology 103, Week of Jan 7 Nutrition & Digestion – Chapter 39 (Lecture Material & textbook) Types of Organisms: Autotroph: self-nutrition; harvest energy and store it (plants) Heterotroph: get complex nutrients from environment; eat other organisms for energy (higher trophic level) (animals) Q: How do heterotrophs get large organic compounds past the cell membrane? A: through digestion  Essential nutrients include: essential amino acids, essential fatty acids, minerals, and vitamins Essential Amino Acids  Easily obtained by carnivores, as meat contains all 20 amino acids Essential Fatty Acids  Polyunsaturated fats are found mainly in plants (herbivores/omnivores); also obtained from fish or tissue of birds and mammals Minerals  Very small amounts required every day; some minerals are secreted from bone (calcium) and other mineral storage areas into the blood Vitamins  Two types: fat soluble (already stored in body) and water soluble (must be ingested regularly – ex. Vitamin C)  Consists of enzymes to break down lipids, proteins, and nucleic acids by hydrolyzing the bonds o These enzymes consist of polysaccharidases, lipases, proteases, and nucleases  Once enzymes digest food, product like minerals, vitamins, and monomers of macromolecules must be absorbed by diffusion or active (energy dependent) transport – small, hydrophobic molecules use passive (or facilitated) diffusion down concentration gradients; minerals and ions actively diffuse; small hydrophilic nutrients use secondary active transport  Digestion is only needed to convert polymers into smaller units so that they may be absorbed across membranes Intracellular Digestion  Protozoa go through phagocytosis  We protect ourselves from microbes (disease causing) using phagocytosis, yet some have escape mechanisms  Phagocytosis is found in the immune system, and white blood cells are very important  In above image, food particle is taken into the cell membrane and surrounded by a vacuole (together called a food vacuole) o Exocytosis is the reverse process, when undigested food is released  Occurs in very simple invertebrates (single celled organisms, sponges)  Phagocytosis (absorption of solids as opposed to liquids) of food directly into food vacuoles in cells Extracellular Digestion (example: mold)  Fungi can also get nutrients from living animals  Fungi can be parasitic or predatory o Parasitic: Athlete’s foot extends fungi branches into foot cells o Predatory: Hyphae (branching filaments of fungus) penetrates nematode worm’s (dead or alive) body (by lassoing it), digestive enzymes are released, and extracellular digestion takes place  Protects cell interior from hydrolytic enzyme actions  Allows animals to consume large pieces of food  Food enters digestive cavity where it’s stored, digested, and absorbed very slowly (hours- weeks)  In Invertebrates: o Digestive cavity called gastrovascular cavity has one opening for entry and exit o Digested food phagocytised into gastrovascular cavity, then is digested intracellularly o Gastrovascular cavity also serves as circulatory (or vascular) system to distribute digested nutrients throughout the body o Food within cavity is partly digested enzymes that are secreted into cavity through lining o When food is small enough, phagocytosis takes place by lining and cells are digested intracellularly o Undigested material is expelled through cavity Digestion Mouth  Saliva contains proteins, mucus, antibacterial agents  When food enters mouth, saliva secretion increases (even by sight or smell of food)  Saliva moistens food, breaks down particles to assist taste buds, kills bacteria, and initiates digestion by secreting amylase, and enzyme  Starch digestion begins in mouth by salivary amylase (breaks down to maltose) Pharynx (Throat), Esophagus, Crop  Process of peristalsis begins – rhythmic waves of muscle contractions beginning near mouth, ending at stomach (helps grazing animals with head lower than stomach continue digesting) o The crop is a storage animal found in some invertebrates after the esophagus where little to no digestion occurs Stomach  When food enters, glands in stomach wall secrete “gastric juices”, HCl and pepsinogen (an inactive molecule) into the stomach lumen  HCl acid converts pepsinogen to the active enzyme, pepsin, which begins protein digestion (production of pepsinogen prevents pepsin from digesting cellular proteins)  Pepsin is an enzyme found in vertebrates, helps them adapt to carnivorous lifestyle  Pepsin is also a protease important for hydrolysis of proteins Why don’t cells in the stomach get hydrolyzed by pepsin and damaged by HCl? o Since pepsin is in its inactive form (zymogen) it is unable to hydrolyze cells o Stomach lining contains viscous mucous with a slightly basic pH (6) to protect lining, which has a resistant membrane regardless o HCl is actually created in the stomach through secretion of H+ and Cl- ions  HCl kills ingested microbes and alters ionization of proteins and makes them more accessible to pepsin  Food particles leaving stomach are called chyme – contains water (most abundant), salt, protein fragments, nucleic acids, polysaccharides, fat – none of these (excluding water) can pass through stomach lining, therefore little absorption occurs in stomach  No significant digestion of carbs or fat in stomach  Stomach’s acidity destroys/inactivates amylase and starch digestion stops here  Pepsin breaks down protein into peptide segments o In birds, stomach is divided into two parts – proventriculus and gizzard o Proventriculus is the glandular portion where acid and pepsinogen are secreted o Gizzard (also found in reptiles) is where partially digested food enters; rough inner lining and muscle grinds food into smaller pieces; tiny stones/sand swallowed by bird also found in gizzard, which act in place of teeth o Herbivores lack cellulase to digest cellulose, therefore, they rely on microbes in their stomachs to break down cellulose into monosaccharides o Some microbes are in the large intestine or cecum (between large and small intestine) Small Intestine  Most absorption happens here  Enzymes secreted by the pancreas, liver, and intestinal glands into the intestinal lumen (some already in lining of intestine) break down molecules into monosaccharides, nucleotides, monoglycerides, and amino acids o Intestinal glands secrete:  maltase – breaks maltose into glucose  proteases – enterkinase, aminopeptidase, dipeptidase which hydrolyze proteins o Pancreas secretes:  bicarbonate ions – restores pH  proteases – carboxypeptidase, trypsin, chymotrypsin(breaks down and elastase (breaks down trypsinogen into trypsin), elastase which hydrolyze proteins  pancreatic amylase – breaks starch into maltose  lipase – breaks fats into fatty acids and monoglycerides  nuclease – breaks nucle
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