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Ch.1: Transformation of Food into Nutrients ;Digestive System 1 What does your food include ????? Inorganic Water Organic Salts Vitamins Bases Acids 2 Macromolecules Carbohydrates Lipids Proteins Nucleic Acids 3 Some molecules are called macromolecules because of their large size. Usually consist of many repeating units. Resulting molecule is a polymer (many parts). Repeating units are called monomers. Some Examples: Category Example Subunit Carbohydrates Polysaccharide Monosaccahrides Lipids Fat Fatty acids + glycerol Proteins Polypeptide Amino Acids Nucleic Acids DNA, RNA Nucleotides 4 Monomers • Smaller units 5 Polymers • Linked up monomers 6 Synthesis & Degradation Synthesis Reactions (Dehydration‐Removal of water molecule) – Used to connect monomers together to make polymers – Example: Polymerization of glucose monomers to make starch Degradation Reactions (Hydrolysis‐Addition of water molecule) – Used to disassemble polymers into monomer parts – Digestion of starch into glucose monomers Specific enzymes required for each reaction – Accelerate reaction – Are not used in the reaction 7 Synthesis and Degradation of Maltose, a Disaccharide 8 Four Classes of Organic Macromolecules: 1 ‐ Carbohydrates Monosaccharides: – Single sugar molecule – Glucose, ribose, deoxyribose Disaccharides: – Contain two monosaccharides joined during dehydration reaction – Sucrose Polysaccharides: – Polymers of monosaccharides – Starch, cellulose, chitin 9 Carbohydrates: Monosaccharides Single sugar molecules Quite soluble and sweet to taste Examples: • Glucose (blood), fructose (fruit) and galactose Hexoses ‐ Six carbon atoms Isomers of C6H12O6 • Ribose and deoxyribose (in nucleotides) Pentoses - Five carbon atoms C5H10O5 & C5H10O4 10 Carbohydrates : Disaccharides Contain two monosaccharides joined by dehydration reaction. Soluble and sweet to taste. Examples: • Sucrose – Table sugar, maple sugar – One glucose and one fructose joined by dehydration • Maltose – Malt sugar – Two glucoses joined by dehydration 11 Carbohydrates : Polysaccharides Polymers of glucose (monosaccharide) Low solubility; not sweet to taste Used for short‐term energy storage Examples – Starch (plant polysaccharide) as in potatoes & corn – Glycogen (animal polysaccharide) stored in animal’s liver & muscles 12 Starch Glucose 13 Polysaccharides More polysaccharide examples • Cellulose Structural element for plants Main component of wood and many natural fibers Indigestible by most animals • Chitin Very resistant to wear and digestion Arthropod exoskeletons, cell walls of fungi 14 Four Classes of Organics: 2 ‐ Lipids Insoluble in water Long chains of repeating CH2 units Renders molecule nonpolar Types of Lipids: Type Organismal Uses Human Uses Fats Long-term energy storage & thermal insulation in animals Butter, lard Oils Long-term energy storage in plants and their seeds Cooking oils Phospholipids Component of plasma membrane Non-stick pan spray Steroids Component of plasma membrane; hormones Medicines Waxes Wear resistance; retain water Candles, polishes 15 Types of Lipids: Triglycerides Triglycerides (Fats) Long‐term energy storage Backbone of one glycerol molecule o Three‐carbon alcohol o Each has an OH‐ group Three fatty acids attached to each glycerol molecule Long hydrocarbon chain o Saturated ‐ no double bonds between carbons o Unsaturated ‐ 1 or more double bonds between carbons 16 Types of Lipids 17 Dehydration Synthesis of Triglyceride from Glycerol and Three Fatty Acids 18 Types of lipids: Phospholipids Derived from triglycerides - Glycerol backbone - Two fatty acids attached instead of three - Third fatty acid replaced by phosphate group o The fatty acids are nonpolar and hydrophobic o The phosphate group is polar and hydrophilic Molecules self arrange when placed in water - Polar phosphate “heads” next to water - Nonpolar fatty acid “tails” overlap and exclude water - Spontaneously form double layer & a sphere 19 Phospholipids Form Membranes 20 Four Classes of Organics: 3 ‐Proteins Functions: Support – Collagen Enzymes –Almost all enzymes are proteins Transport – Hemoglobin; membrane proteins Defense – Antibodies Hormones –Many hormones; insulin Motion –Muscle proteins, microtubules 21 Amino Acids Proteins are polymers of amino acids. Each amino acid has a central carbon atom (the alpha carbon) to which are attached: - a hydrogen atom, - an amino group –NH2, - a carboxylic acid group –COOH - one of 20 different types of – R groups There are 20 different amino acids that make up proteins. All of them have basically the same structure except for what occurs at the placeholder R. 22 20 Amino Acids 23 The Polypeptide Backbone • Amino acids joined together end‐to‐end – COOH of one AA covalently bonds to the NH2 of the next AA – Special name for this bond ‐ Peptide Bond • Two AAs bonded together – Dipeptide • Three AAs bonded together – Tripeptide • Many AAs bonded together – Polypeptide – Characteristics of a protein determined by composition and sequence of AA’s – Virtually unlimited number of proteins 24 Synthesis and Degradation of a Peptide 25 What does your digestive system look like? The tube starts here: And although there are a few twists and turns along the way… It comes out here: Anything that goes in the top hole (mouth) does not become part of the body until it is broken down then absorbed though a series of specialized structures. 26 What does the digestive system do? • INGESTION: – Eating or taking in the food • DIGESTION: – Mechanical vs. chemical digestion • Mechanical is breaking the food into smaller pieces • Chemical is using enzymes and chemical reactions to break apart the molecule • ABSORPTION: – Moving the broken down food into the blood or the lymph to be carried around the body • ELIMINATION: – Getting rid of anything that you can’t digest 27 Label the Digestive System Mouth Tongue Salivary glands Oral cavity Pharynx Esophagus Stomach Pyloric sphincter Liver Gall-bladder Pancreas Small intestine Large intestine Anus Rectum 28 29 Mouth • The part where digestion starts • Tongue – moves around the food and forms a bolus (a ball of food) • Contains the digestive juice saliva that is produced by the salivary glands. 30 • What’s in saliva and what does it do? • Water – Makes food soft • Mucus – Helps food slide down the esophagus • Bicarbonate ions – neutralize acid produced by bacteria (helps prevent tooth decay) • Salivary amylase – breaks down starch in the presence of water – Starch maltose (a disaccharide of glucose) How much saliva do you produce in a day? About 1-2 litres! 31 Traveling to the stomach… • Esophagus – Tube from pharynx to stomach – It has: • Mucus membranes – Helps the food slide down • Muscle – Pushes the food down the tube • Food moves down by peristalsis 32 Reaching the stomach… • Bolus arrives at the cardiac sphincter – This is the “door” at the top of the stomach – Made of muscle • What is heartburn and what causes it? • Opening of the cardiac sphincter allowing food (soaked in stomach acid) to enter the esophagus. http://www.youtube.com/watch?v=1ZIK6Ua20JA 33 The Stomach • How big is your stomach? – About 1.5 to 2L in an adult human (300L in a cow!) This is a rabbit stomach 34 The Stomach • J-shaped organ • Three layers of muscle – Mix up and break up the food • Gastric glands make gastric juice • Gastric juice has: – Pepsinogen + Hydrochloric acid Pepsin • PEPSIN • an enzyme it breaks down proteins into peptides (small protein sections) 35 Within the walls of the stomach… Pepsinogen Pepsin HCl (Activates more Pepsinogen) Gastric gland Mucus cell (shown in red) Parietal Cell Peptic cell 36 Why doesn’t the stomach digest itself? • HCl could eat through the stomach Stopped by the mucus layer • Pepsin could digest protein in the stomach cells Pepsin is only made when pepsinogen mixes with HCl Stopped by the mucus layer 37 When things go wrong… • Bacterial infections – Cells can’t make mucus – Can cause ulcers and stomach cancer http://www.youtube.com/watch?v=1ZIK6Ua20JA&feature=channel_page 38 • How long does food stay in your stomach? – 2 - 6 hours • Chyme = liquid food that leaves your stomach • Enters the small intestine controlled by the PYLORIC SPHINCTER “Door” of muscle at the bottom of the stomach 39 Small intestine • Most of digestion and absorption of nutrients occur here • How long is your small intestine? About 6m (20 feet!) 40 Small intestine zones • 3 Zones: – Duodenum, Jejunum, Ilium • First 25 cm is the duodenum • 3 helping organs secrete liquids to the duodenum: – 1. Liver – 2. Pancreas – 3. Gall Bladder 41 How it all fits together… 42 Liver • produces bile (up to 1.5L per day!), stored in the Gall Bladder – a thick green liquid – breaks fat into droplets • What kind of digestion does bile perform? – Mechanical or Chemical? 43 The Pancreas • Connected to the duodenum by a duct • Pancreatic juice has: – Sodium bicarbonate neutralizes the acidic chyme – Enzymes to further break down food • Pancreatic amylase Starch maltose • Trypsin Protein peptides • Lipase Fats glycerol and 3 fatty acids 44 Fats break down to molecular level! Lipase Fatty Acid Glycerol Fatty Acid Fatty Acid Fat Fatty Acids and Glycerol 45 Intestinal Glands • Cells lining the small intestine provide the rest of the enzymes we need – Peptidases break down proteins – Maltase breaks down maltose • Other disaccharides are also broken down, e.g. lactase breaks down lactose – Nucleosidases breaks down nucleotides 46 Digestive Enzymes from the Interstitial glands Maltase Glucose Maltose Peptidase Peptide Amino Acids 47 Inside the small intestine • Large folds line the intestine • Villi stick out from the folds • Microvilli stick out from the villi ~600m2= LOTS of surface (size of a baseball diamond) area 48 The Villi Outer wall Pathway for Food Inner wall 49 Villi • Each villus has a very thin layer of cells around it (epithelium) • A lymphatic vessel called a lacteal is at the centre • Blood capillaries surround the lacteal 50 Absorbing nutrients • Fatty acids and glycerol are absorbed recombine into fat molecules in the epithelial cells • Fats then move into the lacteal and enter the Lymphatic System 51 Absorbing nutrients • sugars and amino acids enter the blood How long is “food” here? Up to 4 hours 52 A close up look at villi 53 Large Intestine • Consists of the colon, the rectum and the opening at the end, the anus. • Colon has 3 parts – ascending – transverse – descending • How long is it? – About 1.5m long (about 5 feet) – Last 20 cm is the rectum 54 Humans have a short caecum (blind pouch) at the start of the large intestine. The appendix is a vestigial organ (not needed). 55 What does the large intestine do? • Reapsorption of water • Absorption of certain vitamins • Also contains: bile pigments, heavy metals, and billions of E. coli (providing colour and odour) • What do E. coli do for you? – break down some indigestible food – produce some vitamins, amino acids, and other growth factors 56