Chapter 33 Animal Nutrition Study Questions Terms 1 Describe our food in terms of the four groups of macromolecules carbs fats proteins and nucleic acids how does this relate to the same groups of macromolecules that our bodies are made of Among other types of molecules our food consists of proteins carbohydrates fats and nucleic acids in varying amounts Proteins are found in the contractile proteins of meat and the storage proteins found in grains seeds eggs and milk Digestion breaks proteins down to amino acids which are used as building blocks to build all the proteins we need in our bodies or in the synthesis of other molecules As a last resort proteins are used as an energy source Carbohydrates are found primarily in the storage organs of plants starch phloem sap sucrose and fruits seeds Vegetables and fruits also contain a great deal of cellulose a structural carbohydrate Human digestion breaks down starch and sucrose to glucose but cellulose remains undigested chemically and is a source of fiber Glucose is the preferred energy source for the production of ATP for all cells but it can be used as a carbon skeleton for the synthesis of other molecules Excess glucose is stored in the human body as glycogen in the liver and skeletal muscle after these stores are full glucose is converted into triglycerides and stored in adipose tissue Fats are found in meat and milk saturated plant seeds and some fruits unsaturated where they function as sources of stored energy Digestion breaks down triglycerides to fatty acids and glycerol which are absorbed into the lymphatic system and then the blood Fats are a good source of energy for ATP production in humans Excess fat in the diet is reformed into triglycerides and stored in adipose tissue Meat and milk are sources of cholesterol which is carried in the blood in the form of LDL and HDL particles to and from the body tissues respectively Finally meat muscle is a source of abundant nucleic acids which break down to nucleotides and then sugar phosphate and nitrogenous base Sugar and phosphate are used to synthesize other needed molecules and bases are broken down to uric acid and other nitrogenous wastes or recycled into other nitrogen containing molecules 2 How Why do we not digest ourselves Chemical digestion takes place in separate compartments protected by a thick secretion of mucus The main concern is inappropriate digestion of proteins Protein digesting enzymes are secreted in inactive form as zymogens and are activated only when they are safely away from organs or ducts which they might digest 3 Why do we need digestive enzymes Digestive enzymes are needed to accelerate the breakdown of large macromolecules via catalysis of spontaneous or non spontaneous reactions 4 When does something we have eaten become part of our bodies Explain Our food becomes part of our bodies only when it is absorbed through the epithelial lining of the small intestine primarily as well as the stomach a bit 5 Why can t animals use the macromolecules in their food directly The macromolecules in food are too large to be absorbed across the epithelial cells of the digestive tracts Also the proteins we ingest are not necessarily the same proteins we need to build and repair our bodies and make it work e g enzymes etc 6 List and describe all the characteristics of saliva and their roles in the digestive process Saliva contains mucin a slimy substance that helps bind food particles into a bolus for swallowing saliva is alkaline to buffer ingested food which tends to be acidic saliva contains lysozyme an enzyme which hastens the lysis of bacteria in our food saliva contains amylase an enzyme that catalyzes the breakdown of food starch into glucose monomers 7 How does swallowed food reach the stomach of a weightless astronaut in orbit A bolus of food is pushed into the pharynx by the tongue The esophageal sphincter opens and permits the bolus to enter the esophagus Peristaltic contractions of the two layers circular and longitudinal of smooth muscle of the esophagus push the bolus past the cardiac sphincter and into the stomach This process is identical with or without gravity 8 Explain why a proton pump inhibitor such as the drug Prilosec relieves the symptoms of gastric reflux A proton pump inhibitor decreases the production of HCl in the stomach the chyme is therefore less acidic and less irritating when it enters the esophagus during acid reflux 9 What would happen if you mixed gastric juice with crushed food in a test tube Gastric juice would begin the digestion of proteins contained in the crushed food first by denaturing them HCl and then hydrolyzing them to smaller polypeptides pepsin 10 Differentiate between the main sections of the small intestine include length names and functions of each section The first section is the duodenum which is about 25 cm long it receives acid chyme from the stomach and mixes it with pancreatic juice from the pancreas and bile from the liver These digestive juices enter the duodenum via the common duct The jejunum is the next section of the SI and it is 2 5 meters long its role is primarily absorptive The ileum is the longest section at 3 5 meters its role is also absorption and it empties into the colon of the large intestine 11 What are the main functions of the colon The colon is the site where water and minerals are extracted and reabsorbed from indigestible food remnants Resident bacteria such as E coli synthesize vitamins also absorbed through the large intestinal epithelium 12 Differentiate elimination excretion Elimination is the evacuation of indigestible remains feces of the food that has been processed by the digestive tract or alimentary canal Excretion is the elimination of nitrogenous waste via the kidneys or like organ in the form of urine or the like Ion and water balance is also the role of the kidney or like organ 13 Why do we eat other than food generally tastes good Food is necessary as an energy source and a source of molecules that the body can use to build and repair tissues Excess energy and building blocks are stored in our bodies primarily as adipose 14 Describe the two ways that our bodies store excess energy with respect to the storage molecule and location in the body Excess carbohydrate is stored as glycogen in the liver and skeletal muscle About a day s worth of energy is stored in this way in the human body Excess dietary carbohydrate protein and fat are stored in the human body as