Chapter 6: Proteins
Chapter 6: Proteins NTRI 2000-002
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This 9 page Class Notes was uploaded by Kaylen Taylor on Tuesday March 29, 2016. The Class Notes belongs to NTRI 2000-002 at Auburn University taught by Michael Winand Greene in Fall 2015. Since its upload, it has received 55 views. For similar materials see Nutrition and Health in Nutrition and Food Sciences at Auburn University.
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Date Created: 03/29/16
Chapter 6: Proteins Wednesday, March 9, 2016 10:55 AM Overview of Proteins o The human body is made up of thousands of proteins. o Contains N, C, O and H. o General Functions: Regulates and maintains body functions Provides essential form of nitrogen (In the form of amino acids) Proteins in the Developed World: Diet is typically rich in protein. Is this an issue? In ages 50-65, a low protein diet is associated with a DECREASED mortality rate. In ages 66+, a low protein diet is associated with an INCREASED mortality rate. In the Developing World: Protein deficiency is an issue. Important to focus on protein in diet planning. Proteins o Aside from water, protein makes up the major part of the lean body tissue. o Makes up about 17% of the body weight. Protein Structure o Amino acids are the building blocks of proteins. Aminoacids contain nitrogen bonded to a carbon. Makes proteins a unique form of carbohydrates and fats. o The proteins in our bodies are made up of 20 different amino acids. Nine of those amino acids are essential. Some of those nine amino acids are limiting. Eleven of those amino acids are nonessential, so the body is able to make them. New Categories of Amino Acids: Conditionally or acquired indispensable Usually in infants or disease states. o The sequence of amino acids is called the protein primary structure. o Primary structure lead to the protein higher order structure. This causes the protein to get into a specific shape. This shape is necessary for the protein to function properly. o The protein's primary structure is determined by the DNA. DNA is kept in the cell's nucleus. o The information of the protein's primary structure gets transcribed into messenger RNA (mRNA) mRNA leaves the nucleus and goes to the ribosome (rough ER) where the protein gets translated (made). Protein Synthesis o DNA contains coded instructions o Copies of codes Transferred to the cytoplasm (via the mRNA) o Amino acids are added one at a time With the aid of transfer RNA (tRNA) o Requires energy. Amino Acid Structure o One central carbon surrounded by an acid group, an amino group, some sort of side group, and hydrogen. The side group for each amino acid is different, making each amino acid unique. Gives each amino acid its own characteristics. Peptide Bond o Amino acids are connected together by a peptide bond. o Two amino acids = dipeptide, Three amino acids = tripeptide, Many amino acids = polypeptide, etc. Disruption of Normal Structure o Denaturation: Protein basically unfolds, thus altering the function of the protein. It won't work properly. Heat Strong Acids Bases Heavy metals How To Change Protein Structure o Genetic Alterations can change the protein's primary structure. Sometimes this is no big deal, sometimes it is. Can lead to genetic disease. Examples: Sickle Cell Anemia A single base substitution that causes one amino acids to be changed in the polypeptide of the hemoglobin protein. Hemoglobin binds oxygen in red blood cells. With sickle cell anemia, RBC become sickle shaped rather than that of a biconcave. Alters the higher order structure of the protein As a result, the protein doesn't work as efficiently. Protein Digestion o Pre-Digestion: Cooking Heat denatures proteins, softening food. o Digestion begins in the stomach HCl denatures proteins. Pepsin (enzyme) breaks the peptide bond of proteins resulting in protein fragments. Pepsin is released in the stomach by cells in the stomach and is activated by the acidic environment. Gastrin regulates the release of Pepsin. It's released inresponse to thinking about food and chewing and digesting food. In the stomach is partially digested proteins and other nutrients - chyme. Then moves into the small intestine by the pyloric sphincter. Chyme stimulates the release of CCK. CCK causes pancreas to release proteolytic enzymes that cleave proteins. Pepsin is inactivated by an elevated pH. Several peptidases are found in the brush border in the small intestine. Small peptides and free amino acids are absorbed by active transport. Any intracellular peptides are digested by enzymes within cells. o Protein Digestion Problems Gluten: A protein found in some grains that gives backed goods their doughy, elastic nature. Celiac Disease: Incomplete gluten breakdown in small intestines leaving small peptides and amino acids. Results in an inflammatory response to peptides and amino acids. Autoimmune response, genetic predisposition. Prevalence in the US: 1 in 133 In people with related symptoms: 1 in 56 Amino Acid Absorption o Amino acids are taken up by the capillaries and taken to the liver by the portal vein. o Liver Used as building blocks for liver proteins Broken down for energy Can be released into the blood. Converted to nonessential amino acids, glucose, or fat. Infant digestion of Proteins o Up to 4 to 5 months of age The GI tract is somewhat permeable to small proteins. o Wait until the infant is at least 6-12 months of age before introducing some foods that can cause allergies. Functions of Proteins in the body o Producing vital body structures Body is in a constant state of turnover. Producing proteins and disassembling proteins. What happens in protein inadequacy Producing proteins slows down Muscles, blood proteins, and vital organs decrease in size. Brain resists breakdown o Maintaining Fluid Balance Blood proteins attract fluids. If protein are inadequate, the fluid shifts into the tissues - called edema. o Contributing to acid-base balance Act as buffers -- maintain pH within a narrow range Keeps blood in an alkaline state. o Forming Hormones and Enzymes Hormones allow us to communicate between cells. Enzymes catalyze reactions in the cells. o Transport and signaling receptors Transport brings nutrients into the cells. Signaling receptors are used for communication in the cell o Contributing to the Immune Function Antibody production If there is protein deficiency, there is a decrease in immune function. o Providing Energy Is need for prolonged exercise and calorie restriction However, cells use primarily fats and CHO More efficient way to get energy. It wastes calories to metabolize amino acids for energy. o Forming Glucose Amino acids can converted into glucose when blood sugar is low. During Starvation: Muscle wasting and edema results from protein breakdown. Glucogenic Amino Acids are the only ones that can be used for glucose. Use both non-essential and essential amino acids o Contributes to Satiety Proteins provide the highest feeling of satisfaction after eating. May contribute to calorie control during weight loss Fate of Amino Acids in Cells o Breakdown of amino acids leave behind ammonia. The ammonia is turned into urea in the liver and then excreted by the kidneys during urination. o Protein Need o If you aren't growing (Adults) Only enough to replace what you lose daily The goal is protein balance. Protein RDA o 0.8 grams/kg of healthy body weight 154/2.2 = 70 kg 70 kg *0.8 = 56 grams So about 10% of total calories. o Food and Nutrition Board sets upper range at 35% o In the U.S., typical protein intake is about 100 grams for men and 65 grams for women. The typical protein intake is greater than what is needed. Protein in Foods o Western diet- 70% of dietary protein typically comes from animal sources. o Water packed tuna is the most nutrient dense source of protein. o Top 5 Contributors Beef Poultry Milk White Bread Cheese o With animal meat, it's likely to the low in fiber, some vitamins, and phytochemicals. High in saturated fat and cholesterol. Red meat, especially processed forms is linked to colon cancer o A high protein diet can cause stress on the kidneys o Some studies show high protein diets are associated with calcium losses in urine. Alternative to high-Protein Diets o Vegetarian: Abstaining from meat consumption o Semi-Vegetarian: May consume fish or poultry, or sometimes other meats on an infrequent basis. o Vegan: Consumes no animal products. o Animal proteins tend to be complete proteins o Plant proteins tend to be incomplete proteins Nuts - Grow on trees Seeds - Grow on veggies or flowering plants Legumes - Beans, peas, etc. o Grains and nuts are deficient in the amino acid lysine. o Veggies and legumes are low in the amino acid methionine. Vegan Diets o Complementary proteins o Nutrient deficiency concerns Vitamin B12 Iron Zinc Calcium Omega-3 fatty acids Complete Proteins in Plants o Quinoa o Amaranth o Soybeans o Buckwheat Food Protein Allergies o Immune system mistakes food proteins for a harmful invader o Soy, peanuts, tree nuts, wheat, milk, eggs, fish, and shellfish account for 90% of food allergies o Reactions range from mild intolerance to fatal. Protein-Calorie Malnutrition o In the developed world: Diet is typically rich in protein o In the developing world: Protein deficiency is an issue Important to focus on protein diet planning Only seen in certain countries. Protein deficiency can: Stunts growth Increased risk of infection Protein-Energy Deficiency Commonly found in Africa Marasmus: Starvation/insufficient protein and calories Kwashiorkor: Marginal amount of calories and insufficient protein o Protein-Energy Malnutrition in the U.S. Found in: Hospital inpatients Long-term care residents Community dwelling older adults Dialysis patients Occurs in older adults ( >65 years old)
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