* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download ch_6_-_the_proteins2
Monoclonal antibody wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Basal metabolic rate wikipedia , lookup
Paracrine signalling wikipedia , lookup
Gene expression wikipedia , lookup
G protein–coupled receptor wikipedia , lookup
Fatty acid metabolism wikipedia , lookup
Expression vector wikipedia , lookup
Peptide synthesis wikipedia , lookup
Ribosomally synthesized and post-translationally modified peptides wikipedia , lookup
Ancestral sequence reconstruction wikipedia , lookup
Magnesium transporter wikipedia , lookup
Interactome wikipedia , lookup
Point mutation wikipedia , lookup
Metalloprotein wikipedia , lookup
Protein purification wikipedia , lookup
Nuclear magnetic resonance spectroscopy of proteins wikipedia , lookup
Western blot wikipedia , lookup
Protein–protein interaction wikipedia , lookup
Genetic code wikipedia , lookup
Amino acid synthesis wikipedia , lookup
Biosynthesis wikipedia , lookup
Two-hybrid screening wikipedia , lookup
HSD 240 – ONLINE CHAPTER 6: THE PROTEINS AND AMINO ACIDS Protein Of prime importance Working proteins -- enzymes, antibodies, transport vehicles, hormones Structural proteins -- muscle tendons (muscle to bone), ligaments (bone to bone), hair, material of nails Structure of Proteins Contain carbon, hydrogen, oxygen AND nitrogen The nitrogen atoms give the name amino (nitrogen containing) to amino acids Amino acids are the building blocks of protein The amino acids in a strand of protein are different from on another – can contain 20 different kinds of amino acids Amino Acids All amino acids have a chemical backbone consisting of single carbon atoms with both an amine group (the amine group) and an acid group (carboxyl group) The differences in amino acids depends on the chemical side chain that is attached to the center carbon of the backbone It is the side chain that gives identity and chemical nature to each amino acid The side chains makes the amino acids differ in size, shape, and electrical charge There are 20 amino acids; the body can make most of them from fragments of carbohydrate or fat to make the backbone, and nitrogen from other sources to make the amine group Essential Amino Acids The body cannot make these amino acids Without them, the body cannot make the proteins it needs to do its work Therefore, we must eat the foods that provide these essential amino acids Phenylalanine, an essential amino acids o Phenylalanine tyrosine (a non-essential amino acid) o If the enzyme needed to convert phenylalanine to tyrosine is absent – condition called PKU o Phenylalanine builds up in the blood and this results in a decrease in IQ in infants Building Protein Amino acids are connected by a peptide bond – formed between the amine group and the acid group of the next amino acid Proteins take on different shapes depending on their charges o If side chain electrically charged – proteins are attracted to water o If side chain are neutral – repelled by water; tuck themselves away from body fluids Several strands of protein may cluster together in a functioning unit Some proteins need a vitamin or mineral to activate it The different shapes of protein allow them to perform different tasks in the body Enzymes – act on other substances to change them chemically; they are proteins Hemoglobin – a globular protein that carries oxygen in the red blood cells No restriction on length of amino aids – they can make up thousands of different proteins The amino acids that make up a protein molecule are specified by hereditary; for each protein there is a proper amino acid sequence; if a wrong amino acid is inherited, the result could be disastrous to health e.g. sickle cell disease Denaturation of Protein Proteins shape can be changed by heat, acids, bases, and alcohol Denaturation = change in shape Denaturation of protein is the first step in its destruction During digestion of protein, the stomach acid opens up the proteins structure Once the structure is open, digestion can break the peptide bonds 1 The Digestion of Protein Stomach Where protein digestion begins Acids (HCl) in the stomach uncoils (denatures) protein into strands Stomach enzymes (pepsin) then begin to break the chemical (peptide) bonds into amino acids Protein ----------------polypeptides --------------tripeptides --------------dipeptides --------------single amino acids --------------few whole proteins Small Intestine Acid from the stomach is neutralized by alkaline juice (bicarbonate) secreted by the pancreas Protein digesting enzymes from the pancreas (trypsin, chymotrypsin, and carboxypeptidase) and intestines (peptidase) continue to break peptide bonds between tripeptides and dipeptides Intestinal cells absorb amino acids and transfer amino acids into the bloodstream Bloodstream transports amino acids to all the body’s cells Protein synthesis occurs in the cells – DNA, mRNA, tRNA – gene expression The Roles of Protein in the Body 1. Regulation of gene expression 2. Providing structure and movement 3. Building enzymes, hormones and other compounds 4. Building antibodies 5. Transporting substances 6. Maintaining fluid and electrolyte balance 7. Maintaining acid-base balance 8. Blood clotting 9. Provide energy and glucose Protein energy Will be used for energy if it has to 1 gram of protein yields 4 kcal When used for energy it loses its amine Amine group either used elsewhere or turned into urea by the liver (deamination) Urea sent to the kidney for excretion in the form of urine Fragments that remain – C, H, O2 – can be used to build CHO and fats Amino acids can be converted to glucose Amino acids can be converted to fat, and fats will be stored So, if need be, protein can help maintain a steady blood glucose and also serve the glucose needs for the brain For Energy In Storage Carbohydrates offer energy Glucose is stored as glycogen Fats offer concentrated energy Fat is stored as triglycerides Proteins offer energy plus nitrogen Protein is not stored – available ONLY as active working molecular and structural components of tissue Summary Amino acids in a cell can be Used to build proteins Converted to other small nitrogen-containing compounds such as vitamins or niacin Converted to other amino acids Stripped of their nitrogen, amino acids can be Converted to glucose Burned as fuel Stored as fat CONSUMER CORNER: Evaluating Protein and Amino Acid Supplements 2 How much protein do we need? Table 6-3 DRI Adults – 0.8 grams per kilogram of body weight The more athletic adult – 1.0-1.2 grams/kg of body weight Women – 46 grams per day Men – 56 grams per day AMDR 10-35% of kcal from protein USDA Food Guide Pyramid (MyPyramid) Other factors to consider: The Body’s Health o Malnutrition and infection increase the body’s need for protein Other Nutrients and Energy o Need a full array of macronutrients and micronutrients Protein Quality o Part of a normal fixed diet Nitrogen balance We need enough protein to maintain nitrogen balance – the amount of nitrogen consumed being equal to the amount of nitrogen excreted Adults need to maintain equilibrium o Infants, children, pregnant and lactating women, body builders, are in positive nitrogen balance – retaining more nitrogen than they are excreting o Surgery, space travel, starvation, results in negative nitrogen balance – muscle tissue being broken down and lost What Foods Provide High Quality Protein? Depends on its amino acid content High –quality protein (formerly “complete protein”) – proteins that provide all of the essential amino acids Animal proteins, eggs Milk , yogurt, cheese Most soybean products If the diet fails to provide enough of the essential amino acids Internal proteins are broken down to liberate the needed essential amino acid Conserve the essential amino acid by limiting the synthesis of protein Limiting Amino Acid An essential amino acid that is present in dietary protein in an insufficient amount, thereby limiting the body’s ability to build protein Complementary Protein: eating two different foods where essential amino acids are lacking (or low) in one are provided in the other and vice versa Two proteins do not need to be eaten together as long as the diet provides enough energy and total protein from a variety of sources Mutual supplementation Legumes – foods of the pea, bean and lentil family that are nitrogen-fixing; their seeds are rich in protein Protein Digestibility Some proteins are more digestible than others Oats vs. eggs Perspective on protein quality Meeting protein needs not a problem for most people in the US even if they were to eat no animal products at all Need to pay attention to mutual supplementation Varied, adequate in calories, nutrient dense What about where food energy is limited (where malnutrition exists) or protein limited Fufu – low-protein staple food of the cassava root Protein Deficiency and Excess What happens when people consume too little protein 3 Deficiency in protein and energy can result in protein-energy malnutrition (PEM), the most widespread form of malnutrition in the world Marasmus o 6-18 months of age o Children fed weak cereal drink, low calorie, low protein quality o Child looks like a wizened old person o Muscle wasting o Little body fat for insulation o Insufficient protein for hemoglobin, antibodies o Dysentery – infection of the digestive tract – diarrhea o Might progress to a point of no return Kwashiorkor – Ghanian name for “the evil spirit that infects the first child when the second child is born” o Breastmilk – high quality protein o When baby is weaned, low quality protein follows o Some symptoms resemble marasmus minus the severe wasting o Edema in belly and legs o Fatty liver – lack of transport proteins o Liver needs to filter toxins PEM at home Is it possible to consume too much protein? Overconsumption of protein offers no benefits and may pose some risks US protein intakes – most consume sufficient amounts of protein; high-protein diets suggesting 65% of calories for weight loss not warranted Heart Disease o Saturated fat from animal protein and milk, yogurt , cheese (full fat varieties) o Homocysteine and heart disease; high protein might raise the level of this amino acid and increase the risk of heart disease Kidney disease- protein diets Adult bone loss - osteoporosis Cancer o Colon and rectum from well-cooked red meats and highly processed meats Is a Low-Gluten Diet Best for Health? o Gluten and celiac disease Food Feature: Getting Enough but Not Too Much Protein Legumes Textured vegetable protein Tofu – curd made from soybeans Controversy 6: Vegetarian and Meat Consuming Diets Vegetarians -- Table C6-1 People who consciously choose not to eat animal some or all products Fruitarian Lacto-ovo vegetarians Lacto-vegetarians Ovo-vegetarian Vegan Partial vegetarians Pesco-vegetarian Positive health effects – reduced risk of o Obesity, heart disease, blood pressure, cancer, diabetes, osteoporosis, diverticular disease Positive aspects of a meat eater’s diet o Energy, B12, vitamin D, calcium, iron, zinc, , omega 3, and protein for all stages of the lifecycle Planning a Vegetarian Diet Vegetarian Food Guide Pyramid - In what way do the food groups differ? See page 226 4