Why is Protein Important?

Transcription

1 Why is Protein Important? Chapter 6 Proteins and Amino Acids: Func7on Follows Form BIOL 103, Spring 2016 A part of every cell Needed in thousands of chemical reac7ons Keep us together structurally In short, proteins have many, many func7ons from replacing skin cells, producing an7bodies to assis7ng in nutrient transport and muscle contrac7ons. Excess protein intake a greater problem in the U.S. Amino Acids are Building Blocks of Proteins Proteins are sequences of amino acids There are 20 amino acids: 1. Essen7al (9) 2. Non- essen7al (11) 3. Condi7onally essen7al (6) Amino acids that are normally dispensable, but become indispensable under certain circumstances such as during cri7cal illness. 1

2 Amino Acids Iden7fied by Side Chains Protein structure: unique 3D shapes and func7ons Amino Acid Sequence Amino acids are linked to each other by pep1de bond: Dipep1de: 2 amino acids Oligopep1de: 3-10 amino acids Polypep1de: >10 amino acids Protein: a chain with >50 amino acids Protein shape A sequence of AA determines protein shape Shape of protein determines its func7on. Protein Structure 2

3 2/17/16 Func7ons of Body Proteins Func7ons of Body Proteins Fluid Balance: Fluids are found inside and outside cells Inside cells: intracellular fluid Outside cells: extracellular Inters11al fluid Intravascular fluid Func7ons of Body Proteins Fluid Balance Blood proteins maintain appropriate fluid levels in vascular system Edema results when diet lacks enough protein to maintain normal levels of blood proteins Edema: Swelling caused by buildup of fluid between cells 3

4 Func7ons of Body Proteins Source of Energy and Glucose Carbohydrates and fat are protein- sparing Body prefers burning them for energy Will resort to burning protein for energy if necessary Body readies protein for use as energy through deamina1on Removal of amino group from an amino acid Protein Denaturaliza7on: Destabilizing a Protein s Shape There are factors that can cause a protein to unfold and lose shape 1. Changes in Acidic or Alkalinity in environment 2. High temperature/heat 3. Alcohol 4. Oxida7on Denatured proteins lose their ability to func7on properly. e.g. egg protein, avidin Protein Diges7on and Absorp7on Protein diges7on In the stomach: Proteins are denatured by hydrochloric acid (HCl) Cells produce proenzyme pepsinogen, an inac7ve precursor to pepsin HCl ac7vates pepsinogen to pepsin Pepsin begins diges7on (~10-20%) Protein Diges7on and Absorp7on In the small intes7ne: Proteases from pancreas and intes7nal lining cells break down remaining proteins à small pep7des and/or amino acids Depending on the amino acid, uses facilitated diffusion or ac7ve transport during absorp7on Q: Why might it be a problem if a person takes amino acid supplementa7on? Once amino acids are absorbed into your intes7nal cells à travel via portal vein to liver à released to general circula7on 4

5 Protein Diges7on and Absorp7on If not digested, con7nues down to GI tract as feces Diseases of the intes7nal tract cause problems with diges7on by decreasing absorp7on efficiency Celiac disease: Cannot digest gluten (a protein found in wheat, rye, barley) à presence of gluten trigger autoimmune response against villi Cys1c fibrosis: s7cky mucus prevents diges7ve enzymes (e.g. proteases) from reaching small intes7ne à poor diges7on à nutrients are not absorbed à malnutri7on Proteins in the Body Protein Synthesis: Amino Acids (AA) assembled in specific sequence If a non- essen7al AA is missing, the cell can either make the AA or obtain it from the liver via bloodstream However, if an essen7al AA missing body may break its own protein down to supply the missing AA If essen7al AA unavailable protein synthesis halts and par7ally completed protein is broken down into individual AA to be used elsewhere in the body Protein in the Body Amino Acid Pool and Protein Turnover When cells make proteins, they use amino acids from amino acid pool: available amino acids in body 7ssues and fluids that can be used to make new proteins. Cells in your body constantly build and breakdown proteins à Protein turnover Protein recycling 5

6 Proteins in the Body Func7on of Blood Amino Acid Pool Synthesis of non- protein molecules Proteins are precursors of DNA, RNA, and neurotransmilers Protein and Nitrogen Excre7on Breakdown of amino acids by removing nitrogen (amino) group/- NH2 Amino groups converted to urea Urea + water = urine à excre7on (in kidney) Nitrogen Balance We can evaluate our nitrogen balance to evaluate what is happening in our body Nitrogen intake vs. nitrogen output Nitrogen equilibrium Nitrogen intake = nitrogen output Healthy adults Posi7ve nitrogen balance Nitrogen intake > Nitrogen output Growth; recovery from illness Nega7ve nitrogen balance Nitrogen intake < Nitrogen output Injury and illness 6

7 Protein in the Diet Recommended Intakes of Protein Adult RDA = 0.8 gram per kilogram of body weight Severe physical stress can increase body s need for proteins Infec7ons, burns, fevers, surgery increase protein losses Diet must replace lost protein Protein Consump7on in the United States Generally higher than recommended range Protein in the Diet True or False: Plant based diet do not contain all the essen7al amino acids human needs. To be healthy, we must either eat animal protein or combine certain plant foods in order to ensure that we get complete proteins. Vegetarian and Protein Diet for a Small Planet, 1971 by Frances Moore- Lappe Study done 100 years ago on baby rats Rats need more proteins to grow than humans Protein given as a percentage of calories We need only % of our calories from proteins That amount can be supplied by common vegetables. Vegetables average around 22% protein by calories, beans 28%, grains 13%. 7

8 Amino Acid need from WHO Protein Quality is not a problem Protein quality is inferior : Quality measure are mostly based on amounts of AA in foods; plant based foods contain as much or more than you need of each individual AA. More is not beler : Animal foods have more protein, but that does not mean ea7ng more protein than your body needs is beler for your body Proteins and Amino Acids as Addi7ves and Supplements Protein and AA addi7ves Contribute to structure, texture, taste of foods Protein and AA supplements Used for a variety of reasons: dieters, athletes, certain diseases. Risks are unknown Vegetarian Ea7ng Why People Become Vegetarians Various reasons, including Religious beliefs Environmental concerns Aversion to ea7ng another living creature Concerns about animal cruelty concerns 8

9 Vegetarian Ea7ng Health Benefits of Vegetarian Diets Less fat, saturated fat, and cholesterol intake More magnesium and folate More an7oxidants More fiber and phytochemicals Reduces risk for heart disease, obesity, hypertension, and cancer Vegetarian Ea7ng Health Risks of Vegetarian Diets Vegan diets may be low in some nutrients Calcium, iron, zinc, vitamin D, and vitamin B 12 Higher intake of phytates Cooking, fermenta7on, or soaking in acid medium can reduce contents of phy7c acid More restric7ve food choices = less nutrients Careful planning needed for growth and overall health 9

10 Health Effects of Too Lille Protein Dietary protein = essen7al amino acids Protein deficiency: occurs when energy and/ or protein intake is inadequate Protein- energy malnutri1on (PEM) Kwashiorkor: severe protein deficiency Symptoms: edema, poor growth, bloated belly Affects those between age of months old Associated with extreme poverty Health Effects of Too Lille Protein Protein- Energy Malnutri7on PEM, cont. Marasmus: severe calorie deficiency Chronic PEM; withering Affects Infants and 6-18 months old children Usually the children are short and thin for their age How to treat? Nutri7onal rehabilita7on Gradual and careful re- feeding Must start with fluid and electrolyte balance, then introduce nutrients 10

11 Health Effects of Too Much Protein 11