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9/8/15
1
Proteins and Amino Acids: Func7on Follows Form
BIOL 103, Chapter 7
Today’s Topics
• Why is Protein Important? • Amino Acids are building blocks of proteins • Func7ons of Body Proteins • Protein Diges7on and Absorp7on • Proteins in the Body • Proteins in the Diet • The Pros and Cons of Vegetarian Ea7ng • The Health Effects of Ea7ng Too LiSle or Too Much Protein
Why is Protein Important?
• 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.
Food Sources of Proteins
• Beef • Chicken • Fish • Milk • Plant foods: beans, peas, grains, nuts, seeds, and vegetables (garlic, green peas, mushrooms)
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Amino Acids are Building Blocks of Proteins
• Proteins are sequences of amino acids • There are ______ amino acids:
1. Essen7al (9) 2. Non-‐essen7al (11) 3. Condi7onally essen7al (6)
• Table 7.1 List of Amino Acids
Amino Acids Iden7fied by Side Chains
Protein structure: unique 3D shapes and func7ons
• Amino Acid Sequence – Amino acids are linked by pep7de bond: • Dipep'de: 2 amino acids • Oligopep'de: 4-‐10 amino acids • Polypep'de: >10 amino acids • Protein: a chain with >50 amino acids
– Protein shape • A _____________ of AA determines protein shape • Shape of protein determines its _______________.
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
• _______________ proteins lose their ability to func7on properly.
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Func7ons of Body Proteins Protein Diges7on
• Protein diges7on – Cells produce proteases (protein-‐diges7ng enzymes) as proenzymes (inac7ve forms of enzymes)
– In the stomach: • Proteins are denatured by HCl • Pepsin begins diges7on: 10-‐20% of proteins • Which one is a protease? A proenzyme?
Protein Diges7on and Absorp7on
• In the small intes7ne: – Proteases (from pancreas) break down remaining proteins à small pep7des
– Intes7nal lining cells break down small pep7des à amino acids
– Amino acids are then absorbed into your intes7nal cells à travel via portal vein to liver à released to general circula7on
Summary of Protein Diges7on and Absorp7on
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Undigested Proteins
• If not digested, con7nues down the GI tract à feces
• Diseases of the intes7nal tract cause problems with diges7on/absorp7on of proteins 1. Celiac disease: allergic to protein gluten 2. Cys'c 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: – Draws on AA pool as needed. If your body is missing… • Non-‐essen7al AA:
– Cell will make that AA – Obtain it from liver
• Essen7al AA: – Body make break down its own protein to supply the AA
Proteins in the Body
• Amino Acid Pool and Protein Turnover – Cells in your body constantly build and breakdown proteins à Protein turnover • “protein recycling”
– 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.
Proteins in the Body
• Synthesis of non-‐protein molecules – Proteins are precursors of DNA, RNA, and neurotransmiSers
• Protein and Nitrogen Excre7on – Breakdown of amino acids by removing nitrogen (amino) group/-‐NH2
– Amino groups converted to ____________ – Urea + water = _________ à excre7on (in kidney)
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Func7on of Blood Amino Acid Pool 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
Proteins in the Diet • Recommended protein intake – Adult RDA = 0.8g/kg of body weight – _________ have highest needs rela7ve to body weight • Why?
– Physical stress ______________ your body’s needs for proteins
– Infec7on, burns, fevers, surgery, intensive weight training
• Consump7on in the US – Generally within or higher than recommended range
Problem Set 7, Ques7on 1:
• How is it that our bodies are able to synthesize so many proteins in our body when our dietary protein requirement is rela7vely low?
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Protein Quality
• Protein Quality – Complete proteins: supply all essen7al amino acids • “high-‐quality proteins” • Examples: animal proteins, soy proteins
– Incomplete proteins: low in one or more essen7al amino acids • “low quality proteins” • Examples: most plant proteins
Protein Quality
• Incomplete and Complementary Proteins – Except soy, proteins in other plant foods is incomplete (lacks 1 or more essen7al AA).
– Two incomplete complementary proteins = complete protein • Examples: rice and beans, peanut buSer and bread, pea soup with crackers, corn and tor7lla.
Evalua7ng Protein Quality
• A high-‐quality protein: 1. Provides all the essen7al amino acids at amounts the
body needs 2. Provides enough other amino acids to serve as
nitrogen sources for making non-‐essen7al amino acids
3. Easy to digest 4. Protein diges'bility-‐corrected amino acid score
(PDCAAS): measure of protein quality that takes account the AA composi7on of the food and the diges7bility of the protein.
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
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Vegetarian vs. Vegan
Vegetarian • “Diet” • Don’t Eat: Meat, seafood • Types:
– Ovo-‐vegetarian: eats eggs – Lacto-‐vegetarian: eats dairy
products
• Products: Don’t mind using animal-‐derived products.
Vegan • “Diet + Lifestyle” • Don’t Eat: Meat, eggs, milk,
honey, or any food derived from animals.
• Products: Avoids using animal-‐derived products including clothing, cosme7cs, household, foods.
Pros and Cons of Vegetarian Ea7ng Problem Set 7, Ques7on 4
Health Benefits • Less fat, saturated fat,
cholesterol • More magnesium, folate • More an7oxidants • More fiber and
phytochemicals • Reduces risk for heart
disease, hypertension, and cancer.
Health Risks • Vegans may be low in:
calcium, iron, zinc, vitamin D, ____________________
• Higher intake of ______________________
• More restric7ve food choices = less nutrients
The Pros and Cons of Vegetarian Ea7ng
• Diet recommenda7ons (pg. 258): 1. Choose a variety of foods 2. Choose whole, unrefined foods 3. Choose a variety of fruits and vegetables 4. Choose lower-‐fat dairy products and eggs in
modera7on 5. Consume a regular source of vitamins B12 and D • For7fied foods or supplements
The Health Effects of Too LiSle Protein
• Dietary protein = essen7al amino acids • Protein deficiency: occurs when energy and/or protein intake is inadequate
• Protein-‐energy malnutri7on (PEM) – Kwashiorkor: severe ______________ deficiency • Symptoms: edema, poor growth, bloated belly • Affects those between age of 18-‐24 months old • Associated with extreme poverty
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The Health Effects of Too LiSle Protein
• PEM, cont. – Marasmus: severe ________________ 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 refeeding • Must start with fluid and electrolyte balance, then introduce nutrients
Protein-‐Energy Malnutri7on
The Health Effects of Too Much Protein Problem Set 7, Q5
• Name two health effects related to consuming a very high protein diet.