Proteins and Amino Acids: Function Follows Form BIOL 103, Chapter 7

Today’s Topics Why is Protein Important? Amino Acids are building blocks of proteins Functions of Body Proteins Protein Digestion and Absorption Proteins in the Body Proteins in the Diet The Pros and Cons of Vegetarian Eating The Health Effects of Eating Too Little or Too Much Protein

Why is Protein Important? A part of every cell Needed in thousands of chemical reactions Keep us “together” structurally In short, proteins have many, many functions from replacing skin cells, producing antibodies to assisting in nutrient transport and muscle contractions.

Food Sources of Proteins Beef Chicken Fish Milk Plant foods: beans, peas, grains, nuts, seeds, and vegetables (garlic, green peas, mushrooms)

Amino Acids are Building Blocks of Proteins Proteins are sequences of amino acids There are 20 amino acids: 1.Essential (9) 2.Non-essential (11) 3.Conditionally essential (6) Table 7.1 List of Amino Acids

Amino Acids Identified by Side Chains

Protein structure: unique 3D shapes and functions Amino Acid Sequence – Amino acids are linked by peptide bond: Dipeptide: 2 amino acids Oligopeptide: 4-10 amino acids Polypeptide: >10 amino acids Protein: a chain with >50 amino acids – Protein shape A sequence of AA determines protein shape Shape of protein determines its function.

Protein Denaturalization: Destabilizing a Protein’s Shape There are factors that can cause a protein to unfold and lose shape (denature) 1.Changes in Acidic or Alkalinity in environment 2.High temperature/heat 3.Alcohol 4.Oxidation Denatured proteins lose their ability to function properly.

Functions of Body Proteins

Protein Digestion Protein digestion – Cells produce proteases (protein-digesting enzymes) as proenzymes (inactive forms of enzymes) – In the stomach: Proteins are denatured by HCl Pepsin begins digestion: 10-20% of proteins Which one is a protease? A proenzyme?

Protein Digestion and Absorption In the small intestine: – Proteases (from pancreas) break down remaining proteins  small peptides – Intestinal lining cells break down small peptides  amino acids – Amino acids are then absorbed into your intestinal cells  travel via portal vein to liver  released to general circulation

Summary of Protein Digestion and Absorption

Undigested Proteins If not digested, continues down the GI tract  feces Diseases of the intestinal tract cause problems with digestion/absorption of proteins 1.Celiac disease: allergic to protein gluten 2.Cystic fibrosis: sticky mucus prevents digestive enzymes (e.g. proteases) from reaching small intestine  poor digestion  nutrients are not absorbed  malnutrition

Proteins in the Body Protein Synthesis: – Draws on AA pool as needed. If your body is missing… Non-essential AA: – Cell will make that AA – Obtain it from liver Essential 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  Protein turnover “protein recycling” – When cells make proteins, they use amino acids from amino acid pool: available amino acids in body tissues 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 neurotransmitters Protein and Nitrogen Excretion – Breakdown of amino acids by removing nitrogen (amino) group/-NH2 – Amino groups converted to urea – Urea + water = urine  excretion (in kidney)

Function 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 Positive nitrogen balance – Nitrogen intake > Nitrogen output – Growth; recovery from illness Negative nitrogen balance – Nitrogen intake < Nitrogen output – Injury and illness

Proteins in the Diet Recommended protein intake – Adult RDA = 0.8g/kg of body weight – Infants have highest needs relative to body weight Why? – Physical stress increase your body’s needs for proteins – Infection, burns, fevers, surgery, intensive weight training Consumption in the US – Generally within or higher than recommended range

Problem Set 7, Question 1: How is it that our bodies are able to synthesize so many proteins in our body when our dietary protein requirement is relatively low?

Protein Quality – Complete proteins: supply all essential amino acids “high-quality proteins” Examples: animal proteins, soy proteins – Incomplete proteins: low in one or more essential 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 essential AA). – Two incomplete complementary proteins = complete protein Examples: rice and beans, peanut butter and bread, pea soup with crackers, corn and tortilla.

Evaluating Protein Quality A high-quality protein: 1.Provides all the essential amino acids at amounts the body needs 2.Provides enough other amino acids to serve as nitrogen sources for making non-essential amino acids 3.Easy to digest 4.Protein digestibility-corrected amino acid score (PDCAAS): measure of protein quality that takes account the AA composition of the food and the digestibility of the protein.

Proteins and Amino Acids as Additives and Supplements Protein and AA additives – 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 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, cosmetics, household, foods.

Pros and Cons of Vegetarian Eating Problem Set 7, Question 4 Health BenefitsHealth Risks

The Pros and Cons of Vegetarian Eating Diet recommendations (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 moderation 5.Consume a regular source of vitamins B12 and D Fortified foods or supplements

The Health Effects of Too Little Protein Dietary protein = essential amino acids Protein deficiency: occurs when energy and/or protein intake is inadequate Protein-energy malnutrition (PEM) – Kwashiorkor: severe protein deficiency Symptoms: edema, poor growth, bloated belly Affects those between age of months old Associated with extreme poverty

The Health Effects of Too Little Protein 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? – Nutritional rehabilitation Gradual and careful refeeding Must start with fluid and electrolyte balance, then introduce nutrients

Protein-Energy Malnutrition

The Health Effects of Too Much Protein

Problem Set 7, Q5 Name two health effects related to consuming a very high protein diet.