Proteins: Crucial Components of All Body Tissues 6 Proteins: Crucial Components of All Body Tissues 1

What Are Proteins? Proteins: large, complex molecules found in cells of all living things Dictated by genetic material (DNA) Contain carbon, hydrogen, oxygen, nitrogen Made from 20 different amino acids The Building Blocks of Proteins 2

Amino Acids Nine essential amino acids Nonessential amino acids Cannot be produced in sufficient quantities to meet physiological needs Must be obtained from food Nonessential amino acids Can be synthesized in sufficient quantities 3

Amino Acids Transamination Conditionally essential amino acid Transfer amine group from an essential amino acid to a different acid group and R group Conditionally essential amino acid Nonessential amino acid becomes essential Phenylketonuria (PKU): tyrosine becomes a conditionally essential amino acid that must be provided by the diet Deanimation/Transanimation 7

How Are Proteins Made? Proteins are long chains of amino acids Peptide bonds join amino acids together Gene expression is the process by which cells use genes to make proteins Gene: segment of deoxyribonucleic acid (DNA) that serves as a template for the synthesis (expression) of a particular protein 9

How Are Proteins Made? Transcription: messenger RNA copies the genetic information from DNA Translation: the genetic information in RNA is converted into the amino acid sequence of a protein 12

How Are Proteins Made? Protein turnover Existing proteins are degraded to provide the building blocks for new proteins Amino acid pool includes amino acids from food and cellular breakdown Protein organization determines function Sequential order of the amino acids Spiral shape from twist in amino acid chain Protein Synthesis 14

Protein Denaturation Proteins uncoil and lose their shape Damaging substances: heat, acid, base, heavy metal, alcohol Protein function is lost Denatured enzyme High fever Blood pH out of normal range During digestion 18

Protein in the Diet For protein synthesis, all essential amino acids must be available to the cell Limiting amino acid Essential amino acid that is missing or in the smallest supply Slows down or halts protein synthesis Inadequate energy consumption Limits protein synthesis 19

Protein in the Diet Incomplete protein (low quality): insufficient essential amino acids Does not support growth and health Complete protein (high quality): sufficient amounts of all nine essential amino acids Derived from animal and soy protein 20

Protein in the Diet Mutual supplementation: combine two or more incomplete protein sources to make a complete protein Complementary proteins: two or more foods are combined to supply all nine essential amino acids for a complete protein 21

Protein Digestion Protein digestion begins in the stomach Hydrochloric acid denatures protein strands and activates pepsin Pepsin: enzyme breaks down proteins into short polypeptides and amino acids Gastrin: hormone controls hydrochloric acid production and pepsin release 23

Protein Digestion Digestion continues in the small intestine Pancreatic enzymes (proteases) complete protein digestion Special sites (small intestine) transport amino acids, dipeptides, tripeptides High doses of individual amino acid supplements can lead to amino acid toxicity and deficiencies Protein Digestion 24

Protein Quality Methods for estimating protein quality Chemical score Protein digestibility corrected amino acid score (PDCAAS) Animal protein and many soy products are highly digestible (90% absorption) Protein Absorption 26

Functions of Proteins Cell growth, repair, maintenance Enzymes and hormones Fluid and electrolyte balance Acid−base balance Immune system Energy source Nutrient transport and storage 27

Protein Adequacy Nitrogen balance determines protein needs Positive nitrogen balance Negative nitrogen balance In nitrogen balance Nitrogen Balance 31

RDA for Protein RDA = 0.8 g per kg body weight per day Recommended percentage of energy is 10−35% of total energy intake Protein needs are higher during growth and development (children, adolescents, and pregnant/lactating women) 33

Too Much Protein Can Be Harmful High cholesterol and heart disease Animal-protein-rich diets are associated with high blood cholesterol levels (saturated fat) Contribution to bone loss High-protein diets increase calcium excretion and possibly lead to bone loss 35

Too Much Protein Can Be Harmful Kidney disease High protein intakes are associated with an increased risk among susceptible individuals People with diabetes have higher rates of kidney disease and may benefit from a lower-protein diet Maximum of 2 g of protein per kilogram body weight each day is safe for healthy people Fat Synthesis from Excess Protein 36

Protein Sources Meats Milk-based products Soy products Legumes Whole grains Nuts Quorn 37

Vegetarian Diets Vegetarianism: restricting the diet to foods of plant origin People chose vegetarianism for: Health benefits Ecological reasons Religious reasons Ethical reasons Concerns over food safety 39

Health Benefits of Vegetarianism Lower fat and total energy intake Lower blood pressure Reduced risk of heart disease Fewer digestive problems Reduced risk of some cancers Reduced risk of kidney disease, kidney stones, and gallstones 41

Challenges of Vegetarian Diets Can be low in some nutrients Associated with disordered eating Varied and adequate diet planning Soy and complementary proteins Vegetarian Food Guide Pyramid Special attention to vitamins D, B12, and riboflavin (B2); minerals zinc and iron 42

Protein-Energy Malnutrition Protein-energy malnutrition: caused by inadequate protein and energy intake Common forms: Marasmus Kwashiorkor 44

Marasmus Grossly inadequate energy and nutrient intake Consequences of marasmus: Wasting and weakening of muscles (heart) Stunted brain development and learning Depressed metabolism Stunted physical growth Deterioration of the intestinal lining (anemia) Severely weakened immune system Fluid and electrolyte imbalances 46

Kwashiorkor Disease resulting from low protein intake Kwashiorkor symptoms include: Some weight loss and muscle wasting Retarded growth and development Edema resulting in distention of the belly Fatty degeneration of the liver Loss of appetite, sadness, irritability, apathy Skin problems and hair loss 47

Genetic Disorders Numerous disorders are caused by defective DNA Genetic disorders include: Phenylketonuria Sickle cell anemia Cystic fibrosis 48