Proteins Presented by Janice Hermann, PhD, RD/LD OCES Adult and Older Adult Nutrition Specialist

Chemistry of Proteins Chemically, proteins contain the same elements as carbohydrates and lipids - carbon (C), hydrogen (H), and oxygen (O) But proteins also contain nitrogen (N). Some also contain sulfur.

Amino Acids All amino acids have a central carbon (C) atom; attached to a hydrogen (H), an amino group (NH2), and an acid group (COOH). Carbons need four bounds, the fourth bond is what distinguished one amino acid from another, this is called the side group.

Amino Acids There are 20 different amino acids, each with a different side group 11 amino acids are nonessential because the body can make them 9 amino acids are essential because the body can’t make them. Therefore they must be provided by the diet.

Essential Amino Acids Nonessential Amino Acids HistidineAlanine IsoleucineArginine LeucineAsparagine LysineAspartic acid MethionineCysteine PhenyalalnineGlutamic acid ThreonineGlutamine TryptophanGlycine ValineProline Serine Tyrosine

Proteins Amino acids are linked end-to-end with a peptide bond in different sequences to form proteins. Two amino acids is a dipeptide Three amino acids is a tripeptide More than three amino acids is a polypeptide

Proteins Most proteins are a few dozen to several hundred amino acids long. The body contains 10,000 to 50,000 different kinds of proteins.

Proteins As amino acids are bonded together to make a polypeptide, the chain folds and twists so that hydrophilic side groups are on the outside and hydrophobic groups are tucked inside away from water. The intricate, coiled shape the polypeptide finally assumes gives it maximum stability.

Protein The unique shapes of proteins enable them to perform their various functions in the body. Some are hollow balls that carry materials Some much longer than they are wide Some function just they are; others need other polypeptides to form larger complexes. Some proteins need minerals to activate them.

Proteins When proteins are exposed to heat, acid, or other conditions that disturbs their stability and they denature. When proteins are denatured they uncoil, lose their shape and consequently their ability to function. An example of denaturation is milk curdling when acid is added

Digestion In the stomach hydrochloric acid uncoils (denatures) each protein so that digestive enzymes can attack the peptide bonds. Hydrochloric acid also converts the inactive form of the enzyme pepsinogen into the active form pepsin. Pepsin breaks proteins, large polypeptides, into smaller polypeptides and some amino acids.

Digestion In the small intestine, pancreatic and intestinal proteases further breakdown polypeptides into short peptide chains, tripeptides, dipeptides and amino acids. Peptidase enzymes on the intestinal cell membrane surfaces split most of the dipeptides and tripeptides into single amino acids. Only a few peptides escape digestion and enter the blood intact.

Misconceptions A common misconception is that enzymes are absorbed intact. Enzymes are proteins and the digestive enzymes will breakdown the enzyme into single amino acids just like any other protein. Another misconception is it is better to consume amino acid supplements. The digestive system handles whole proteins better than individual amino acids.

Protein Synthesis in the Body The body contains 10,000 to 50,000 different kinds of protein Each protein has a specific function determined by its amino acid sequence The process of making proteins involves DNA, messenger RNA, ribosomes, and transfer RNA, amino acids and enzymes

Protein Synthesis in the Body DNA gene carries the protein code Messenger RNA copies the protein code and leaves the nucleus Messenger RNA attached to the ribosome Transfer RNA brings amino acids to the ribosome and line them up in the order of the protein code Enzymes bind the amino acids together

Protein Synthesis

Functions Building Materials Body cells and tissues Muscles Blood Skin Hair and fingernails Collagen (bone and tooth matrix, ligaments, tendons, wound healing)

Functions Enzymes are protein Smaller proteins that catalyze (speed up) chemical reactions. Enzymes are needed for most metabolic reactions in body cells Enzymes breakdown substances, build substances and transform one into another Half the protein eaten daily is used to make new enzymes

Functions Some hormones are protein Hormones are messengers that turning on and off metabolic processes. Some examples of protein hormones include: Insulin, thyroid hormones, histimine, adrenaline, serotonin.

Functions Proteins help maintain fluid and electrolyte balance. Body fluids can flow freely and are contained inside and outside cells and between cells and within blood vessels. Proteins are larger and cannot cross freely Proteins attract water

Functions Acid-base balance Metabolic processes produce acids and bases which are released into the blood for excretion By accepting and releasing hydrogen, proteins act like buffers to help maintain the body’s acid-base balance.

Functions Proteins act as carriers or transporters for nutrients and other molecules Hemoglobin carries oxygen Lipoproteins carry lipids Some proteins nutrients across cell walls, other carry nutrients in body fluids

Functions Antibodies are proteins When the body detects an in invading antigen, it makes antibodies, giant protein molecules designed to combat them. Without sufficient protein, the body cannot maintain its antibodies to resist disease. Each antibody is designed to destroy one specific antigen.

Functions Energy If glucose is limited the body can metabolize amino acids for energy. 4 calories per gram protein. The body will break down body tissues in order to provide amino acids for energy, which can lead to lean body tissue wasting.

Other Functions Blood clotting An injury starts a chain reaction leading to production of fibrin, a stringy protein that forms a clot. Protein collagen forms a scar to replace the clot and heals the wound. Vision Opsin is a light sensitive protein pigment in the retina. It responds to light by changing its shape, initiating the nerve impulses conveying the sense of sight to the brain.

Metabolism Using Amino Acids to Make Proteins or Nonessential Amino Acids If a nonessential amino acid is missing, body cells can make if from another amino acid. If an essential amino acid is missing, the body may break down some of its own proteins to obtain it.

Metabolism Using Amino Acids to Make Other Compounds Tyrosine can be made into the pigment melanin Tyrosine can also be made into the hormone thyroxin Tryptophane serves as a precursor for the vitamin niacin and for serotonin (a neurotransmitter)

Metabolism Using Amino Acids for Energy and Glucose When glucose or fatty acids are limited, cells are forced to use amino acids for energy and glucose. The body does not make a specialized storage form of protein, so the body dismantles its tissue proteins and uses them for energy. This can lead to lean body tissue wasting.

Metabolism Deaminating Amino Acids When amino acids are broken down they are first deaminated, the nitrogen group is removed, which is convered into ammonia and then urea and excreted The remaining carbon fragments of the deaminated amino acids can be used for energy or for the production of glucose, ketones, cholesterol or fat.

Metabolism Amino acids can be used to make fat When calorie and protein intakes exceed needs and carbohydrate intake is adequate, amino acids are deaminated, the nitrogen is excreted, and the remaining carbon fragments are converted to fat and stored for later use.

Protein Quality High-quality proteins provide enough of all the essential amino acids needed to support the body’s work and low-quality proteins don’t. Two factors affect protein quality, the protein’s digestibility and its amino acid composition.

Protein Digestibility Protein digestibility depends on such factors as the protein’s source and the other foods eaten with it. Digestibility of most animal proteins is high (90 to 99 percent); plant proteins are less digestible (70 to 90 percent for most, but over 90 percent for soy and legumes).

Amino Acid Composition All amino acids are needed simultaneously to make protein. Nonessential amino acids can be made if in short supply but if essential amino acids are limited protein must be dismantled. To prevent protein breakdown, dietary protein must supply at least the nine essential amino acids.

Amino Acid Composition Animal foods (meat, fish, poultry, cheese, eggs, yogurt, and milk) provide high-quality proteins. Plant proteins (vegetables, nuts, seeds, grains, and legumes) have more diverse amino acid patterns and tend to be limiting in one or more essential amino acids. A few such as soy protein are high quality.

Complementary Proteins The quality of plant proteins can be improved by combining plant protein foods that have different but complementary amino acid patterns. This strategy produces complementary proteins that together contain all the essential amino acids

Complementary Proteins Complement a plant protein by combining one plant protein low in one amino acid, with another plant protein high in that amino acid. Another way is to combine a plant protein with a small amount of animal protein. When complementary proteins are eaten together or within the course of the day all essential amino acids are provided.

Complementary Proteins Plant proteins low in certain amino acids Wheat and rice low in lysine Corn low in lysine and tryptophane Beans low in methionine Examples of complementary proteins Rice and beans Peanut butter and bread Corn bread and beans Corn tortillas and beans Macaroni and cheese

Protein Requirement The RDA for adults for protein is 0.8 grams protein/kg body weight. The RDA covers the needs for replacing worn-out tissue, so it increases for larger people; it also covers the needs for building new tissue during growth, so it increases for infants, children and pregnant women. The protein RDA is the same for athletes as for others.

USDA Daily Food Plan For a reference 2,000 calorie intake the USDA Daily Food Plan can provide adequate protein 18 g protein from 6 oz grain 10 g protein from 2 ½ cups vegetables 24 g protein from 3 cups dairy 38 g protein from 5 ½ protein foods 90 g protein total, which would be adequate protein for a 250 lb adult

Lowering Fat and Cholesterol Many people limit meat and dairy foods to lower fat and cholesterol. Lowering fat doesn’t mean omitting meat and dairy products. These foods are part of a well balanced diet. Choose lower fat, use lower fat preparation methods and watch portions

Protein and Amino Acid Supplements Protein and amino acid supplements don’t perform miracles and they can cause harm. Using muscles builds muscles, not supplements. Protein is not found as single amino acids in food and taking single amino acids is not benefit.

Too Much Protein If more protein is consumed than the body needs to build or repair body tissues or to provide energy the excess is converted into fatty acids and stored as fat for later use. In this process nitrogen groups are removed from the amino acids which are converted into urea and excreted in the urine.