Chapter 6 Nutrition - Lecture notes 1 PDF

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Kate Yerxa was the professor, and these are the notes I took during lecture. ...

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Chapter 6- Proteins Structure of Proteins Different from Cho and fats 1. Proteins contain Nitrogen atoms in addition to the C, H, and O atoms ● Proteins are made of amino acids 2. Amino acids (AA) in a strand of protein are different from one another ● Different from CHOs that are made up of repeating glucose molecules ● 20 different amino acids ● AA are the building blocks of proteins Amino Acids ● Each amino acid consists of a single carbon atom attached to a nitrogen-containing amine group and to an acid group ● The side chains vary among the different amino acids and give the amino acid different sizes, shapes, and charges Essential Amino Acids ● 9 essential AA ● 11 non essential AA ● A nonessential amino acid can become essential= conditionally essential AA Recycling Amino Acid ● The body can recycle amino acids from proteins no longer needed ● These amino acids can be used to build new proteins or provide energy if glucose is lacking in the diet Essential ● Histidine ● Isoleucine ● Leucine ● Lysine ● Methionine ● Phenylalanine ● Threonine ● Tryptophan ● Valine Conditionally Essential ● Arginine ● Cysteine ● Glutamine ● Glycine

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Proline Tyrosine

Nonessential ● Alanine ● Asparagine ● Aspartic acid ● Glutamic acid ● Serine How do AAs build proteins? ● Build a strand of AA: Amino acids are joined together through peptide bonds ○ Peptide bonds- connects the amine group of one AA to the acid group of the zs next AA ○ A strong of 10 AA is known as polypeptide ● Coil the strand: the strand of AA takes on a spring-like shape as the side chains either attract or repel each other ● Foiling the coil: the coil folds and flops over itself to take on a functional shape ● Once coiled and folded, the protein may be functional as it is, or it may need to join with other proteins or add a CHO, a vitamin, or a mineral (iron) The Variety of Proteins ● Protein shapes enable performance of different tasks ○ Collagen, hemoglobin, insulin, and enzymes ● Inherited amino acid sequences ○ Alterations to sequence ■ Sickle-cell disease: a glutamic acid in one strand replaced with a valine Denaturation of Proteins ● Proteins can be denatured (distorted in shape) by heat, radiation, alcohol, acids, bases, or the salts of heavy metals ● During digestion, stomach acid denatures proteins, permitting digestive enzymes to make contact with the peptide bonds and cleave them ● Denaturation also occurs during cooking Protein Digestion 1. Mouth: No digestion happens 2. Stomach: enzymes (pepsin) activated by stomach acid digest proteins in food, denatured by acid ● Pepsin is the chief digestive enzyme in the stomach, which breaks down proteins into polypeptides ● The mucus coating secreted by the stomach wall protects its own proteins from attack by either enzymes or acid

3. Small intestine: by the time most proteins enter the small intestine, they are denatured and broken into smaller pieces ● A few single amino acids; most are large strands called polypeptides ● In the small intestine, bicarbonate acts to raise pH and enzymes (trypsin) continue digesting the strands into single amino acids or dipeptides and tripeptides Protein Absorption 1. Small Intestine ● Single AAs are absorbed by the cells of the small intestine ● Dipeptides and tripeptides are split into single AAs by brush border enzymes ○ A few larger peptides in bypass the digestive process and enter the bloodstream intact ○ May stimulate an an immune response ● Cells of the small intestine possess separate sites for absorbing different types of AAs ● The same AAs may compete for absorption sites ○ Limit megadoses of single AA supplements for this reason 2. Bloodstream ● Amino acids are absorbed from the small intestine and enter the bloodstream and are carried to the liver 3. Liver ● Amino acids may be used or released into the bloodstream to be used by other body cells ○ Amino acids can be used to make proteins needed by the cells ● When necessary, body cells can use amino acids for energy Video Review ● The importance of Protein ● Amino acids must be continuously available ○ Build proteins of new tissue ○ Replace worn-out cells ● Protein turnover: entire process of breakdown, recovery, and synthesis Roles of protein in the body 1. Structure and Movement ● Muscle tissue makes up about 40% of all of the body’s proteins ● Specialized muscle protein structures permit body movement ● Muscle proteins can release amino acids for energy if needed (starvation) ● Structural proteins strengthen bones, teeth, skin, tendons, cartilage, and blood vessels 2. Enzymes and Hormones ● Enzymes: act as catalyst (speeds up a reaction that would happen anyway)

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○ Each enzyme facilitates a specific chemical reaction ○ Thousands of enzymes can be inside a single cell ● Hormones: body’s messenger molecules, primarily made from amino acids ● Various body glands release hormones when changes occur in the body’s internal environment ○ Insulin and glucagon Antibodies ● Antibodies are proteins produced by white blood cells that defend against foreign proteins and other foreign substances within the body ● Each antibody protein is specific for one invader and a new type is made each time the body encounters a new invader ● The immune system “remembers” each specific invader and can produce antibody proteins quickly if the body encounters the same invader again Transport System ● Some proteins specialize in transporting substances: lipids, vitamins, minerals and oxygen around the body ○ Hemoglobin transports oxygen from the lungs to the cells Fluid and Electrolyte Balance ● Proteins help regulate the body’s electrolytes and fluids ○ Proteins attract water ○ Too much fluid in the tissues is called edema ● Cells have transport proteins that allow certain molecules to move into or out of the cells Acid Base Balance ● Normal processes of the body continually produce acids and bases ● Proteins buffer the blood against excess acidity or alkalinity ○ Too much acid in the blood or tissues is called acidosis ○ Too much base is called alkalosis Blood Clotting ● Proteins the clot the blood prevent death from uncontrolled bleeding ● Clot is replaced by scar tissue after wound healing

Role of Protein Providing Energy and Glucose ● Drawing Amino Acid from Tissues ● Protein is not stored in the body, unlike glucose (stored as glycogen) and fats (stored as triglycerides) ● When insufficient carbohydrate and fat are consumed to meet the body’s energy need, food protein and body protein re sacrificed to supply energy ● The body will first use protein from the muscles but may need to use from organs like the heart if the need arises When are proteins used for energy? ● High protein, low carb, low fat diets

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○ Not enough energy from carbs and fats Prolonged fasting or very low-calorie diet ○ Muscle wasting Prolonged exercise ○ Branched amino acids preferred

Using Excess Amino Acids ● Surplus amino acids are not stored ● Amino Groups are first removed and then the remains can be used for: 1. Meet immediate energy needs 2. Make glucose for storage as glycogen 3. Make fat for energy storage Review: Life of an Amino Acid ● When an amino acid arrives in a cell, it can be: 1. Used as is to build protein 2. Altered somewhat to make another needed compound 3. Dismantled to use its amine group to build a nonessential amino acid ● The remaining carbon, hydrogen, and oxygen atoms can be converted to glucose or fat ● In a cell starved for energy with no glucose or fatty acids: 1. The amino acid is stripped of its amine group (nitrogen part) and the remainder of its structure is used for energy 2. The amine group is excreted from the cell and then from the body in the urine ● A cell that has a surplus of energy and amino acids 1. Takes the amino acid part 2. Excretes the amine group 3. Uses the rest for energy or converts it to glucose or fat for storage ● Amino acids are “wasted” when: a. Energy is lacking from other sources b. Protein is overabundant c. An amino acid is oversupplied is supplement form d. The quality of the diet’s protein is too low (too few essential amino acids) Protein Requirements DRI: 0.8 grams protein/kg healthy body weight/day ● Energy intake must be adequate AMDR: 10-35% total calories from protein Food Protein: Need and Quality ● Body’s Health ○ Protein needs are increased by malnutrition or infection

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Malnutrition may cause a reduction of of digestive enzyme production, which can impair protein digestion and absorption During infection, more protein is needed for enhanced immune functions

Nitrogen Balance ● Nitrogen excreted compared to nitrogen eaten ○ ● Positive balance ○ Examples ● Negative balance ○ Examples

Protein Quality If the diet does not provide enough of an essential amino acid, the cells: a. b. Limiting Amino Acids ● Protein synthesis slows when ● Partially completed proteins are dismantled; ● The amino acids Complementary Proteins ● If a person does not consume all the essential amino acids needed, ● Dietary proteins lacking essential amino acids can be used only Protein Digestibility ● Digestibility of protein varies from food to food ● ● ● Protein Deficiency and Excess ● Protein Deficiency ● When the diet provides too little protein, the body slows synthesis of proteins, while increasing breakdown of body tissue protein to supply the needed amino acid ● Protein Energy Malnutrition (PEM) ● Symptoms ○ Slow growth in children ○ Impaired brain function ○ Impaired Kidney function ○ Weakened immunity

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Impaired nutrient absorption

Protein Excess ● Weight loss on high protein diets ○ Comes from calorie reduction, not proportion of energy nutrients ● Heart disease ○ Animal derived protein rich foods = high saturated fat ● Adult bone loss ○ Evidence indicates that high protein intakes from foods may not increase calcium loss ○ Too little protein may weaken the bones in malnourished elderly individuals ● Cancer ○ Population studies suggest a correlation between high intakes, of red meats and processed meats and come types of cancer, particularly of the colon Types of Vegetarian Diets Planning a Vegetarian Diet ● Nutrients of concern for vegetarians: ○ ● Choosing within the food groups ○ ○ ○ Vegans need to consume...