Protein: Amino Acids Overview
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Questions and Answers

What is the primary reason for the body's need for dietary protein?

  • To improve carbohydrate metabolism.
  • To enhance hydration levels.
  • To provide energy for metabolic processes.
  • To supply essential amino acids. (correct)

    • What percentage of total food energy is recommended for protein intake in a balanced diet?

  • 10 to 35 percent (correct)
  • 30 to 40 percent
  • 20 to 25 percent
  • 15 to 40 percent

    • What is the RDA for protein intake for adults in grams per kilogram of body weight?

  • 0.8 gram (correct)
  • 0.6 gram
  • 1.2 grams
  • 1.0 gram

    • How should protein foods be proportionately distributed over a week according to the USDA Food Patterns?

    <p>20% from seafood, 70% from meat, 10% from nuts.</p> Signup and view all the answers

    What is the recommended protein intake per meal for muscle health?

    <p>25–35 grams of high-quality protein.</p> Signup and view all the answers

    What is the primary function of hydrochloric acid in the stomach regarding protein digestion?

    <p>It uncoils protein strands and activates pepsinogen.</p> Signup and view all the answers

    What characterizes essential amino acids?

    <p>They must be obtained from the diet.</p> Signup and view all the answers

    Which of the following best describes the process of protein digestion in the small intestine?

    <p>Pancreatic and intestinal proteases hydrolyze proteins into shorter chains before absorption.</p> Signup and view all the answers

    What ultimately happens to most dipeptides and tripeptides during protein absorption?

    <p>They are hydrolyzed to single amino acids before absorption.</p> Signup and view all the answers

    Which amino acid becomes conditionally essential in cases of phenylketonuria?

    <p>Tyrosine</p> Signup and view all the answers

    What is the fate of amino acids once they enter the intestinal cells?

    <p>They can be used for energy or to synthesize compounds.</p> Signup and view all the answers

    What type of bond is formed between amino acids during the condensation reaction?

    <p>Peptide bond</p> Signup and view all the answers

    What defines the primary structure of a protein?

    <p>The sequence of amino acids in a polypeptide chain.</p> Signup and view all the answers

    How does predigested protein intake impact the digestive system?

    <p>It leads to a less efficient absorption of amino acids.</p> Signup and view all the answers

    How does the body create nonessential amino acids?

    <p>Through the synthesis using nitrogen and carbon fragments.</p> Signup and view all the answers

    What is one of the major roles of pepsin in protein digestion?

    <p>To hydrolyze large proteins into smaller peptides.</p> Signup and view all the answers

    Which statement is true regarding the absorption of amino acids from the intestinal cells?

    <p>Some amino acids are transported into surrounding fluids and then to the liver.</p> Signup and view all the answers

    What is the role of sulfur in some amino acids?

    <p>It is a structural component in some amino acids.</p> Signup and view all the answers

    Which of the following amino acids is considered nonessential?

    <p>Aspartic acid</p> Signup and view all the answers

    What enzyme is converted from its inactive form in the stomach to facilitate protein digestion?

    <p>Pepsin.</p> Signup and view all the answers

    What happens to tyrosine during situations where phenylalanine is deficient?

    <p>It becomes an essential amino acid.</p> Signup and view all the answers

    Which of the following processes primarily occurs in the stomach during protein digestion?

    <p>Denaturation of proteins facilitated by hydrochloric acid.</p> Signup and view all the answers

    What is the main reason dietary protein must supply essential amino acids?

    <p>To prevent protein breakdown in the body.</p> Signup and view all the answers

    What defines a high-quality protein?

    <p>It contains all essential amino acids and some nonessential amino acids in appropriate amounts.</p> Signup and view all the answers

    Which of the following amino acids is typically a limiting amino acid in plant proteins?

    <p>Lysine</p> Signup and view all the answers

    What is a reference protein used to determine?

    <p>The essential amino acid composition for preschool-age children.</p> Signup and view all the answers

    Which food source is NOT considered a high-quality protein?

    <p>Gelatin</p> Signup and view all the answers

    How do vegetarians often address the quality of plant proteins in their diets?

    <p>By combining different plant-protein foods for complementary amino acid profiles.</p> Signup and view all the answers

    What common misconception exists regarding plant proteins?

    <p>All plant proteins contain adequate levels of essential amino acids.</p> Signup and view all the answers

    Which type of protein is found to have more diverse amino acid patterns?

    <p>Plant proteins</p> Signup and view all the answers

    What happens if an essential amino acid is deficient in the diet?

    <p>The body must break down its own proteins to obtain it.</p> Signup and view all the answers

    What is a characteristic of lower quality plant proteins?

    <p>They are commonly deficient in one or more essential amino acids.</p> Signup and view all the answers

    Which type of protein-rich foods may lower the risk of some cancers?

    <p>Fish and legumes</p> Signup and view all the answers

    What factor significantly influences the effect of protein on adult bone health?

    <p>Adequacy of calcium in the diet</p> Signup and view all the answers

    Why might high-protein diets be effective for weight loss?

    <p>They are typically low in calories.</p> Signup and view all the answers

    How does high protein intake relate to kidney health in chronic kidney disease patients?

    <p>It accelerates deterioration but doesn't cause disease.</p> Signup and view all the answers

    What is the classification of red meat according to health organizations?

    <p>A probable carcinogen</p> Signup and view all the answers

    What effect does excess protein have on calcium metabolism?

    <p>It increases calcium excretion.</p> Signup and view all the answers

    What role does protein play in establishing feelings of satiety in high-protein diets?

    <p>It increases feelings of fullness.</p> Signup and view all the answers

    What conclusion did the DRI Committee reach regarding protein and calcium recommendations?

    <p>No adjustments for calcium are needed based on protein intake.</p> Signup and view all the answers

    Which food is positively associated with a lower risk of breast cancer?

    <p>Soy products</p> Signup and view all the answers

    What is a potential effect of excess calories, irrespective of protein intake?

    <p>Increased body fat across all groups.</p> Signup and view all the answers

    Study Notes

    Protein: Amino Acids

    • Proteins are composed of carbon, hydrogen, oxygen, and nitrogen atoms, arranged into amino acids linked in a chain, some also contain sulfur.
    • The body can make nonessential amino acids, but needs to obtain essential amino acids from the diet.
    • Nine amino acids are essential for humans as the body can't make them or can't make them in sufficient quantities.
    • A conditionally essential amino acid is normally nonessential, but must be supplied by the diet in special circumstances when the need for it exceeds the body’s ability to make it.
      • For example, tyrosine is normally nonessential as it is made by the body using phenylalanine.
      • If the diet fails to supply enough phenylalanine, or if the body cannot make the conversion for some reason, tyrosine becomes a conditionally essential amino acid.
    • Condensation reactions connect amino acids together to form a dipeptide.
    • Peptide bond: A bond that connects the acid end of one amino acid with the amino end of another, forming a link in a protein chain.
    • The primary structure of a protein is determined by the sequence of amino acids.
    • Amino acid sequences within proteins vary.
    • When protein is consumed, enzymes break down the long polypeptides into short polypeptides, the short polypeptides into tripeptides and dipeptides, and, finally, the tripeptides and dipeptides into individual amino acids.
    • The major event in the stomach is the partial breakdown of proteins (hydrolysis).
    • Hydrochloric acid uncoils (denatures) each protein strand, allowing digestive enzymes to attack the peptide bonds.
    • Pepsinogen is converted into pepsin by hydrochloric acid, pepsin cleaves proteins into small polypeptides and amino acids.
    • In the small intestine, pancreatic and intestinal proteases further hydrolyze polypeptides into short peptide chains, tripeptides, dipeptides, and amino acids.
    • Then peptidase enzymes on the membrane surfaces of the intestinal cells split most of the dipeptides and tripeptides into single amino acids.
    • Only a few peptides escape digestion and enter the blood intact.
    • Specific carriers transport amino acids (and some dipeptides and tripeptides) into the intestinal cells.
    • Amino acids inside the intestinal cells may be used for energy or to synthesize needed compounds.
    • Amino acids not used by the intestinal cells are transported across the cell membrane into the surrounding fluid where they enter the capillaries on their way to the liver.
    • The digestive system is better equipped to handle whole proteins than predigested ones (amino acid supplements) as it dismantles and absorbs amino acids at rates that are optimal for the body's use.
    • If an essential amino acid is missing, the body must dismantle its own proteins to obtain it.
    • Dietary protein needs to supply the nine essential amino acids plus enough nitrogen-containing amino groups and energy to synthesize nonessential ones.
    • The quality of a food protein is determined by comparing its amino acid composition with the essential amino acid requirements of preschool-age children, this is called a reference protein.
    • Limiting amino acid: The essential amino acid found in the shortest supply relative to the amounts needed for protein synthesis in the body.
    • Foods derived from animals (meat, seafood, poultry, eggs, and milk and milk products) provide high-quality proteins, although gelatin is an exception.
    • Proteins from plants (vegetables, nuts, seeds, grains, and legumes) have more diverse amino acid patterns and tend to be limiting in one or more essential amino acids.
    • Some plant proteins are low quality (for example, corn protein).
    • A few others are high quality (for example, soy protein).
    • Plant proteins are lower quality than animal proteins, and plants also offer less protein.
    • Vegetarians can improve the quality of their diets by combining plant-protein foods that have different but complementary amino acid patterns.
    • This strategy yields complementary proteins that together contain all the essential amino acids in quantities sufficient to support health.
    • Protein is not a major factor contributing to cancer risk.
    • The World Health Organization (WHO) has classified processed meat as a carcinogen, and red meat as a probable carcinogen.
    • Soy, fish, and milk may lower the risk of some cancers.
    • High protein intake may increase calcium excretion which may affect bone health, but depends on the adequacy of calcium in the diet.
    • The DRI Committee did not find sufficient evidence to warrant an adjustment for calcium or a UL for protein.
    • Weight-loss diets that encourage a high-protein, low-carbohydrate diet may be effective because they are low-kcalorie diets.
    • Including sufficient protein at each meal may help with weight loss by providing satiety.
    • Excretion of the end products of protein metabolism depends on an adequate fluid intake and healthy kidneys.
    • High protein intake increases the work of the kidneys, but it does not cause kidney disease.
    • It may, however, accelerate kidney deterioration in people with chronic kidney disease.
    • Restricting dietary protein especially red meat helps slow the progression of kidney disease in people who have this condition.
    • The body continuously breaks down and loses some protein and it cannot store proteins or amino acids.
    • Dietary protein is the only source of essential amino acids and nitrogen to build the nonessential amino acids and other nitrogen-containing compounds.
    • The average intake of protein in the US is 80 grams per day.
    • The RDA for adults is 0.8 gram per kilogram of healthy body weight per day.
    • For infants and children, the RDA is slightly higher.
    • An ounce of most protein foods delivers about 7 grams of protein.
    • Over a week’s time, the total recommended intake of protein foods should be about:
      • 20 % from seafood.
      • 70 % from meat, poultry, and eggs.
      • 10 % from nuts, seeds, and legumes.
    • The only other food group that provides significant amounts of protein per serving is the milk and milk products group.

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    Description

    This quiz explores the fundamentals of proteins and amino acids, including the distinction between essential and nonessential amino acids. Understand the importance of dietary sources, the role of conditional amino acids, and how peptide bonds form between amino acids. Test your knowledge on this critical aspect of biochemistry!

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