Chapter 6: The Proteins and Amino Acids

1. Chapter 6: The Proteins and Amino Acids Dr. Fralinger 10/8/07

2. The Structure of Proteins Proteins are unique among the energy nutrients in that they possess nitrogen-containing amine groups and are composed of 20 different amino acid units Of the 20 amino acids, some are essential and some are essential only in special circumstances

3. The Structure of Proteins Proteins Compounds composed of carbon, hydrogen, oxygen, and nitrogen and arranged as strands of amino acids Amino acids The building blocks of protein Amine group The nitrogen-containing portion of an amino acid

4. The Structure of Proteins Side chain The unique chemical structure attached to the backbone of each amino acid that differentiates one amino acid from another Essential amino acids Amino acids that either cannot be synthesized at all by the body or cannot be synthesized in amounts sufficient to meet physiological needs

6. The Structure of Proteins Conditionally essential amino acid Amino acid that is normally nonessential, but must be supplied by the diet in special circumstances when the need for it exceeds the body�s ability to produce it Peptide bond Bond that connects one amino acid with another, forming a link in a protein chain Amino acids link into long strands that coil and fold to make a wide variety of different proteins

8. The Variety of Proteins Collagen Type of body protein from which connective tissues such as scars, tendons, ligaments, and the foundations of bones and teeth are made Enzymes Protein catalysts Hemoglobin Globular protein of red blood cells, whose iron atoms carry oxygen around the body via the bloodstream

10. The Variety of Proteins Inherited amino acid sequences Each type of protein has a distinctive sequence of amino acids and so has great specificity Often, cells specialize in synthesizing particular types of proteins in addition to the proteins necessary to all cells Nutrients and gene expression Nutrients act as environmental signals affecting genetic activities

13. The Variety of Proteins Denaturation of Proteins Denaturation � the irreversible change in a protein�s shape brought about by heat, acids, bases, alcohol, salts of heavy metals, or other agents Denaturation begins the process of digesting food protein and can also destroy body proteins

14. Can eating extra protein make muscles grow larger? No! Hard work is the trigger for he genes to build more muscle tissue Exercise generates cellular messages that stimulate DNA to begin the process of building up muscle fibers (made of protein)

15. Can eating extra protein make muscles grow larger? A snack rich in protein and carbs eaten directly after exercise may be of some help The path to bigger muscles is rigorous physical training with adequate energy and nutrients from balanced, well-timed meals, not consuming excess protein

16. Digestion and Absorption of Protein Each protein performs a special task in a particular tissue of a specific kind of animal or plant When you eat food proteins, the body must first alter them by breaking them down into amino acids; only then can it rearrange them into specific human body proteins

17. Protein Digestion Involves denaturation by stomach acid, then enzymatic digestion in the stomach and small intestine to amino acids, dipeptides, and tripeptides

18. Protein Digestion Polypeptides Protein fragment of many (>10) amino acids bonded together Dipeptides Protein fragments that are two amino acids long Tripeptides Three amino acids long

20. After protein is digested, what happens to amino acids? The cells of the small intestine complete digestion, absorb amino acids and some larger peptides, and release them into the bloodstream for use by the body�s cells

22. The roles of proteins in the body Support growth and maintenance Build enzymes, hormones, and other compounds Build antibodies Maintain fluid and electrolyte balance Maintain acid-base balance Clot blood Provide energy and glucose

23. Supporting growth and maintenance The body needs dietary amino acids to grow new cells and to replace worn-out ones Protein turnover The continuous breakdown and synthesis of body proteins involving the recycling of amino acids

24. Building Enzymes, hormones, and other compounds Enzymes are among the most important because they act as catalysts that facilitate chemical reactions Hormones Chemical messengers secreted by a number of body organs in response to conditions that require regulation Each hormone affects a specific organ or tissue and elicits a specific response

26. Building Enzymes, hormones, and other compounds Serotonin Compound related in structure to (and made from) the amino acid tryptophan Serves as one of the brain�s principal neurotransmitters

27. Building antibodies Antibodies are proteins that defend against foreign proteins and other foreign substances within the body Antibodies Large proteins of the blood, produced by the immune system in response to an invasion of the body by foreign substances (antigens) Combine with and inactiveate the antigens

28. Building antibodies Immunity Protection from or resistance to a disease or infection by development of antibodies and by the actions of cells and tissues in response to a threat

29. Maintaining Fluid and Electrolyte Balance Proteins help to maintain the fluid and electrolyte balance by regulating the quantity of fluids in the compartments of the body

30. Maintaining Fluid and Electrolyte Balance To remain alive, cells must contain a constant amount of fluid Too much can cause them to rupture Too little makes them unable to function By maintaining stores of internal proteins and also of some minerals, cells retain the fluid they need Edema Swelling of body tissue caused by leakage of fluid from the blood vessels Seen in protein deficiency

31. Maintaining acid-base balance Proteins buffer the blood against excess acidity or alkalinity Acids Compounds that release hydrogens in a watery solution Bases Compounds that accept hydrogens from solutions Acid-base balance Equilibrium between acid and base concentrations in the body fluids

33. Maintaining acid-base balance Buffers Compounds that help keep a solution�s acidity or alkalinity constant Acidosis Condition of excess acid in the blood, indicated by a below-normal pH Alkalosis Condition of excess base in the blood, indicated by an above-normal blood pH

34. Clotting of blood Proteins that clot the blood prevent uncontrolled bleeding from injuries Proteins form a stringy net that traps blood cells to form a clot Clot acts as a plug to stem blood flow from the wound As the wound heals, the protein collagen finishes the job by replacing the clot with scar tissue

35. Providing Energy and Glucose When insufficient carbs and fat are consumed to meet the body�s energy need, food protein and body protein are sacrificed to supply energy The nitrogen part is removed from each amino acid, and the resulting fragment is oxidized for energy

36. Providing Energy and Glucose No storage form of amino acids exists in the body Urea Principal nitrogen-excretion product of protein metabolism Generated mostly by removal of amine groups from unneeded amino acids or from amino acids being sacrificed to a need for energy

38. The fate of an amino acid Can be metabolized to protein, nitrogen plus energy, glucose, or fat Will be metabolized to protein only if sufficient energy is present from other sources The diet should supply all essential amino acids and a full measure of protein according to guidelines

39. The fate of an amino acid Amino acids in a cell can be: Used to build protein Converted to other amino acids or small nitrogen-containing compounds Stripped of their nitrogen, amino acids can be: Burned as fuel Converted to glucose or fat

40. The fate of an amino acid Amino acids are wasted when: Energy is lacking Protein is overabundant An amino acid is oversupplied in supplement form The quality of the diet�s protein is too low (too few essential amino acids)

41. Food Protein: Quality, Use, and Need The body�s response to protein depends on many factors: Body�s state of health Other nutrients and energy taken with the protein The protein�s quality

42. Which kinds of protein-rich foods are easiest to digest? Digestibility of protein varies from food to food, and cooking can improve or impair it Legumes Plants of the bean, pea, and lentil family that have roots with nodules containing special bacteria Bacteria can trap nitrogen from the air in the soil and make it into compounds that become part of the plant�s seeds

43. Amino Acid Composition A protein�s amino acid assortment greatly influences its usefulness to the body Proteins lacking essential amino acids can be used only if those amino acids are present form other sources

44. Amino Acid Composition High-quality proteins Dietary proteins containing all the essential amino acids in relatively the same amounts that human beings require May also contain nonessential amino acids Amino acid pools Amino acids dissolved in the body�s fluids that provide cells with ready raw materials from which to build new proteins or other molecules

45. Amino Acid Composition Limiting amino acid Essential amino acid that is present in dietary protein in an insufficient amount, thereby limiting the body�s ability to build protein Complementary proteins Two or more proteins whose amino acid assortments complement each other in such a way that the essential amino acids missing from one are supplied by the other

46. Amino Acid Composition Mutual supplementation The strategy of combining two incomplete protein sources so that the amino acids in one food make up for those lacking in the other food

47. Measuring Protein Quality The quality of a protein is measured by its amino acids Its digestibility By how well it meets human needs Protein digestibility-corrected amino acid score (PDCAAS) Measuring tool used to determine protein quality Reflects protein�s digestibility as well as the proportions of amino acids that it provides

48. How much protein do people really need? The amount of protein needed daily depends on size and stage of growth DRI recommended intake for adults is 0.8 gram or protein per kilogram of body weight Protein recommendations are based on nitrogen balance studies, which compare nitrogen excreted from the body with nitrogen ingested in food

49. How much protein do people really need? To figure your protein need: Find your body weight in pounds Convert pounds to kilograms by dividing pounds by 2.2 Multiply kilograms by 0.8 to find total grams of protein recommended

50. How much protein do people really need? Nitrogen balance Amount of nitrogen consumed compared with the amount excreted in a given time period

51. Protein Deficiency and Excess Protein-deficiency symptoms are always observed when either protein or energy is deficient Extreme food energy deficiency is marasmus Extreme protein deficiency is kwashiorkor The two diseases overlap most of the time and together are called PEM

52. Protein Deficiency and Excess Protein-energy malnutrition (PEM) World�s most widespread malnutrition problem Includes both marasmus and kwashiorkor and states of overlap Hunger Physiological craving for food Progressive discomfort, illness, and pain resulting from the lack of food

53. Protein Deficiency and Excess Marasmus Calorie-deficiency disease; starvation Kwashiorkor Disease related to protein malnutrition, with a set of recognizable symptoms, such as edema Dysentery Infection of the digestive tract that causes diarrhea

54. Is it possible to consume too much protein? Health risks may follow the overconsumption of protein-rich foods DRI recommends that the diet contain no more than 35% of calories from protein to decrease risks of chronic diseases Overconsumption may pose risks for the heart, weakened kidneys, and for the bones