1 Protein & Amino Acids Readings: Chapter 6

2 Outline What are Proteins? Amino Acids (essential AA) Protein structure Digestion and Absorption Protein Synthesis in the cell Functions of Proteins in the body –Structure, enzymes, hormones, immunity, fluid and acid balance, transport and energy Protein turnover and nitrogen balance Recommended intake Protein Quality Protein malnutrition Too much Protein? Vegetarian Diets –Complementary proteins

3 Introduction proteins are the building blocks of the human body, forming about 17% of body weight

4 What are Proteins? organic compounds contain carbon, hydrogen, oxygen and nitrogen atoms formed from “building blocks” called amino acids

5 Amino Acids building blocks of proteins have 5 components: –central carbon atom (C) –a hydrogen atom (H) –an acid group (COOH) –an amino group (NH2) –a side chain the side chain for each type of amino acid is UNIQUE there are 20 common amino acids HC H N H HC O O Figure 6-1 page 168 side chain acid group amino group

6 Essential Amino Acids nine of the amino acids are essential and must be obtained in the diet (text refers to them as indispensable) the non-essential amino acids can be synthesized by the body in certain conditions, some non-essential amino acids may become conditionally essential histadine isoleucine leucine lysine methionine phenylalanine threonine tryptophan valine

7 amino acids are linked together by peptide bonds to form peptides and proteins occurs via a condensation reaction three amino acids = a tripeptide many amino acids = a polypeptide Amino Acids (A.A.) = a DIPEPTIDE

8 Protein Structure: A.A. Sequence the primary structure of a protein refers to its sequence of amino acids similar to the letters of the alphabet used to make words, sentences, poems, novels form an almost infinite variety of sequences to make an estimated 100, ,000 different proteins in the human body Figure 6-4 page 170

9 Protein Shape proteins have complex three dimensional shapes depending on the amino acid sequence –secondary structure –tertiary structure –quaternary structure these unique structures are important for the protein to function properly in the body

10 Protein Shape

11 Protein Shape

12 Protein Shape

13 Protein Digestion Mouth chewing no enzymatic digestion Stomach hydrochloric acid (HCl) denatures the protein –protein loses structure and shape –Also occurs with exposure to alkalinity, agitation, alcohol or cooking

14 Stomach cont. hydrochloric acid (HCl) also activates the enzyme pepsin enzyme cleaves large polypeptides into smaller polypeptides and amino acids pepsin is responsible for % of protein digestion Protein Digestion pepsinogenpepsin HCl

15 Protein Digestion Small Intestine site of most protein digestion pancreatic and intestinal cells secrete enzyme precursors called proenzymes –when proenzymes reach the lumen of small intestine, part of proenzyme is cleaved off, activating the enzyme –this is important because it protects the cells that secrete the enzymes from being digested enzymes that digest proteins are called proteases

16 Protein Digestion Small Intestine cont. an enzyme secreted by the intestinal cells called enteropeptidase activates the enzyme trypsin trypsin digests polypeptides and activates other enzymes dipeptidases & tripeptidases digest dipeptides & tripeptides into single a.a.’s trypsinogentrypsin enteropeptidase

17 Protein Absorption requires specific transporters for individual amino acids, dipeptides, and tripeptides –some absorbed by active transport –others absorbed by facilitated diffusion some amino acids compete for the same transporter intestinal cells keep the amino acids they need the rest enter the blood and travel to the liver

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19 Protein Synthesis the sequences in which amino acids are joined to form proteins is determined by our genes genes are small segments of DNA, which serves as a template for protein synthesis DNA is composed of two strands of linked nucleotide chains that are twisted together to form a double helix like a code, the sequence of nucleotides determines the order in which the amino acids are combined

21 Protein Synthesis if a non-essential amino acid is missing during protein synthesis, the cell may either: - make the amino acid, or - obtain it from the liver if an essential amino acid is missing during protein synthesis: - the body may break down another body protein to provide the essential amino acid - if the essential amino acid is not available, protein synthesis will stop

22 Protein Synthesis Genetic disorders result from either: an error in the original DNA copy errors in translating the DNA sequence into the corresponding amino acid sequence Example: sickle cell anemia due to a genetic mutation in the protein hemoglobin which carries O 2 in the blood hemoglobin is unable to carry oxygen efficiently, results in many medical problems

Structure Enzymes Hormones Antibodies Fluid Balance Acid-Base Balance Membrane Transporters Transport in the blood Synthesis of non-protein compounds Functions of Proteins

24 Structure & Mechanical Functions building blocks of most body structures important for growth and development also needed for REPAIR & MAINTENANCE of tissues examples: collagen, keratin, motor proteins

25 Figure 6.7, pages 212 & 213 Enzymes acts as catalysts to facilitate chemical reactions change other molecules while remaining unchanged themselves Example: digestive enzymes Figure 6-9, page 177

26 Hormones hormones are messenger molecules that travel through the blood regulate many body processes Examples: insulin, glucagon

27 Immune Functions form antibodies that help fight off infectious disease synthesized by immune cells called lymphocytes in response to an infection label the pathogen so that other immune cells can recognize the pathogen and destroy it

28 Regulation of Fluid Balance all compartments within the body are filled with fluid proteins are required to balance fluid distribution between these compartments CELL INTERSTITIAL SPACE CAPILLARY

29 Regulation of Fluid Balance pressure of blood against the walls of the capillary tends to push fluid out INTERSTITIAL SPACE BLOOD

30 Regulation of Fluid Balance pressure of proteins tends to pull fluid in INTERSTITIAL SPACE PROTEINS

31 Regulation of Fluid Balance a  in plasma proteins  ’s the forces holding fluid in the blood & fluid leaks into the interstitial space causing edema

32 Regulation of Fluid Balance Occurs with inadequate dietary protein, kidney disease, burns, & liver disease. Edema of the leg

33 Acid-Base Balance the acidity of a solution is determined by the amount of hydrogen ions it contains measured on a logarithmic scale called the pH scale Acids: release H + into a solution Bases: accept H + from a solution proteins accept & release H + to regulate pH  acidity  pH  acidity  pH ALKALOSISACIDOSIS

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35 Transport Functions a) transport molecules in the blood Examples: –lipoproteins –hemoglobin –transferrin b) transport molecules across membranes Examples –sodium - potassium pump (Na + /K + pump)

36 Source of Energy and Glucose provides 4 kcal per gram normally does NOT contribute much to energy supply of body Conditions in which protein is used for energy: –consumed in excess of body’s needs to synthesize body proteins –dietary intake of carbohydrate is insufficient to supply glucose –athletic endurance events

37 Source of Energy & Glucose in order to use proteins as energy, the amino group (NH 3 ) must be removed –process is called deamination produces: –KETO ACID: excess can disrupt acid-base balance –AMONIA: converted to UREA by the LIVER, then excreted by the KIDNEY remaining components (carbon skeleton) used to provide energy or synthesize glucose

38 A.A. Pool & Protein Turnover Amino Acid Pool = amino acids free in body tissues & fluids available for new protein synthesis Protein Turnover = the constant synthesis & breakdown of proteins in the body

39 Protein and Nitrogen Balance cells are constantly turning over protein balance between protein degradation and synthesis can be determined by measuring: –the amount of nitrogen in protein consumed –the amount of nitrogen excreted from the body N in = N out  NITROGEN EQUILIBRIUM in healthy adults, protein synthesis is balanced with degradation

40 Protein and Nitrogen Balance N in > N out  positive nitrogen balance if the body synthesizes more protein than it degrades, positive nitrogen status occurs when does this occur? N in < N out  negative nitrogen balance body degrades more than it synthesizes resulting in a net protein loss from the body when does this occur?

41 Food Sources of Protein meats fish & seafood poultry LEGUMES NUTS & SEEDS

42 Recommended Intakes recall: DRI are meant for healthy people recommendations assume protein is consumed with adequate carbohydrate & fat to provide a healthy energy intake typical NA intake is 95 g/day (men) & 65 g/day (women) AMDR = 10-35% of caloric intake generally overestimates needs

43 Recommended Intakes Healthy Adults Pregnancy Power Athletes Endurance Athletes 0.8 g/kg/day 0.8 g/kg/day + 25 g g/kg/day g/kg/day

44 Proteins in the Diet: Sources of Protein Example: male weighing 160 pounds (72.7 kg) needs 58 grams of protein per day chicken drumstick 12 g 1 egg 6 g ¼ cups peanuts 9.5 g ½ cup chopped broccoli3 g ½ cup lentils 9 g 1 bagel 7 g 1 banana 1 g 1 cup skim milk 9 g ½ cup tuna 19.5 g

Breakfast 14 g Lunch 18 g Which supper would you choose to provide sufficient protein without exceeding the RDA for an individual who weighs 132 pounds (60 kg)? RDA = 0.8 g/kg x 60 = 48 g 27 g 18 g 51 g = 32 g

46 Protein Quality determined by the protein’s ability to supply the essential amino acids and how well it is used in the body Complete Proteins contain all the essential amino acids in relatively the same amounts as the body requires Examples: most animal derived proteins SOY PROTEIN

47 Protein Quality Incomplete Proteins fail to provide all of the essential amino acids in sufficient quantities to support the bodies needs Examples: vegetables, legumes, grains

48 Protein Quality Limiting Amino Acid the essential amino acid found in the LEAST amount relative to the amounts needed to support protein synthesis in the body Examples: –legumes often have insufficient methionine and tryptophan –grains commonly have insufficient isoleucine and lysine

49 Protein Quality What happens if the diet is lacking one or more of the essential amino acids? PROTEIN SYNTHESIS WILL BE LIMITED!

50 Protein Quality Digestibility a measure of the amount of amino acids absorbed from a given protein intake influenced by: –the proteins food source –other foods consumed with it PLANT PROTEINS are LESS digestible because they are contained within cell walls that resist digestion

51 Protein Quality Reference Proteins used as a standard for measuring protein quality, assigned a value of 100 Chemical or Amino Acid Scoring compares a protein’s aa pattern with a reference protein Protein Efficiency Ratio (PER) measures growth of an animal (rats) compared to the animal’s protein intake Net Protein Utilization (NPU) / Biological Value measures how efficient a protein is at supporting the body’s needs PDCAAS calculate amino acid score multiply by the digestibility

52 Protein Energy Malnutrition (PEM) results when an individual is deprived of PROTEIN or ENERGY or BOTH Protein AND Energy more common in children most prevalent form of malnutrition worldwide, affecting over 500 million children associated with infections, diarrhea, and multiple nutrient deficiencies two forms: marasmus & kwashiorkor

53 Marasmus “dying away” chronic protein AND energy deficiency most common in children mos. “skin and bones” appearance muscle & tissue wasting cessation of growth impaired brain development & learning ability increased incidence of infections

54 Kwashiorkor develops rapidly (acute) severe protein deficiency, diet still provides limited energy occurs between mos. characterized by edema in face and limbs & a bloated belly development of a fatty liver increased incidence of infections also see loss of appetite, apathy, skin lesions

55 Too much Protein?

56 Protein Supplements Build Muscle? physical training builds muscle  requiring some extra protein recommendation for power athletes is grams of protein per kilogram of body weight exercise does not require protein to provide energy beyond 2 g/kg, studies show no increased synthesis of muscle protein

57 Amino Acid Supplements Improve Health? body not designed to handle high concentration (increases demand for transporter), may cause deficiency of another, potentially dangerous

58 Vegetarian Diets Types of Vegetarians: - Vegan - Lacto-Vegetarian –(“lacto” = milk) - Lacto-Ovo-Vegetarian –(“ovo” = egg) - Lacto-Ovo-Pesca-Vegetarian –(“pesca” = fish)

59 Vegetarian Diets: Health Benefits? healthier body weight lower blood pressure  risk of coronary artery disease  incidence of cancer

60 Protein in a Plant-Based Diet in general plant derived proteins are lower quality than animal derived proteins need to ensure adequacy of the essential amino acids dairy and eggs provide high quality proteins for lacto-ovo-vegetarians employing the dietary planning principle of variety ensures vegans are not lacking involves combining plant protein foods that have different but complementary amino acid patterns

61 Protein in a Plant-Based Diet Complementary Proteins two or more proteins that make up for each others inadequate supply of specific essential amino acids (i.e. the LIMITING AMINO ACIDS) so that together they yield a sufficient amount of all nine essential amino acids IleLysMetTrp legumes grains together

62 Protein in a Plant-Based Diet Mutual Supplementation the dietary strategy that brings complementary proteins together so that each food supplies the amino acids lacking in the other

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64 Health Risks of Vegetarianism? a poorly planned vegetarian diet can potentially lead to several nutrient deficiencies: Iron Zinc Calcium Vitamin B 12 Vitamin B 6 Vitamin D remember that a vegetarian diet is also not necessarily low in fat & high in fiber!

65 Dietary Recommendations for Vegetarians choose a variety of foods, including whole grains, vegetables, fruits, legumes, nuts, seeds, and if desired, dairy products and eggs choose whole, unrefined foods often; minimize intake of highly sweetened, fatty, and heavily refined foods if dairy products and eggs are consumed, limit consumption of high fat dairy foods and eggs vegans should consume a regular source of Vitamin B 12 (and if sun exposure is limited, Vitamin D also)