Understanding Proteins: Structure, Function, metabolism and Dietary Needs
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This comprehensive PowerPoint presentation offers a detailed overview of proteins, their structure, classification, sources, digestion, absorption, functions, and daily requirements. It also explores the clinical significance of protein intake, including deficiency disorders like kwashiorkor and marasmus. Perfect for nursing students, clinical nutrition learners, NEET/UGC-NET aspirants, and anyone interested in understanding the role of proteins in health and disease. Well-organized content, clear visuals, and exam-friendly points make this presentation a valuable study and teaching resource.
Understanding Proteins: Structure, Function, metabolism and Dietary Needs
- 2. INTRODUCTI ON • Proteins are complex macromolecules essential for the growth, repair, and functioning of the body. They play structural, enzymatic, hormonal, and immune roles. Proteins are made up of chains of amino acids linked together by peptide bonds. • Proteins are composed of amino acids, which contain carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sometimes sulfur (S).** There are 20 standard amino acids that combine in various sequences to form different proteins.
- 3. CLASSIFICATIO N OF PROTEINS Proteins are classified based on different criteria: • 1. Based on Composition • Simple Proteins – Yield only amino acids on hydrolysis (e.g., Albumin, Globulin). • Conjugated Proteins – Contain a non-protein part (e.g., Hemoglobin, Glycoproteins). • Derived Proteins – Breakdown products of proteins (e.g., Peptones, Proteoses). 2. Based on Function • Structural Proteins – Provide strength and support (e.g., Collagen, Keratin). • Enzymatic Proteins – Catalyze biochemical reactions (e.g., Amylase, Pepsin). • Hormonal Proteins – Regulate physiological processes (e.g., Insulin, Growth hormone).
- 4. AMINO ACIDS • Amino acids are the building blocks of proteins. They are organic compounds containing carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sometimes sulfur (S). Amino acids are linked by peptide bonds to form proteins, which play vital roles in the body's structure and functions. • Each amino acid has: ✅ A central carbon (C) ✅ An amino group (-NH₂) ✅ A carboxyl group (-COOH) ✅ A hydrogen atom (H) ✅ A side chain (R-group), which varies for each amino acid
- 5. • Transport Proteins – Carry molecules (e.g., Hemoglobin, Albumin). • Defensive Proteins – Help in immunity (e.g., Antibodies). • Contractile Proteins – Assist in movement (e.g., Actin, Myosin). • Storage Proteins – Store essential substances (e.g., Ferritin for iron storage). 3. Based on Shape • Fibrous Proteins – Long, insoluble, structural proteins (e.g., Collagen, Elastin). • Globular Proteins – Spherical, soluble proteins (e.g., Hemoglobin, Enzymes).
- 6. TYPES OF AMINO ACIDS Essential Amino Acids (EAA) • Essential amino acids cannot be synthesized by the body and must be obtained from the diet. These are crucial for protein synthesis, enzyme function, and overall growth. List of Essential Amino Acids: • Histidine • Isoleucine • Leucine • Lysine • Methionine • Phenylalanine • Threonine • Tryptophan • Valine
- 7. Non- Essential Amino Acids (NEAA) Non-essential amino acids can be synthesized by the body from other nutrients, so they don’t necessarily need to come from the diet. List of Non-Essential Amino Acids: • Alanine • Asparagine • Aspartic acid • Glutamic acid
- 8. Conditionall y Essential Amino Acids Some amino acids become essential under certain conditions, such as illness, stress, or rapid growth. List of Conditionally Essential Amino Acids: • Arginine • Cysteine • Glutamine • Glycine • Proline • Serine • Tyrosine • Example: Arginine is essential for infants but not for healthy adults.
- 9. Digestion, Absorptio n, Metabolis m, and Storage of Proteins 1. Digestion of Proteins Protein digestion starts in the stomach and continues in the small intestine with the help of enzymes. A. In the Stomach • Pepsin (activated from pepsinogen by HCl) breaks proteins into polypeptides and peptides. • Hydrochloric Acid (HCl) denatures proteins, making them more accessible for enzymatic digestion. B. In the Small Intestine • Pancreatic Enzymes: • Trypsin (from trypsinogen) • Chymotrypsin (from chymotrypsinogen) • Carboxypeptidase These enzymes break polypeptides into smaller peptides and amino acids. • Intestinal Enzymes: • Aminopeptidase and Dipeptidase further break peptides into free amino acids for absorption.
- 10. 2. Absorptio n of Proteins • Occurs in the small intestine (jejunum and ileum) via active transport. • Amino acids are absorbed into the blood and transported to the liver via the portal vein. • Small peptides may be absorbed and further broken down inside intestinal cells.
- 11. 3. Metabolism of Proteins Protein metabolism involves the breakdown, utilization, and disposal of amino acids in the body. This process ensures that proteins are properly used for growth, repair, and energy production. 1. Protein Breakdown (Catabolism) • Proteins from food and body tissues (muscle proteins) are broken down into amino acids. • This process occurs mainly in the stomach and small intestine with the help of enzymes like pepsin, trypsin, and chymotrypsin. • The amino acids then enter the amino acid pool, which is available for different metabolic pathways. 2. Amino Acid Utilization Once in the amino acid pool, amino acids have three possible fates: - Protein Synthesis – Used to build new proteins (enzymes, hormones, muscle, etc.). - Energy Production – If needed, amino acids are broken down for energy. - Storage as Fat or Glucose – Excess amino acids are converted into other forms.
- 12. 3. Transamination (Amino Acid Conversion) • If the body needs a specific amino acid that is not available, it can convert one amino acid into another. • This occurs through transamination, where an amino group (-NH₂) is transferred from one amino acid to a keto acid. • Enzymes like aminotransferases help in this process. • Example: Glutamate can donate its amino group to form alanine or aspartate.
- 13. 4. Deamination (Removal of Ammonia) • When amino acids are used for energy, their nitrogen group must be removed. • This happens through deamination, where the amino group is separated, forming ammonia (NH₃). • The remaining carbon skeleton is converted into energy or stored as fat.
- 14. 5. Urea Cycle (Ammonia Detoxification) • Ammonia (NH₃) is toxic to the body, so it must be converted into a non-toxic form. • The liver converts ammonia into urea through the urea cycle (also called the ornithine cycle). • Urea is then transported to the kidneys and excreted in the urine. • Steps in the Urea Cycle: • Ammonia combines with CO₂ to form carbamoyl phosphate. • Ornithine reacts with carbamoyl phosphate, forming citrulline. • Citrulline is converted into argininosuccinate using aspartate. • Argininosuccinate splits into arginine and fumarate. • Arginine is converted into urea and ornithine, completing the cycle.
- 15. 6. Fate of Carbon Skeleton (Energy Production & Storage) • After deamination, the remaining carbon skeleton of amino acids can be used in different ways: - Gluconeogenesis – Converted into glucose (for energy) when carbohydrate levels are low. - Ketogenesis – Converted into ketone bodies if glucose is not needed. - Fat Synthesis (Lipogenesis) – If protein intake exceeds the body's needs, amino acids are converted into fatty acids and stored as fat. • Amino acids are classified based on their metabolic fate: • Glucogenic amino acids Converted into glucose (e.g., Alanine, Aspartate). → • Ketogenic amino acids Converted into ketones (e.g., Leucine, Lysine). → • Both glucogenic and ketogenic (e.g., Isoleucine, Phenylalanine, → Tyrosine).
- 16. STORAGE Unlike carbohydrates (stored as glycogen) and fats (stored as adipose tissue), proteins are not stored in a specific form in the body. Instead, the body maintains a dynamic amino acid pool that is constantly being used and replenished. 1. Amino Acid Pool - The body keeps a circulating pool of free amino acids in the blood and cells. - These amino acids come from digested dietary proteins or protein breakdown (catabolism) from muscles and tissues. - The amino acid pool is used for protein synthesis, enzyme production, and other functions. 2. Excess Amino Acids: Fate of Unused Proteins Since there is no storage depot for proteins, excess amino acids undergo: Deamination (Removal of the Amino Group) - The nitrogen part is removed, forming ammonia (NH₃). - Ammonia is converted to urea in the liver and excreted via the kidneys. Conversion to Glucose (Gluconeogenesis) - Some amino acids are converted into glucose and stored as glycogen in the liver and muscles. - This happens during fasting or when carbohydrate intake is low. Conversion to Fat (Lipogenesis) - If protein intake exceeds the body's needs, amino acids are converted into fatty acids and stored as adipose tissue. 3. Functional Protein as a Backup - When needed, the body can break down muscle proteins to supply amino acids for energy or essential functions. - This happens in cases of starvation, prolonged fasting, or protein deficiency.
- 17. FUNCTION OF PROTEINS 1. Structural Function Proteins provide structural support to cells, tissues, and organs. Examples: • Collagen – Found in skin, bones, cartilage, tendons, and ligaments; provides strength and elasticity. • Keratin – Found in hair, nails, and the outer layer of the skin; provides protection. • Elastin – Present in connective tissues and blood vessels; provides flexibility. 2. Enzymatic Function (Catalysts of Biochemical Reactions) ⚙️ Proteins act as enzymes, which speed up biochemical reactions in the body. Examples: • Amylase – Breaks down starch into sugars. • Pepsin – Aids in protein digestion in the stomach. • Lipase – Helps digest fats. • DNA Polymerase – Involved in DNA replication. Without enzymes, chemical reactions in the body would be too slow to sustain life.
- 18. 3. Transport Function (Carrier Proteins) Proteins help in the transport of essential molecules across the body. Examples: • Hemoglobin – Transports oxygen in the blood. • Myoglobin – Stores oxygen in muscles. • Albumin – Carries hormones, fatty acids, and drugs in the blood. • Lipoproteins (LDL & HDL) – Transport cholesterol and lipids in the blood 4. Immune Function (Defense & Protection) Proteins play a vital role in the immune system, helping to protect the body from infections and diseases. Examples: • Antibodies (Immunoglobulins) – Identify and neutralize pathogens (e.g., bacteria, viruses). • Complement Proteins – Assist in immune responses by destroying microbes. • Cytokines – Signal immune cells to respond to infections. Without proteins, the immune system would not function effectively.
- 19. 5. Hormonal Function (Chemical Messengers) Some proteins act as hormones, which regulate bodily functions by transmitting signals between cells and organs. Examples: • Insulin – Regulates blood sugar levels. • Glucagon – Works opposite to insulin, increasing blood sugar when needed. • Growth Hormone (GH) – Stimulates growth and cell regeneration. • Thyroid Hormones (T3 & T4) – Control metabolism. 6. Contractile Function (Muscle Contraction & Movement) Proteins are essential for movement at both the cellular and muscular levels. Examples: • Actin & Myosin – Key proteins in muscle contraction. • Tropomyosin & Troponin – Regulate muscle movements. • Dynein & Kinesin – Involved in intracellular transport. Without contractile proteins, movements like walking, running, and even blinking wouldn’t be possible.
- 20. 7. Storage Function (Nutrient Storage & Supply) Some proteins serve as storage molecules for essential nutrients. Examples: • Ferritin – Stores iron in the liver. • Casein – Found in milk; provides essential amino acids for infant growth. • Ovalbumin – Found in egg whites; serves as a protein source for embryo development. 8. Regulatory Function (Gene Expression & Cellular Activities) Proteins regulate gene expression and cellular functions by interacting with DNA and RNA. Examples: • Histones – Help in DNA packaging and gene regulation. • Transcription Factors – Control gene activation. These proteins determine which genes are turned "on" or "off" in cells. 9. Energy Source (Alternative Fuel During Starvation) Proteins can be broken down for energy when carbohydrate and fat stores are low. • Proteins undergo deamination, where the nitrogen part is removed. • The remaining carbon skeleton is converted into glucose or ketones for energy. Though proteins provide energy (4 kcal/g), their primary role is not energy production but rather building and repairing tissues.
- 21. Summary Table of Protein Functions Function Examples Structural Collagen, Keratin, Elastin Enzymatic Amylase, Pepsin, Lipase, DNA Polymerase Transport Hemoglobin, Myoglobin, Albumin, Lipoproteins Immune Antibodies, Complement Proteins, Cytokines Hormonal Insulin, Glucagon, Growth Hormone, Thyroid Hormones Contractile Actin, Myosin, Tropomyosin, Dynein Storage Ferritin (Iron), Casein (Milk), Ovalbumin (Eggs) Regulatory Histones, Transcription Factors Energy Proteins converted into glucose or ketones during starvation
- 22. Protein Deficiency Protein deficiency occurs when the body does not get enough protein from the diet, leading to various health issues. This condition is common in malnourished individuals, people with chronic illnesses, and those following extremely low-protein diets. 1. Causes of Protein Deficiency • Inadequate dietary intake (poverty, food shortages, unbalanced diet) • Malabsorption disorders (Crohn’s disease, celiac disease) • Increased protein requirements (pregnancy, lactation, infections, burns) • Excessive protein loss (kidney diseases, severe wounds) 2. Symptoms of Protein Deficiency • Muscle Wasting – The body breaks down muscle proteins for energy. • Edema (Swelling) – Due to low albumin levels, which regulate fluid balance. • Hair Loss & Brittle Nails – Hair becomes thin and falls out. • Weak Immunity – Increased infections due to weak antibody production. • Fatty Liver – Protein deficiency disrupts fat metabolism in the liver. • Slow Wound Healing – Due to impaired tissue repair. • Stunted Growth in Children – Leads to poor development and weak bones.
- 23. PROTEIN ENERGY MALNUTRITION A. Kwashiorkor ("Edematous Malnutrition") Cause: Extreme protein deficiency despite adequate calorie intake Symptoms: • Swollen belly (fluid retention) • Skin and hair changes (discoloration, thinning) • Growth failure • Mental apathy and irritability B. Marasmus ("Severe Malnutrition") Cause: Severe protein & calorie deficiency (starvation). Symptoms: • Severe weight loss • Muscle wasting (thin arms & legs) • Weak immune system • Dehydration
- 24. Protein Overconsumption Eating too much protein—especially from animal sources—can have negative effects on the body. 1. Causes of Excess Protein Intake • High-protein diets (e.g., Keto, Atkins, Paleo) • Overuse of protein supplements • Extreme bodybuilding diets 2. Short-Term Effects of Excess Protein • Dehydration – High protein intake increases kidney workload, leading to water loss. • Digestive Issues – Constipation or diarrhea due to lack of fiber in high-protein diets. • Bad Breath (Ketosis) – Caused by excessive ketone production. 3. Long-Term Health Risks of Excess Protein A. Kidney Damage (Risk for Kidney Patients) 🚨 • Excess protein increases urea production, burdening the kidneys. • People with kidney disease should limit protein intake to avoid kidney failure. B. Bone Loss & Osteoporosis 🦴 • High-protein diets increase calcium excretion in urine, leading to weak bones. • Over time, this may contribute to osteoporosis.
- 25. C. Increased Risk of Heart Disease • High animal protein intake (red meat, processed meats) raises cholesterol levels. • Saturated fat in meats increases the risk of heart disease & stroke. D. Liver Strain & Fatty Liver Disease • Excess protein can lead to non-alcoholic fatty liver disease (NAFLD). • This is due to excess amino acids being converted into fat. E. Increased Cancer Risk • Diets rich in red meat & processed meat are linked to colon cancer. • Excess animal protein may promote cancer cell growth due to high IGF-1 levels.
- 26. Difference between complete protein and incomplete protein
- 27. RECOMMENDED DIETARY ALLOWANCE Age Group Protein Requirement (g/day) Infants (0–6 months) 9–10g Children (1–3 years) 13g Children (4–8 years) 19g Teens (14–18 years) 46g (girls), 52g (boys) Adults (19–50 years) 46g (women), 56g (men) Pregnant/Lactating Women 60–71g
- 28. Bioavailability Animal Sources Plant Sources High (90-100%) - Whole Egg (~100) - Whey Protein (~100) - Casein (~100) - Milk (~95) - Fish (~90-95) - Poultry (~90-95) - Lean Meats (~90-95) - Soy Protein Isolate (~90) Moderate (70-90%) - Cheese (~75-85) - Yogurt (~80-90) - Legumes (Lentils, Chickpeas, Beans: ~70-85) - Tofu (~75-85) - Quinoa (~80- 90) Low (50-70%) - None - Whole Grains (Brown Rice, Oats, Wheat: ~50-70) - Nuts & Seeds (Almonds, Peanuts, Sunflower Seeds: ~50-70) - Vegetables (~50-70) Very Low (<50%) - Gelatin (~30-40, lacks essential amino acids) - Corn (~40-50)
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