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Proteins: Classification, Structure, and Biological Roles
- 1. A Constituent Collegeof Yenepoya (Deemed to be University) Naringana, Mangaluru Proteins Ms.Sajini Assistant professor Department of Pharmaceutical chemistry
- 2. Table of content •Definition, and classification of protein • Definition and classification of amino acids • Structure of proteins • Biological role of protein and aminoacids • Disease related to malnutrition of proteins
- 3. Introduction Proteins are naturallyoccurring polymers made up of amino acids linked together by peptide bonds (-CONH-) having high molecular weight found in all living cells
- 4. Classification of protein Proteins Conjugated proteins Derivedproteins Simple proteins Albumin Globulin Glutelin Prolamines Scleroproteins Histones Nucleoproteins Phosphoproteins Glycoproteins Prophyrinoproteins Lipoproteins Flavoproteins metalloproteins Primary derived proteins Eg. Myosin, fibrin, coagulated albumin Secondary derived proteins Globular proteins Eg, insulin, globulin, albumin Fibrous proteins, eg, keratin, fibrin, collagen
- 5. Proteins can beclassified based on their composition and solubility into the following major categories Simple Proteins (Homoproteins) Composition: These proteins are composed only of amino acids or their derivatives Solubility: Their solubility can vary depending on the specific protein but can be broadly categorized into: Albumins: Soluble in water and dilute salt solutions (e.g., serum albumin) Globulins: Soluble in dilute salt solutions but insoluble in pure water (e.g., immunoglobulin s) Glutelins: Soluble in dilute acids or bases, insoluble in water (e.g., gluten in wheat Prolamins: Soluble in 70– 80% ethanol, insoluble in water (e.g., gliadin in wheat) Scleroproteins (Fibrous proteins): Insoluble in water and resistant to digestive enzymes (e.g., collagen, keratin)
- 6. Conjugated Proteins (Heteroproteins): Composition:These proteins consist of amino acids combined with a non-protein prosthetic group. The type of prosthetic group influences solubility. Phosphoprot eins: Contain phosphate groups, generally soluble (e.g., casein) Chromoprotei ns: Contain pigmented prosthetic groups (e.g., hemoglobin is soluble in water) Metalloprotei ns: Contain metal ions, typically soluble (e.g., ferritin) Nucleoprot eins: Contain nucleic acids, often soluble (e.g., ribosomes) Lipoproteins: Contain lipid groups, vary in solubility depending on the lipid content (e.g., HDL, LDL). Glycoproteins : Contain carbohydrate groups, typically soluble (e.g., mucins)
- 7. Derived Proteins: Composition: Theseproteins result from the hydrolysis or partial breakdown of simple or conjugated proteins. Secondary derived proteins: Completely broken down products like peptones and peptides, often more soluble than the original protein Primary derived proteins: Slightly changed from the native protein, like denatured proteins, and can vary in solubility
- 8. Fibrous vs. GlobularProteins (Based on structure and solubility): Fibrous Proteins: Composition: Long, thread-like structures. Solubility: Insoluble in water and organic solvents (e.g., collagen, keratin). Globular Proteins: Composition: Spherical, compact structures. Solubility: Usually soluble in water or aqueous solutions (e.g., enzymes, hemoglobin)
- 9. Classification of aminoacids Amino acid are the monomers of proteins having an amino and carboxyl group attached to the same carbon atom
- 11. Amino acid classifiedinto three groups Neutral amino acids Glycine Alanine Valine Leucine Serine Basic amino acid Lysine Arginine Histidine Acidic amino acid Aspartic acid Glutamic acid According to dietary value Essential amino acids Leucine Isoleucine Arginine Non essential amino acids Alanine Glycine tyrosine Aliphatic amino acids Glycine Alanine Aromatic amino acids Phenyl alanine Tyrosine Tryptophan Sulphur amino acids Cysteine methionine
- 12. • Neutral AminoAcids: Their side chains do not ionize at physiological pH • BasicAmino Acids: They have positively charged side chains at physiological pH • AcidicAmino Acids: They carry negatively charged side chains due to the loss of protons from carboxyl groups
- 13. • AliphaticAmino Acids:Have simple, non-polar side chains with only carbon and hydrogen atoms. • Aromatic Amino Acids: Contain aromatic rings in their side chains • Sulfur-ContainingAmino Acids: Include sulfur atoms, playing roles in protein structure (cysteine) or serving as important functional groups (methionine).
- 14. Essential Amino Acids: •These cannot be synthesized by the human body and must be obtained through the diet. They are crucial for protein synthesis and overall health • Leucine • Isoleucine • Arginine Non-Essential Amino Acids: • These amino acids can be synthesized by the body and do not need to come from the diet. • Alanine • Glycine • tyrosine
- 15. Amino acids canbe classified based on their chemical nature Nonpolar (Hydrophobic) Amino Acids Polar (Uncharged) Amino Acids Negatively Charged (Acidic) Amino Acids Positively Charged (Basic) Amino Acids
- 16. Nonpolar (Hydrophobic)Amino Acid •Characteristics: These amino acids have hydrophobic nonpolar side chains, meaning they do not interact well with water. They tend to be located in the interior of proteins. Examples: • Aliphatic: Glycine, Alanine, Valine, Leucine, Isoleucine, Proline • Sulfur-containing: Methionine • Aromatic: Phenylalanine, Tryptophan
- 17. Polar (Uncharged) AminoAcids Characteristics: These amino acids have side chains that are polar but uncharged, making them hydrophilic. They can form hydrogen bonds with water and other polar molecules. Examples: • Hydroxyl-Containing: Serine, Threonine • Amide-Containing: Asparagine, Glutamine • Aromatic: Tyrosine (also partially hydrophobic
- 18. Positively Charged (Basic)Amino Acids • Characteristics: These amino acids have side chains that are positively charged at physiological pH, making them basic. They often participate in interactions with negatively charged molecules. • Examples: Lysine, Arginine, Histidine (Histidine is slightly less basic and can be neutral at certain pH levels)
- 19. Negatively Charged (Acidic)AminoAcids • Characteristics: These amino acids have side chains that are negatively charged at physiological pH, making them acidic. They often engage in ionic interactions with positively charged molecules. • Examples: Aspartic acid, Glutamic acid
- 20. Structure of aminoacid Amino acid with aliphatic sidechain
- 21. Amino acids containingaromatic ring
- 22. Amino acids withsidechain containing sulphur atom
- 23. Amino acids containinghydroxyl group
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- 27. Structure of proteins •Primary structure • Secondary structure • Tertiary structure • Quaternary structure
- 28. Primary Structure: This isthe unique sequence of amino acids in the polypeptide chain, linked by covalent peptide bonds. The primary structure determines all higher levels of protein structure and, ultimately, the protein’s function Example : insulin
- 29. Secondary Structure: Thislevel refers to the local folding patterns within a polypeptide chain, primarily held together by hydrogen bonds. The most common secondary structures are: • Alpha Helix: A coiled structure stabilized by hydrogen bonds between the carbonyl oxygen of one amino acid and the amide hydrogen of another • Beta Sheet:Formed by hydrogen bonding between strands running parallel or anti-parallel to each other • Example : Keratin, Fibroin
- 31. Tertiary Structure: The tertiarystructure of a protein is the three- dimensional shape formed by the folding and interactions of its polypeptide chain. • Stabilized by various interactions: Hydrophobic interactions • Hydrogen bonds • Ionic bonds • Disulfide bridges Example : Myoglobin
- 33. Quaternary Structure: The quaternarystructure of a protein refers to the arrangement and interactions of multiple polypeptide chains The arrangement of these subunits is stabilized by the same forces as the tertiary structure Example: Hemoglobin, which has four subunits (two α and two β chains)
- 35. The biological roleof protein Source of energy • Proteins can be broken down to provide energy • ex: amino acids are converted into glucose through gluconeogenesis Structural Role • Proteins provide structure and support to cells and tissue • Ex: Collagen: Provides tensile strength to skin, tendons, and cartilage • Keratin: A structural component of hair, nails, and the outer layer of skin
- 36. Enzymatic Role • Proteinsact as enzymes to catalyze biochemical reactions • Ex:Amylase: Breaks down starch into sugars Transport and Storage • Proteins transport molecules across membranes and store essential molecules • Ex:Hemoglobin: Transports oxygen in the blood. • Ferritin: Stores iron in cells.
- 37. Hormonal Role • Proteinsfunction as hormones, acting as chemical messengers to regulate physiological processes • Ex:Insulin: Regulates blood glucose levels. • Glucagon: Stimulates the release of glucose from glycogen stores Immune Response • Proteins play a critical role in defending the body against pathogen • Ex: Antibodies: Identify and neutralize foreign substances like bacteria and viruses
- 38. Movement and Motility •Proteins are involved in muscle contraction and cellular movement • Ex: Actin and Myosin: Work together in muscle contraction Cell Communication • Proteins function as receptors and signaling molecules in cellular communication • Ex: G-protein Coupled Receptors (GPCRs): Transmit signals across cell membranes. • Cytokines: Mediate communication between immune cells.
- 39. Disease related tomalnutrition of proteins • Kwashiorkor disease • Marasmus disease • Nutritional oedema
- 40. Kwashiorkor disease • Itis a protein deficiency disease occurring commonly in children • It is a qualitative and quantitative deficiency of proteins Causes Large family size Poor health of the mother Premature termination of breastfeeding Poor environmental condition Delayed supplementary feeding Use of diluted cow milk to infants
- 41. Symptoms • Retard growth •Changes or alterations in pigmentation of skin and hair • Enlargement of liver • Hypoalbuminemia(low levels of albumin in the blood) • GIT disturbance • Psychic changes • Hypoglycaemia • Stools containing a much higher quantity of digested food • Anaemia
- 42. Treatment • Supply ofdiet rich in protein • First choice milk and egg, soybean, meat, seafood • In severe conditions blood transfusion is required
- 43. Marasmus disease • Itis a protein deficiency disease commonly found in infants below 1 year of age Causes • It is caused by a deficiency of proteins and carbohydrates with some other nutritional factors • Protein and energy deficiency disease of such type is also known as marasmic kwashiorkor • Absence of maintaining a proper diet • Early stop breastfeeding
- 44. Symptoms • Retard growth •Complete loss of body fat • Changes in the texture of skin • Alteration in pigmentation of skin and hair • GIT disturbances • Oedema Treatment Providing a diet rich in calories Providing protein diet
- 45. Nutritional oedema This isa disease caused by prolonged and significant protein deficiency commonly found in adults Symptoms • Loss of body weight • Reduced subcutaneous fat • Anaemia • Much higher susceptibility to the infection • General lethargy • Increase in frequency of watery stools • Inability to carry out sustained work • oedema
- 46. Treatments • The dietconsisting mainly of milk, milk products, eggs and soyabean is given • It is always better to adopt preventive action by regulating protein content of the daily diet
- 47. Reference V.N raje, Biochemistryand clinical pathology-3rd edition