Protein Chemistry and Functions
- 1. Ms. Jigisha Pancholi Head Dept. of Biochemistry & Microbiology IIAPS Gujarat Ayurved University
- 2. A complex polymer containing carbon, hydrogen, oxygen, nitrogen and usually sulfur & Phosphorus and composed of chains of amino acids linked by peptide bond (−CO•NH−). • Two amino acids = Dipeptide • Three amino acids = Tripeptide • Four amino acids = Tetrapeptide • < 10 amino acids together = Oligopeptide • 10 -50 amino acids = Polypeptide
- 3. Even though there are 20 amino acids, by changing the sequence of combination of these amino acids, nature produces enormous number of different proteins. There are about 100, 000 different proteins in the human body. Makes 75% of the dry weight of the body.
- 4. • It’s a partial double bond. • The C-N bond is ‘trans’ in nature and there is no freedom of rotation. • The distance is 1.32Å which is midway between single bond(1.42Å) and a double bond(1.27Å).
- 5. It can also be called an eupeptide bond to separate "it" from an isopeptide bond, a different type of amide bond between two amino acids. An isopeptide bond is an amide bond that can form for example between the carboxyl group of one amino acid and the amino group of another. At least one of these joining groups is part of the side chain of one of these amino acids. Lysine for example has an amino group on its side chain and glutamic acid has a carboxyl group on its side chain.
- 6. There are two ends in a peptide chain: N- terminal end/ Amino terminal end C- terminal end/ Carboxy terminal end The N-terminal amino acid is written on left hand side when the sequence is denoted. Biosynthesis of protein also starts from the amino terminal end.
- 7. Primary Structure Secondary Structure Tertiary Structure Quaternary Structure
- 8. PRIMARY STRUCTURE • Primary structure denotes the number and sequence of amino acids in the protein. • Higher levels of organization are decided by this structure. • Each polypeptide chain has a unique amino acid sequence decided by the genes. • The primary structure is maintained by the covalent bonds of the peptide linkages. • One should be very clear by the term “sequence” see e.g. Gly-Ala-Val(1) Gly-Val-Ala(2)
- 9. Some organisms, like bacteria and fungi can also make short peptides by non-ribosomal peptide synthesis, which often use amino acids other than the standard 20, and may be cyclized, modified and cross-linked. Non ribosomal peptides are synthesized by nonribosomal peptide synthetases, which, unlike the ribosomes, are independent of messenger RNA. Non ribosomal peptides often have cyclic and/or branched structures, can contain non-proteinogenic amino acids including D-amino acids, carry modifications like N-methyl and N-formyl groups, or are glycosylated, acylated, halogenated, or hydroxylated.
- 10. • Even a single amino acid change (mutation) in the linear sequence may have profound biological effects on the function. • For example, in HbA (normal Hb), the 6th amino acid in the beta chain is glutamic acid; it is changed to valine in HbS(sickle cell anemia).
- 11. ” denotes the configurational relationship between residues which are about 3-4 amino acids apart in The spatial arrangement of polypeptide chain by twisting or folding is called as secondary structure. Protein secondary structure is the three dimensional form of local segments of proteins. The bonds stabilizing structure are: Hydrogen bond, electrostatic bond, hydrophobic interaction,Vander walls bond. Hydrogen bond mainly stabilize the secondary structure. Two kinds of common secondary structures: a. Alpha helix b. Beta pleated sheet
- 13. It is also called as Pauling–Corey–Branson α-helix. It is a spiral structure. The polypeptide bonds form the backbone and side chain of amino acids extend outward. It is stabilized by hydrogen bonds between NH and C=O groups of the main chain. Each turn is formed by 3.6 residues. Distance between each aa. residue is 1.5Å Right handed because amino acids found in proteins are of L- variety.
- 15. α-helix
- 16. The polypeptide chains are fully extended. The distance between adjacent a.a. is 3.5Å. It is stabilized by hydrogen bonds. Adjacent strands in a sheet can run in the same direction (parallel) or in opposite direction (anti parallel beta sheet).
- 17. β- pleated sheet
- 18. Three dimensional structure of the polypeptide chain. The tertiary structure will have a single polypeptide chain "backbone" with one or more protein secondary structures, the protein domains. It is maintained by non-covalent interactions such as hydrophobic bonds, electrostatic bonds, van der Waals forces and the disulphide bonds. A protein domain is a conserved part of a given protein sequence and tertiary structure that can evolve, function, and exist independently of the rest of the protein chain. Each domain forms a compact three-dimensional structure and often can be independently stable and folded. Chaperone proteins present in R.E.R. conduct the folding of proteins.
- 20. Certain polypeptides will aggregate to form one functional protein known as quaternary structure. The protein will lose its function when the subunits are dissociated. It is stabilized by hydrogen bonds, electrostatic bonds, hydrophobic bonds and van der Waals forces. Depending on the number of the monomers, the protein may be termed as dimer(2), tetramer(4) etc.. Each polypeptide chain is termed as Subunit or Monomer.
- 21. Hemoglobin 2 alpha and 2 beta chains
- 22. Structure of IgG 2 heavy chains & 2 light chains
- 23. Hierarchical nature of protein structure Primary structure (Amino acid sequence) ↓ Secondary structure （α-helix, β-sheet） ↓ Tertiary structure （Three-dimensional structure formed by assembly of secondary structures） ↓ Quaternary structure （Structure formed by more than one polypeptide chains）
- 25. Proteins are classified according to: A. Function B. Structure C. Composition D. Nutritional value
- 26. Catalytic proteins: Enzymes like hexokinase, urease etc. Structural proteins: Collagen, keratin etc. Contractile proteins: Myosin , actin, flagellin. Transport proteins: Haemoglobin, myoglobin, albumin etc. Regulatory proteins: Insulin, growth hormone etc. Genetic proteins: Histone Protective proteins: Antibodies, clotting factors etc.
- 27. Storage Proteins: Globulins in pulses, Prolamines in cereals, glutelins in rice, albumin in egg and casein in milk Toxic proteins: Ricin in castor bean, lectin in legumes, cholera toxin Secretory proteins: Fibroin is a protein secreted by spiders and silkworms to form webs and cocoons. Exotic proteins: Antarctic fishes live in -1.9ºC waters, well below the temperature at which their blood is expected to freeze. These fishes are prevented from freezing by antifreeze glycoproteins present in their body.
- 28. Simple : Only made up of amino acids. Eg: Albumin, histone etc.
- 29. Conjugated: Has protein + non protein part A. Glycoprotein: Carbohydrate+ Protein. Eg: Antibody B. Lipoprotein: Lipid + Protein. Eg: LDL, HDL C. Nucleoprotein: Nucleic acid + Protein. Eg: Histone, ribosome D. Chromoprotein: Coloured pigments + Protein. Eg: Hemoglobin, Cytochrome, hemocyanin E. Phosphoprotein: Phosphorus + Protein. Eg: Casein G. Metalloprotein: Metal + Protein. Eg: Hemoglobin, zinc finger
- 30. Derived: Derived by degradation or denaturation of proteins. Eg. : Coagulated proteins, peptides, fibrin from fibrinogen etc.
- 31. Globular proteins: Eg: Albumin, Globulin etc. Fibrous protein: Eg: Keratin, Elastin, Silk etc.
- 32. Nutritionally rich proteins: Has all the essential amino acids. Eg: Casein, egg albumin etc. Partially incomplete proteins: Lack one essential amino acid. Eg: Wheat and Rice protein lacks Lysine. Incomplete proteins: Lack more than one essential amino acid. Eg: Zein from corn lacks trp and lys.
- 33. Proteins are essential nutrients for the human body. Serve as a fuel source, generating 4 kcal/ gm.
- 34. Enzymes are proteins. Hormones are proteins.
- 35. Form structural unit inside the body. Transport of molecules.
- 36. Forms channels and carriers. Involved in cell signaling.
- 37. Binds to DNA and helps in folding. Involved in cell cell adhesion.
- 38. Forms the cytoskeletal network Forms cilia, flagella and spindle fibres.
- 39. Involved in contraction of muscles. Protects the body from infections and blood loss.
- 40. In therapy, like Insulin, vaccines, interferon etc. Poison like Snake poison, spider venom etc.
- 41. Monoclonal antibodies are used for blood group testing Antibodies are used to treat diseases like rheumatoid arthritis, multiple sclerosis, Alzheimer's disease and different types of cancers.
- 42. Antibodies are used as anti sera / anti venom
- 43. Antibodies are used in ELISA, RIA and immuno electrophoresis and diffusion reactions Enzymes are used in ELISA
- 44. Gelatin, which is used in food and industry, is collagen that has been irreversibly hydrolyzed
- 45. Collagen has been widely used in cosmetic surgery, as a healing aid for burn patients for reconstruction of bone and a wide variety of dental, orthopedic, and surgical purposes. Both human and bovine collagen is widely used as dermal fillers for treatment of wrinkles and skin aging
- 46. Keratin is used for hair treatment Silk is used for making clothes
- 47. Enzymes are used in diagnosis of disease, treatment, food industry, textile industry, detergents, cosmetics, genetic engineering etc.
- 48. Whey protein is taken by the body builders to enhance muscle mass. Proteases and lipases are used in washing powders to remove biological stains
- 49. Protease enzyme trypsin is added into the baby food to help digest the food.
- 50. Slimming food contain isomerase enzyme that converts glucose to fructose Proteases are used to make cheese