Protein sturucture

download Protein sturucture

of 70

  • date post

  • Category


  • view

  • download


Embed Size (px)

Transcript of Protein sturucture

  • 1.Protein Structure and FunctionCompiled & Edited by Dr. Syed Ismail VN Marathwada Agril. University Parbhani

2. DEFINITIONS OF PROTEIN Proteins are one of the essential building blocks of the human body. They provide amino acids, which are a nutritional requirement of the body to produce its own proteins and a variety of nitrogen-based molecules. It is common for programs to recommend a minimum of 50 grams of protein per day to maintain healthy levels. Proteins vary in structure as well as function. They are constructed from a set of 20 amino acids and have distinct three-dimensional shapes. 3. General Characteristics of Proteins They are the most complex and most diverse in chemical composition, conferring upon the different tissues. Protein molecule contains elements of C, H, O,N, S, and P together with traces of Fe, Cu, I, Mn, and Zn. It has a molecular weight of 5,000 to 3,000,000 They are the most important of the biologic substances being the fundamental constituent of cell cytoplasm. They supply not only heat and energy but also material for building and repair. Unlike carbohydrates and lipids, only small amounts of protein is temporarily stored in the body, and which can be quickly used up upon demand. 4. FUNCTIONS OF PROTEIN 5. FUNCTIONS OF PROTEIN Antibodies - are specialized proteins involved in defending the body from antigens (foreign invaders). One way antibodies destroy antigens is by immobilizing them so that they can be destroyed by white blood cells. Enzymes - are proteins that facilitate biochemical reactions. They are often referred to as catalysts because they speed up chemical reactions. Examples include the enzymes lactase and pepsin. Lactase breaks down the sugar lactose found in milk. Pepsin is a digestive enzyme that works in the stomach to break down proteins in food. Hormonal Proteins - are messenger proteins which help to coordinate certain bodily activities. Examples include insulin, Insulin regulates glucose metabolism by controlling the bloodsugar concentration. 6. FUNCTIONS OF PROTEIN Contractile Proteins - are responsible for movement. Examples include actin and myosin. These proteins are involved in muscle contraction and movement. Structural Proteins - are fibrous and stringy and provide support. Examples include keratin, collagen, and elastin. Keratins strengthen protective coverings such as hair, quills, feathers, horns, and beaks. Collagens and elastin provide support for connective tissues such as tendons and ligaments. Storage Proteins - store amino acids. Examples include ovalbumin and casein. Ovalbumin is found in egg whites and casein is a milk-based protein. Transport Proteins - are carrier proteins which move molecules from one place to another around the body. Examples include hemoglobin and cytochromes. Hemoglobin transports oxygen through the blood. Cytochromes operate in the electron transport chain as electron carrier proteins. 7. Classification of Proteins Based on Composition: Simple proteins composed of entirely amino acids only. Ex. Albumin, Globulin Complex or Conjugated proteins made up of amino acids and other organic compounds. The nonamino acid group is termed as the prosthetic group. Ex. Nucleoproteins, lipoproteins, glycoproteins, metalloproteins 8. Classification of Proteins Based on Axial Ratio: Axial ratio is the ratio of the length to the breath. Globular proteins with axial ratio less than 10 but not below 3 or 4. They are compactly folded and coiled. Ex. Insulin, plasma albumin, globulin, enzymes Fibrous proteins with axial ratio greater than 10. They are spiral and helical and are cross linked by disulfide and hydrogen bonds. Ex. Keratin, myosin, elastin, collagen 9. Globular Proteins Globular proteins have their axial ratio less than 10 but not below 3 or 4. They are compactly folded and coiled. Examples are insulin, plasma albumin, globulin, enzymes 10. Fibrous Proteins Fibrous proteins are spiral and helical and are cross linked by disulfide and hydrogen bonds Examples are keratin, myosin, elastin, collagen 11. Based on Biological Functions Structural proteins: collagen, elastin, keratin, fibroin of silk and webs Transport proteins: hemoglobin, myoglobin, lipoproteins Protective proteins: immunoglobulins, fibrinogen, thrombin, snake venoms, bacterial toxins Contractile proteins: actin, myosin, tubulin Catalytic proteins: enzymes Regulatory proteins: hormones Storage proteins: ferritin, hemosiderin, gluten, casein, ovalbumin Reception of Stimuli: rhodopsin, membrane receptor proteins, acethylcholine, insulin Germicidal proteins: Polymyxin B1, Gramicidin S 12. Shape = Amino Acid Sequence Proteins are made of 20 amino acids linked by peptide bonds Polypeptide backbone is the repeating sequence of the N-C-C-N-C-C in the peptide bond The side chain or R group is not part of the backbone or the peptide bond 13. Proteins Composed of a chain of amino acids. 20 possible groupsR | H2N--C--COOH | H 14. NH 3 C COO - NH 3 C COO NH 3 C CO NH C COO - H2 0 15. Different Amino Acid Classes H2N HOC CCHH2NOHGenericHHNon-polarH OCO C CCAcid OHHOAmine H2NAspartic acid H2NHOH?RC CHSCPolarAcidCCysteineCOAlanineOHHHOHOHH2N HHBasicCCH+NCCC H NH CHistidine OHH 16. Non-Polar Amino AcidsGlycine O H2NC COHValine OHHH2N H HC COHHCCC HHCH3OHHH2NCH3H H3CC CC HCHHC HO IsoleucineH3CHOHHCCOHHHCCCCH3CH PhenylalanineO H2NH2NHHCH3CHCHCOHCH2NLeucine OCH2NAlanine OMethionineOOHHH3C TryptophanO H2NHHSC CC H NH H2C H2COHH Proline O H2N+ C CCH2HProtein StructureOH 17. Polar Amino Acids Serine O H2N HC CCH2NOHHHHCH3HOCysteine O H HSC CC HC CCH2NHH OOHHHC COHHC HHAsparagine O OHH2NOHCHH2NTyrosine OThreonine OC CCCH NH2Glutamine OHOH2NOHH HH OH HNH2CCCCC HOH 18. Acidic Amino AcidsOAspartic O acid C H2N C H H C COH HH OHOGlutamic O acid C H2N C H H C HCCH OHOH 19. Basic Amino Acids Histidine O H2N H C C H+NC CCH2NHHH NH CLysine OOHH HHC +H N 3CC CCOHArginine OHH2NHCHHHHHH +H N 2NCCC CCOHHHC H HHNH2 Protein Structure 20. Levels of Protein Organization Primary Structure - The sequence of amino acids in the polypeptide chain Secondary Structure - The formation of helices and b pleated sheets due to hydrogen bonding between the peptide backbone Tertiary Structure - Folding of helices and sheets influenced by R group bonding Quaternary Structure - The association of more than one polypeptide into a protein complex influenced by R group bonding 21. Levels of Protein Organization Primary StructureMet-Gly-Ala-Pro-His-Ile-Asp-Glu-Met-Ser-Thr-.. The sequence of amino acids in the primary structure determines the folding of the molecule.Protein Structure 22. Protein Secondary Structure The peptide backbone has areas of positive charge and negative charge These areas can interact with one another to form hydrogen bonds The result of these hydrogen bonds are two types of structures: helices b pleated sheets 23. H NC OC C OCProtein Secondary Structure: Helix H NH N CH NH N C OC OC OC OCCC OH C NHHH NH H-ON CC C+ HONH H C H HOC C HHOH 24. H NProtein Secondary Structure: H C Helix C N O H C C O N H - + C H O H O C N OC C OH NH N C OHC OCCC OH NH HNCCCNH H C H HOC HC HOH 25. Protein Secondary Structure: Helix R groups stick out from the helix influencing higher levels of protein organizationRRRR RRRRRRRRRR 26. MLLSRQSIRF TLFKA RCYPPSLThe order of the amino acids determines the hydrogen bondingNeutral Non-polar Polar Basic AcidicMLSLRQSIRFFKPATRTLCSSRYLLTSRYeast Cytochrome C Oxidase Subunit IV Leader This would localise specific classes of amino acids in specific parts of the helix 27. Protein Secondary Structure: b Pleated Sheet CO CH C NN H O CN HCC OCC OH NCO CH C NN H O CN HCC OCC OH NCO CH C NN H O CN HCC OCC OH NCO CH C NN H O CN HCC OC OH NC 28. Protein Secondary Structure: b Pleated Sheet CO C N H O CCH C NN H O CN HCC OC OH NH C NCC OO C N H O CCCH C NN H O CN HCC OC OH NH C NCC OO C N H O CCCH C NN H O CN HCC OC OH NH C NCC OO C N H O CCCH C NN H O CN HCC OC OH NH C NC OC 29. Levels of Protein Organization Tertiary Structure Tertiary structure results from the folding of helices and b pleated sheets Factors influencing tertiary structure include: Hydrophobic interactions Hydrogen bonding Disulphide bridges Ionic bonds 30. Hydrophobic interactions Valine O H2N H H3CCC CHCH3OH Glycine O H2N HH2C H2CC COHHProline O H2N+ C C CH2HOH 31. Hydrogen Bonding Glutamine OAsparagine O H2N HOC CCCH NH2H2NOHHHH ON-------H (+) slightlyCCHHCCCH NH2(-) O -------C slightlyOH 32. Disulphide bridges Cysteine O H2N H HSC CCHCysteine OOHH2NHH Cysteine O H2N H HSCCC HSC CCOHHHCysteine OOHH2NHHSC CC HHOH 33. Ionic BondsH OGlutamic O acid C H2N C H H CArginine OHCCOHH2NHHO-H H+H N 2N C NH2C HCC HC HHC HOH 34. e.g.G-3-P Dehydrogenase Tertiary Structure 35. Levels of Protein Organization Quaternary Structure Quaternary structure results from the interaction of independent polypeptide chains Factors influencing quaternary structure include: Hydrophobic interactions Hydrogen bonding The shape and charge distribution on amino acids of associating polypeptides 36. G-3-P Dehydrogenase from Bacillus stearothermophilus 37. Protein structure 38. Globular e.g. haemoglobin 3 structure normally folds up in a ball hydrophilic R groups point outwards Hydrophobic R groups point inwards soluble metabolic functionsandFibrous e.g. collagen 2 structure does not fold up, form fibres not surrounded by hydrophilic R groups insoluble structural functions 39. Haemoglobin Haemoglobin is a globular protein with a prosthetic iron group In adults, hemoglobin is made up of 4 polypeptides (2 polypeptide chains and 2 b polypeptide chains) Each polypeptide surrounds a prosthetic haem group Hydrophobic interactions between side groups pointing inwards maintain the structure Hydrophilic side chains point outwards making it solubleb Feb 40. Polypeptide Backbone 41. Amino Acids (magic 20) You need to know theseHydrophilicHydrophobic