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Secondary, Tertiary, Quaternary Protein Structure and Denaturation

Secondary, Tertiary, Quaternary Protein Structure and Denaturation. Girma Admasu , Kalkidan Molla , Erika Belan , & Alexis Alberto. SECONDARY PROTEIN STRUCTURE.

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Secondary, Tertiary, Quaternary Protein Structure and Denaturation

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  1. Secondary, Tertiary, Quaternary Protein Structure and Denaturation GirmaAdmasu, KalkidanMolla, Erika Belan, & Alexis Alberto

  2. SECONDARY PROTEIN STRUCTURE • Secondary protein structures formed when the sequence of amino acids start to coil, fold and link to each other by hydrogen bonds. • Hydrogenbonding occurs between the carboxyl oxygen of one amino acid and the hydrogen on another amino group. • The oxygen atom in the carboxyl group has partial negative charge , while the hydrogen atom in the amino acid group has a partial positive charge. The oxygen donates electrons for hydrogen. That is how the hydrogen bond formed between the carboxyl oxygen of one amino acid and the hydrogen on another amino group.

  3. Secondary structure protein consist of alpha helices and Beta- pleated sheets. • Alpha –helices form when hydrogen bonds form within a single protein chain. • The peptides have two terminals. • The end of the peptide chain with –NH2 group is called the N-terminal, and the end with –COOH group is called the C-terminal. • Hydrogen bonding between section of the backbone is possible when different parts of the same polypeptide bend in a way that puts carboxyl and amino groups close together.

  4. The Beta-pleated sheet • Beta-pleated sheet is formed when two or more protein chains lie side by side and held by the hydrogen bond formed between the carbonyl oxygen of one chain and the amide hydrogen of an adjacent chain.

  5. Antiparallel beta-pleated sheet is more stable than parallel beta-pleated sheet because it has well aligned H-bonds.

  6. Tertiary structure in protein • Occurs due to the interaction between R side chains of the amino acid residues. • There are 4 types of R-group interaction • Hydrogen bonds • Disulfide bridge • Hydrophobic interaction • Salt bridge

  7. Tertiary Structure: Hydrogen bonds • Are created between different side chains mainly in those that contains OH,NH2 and amide group. • Also determines secondary structure of protein. • Occurs within the R groups.

  8. Tertiary Structure: Disulfide bridge • In the insulin structure two cysteine residues that are close to each other in the same chain can be caused due to disulfide linkage. • Tertiary structure includes the location and existence of disulfide bridge since the interaction holds the protein chain in loop.

  9. Tertiary Structure: Hydrophobic interaction • Occurs when non polar groups are attracted or forced together by their mutual repulsion. • Are common among R groups. • The shape of globular protein is resulted because the non polar groups are pointed inwards from the water molecules while the polar groups are pointed outward the aqueous solvent. • Is weaker compared to the others. • It’s strong enough to stabilize the tertiary structure.

  10. Tertiary Structure: Salt bridge • Is the result of ionic bonds formed within the ionized side chain of an acidic amino acid and basic amino acid.

  11. Quaternary Protein Structure and Denaturation

  12. Some proteins are composed of more than one polypeptide chain, usually called subunits. • Quaternary Structure refers to how these chains are arranged in relation to one another. • Atoms in each chain in a protein are held together by covalent bond. Chains are attracted to each other by intramolecular forces.

  13. Comparison between Primary, Secondary, Tertiary and Quaternary Structures • Primary: The Sequence of Amino Acids in a polypeptide chain • Secondary: The spacial arrangement of the amino acid sequences into regular patterns such as helices, sheets and turns • Tertiary: The overall three-dimensional shape of polypeptide chain caused by the folding of various regions • Quaternary: the spatial interaction of two or more polypeptide chains in a protein • Complexes of two or more polypeptides (i.e. multiple subunits) are called multimers • http://www.youtube.com/watch?v=lijQ3a8yUYQ

  14. Hemoglobin: best example of Quaternary Structure. • In all vertebrates, the respiratory protein hemoglobin acts as oxygen carrier in the blood, transporting oxygen from the lung to body organs and tissues • Each molecule of human hemoglobin consists of four peptide chains, two α-chains and two β-chains; i.e., it is a tetramer • The four subunits are linked to each other by hydrogen bonds and hydrophobic interaction.

  15. Because the four subunits are so closely linked, the hemoglobin tetramer is called a molecule, even though no covalent bonds occur between the peptide chains of the four subunits.

  16. Denaturation • Modifies the molecular structure of a protein. • Destroys secondary and tertiary structure • Uncoils proteins into random shape • Reactions cannot destroy peptide bonds

  17. Denaturation: Heat • Heat disrupts hydrogen bonds and non-polar hydrophobic interactions • Kinetic energy increases, vibrations disrupt bonds • Example: Cooked eggs and sterilization of medical supplies

  18. Denaturation: pH Levels • Acids and bases disrupts salt bridges • Exchange of positive and negative ions between salt with new acid or base • Example: Curdling of milk in digestive system, acid in stomach

  19. Denaturation: Alcohols • Alcohols disrupt hydrogen bonding • Disrupts amide groups in secondary structures and side chains in tertiary structures • New hydrogen bonds between protein structure and alcohol

  20. Denaturation: Heavy Metal Salts • Hg+2, Pb+2, Ag+1 Tl+1, Cd+2 and other metals with high atomic weights • Act like acids and bases, disrupt salt bridges • Leads to insoluble metal protein salt • Example: AgNO3 prevent gonorrhea infections in eyes of newborns

  21. Denaturation: Reducing Agents • Oxidizing agent make disulfide bonds • Reducing agents split disulfide bonds apart • Hydrogen atoms added to make thiol group (-SH)

  22. Some denaturations are irreversible , such as egg white. A common consequence of denaturation is loss of biological activity (e.g., loss of the catalytic ability of an enzyme). • Renaturation - original structure of protein is regenerated. • Remove denaturing agent and restore ideal environmental conditions

  23. Work Cited • C.Geourjon & G. Deleage,Protein Engineering, 7, 157-164 (1994). • Freeman, Scott. Biological Science. San Francisco: Pearson/Benjamin Cummings, 2007. Print. • Seager, Spencer L., and Michael R. Slabaugh. Chemistry for Today: General, Organic, and Biochemistry. Belmont, CA: Brooks/Cole, Cengage Learning, 2011. Print http://www.click4biology.info/

  24. Work Cited • Seager,Spencer; Slabaugh,Micheal. Chemistry for today: tertiary structure of proteins. 6th ed. • David Harris, 2008; pp 598-600.

  25. Work Cited • Introductory Chemistry: An Active Learning Approach, 4th Edition; Cracolice, Peters; ISBN: 0-495-55847-8 • Protein. (2011). In Encyclopædia Britannica. Retrieved from http://www.britannica.com/EBchecked/topic/479680/protein

  26. Work Cited • Ophardt, Charles E. "Denaturation Protein." Elmhurst College: Elmhurst, Illinois. 2003. Web. 01 Dec. 2011. <http://www.elmhurst.edu/~chm/vchembook/56 8denaturation.html>.

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