Presentation on theme: "S ECONDARY, T ERTIARY, Q UATERNARY P ROTEIN S TRUCTURE AND D ENATURATION Girma Admasu, Kalkidan Molla, Erika Belan, & Alexis Alberto."— Presentation transcript:
S ECONDARY, T ERTIARY, Q UATERNARY P ROTEIN S TRUCTURE AND D ENATURATION Girma Admasu, Kalkidan Molla, Erika Belan, & Alexis Alberto
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. Hydrogen bonding 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.
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.
T HE B ETA - 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.
Antiparallel beta-pleated sheet is more stable than parallel beta-pleated sheet because it has well aligned H-bonds.
T ERTIARY 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
T ERTIARY S TRUCTURE : H YDROGEN 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.
T ERTIARY S TRUCTURE : D ISULFIDE 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.
T ERTIARY S TRUCTURE : H YDROPHOBIC 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.
T ERTIARY S TRUCTURE : S ALT BRIDGE Is the result of ionic bonds formed within the ionized side chain of an acidic amino acid and basic amino acid.
Q UATERNARY P ROTEIN S TRUCTURE AND D ENATURATION
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.
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
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.
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.
D ENATURATION Modifies the molecular structure of a protein. Destroys secondary and tertiary structure Uncoils proteins into random shape Reactions cannot destroy peptide bonds
D ENATURATION : H EAT Heat disrupts hydrogen bonds and non-polar hydrophobic interactions Kinetic energy increases, vibrations disrupt bonds Example: Cooked eggs and sterilization of medical supplies
D ENATURATION : P H L EVELS 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
D ENATURATION : A LCOHOLS Alcohols disrupt hydrogen bonding Disrupts amide groups in secondary structures and side chains in tertiary structures New hydrogen bonds between protein structure and alcohol
D ENATURATION : H EAVY M ETAL S ALTS 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
D ENATURATION : R EDUCING A GENTS Oxidizing agent make disulfide bonds Reducing agents split disulfide bonds apart Hydrogen atoms added to make thiol group (-SH)
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
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