Tertiary Protein Structure

8/4/2019 Tertiary Protein Structure

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Tertiary Protein Structure


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Tertiary Protein Structure

Refers to three-dimensionalstructure of a single protein

molecule. Result from the interactions

between amino acid sidechain that are widelyseparated from each other

with a peptide chain.


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Interaction Responsible forTertiary Structure

Disulfide bonds

Hydrophobicinteractions

Hydrogen bonds Ionic Bond


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Covalent Disulfide bonds

usually formed fromthe oxidation of sulfhydryl (-SH)groups

2 RSH RS-SR + 2 H+ + 2 e-


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Covalent Disulfide bonds


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Hydrogen bond

Attractive interaction ofa hydrogen atom withan electronegative atom, such as

nitrogen, oxygen or fluorine, thatcomes from another moleculeor chemical group


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Hydrogen bond


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Ionic Bond

a type of chemical bond formedthrough an electrostatic attractionbetween two oppositely

charged ions. Also called salt bridge, always

involve the interaction between

acidic side chain and a basic sidechain.

COOH = COO- and NH2 = NH3+


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Ionic Bond


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Hydrophobic interactions

Result when two non polar sidechains are close to each other. Inaqueous solution, many proteins

have their polar R groups outward,toward the aqueous solvent andtheir non polar R groups inward.

The non polar R groups theninteract with each other.


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Protein Hydrolysis

the breakdown of protein into smallerpeptides and free amino acid.


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Protein Denaturation

Involves the disruption and possibledestruction of both the secondaryand tertiary structures. Since

denaturation reactions are notstrong enough to break the peptidebonds, the primary structure

(sequence of amino acids) remainsthe same after a denaturationprocess. Denaturation disrupts thenormal alpha-helix and beta sheetsin a protein and uncoils it into a


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Protein Denaturation

Denaturation occurs because thebonding interactions responsible forthe secondary structure (hydrogen

bonds to amides) and tertiarystructure are disrupted. In tertiarystructure there are four types ofbonding interactions between "side

chains" including: hydrogen bonding,salt bridges, disulfide bonds, and non-polar hydrophobic interactions. whichmay be disrupted. Therefore, a

variety of reagents and conditions cancause denaturation.


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Protein Denaturation Factors

Heat

Alcohol Disrupts Hydrogen

Bonding Acids and Bases Disrupt

Salt Bridges

Reducing Agents DisruptDisulfide Bonds


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Heat

Heat can be used to disrupt hydrogenbonds and non-polar hydrophobicinteractions. This occurs because heatincreases the kinetic energy and

causes the molecules to vibrate sorapidly and violently that the bondsare disrupted. The proteins in eggsdenature and coagulate during

cooking. Other foods are cooked todenature the proteins to make iteasier for enzymes to digest them.Medical supplies and instruments aresterilized by heating to denature

proteins in bacteria and thus destroy


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Alcohol Disrupts HydrogenBonding

Hydrogen bonding occurs betweenamide groups in thesecondary protein structure.

Hydrogen bonding between "sidechains" occurs in tertiary protein structure in a variety

of amino acid combinations. All ofthese are disrupted by the additionof another alcohol.
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Alcohol Disrupts HydrogenBonding

A 70% alcohol solution is used as adisinfectant on the skin. Thisconcentration of alcohol is able topenetrate the bacterial cell wall and

denature the proteins and enzymesinside of the cell. A 95% alcoholsolution merely coagulates theprotein on the outside of the cell wall

and prevents any alcohol fromentering the cell. Alcohol denaturesproteins by disrupting the side chainintramolecular hydrogen bonding.New hydrogen bonds are formed

instead between the new alcohol


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What is the difference between thealpha-helix and the beta-sheet protein

conformations?

Alpha-helix and beta-sheetconformations are the two main types ofsecondary structure of a protein molecule.According to the primary protein structure

its secondary structure can be of one typeor the other.

In the alpha-helix structure the polypeptidecurls longitudinally by the action of

hydrogen bonds forming a spiral, or helix.In the beta-sheet conformation the proteinis more distended and the hydrogenbonds form a zig-zag-shaped proteinstructure called B-strand. Many assembledbeta-strands make a beta-sheet.

a s pro e n ena ura on s


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a s pro e n ena ura on sthere any change in the primary

structure when a protein is

denatured? Secondary, tertiary and quaternarystructures of proteins are spatialstructures. Denaturation is

modification in any of these spatialstructures that makes the proteindeficient or biologically inactive.

After denaturation the primaryprotein structure is not affected.

What Is the Difference


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What Is the DifferenceBetween an Ionic and Covalent

Chemical Bond? In an ionic bond, the atoms are boundtogether by the attraction betweenoppositely-charged ions. For example,sodium and chloride form an ionic

bond, to make NaCl, or table salt. In acovalent bond, the atoms are boundby shared electrons. If the electron isshared equally between the atoms

forming a covalent bond, then thebond is said to be nonpolar. Usually,an electron is more attracted to oneatom than to another, forming a polarcovalent bond. For example, the

atoms in water H2O are held

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Tertiary Protein Structure