Protein Structure
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Transcript of Protein Structure
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PROTEIN STRUCTURE
Brianne Morgan, Adrienne Trotto, Alexis Angstadt
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Secondary Structure 14.9 A repetitive structure of the protein
backbone. The two most common secondary
structures encountered in proteins are the α-helix and the β-pleated sheet.
The protein conformations that do not exhibit a repeated pattern are called random coils.
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Helix In the α-helix form, a single protein chain
twists in such a manner that its shape resembles a right-handed coiled spring-that is, a helix.
The shape of the helix is maintained by numerous intramolecular hydrogen bonds that exist between the backbone – C=O and H-N- groups.
All the amino acid side chains point outward from the helix.
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B-pleated sheet In this case, the orderly alignment of
protein chains is maintained by intermolecular or intramolecular hydrogen bonds.
The β-pleated sheet structure can occur between molecules when polypeptide chains run parallel (all N-terminal ends on one side) or antiparallel (neighboring N-terminal ends on opposite sides.)
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Few proteins have predominately α-helix or β-sheet structures.
Most proteins, especially spherical ones, have only certain portions of their molecules in these conformations. The rest of the molecules consist of random coil.
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Keratin is a fibrous protein of hair, fingernails, horns, and wool and it doesn’t have a predominately α-helix structure.
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Extended Helix Another repeating pattern classified as a
secondary structure is the extended helix of collagen.
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Tertiary Structure 14.10 3-D arrangement of every atom in the
molecule Includes interactions of side chains, not
just the peptide backbone Stabilized in 5 ways: Covalent Bonds,
hydrogen bonding, salt bridges, hydrophobic interactions, metal ion coordination
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Covalent Bonds Disulfide bond is most often involved in
the stabilization When a cysteine residue is in 2 different
chains, formation of a disulfide bond provides a covalent linkage that binds together the 2 chains
EX: structure of insulin
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Hydrogen Bonding Stabilized by hydrogen bonding between
polar groups on side chains or between side chains and the peptide backbone
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Salt Bridges Also called electrostatic attractions Occur between 2 amino acids with
ionized side chains Held together by simple ion-ion
attraction
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Hydrophobic Interactions Result of polar groups turned outward
toward the aqueous solvent and the nonpolar groups turned inward away from the water molecules
Weaker than hydrogen bonding or salt bridges
Acts over large surfaces
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Metal Ion Coordination 2 side chains can be linked with a metal
ion Human body requires certain trace
minerals Necessary components of proteins
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Primary structure of a protein determines the secondary and tertiary structure
When particular R- groups are in proper position, all of the stabilization can form
The side chains allow some proteins to fold
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Quaternary Structure of a Protein 14.11
The highest level of protein organization Applies to proteins with more than 1
polypeptide chain
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Hemoglobin Each chain surrounds an iron- containing
heme unit Proteins that contain non-amino portions
are called conjugated proteins The non-amino acid portion of a conjugated
protein is called a prosthetic group Early development stage of the fetus,
hemoglobin contains 2 alpha and 2 gamma chains
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Collagen The triple helix units called tropocollagen
constitute the soluble form of collagen Structural protein of connective tissue Provides strength and elasticity Stabilized by hydrogen bonding between
the backbones of the 3 chains Most abundant protein in humans
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Integral Membrane Proteins Traverse partly 1/3 of proteins
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How are Proteins Denatured? 14.12
Secondary and tertiary structures stabilize the native conformations of proteins
Physical and chemical agents destroy these structures and denature proteins
Protein functions depend on native conformation; when a protein is denatures, it can no longer carry out its function
Some is reversible, some chaperone molecules may reverse denaturation