chapter 14.9-14.12 proteins: secondary, tertiary, quaternary, and denaturation
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α -helixTRANSCRIPT
Chapter 14.9-14.12Proteins: Secondary, Tertiary, Quaternary, and Denaturation
14.9- What is the secondary structure of a protein?Regular and repeating structural
patterns2 kinds of repeating patterns proposed
by Linus Pauling and Robert Corey in 1940’s:1. α-helix2. β-pleated sheet
Hydrogen bonds hold polypeptide chain in place
Hydrogen bond connects carbonyl oxygen with amide hydrogen atom of another(–C=O---H-N-)
α-helix
α-helix
single protein chain coiled in a spiral with a right-handed twist
held together by hydrogen bonds parallel to the axis of the coil
β-pleated sheet
β-pleated sheetBackbone of two protein chains is
held together by hydrogen bonds
Secondary Proteins can be classified as:1. Fibrous proteins2. Globular proteins
Fibrous proteins:Tough, insoluble proteins in which
chains form long fibers or sheets◦Wool, hair, and fingernails made of
α-keratins(fibrous protein)◦α-keratins are composed of α-helixes◦Natural silk and spider webs are
made of fibroin, proteins mainly composed of β-pleated sheets
Globular proteins:Water-proteins whose chains are
folded into compact, globelike shapes
Presence of hydrophilic side chains on outer surfaces account for water solubility –allowing them to travel through blood and other body fluids to sites where activity is needed
14.10- What is the tertiary structure of a protein?Three-dimensional shapeUnlike secondary, it depends on
interactions of amino acid side chains
Tertiary Structures are stabilized five ways:1. Covalent Bonds2. Hydrogen Bonding3. Salt Bridges4. Hydrophobic Interactions5. Metal Ion Coordination
14.11 What is the Quaternary Structure of a protein?The way in which 2 or more
protein chains form a single three-dimensional unit
2 important quaternary proteins:1. Hemoglobin2. Collagen
Hemoglobin:Composed of 4 polypeptide
chains 2α chains (141 amino acids) and
2 β chains(146 amino acids)Held together by interaction
hydrophobic groups and heme groups (iron in center of heterocyclic ring)
Conjugated proteins- contain non-amino acid portions
Oxygen carrier in red blood cells
Collagen:Most abundant of all proteins in
mammalsMakes up 30% or more of the
totalMajor constituent of skin,
tendons, bones, blood vessels, and other connective tissues
14.12 How are proteins denatured?Denaturation:
◦Loss of secondary, tertiary, or quarternary protein structure by a chemical or physical agent
◦Leaves peptide bonds and primary structure intact
Agents that cause denaturation:HeatpH changeInorganic saltsOrganic compounds
Most denaturation is:Irreversible, hard boiled eggs
don’t soften much when their temperature is lowered