Chapter 14.9-14.12
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Transcript of Chapter 14.9-14.12
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)
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
How are proteins denatured?Denaturation- the loss of the
secondary, tertiary, and quaternary structures of a protein by chemical or physical agent that leaves the primary structure intact
Enzymes lose their catalytic activity and other proteins can’t carry out their biological functions when denatured
Denatured by:Heat Denaturing chemicalspH changeAlcohol
Denaturation Does not affect primary
structuresMost denaturation is irreversible
Dietary Protein:Protein structure must be destroyed before
it can provide the nutrition for the bodyDigestion involves denaturation and
hydrolysisStomach acids denature proteinsProteolytic enzymes in stomach and small
intestine hydrolyze proteins to smaller fragments until free amino acids are formed and can be absorbed through intestinal membranes into the blood stream