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What are the 4 levels of Protein Structure?

Primary, Secondary, tertiary and Quaternery structure of protein

Proteins are biopolymers made of amino acids joined by peptide bond.

This 8 minute video will give you an overall concept about protein structure

Primary Structure

  • Primary Structure is the unique linear sequence of amino acids joined by peptide bond in a polypeptide chain or amino acid sequence structure
What are the 4 levels of Protein Structure?
  • It has an amino-terminal end and the carboxyl-terminal end.
  • It refers to the sequence order and no. of amino acids

Secondary Structure

  • Regular, ordered repeated folding of the polypeptide chain by H bonding between adjacent folds
  • 2 most common : Alpha Helix structure and Beta pleated sheets
Alpha helix: 

alpha helix of Protein
  • It is the right handed helical coiling formed by H bond btw adjacent coils (N-H….O=C)
  • The carbonyl O of one amino acid and the amino H of another.
  • 3.6 amino acid residues per turn eg: myoglobin

Beta pleated sheets: 

beta sheets of silk fibroin

Two or more segments called beta stands of a polypeptide chain in same direction (parallel) or opposite direction (anti parallel) line up next to each other, forming a sheet-like structure held together by hydrogen bonds. Eg: Silk fibroin

what is parallel and anti parallel beta sheets

Tertiary Structure

  • The tertiary structure of a protein refers to the overall three-dimensional arrangement of its polypeptide chain in space.
tertiary structure of a protein
  • Biologically active confirmation stabilized by disulphide bond, hydrophobic interactions, vanderwaals forces, ionic interactions other than peptide bond and hydrogen bond

Quaternary structure exists in proteins with two or more identical or different polypeptide chains (subunits). It refers to the number and the arrangement of subunits that form a protein.

Quaternary structure exists in proteins

It is stabilized by disulphide bond, hydrophobic interactions, vanderwaals forces, ionic interactions other than peptide bond and hydrogen bond.

Hemoglobin is made up of 4 polypeptide chains-2 alpha chain and 2 beta chains; thus exhibiting the quaternery structure

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