Question

3. Discuss the organization of a protein, from its linear amino acid sequence, to its final three– dimensional configuration, which may include one or more polypeptides. Include what types of bonds help to stabilize each structural level, from primary through quaternary.

Answer 1

Answer=

Organization of a protein

there are four levels of organization of proteins:primary,secondary,tertiary and quaternary structure.

1.primarystructure =

The unique linear sequence of amino acids joined by peptide bond i.e. amide bond that amke up a protein or polypeptide chain.secondary,tertiary and quaternary structure.

-Higher levels of organization of proteins are dependent on the primary structure.

-primary structure is stabilized by peptide bond.

-Example of primary structure -

1. The simplest protein is insulin.consists of 51 amino acid residues.

-It is the first protein to have its primary structure determined.

- Insulin is a protein hormone composed of two polypetide chains: A chain (21 amino acids) and B chain(30 amino acids).

-A and B chains are linked together by two disulfide bonds.It also have an additional disulfide bond formed within chain A.

2.secondary structure = The spatial arrangement of amino acid residues that are adjacent in the primary structure by twisting and folding of the polypeptide chain.

there are types of sec.structures: helix, pleated sheet,loops and turns.

secondary structure is stabilized by Hydrogen bonding.

3.Tertiary structure=peptide chain with its secondary structure may be folded and twisted about itself forming 3D arrangement of a functional protein.

- Ter.structure is the complete three dimensional arrangement of polypetide chain.

- It is a compact structure.Hydrophobic side chains held interior and hydrophillic groups are on the surface of the protein molecule.

-The function of protein depends on its tertiary structure.

-the final 3D shape is determined by a variety of bonding interactions between the "side chains" on the amino acids.

• Hydrogen bonds
• Ionic bonds
• Disulfide bridges
• Hydrophobic interactions- greatly contribute to the folding and shaping of a protein.

The "R" group either hydrophobic or hydrophillic.

Example- Myoglobin

4.Quaternary structure= refers to the structure of a protein macromolecule formed by interactions between multiple polypeptide chains.Each polypeptide chain is referred to as subunit.Proteins with quaternary structure may consist of more than one of the same type of protein subunit.They may be composed of different subunits.

Example- Hemoglobin -it contains four subunits:2 alpha and 2 beta subunits.