Question

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1A)Explain the difference between primary, secondary, tertiary, and quaternary structure of proteins, including similarities and differences in hydrogen bonding of EACH STRUCTURE WITH ONE ANOTHER

1 B) Distinguish between parallel and antiparallel BETA-sheets

1C) which kinds of forces stabilize proteins at different levels of structure, i.e., what stabilizes secondary structure, what causes protein chains to fold into tertiary structure, what holds oligomers together?

1D) which bonds can rotate in proteins, and WHAT ARE the names of the angles describing that rotation

1E) . Describe what an enzyme assay is, and how it is used in a protein purification.

Answer 1

Ans 1- Proteins structures are made by condensation of amino acids forming peptide bonds.

Primary structure of a polypeptide is its amino acid sequenc .amino acids are connected by peptide bonds. primary structure of polypeptide determine the higher level of structural organisation.

The secondary structure is determined by the dihedral angles of the peptide bonds.

The most common types of secondary stucture are the Alpha helix and beta pleated sheet both Alpha helix and beta sheets patterns are stabilized by hydrogen bonds between the carbonyl and N- H groups in the polypeptide back bone.

Tertiary structure by the folding of proteins chains in space. The term tertiary structure refers to the unique 3D confirmation that globular protein assume as a consequence of the interaction between the side chains in their primary structure.

All information needed to hold the protein into its native tertiary structure is contained within the primary structure of the peptide chain itself.

Quaternary structure- Association of folded polypeptide molecules to complex functional proteins results in quaternary structure.Many protein like hemoglobin are composed of two or more polypeptide Chain and each polypeptide chain is called a sub unit. Subunits in a multimeric protein may be identical or quite different.

Ans2-  Distinguish between parallel and antiparallel BETA-sheets.

Beta pleated sheets form when two or more polypeptide chain segments line up side by side.In parallel beta-sheets the strands all run in one direction, whereas in antiparallel sheets they all run in opposite directions.

Ans3- which kinds of forces stabilize proteins at different levels of structure

Types of covalent and noncovalent interactions stabilize these structure-like

• hydrophobic interaction
• electrostatic interactions
• hydrogen bonds
• Van der wall force of interaction
• covalent bonds

Ans 4- which bonds can rotate in proteins, and WHAT ARE the names of the angles describing that rotation

While the peptide bond is rigid, there is a single bond between the Ca(1) and C atoms and the N and C(2) which are free to rotate.Thus, while the Ca (1) - C (O) - N (H) - Ca (2) atoms are all planar, this planar peptide bond has two degrees of rotational freedom.

two rotation angles are known by the greek letters F (phi) and Y (psi). Y is the rotation angle about the Ca (1) - C bond and F is the rotation angle about the N - Ca (2) bond.

Ans 5-Describe what an enzyme assay is, and how it is used in a protein purification.

Enzyme assays are laboratory methods for measuring enzymatic activity.