Question

Different levels of structural organization of proteins

Answer 1

Interactive diagram of protein structure, using PCNA as an example. (PDB: 1AXC​)

Protein structure is the three-dimensional arrangement of atoms in an amino acid-chain molecule. Proteins are polymers – specifically polypeptides – formed from sequences of amino acids, the monomers of the polymer. A single amino acid monomer may also be called a residue indicating a repeating unit of a polymer. Proteins form by amino acids undergoing condensation reactions, in which the amino acids lose one water molecule per reaction in order to attach to one another with a peptide bond. By convention, a chain under 30 amino acids is often identified as a peptide, rather than a protein.[1] To be able to perform their biological function, proteins fold into one or more specific spatial conformations driven by a number of non-covalent interactions such as hydrogen bonding, ionic interactions, Van der Waals forces, and hydrophobic packing. To understand the functions of proteins at a molecular level, it is often necessary to determine their three-dimensional structure. This is the topic of the scientific field of structural biology, which employs techniques such as X-ray crystallography, NMR spectroscopy, and dual polarisation interferometry to determine the structure of proteins.

Protein structures range in size from tens to several thousand amino acids.[2] By physical size, proteins are classified as nanoparticles, between 1–100 nm. Very large aggregates can be formed from protein subunits. For example, many thousands of actin molecules assemble into

Answer 2

Answer:

Structure of Proteins: Proteins are heteropolymers of twenty types of amino acids. Protein structure is described as 4 levels.

1. Primary Structure: It is linear sequence of amino acids. The first amino acid is also called as N-terminal amino acid and last amino acid is called C-terminal amino acid.

2. Secondary Structure: The linear string is folded in the form of helix similar to a revolving staircase.

3. Tertiary Structure:

 Helix folds further to form hollow woollen ball like structure to give rise to tertiary structure.

 Tertiary folding gives the protein 3-D structure.

 Tertiary structure is absolutely necessary for many biological activities of proteins such as enzymes.

4. Quaternary Structure:

 It is found only in multimeric proteins which consist of more than one polypeptide chains.

 Each polypeptide develops its own tertiary structure and functions as a subunit.

 Different subunits pack together to attain quaternary structure.

Example:  Haemoglobin consists of 4 subunits. Two α-subunits and two β-subunits together constitute haemoglobin (Hb: α2β2).

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Explanation: