The sequence in which amino acids are arranged in protein is called as

primary structure

The correct answer is option 1. primary structure.

Let us break down the different levels of protein structure and focus on the primary structure.

Primary Structure

The primary structure of a protein is the linear sequence of amino acids as they are linked together by peptide bonds to form a polypeptide chain. This sequence is determined by the gene encoding the protein and is crucial because it dictates the final three-dimensional shape and function of the protein.

Amino Acids: The building blocks of proteins, each amino acid has a central carbon atom (alpha carbon) attached to an amino group \((NH_2)\), a carboxyl group \((COOH)\), a hydrogen atom, and a variable side chain (R group) that determines the properties of each amino acid.
Peptide Bonds: These covalent bonds link amino acids together in a polypeptide chain. They form between the carboxyl group of one amino acid and the amino group of the next, releasing a molecule of water (a dehydration synthesis reaction).

The specific order of amino acids in the primary structure is critical because it determines how the protein will fold into its secondary, tertiary, and quaternary structures, which in turn dictate the protein's function.

Secondary Structure

The secondary structure refers to local folded structures that form within a polypeptide due to interactions between atoms of the backbone (not the side chains). The most common types of secondary structures are:

Alpha Helix: A right-handed coil resulting from hydrogen bonds between the carbonyl oxygen of one amino acid and the amide hydrogen of another amino acid four residues earlier.

Beta Sheet: Consists of beta strands connected laterally by at least two or three backbone hydrogen bonds, forming a sheet-like arrangement.

Tertiary Structure

The tertiary structure is the overall three-dimensional shape of a single polypeptide chain, resulting from interactions between the side chains (R groups) of the amino acids. These interactions include:

Hydrophobic Interactions: Nonpolar side chains typically cluster away from water.

Hydrogen Bonds: Between polar side chains.

Ionic Bonds: Between oppositely charged side chains.

Disulfide Bridges: Covalent bonds between the sulfur atoms of cysteine residues.

The tertiary structure is essential for the protein's functionality, as it determines the spatial arrangement of its active sites and binding sites.

Quaternary Structure

The quaternary structure arises when a protein consists of more than one polypeptide chain (subunit). The arrangement and interactions of these subunits define the quaternary structure. Examples include:

Hemoglobin: Consists of four polypeptide subunits (two alpha and two beta chains).

DNA Polymerase: Made up of multiple subunits that work together to replicate DNA.

Summary

The primary structure of a protein is its unique sequence of amino acids, which is critical as it sets the stage for the higher levels of protein structure:

Primary Structure: Linear sequence of amino acids.

Secondary Structure: Local folding into alpha helices and beta sheets.

Tertiary Structure: Three-dimensional shape formed by the entire polypeptide chain.

Quaternary Structure: Arrangement of multiple polypeptide subunits in a multi-subunit complex.

Each level of structure is essential for the final function of the protein, but it all starts with the primary structure, the specific order of amino acids in the polypeptide chain.