1. primary structure of a protein: this is the number and sequence of amino acids held together by the peptide bond in a polypeptide chain.
2. secondary structure of a protein: this described the interaction of the sequence of amino acids in a polypeptide chain, and the bond formed is hydrogen bond.
3. tertiary structure of a protein this is a 3 dimension structure of a protein in the polypeptide chain and the bond formed are hydrogen bond, ionic bond and disulfide bond.
4. quartenary structure of a protein this is a combination of more than one structure which is primary structure, secondary structure and tertiary structure. bond formed are disulfide bond and so on.
Ribosomes are used in cells for growth and repair they are held in the cytoplasm of the cell not the nucleus therefore they are never in contact with dna