The hemoglobin holoenzyme (active enzyme) is a complex of an iron ion and 4 subunits- 2 hemoglobin alpha and two hemoglobin beta. People with sickle cell disease have mutated beta hemoglobins. The mutation is a single nucleotide exchange, that changes the 6th amino acid of  protein primary struture - a Glutamic acid into Valine. This one alteration changes the tree dimentional structure of hemoglobin beta so, that it forms lond fibres that disrupt the normal circular form of the red blood cells.
        
             
        
        
        
The fact or state of being engrossed within something.
or
the process or action by which one thing that absorbs or it is absorbed by something else.
        
                    
             
        
        
        
Polymers are made of individual subunit called monomer.
<u>Explanation:</u>
Polymers are lengthy chains built up of replicating molecular subunits, named monomers. The term polymer becomes from poly- (many) and -mer (part). A polymer may be a real or manufactured macromolecule composed of recurring units of a smaller molecule (monomers). The term monomer comes from mono- (one) and -mer (part). 
 Monomers make polymers by creating chemical bonds or confining supramolecular by a method called polymerization. Examples of polymers comprise plastics like polyethylene, silicones. Polymerization is the method of covalently bonding the smaller monomers into the polymer. While polymerization, chemical groups are failed from the monomers so that they may join together.