Between CH1 and CH2, there are many cysteine and proline residues. This is known as the hinge region and confers flexibility to the Fab arms of the Ig molecule. This is used when antibody interacts with antigen. Antibodies are synthesised by lymphocytes. Antibodies are made by B lymphocytes and exist in 2 forms - either membrane bound or secreted.
B lymphocytes use membrane bound antibody to interact with antigens.
The clone will continue making antibody of the same specificity. Simultaneously, there will be lots of other clones of different specificity. This is known as a polyclonal response. Antigens have determinants called epitopes. Epitopes are molecular shapes recognized by antibodies, which recognise 1 epitope rather than whole antigen.