dynamic queries vs static queries

Hi,

Is there any performance difference between dynamic queries vs statis
queris in PL/pgSQL functions?

For example:

create function static_fn(int, character varying)...
  pk_id ALIAS $1;
  a_str ALIAS $2;
begin
  update a_table
  set a_column = a_str
  where pk=pk_id;
...
END;
' LANGUAGE 'plpgsql';

vs
create function dynamic_fn(int, character varying)...
  pk_id ALIAS $1;
  a_str ALIAS $2;
begin
  EXECUTE ''update a_table '' ||
    ''set a_column = '' || a_str ||
    '' where pk='' || pk_id;
...
END;
' LANGUAGE 'plpgsql';