SQL Server stored procedure concat string as query

I wonder if can I define some parts of the my sql query as a string.

I worked on the code below but I could not manage to concat that pre-defined string part to the existing query.

Actually @sirketid, @uzman, @basvurukodu params works well, however the @ORA_BASVURU_KESIN_KOSUL param is causing a problem.

I think because it has some sql-spesific expression like and, it is treated diffrently than simple variables used for comparison or assigning such as @sirket_id.

It does not throw any error message, the code simply does not excute the operation.

SET @ORA_BASVURU_KESIN_KOSUL = 'and akftif = 1';

UPDATE basvuru 
SET sirket = @sirketid,
    talep_gorevlendirme_rapor = 'G',
    birimi = 'SS', 
    uzman = @uzman,
WHERE
    kod = @basvurukodu + ' ' + @ORA_BASVURU_KESIN_KOSUL; 

Can I concat query parts like this, if so, how?

Thanks