Practice question

3'-end labeling adds labeled nucleotides specifically to the free 3'-hydroxyl terminus of nucleic acids. Terminal deoxynucleotidyl transferase is a template-independent DNA polymerase that catalyzes sequential addition of deoxynucleotides to 3' ends without requiring duplex formation. Using substrates like [alpha-32P]dideoxyATP, [alpha-32P]cordycepin, or biotin-dUTP, it creates singly or multiply tailed labeled probes. This enzyme efficiently labels single-stranded DNA, double-stranded DNA, and RNA primers. Klenow fragment requires a template and primer, Taq polymerase needs thermal cycling and template, and ligase joins ends rather than incorporating labels.