Magine you are in a laboratory. You are exploring the following reaction: A + B → C When the product C is created, bubbles form. When 10mL of A is added to 10mL of B, the reaction takes twenty seconds. Your teacher gives you three unknown substances (X, Y, and Z), one of which is a catalyst for the reaction.

Design an experiment to test substances X, Y, and Z to determine which one is a catalyst for the reaction.

step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.