Drag the words to complete the sentences. linear
single
circular
eukaryotic
prokaryotic
multiple
Before a cell divides, its DNA must be replicated without errors so that
the genetic codes for proteins are expressed properly. In
cells, which have linear chromosomes, replication
occurs in
locations and ends when all the
chromosomes are copied. In prokaryotic cells, which have
DNA, replication starts in only a single location and
proceeds until the entire chromosome is copied.

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.