We have analysed the causes of asymmetry in nucleotide composition of DNA complementary strands of prokaryotic chromosomes. Analysing DNA walks we have separated the effect of replication-associated processes from the effect introduced by transcription and coding functions. The asymmetry introduced by replication switches its polarity at the origin and at the terminus of replication, which is observed in both noncoding and coding sequences and varies with respect to positions in codons. Coding functions introduce very strong trends into protein coding ORFs, which are specific for each nucleotide position in the codon. Using detrended DNA walks we have eliminated the effect of coding density and we were able to distinguish between mutational pressure associated with replication and compositional bias for genes proximal and distal to the origin of replication.