Transcription is the process through  which a DNA sequence is enzymatically copied by an RNA polymerase to produce  a complementary RNA. Or, in other words, the transfer of genetic information from DNA  into RNA. 

Prokaryotic transcription occurs in the cytoplasm alongside translation. Eukaryotic transcription is more complex transcriptional regulatory mechanism than prokaryotes. In eukaryotes transcription occurs in the nucleus and translation occurs in the cytoplasm.

Replication is the process whereby DNA makes exact copies of itself.

Replication vs Transcription
Prokaryotic DNA replication
It occurs in the S phase of cell cycle. It occurs in the G1 and G2 phases of cell cycle.
It is catalysed by DNA polymerase enzymes. It is catalysed by RNA polymerase enzymes.
Deoxyribonucleoside triphosphate (dATP, dgtp, dTTP, dCTP) serve as raw materials. Ribonucleoside triphosphate(ATP, UTP, GTP, CTP) serve as raw materials.
Replication occurs along the strands of DNA. It takes place along one strand of DNA.
It involves unwinding and splitting of the entire DNA molecule(chromosome). Involves unwinding and splitting of only those genes which are to be transcribed.
It involves copying of the entire genome. It involves copying of certain individual genes only.
Replicated DNA strand remains hydrogen bonded to its template DNA strand. Transcribed RNA strand separates from its DNA template strand.
Two double stranded DNA molecules are formed from one DNA molecule. A single one stranded RNA molecule is formed from a segment of one strand.
Products remain within nucleus. Greater part of the products passes from the nucleus into the cytoplasm.
Products are not degraded. Products are degraded after their function is over.
Serve to conserve the genome for the next generation of cells and individuals. Serves to form DNA copies of individual genes for immediate use in protein synthesis.
It require RNA primer to start replication. No primer is required to start.
I produces normal DNA molecules that do not need any processing. It produces primary RNA transcript molecules which need processing to acquire final form and size.

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