Transcription
7.3.1 State that transcription is carried out in a 5' - 3' direction
Transcription is carried out in a 5' - 3' direction (of the new RNA strand)
7.3.2 Distinguish between the sense and antisense strands of DNA
DNA consists of two polynucleotide strands, only one of which is transcribed into RNA
 The
antisense strand is transcribed into RNA
 Its sequence will be complementary to the RNA sequence and will be the
"DNA version" of the tRNA anticodon sequence
 The sense strand is not transcribed into RNA
 Its sequence will be the "DNA version" of the RNA sequence (identical
except for T instead of U)
7.3.3 Explain the process of transcription in prokaryotes, including the role of the
promoter region, RNA polymerase, nucleoside triphosphates and the terminator
A gene is a sequence of DNA which is transcribed into RNA and contain three main
parts:
 Promoter:
Responsible for the initiation of transcription (in prokaryotes, a
number of genes may be regulated by a single promoter - this is an operon)
 Coding Sequence: The sequence of DNA that is actually transcribed (may
contain introns in eukaryotes)
 Terminator: Sequence that serves to terminate transcription (mechanism of
termination differs between prokaryotes and eukaryotes)
Transcription is the process by which a DNA sequence (gene) is copied into a
complementary RNA sequence and involves a number of steps:
 RNA
polymerase binds to the promoter and causes the unwinding and
separation of the DNA strands
 Nucleoside triphosphates (NTPs) bind to their complementary bases on the
antisense strand (uracil pairs with adenine, cytosine pairs with guanine)
 RNA polymerase covalently binds the NTPs together in a reaction that involves
the release of two phosphates to gain the required energy
 RNA
polymerase synthesises an RNA strand in a 5' - 3' direction until it reaches
the terminator
 At the terminator, RNA polymerase and the newly formed RNA strand both
detach from the antisense template, and the DNA rewinds
 Many RNA polymerase enzymes can transcribe a DNA sequence sequentially,
producing a large number of transcripts
 Post-transcriptional modification is necessary in eukaryotes
Overview of Transcription
7.3.4 State that eukaryotic RNA needs the removal of introns to form mature mRNA
 Euakaryotic
genes may contain non-coding sequences called introns that need to
be removed before mature mRNA is formed
 The process by which introns are removed is called splicing
 The removal of exons (alternative splicing) can generate different mRNA
transcripts (and different polypeptides) from a single gene