Transcription

1. RNA uses ribose sugar, not deoxyribose.
2. RNA bases are A, G, C, and uracil (U).
3. Uracil (U) pairs with adenine (A). (As in DNA, C pairs with G.)

1. Only one small region of one DNA strand is used as a template.
2. RNA polymerase is used instead of DNA polymerase to catalyze nucleotide addition.
3. The result of transcription is a single-stranded RNA.

For transcription to occur, RNA polymerase must first bind to a promoter. A promoter is a base sequence in the DNA that signals the start of a gene. Transcription begins when RNA polymerase binds to a promoter region and then moves along to the end of a gene. This results in formation of an RNA transcript.

Newly formed mRNA is modified by the addition of a cap to the 5' end (a "start" signal for protein synthesis) and a poly-A tail to the 3' end.

Additionally, the mRNA transcript must be edited . The introns (noncoding portions) are removed before the transcript leaves the nucleus. Only the exons (portions that will eventually be translated) remain in the finished transcript that leaves the nucleus.

This animation (Audio - Important) describes editing of mRNA.

This would be a good time to look at the Transcription tutorial (Audio - Important).

These animations (Audio - Important) review transcription:
transcription 1,
transcription 2.

REVIEW: Which of the following carries amino acids to ribosomes, where amino acids are linked into the primary structure of a polypeptide?
Answer tRNA