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Unit 6

6.3 Transcription and RNA Processing

2 min readnovember 29, 2021


Lani Himegarner

AP Biology 🧬

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The process of converting DNA into RNA is called transcription. After replication, the Messenger RNA (mRNA) molecules carry the new DNA strand (which will act as a template) from the nucleus to a ribosome. rRNA molecules are what allows the ribosomes to be functional. 

🧬 The DNA Strand

The DNA strand acts as the template strand and may also be called a non-coding strand, minus strand, or antisense strand. This is because this strand only serves as a template so that a different strand can be transcribed to match it. The sequence of nucleotides in the single DNA strand is eventually translated into a sequence of amino acids which creates a protein.

Image courtesy of Flickr.

RNA Molecules

RNA polymerase (an enzyme in the transcription process) synthesizes the mRNA molecule in the 5’ → 3’ direction as well, and does so by reading the template strand in the opposite direction (3’ → 5’). Then tRNA molecules bind the amino acids that correlate with the anticodon sequences presented on the mRNA.
In eukaryotic cells, enzymes modify the mRNA transcript in a few ways:
  1. It can add a Poly-A tail. A few extra adenine nucleotides are added to the 3’ end (hence why it is called a poly-a tail). Poly-A tails are added so that when they are cut or deleted, there is no deletion to the actual code.
  2. It can add a GTP cap. A GTP cap (Guanine Triphosphate) is added at the beginning of the strand (the 5’ end) to act as a recognition signal for the ribosome to bind to the mRNA strand.
  3. Alternative Splicing. The purpose of splicing is to remove introns and “splice” the exons together. It essentially deciphers patterns that aren’t necessary (the introns) and removes them. Then, the remaining sections of exons are placed back together.
Check out the AP Bio Unit 6 Replays or watch the 2021 Unit 6 Cram


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