Test yourself on Protein Synthesis — Transcription and Translation with exam style questions, marked instantly.
Flashcards that come back just before you would forget them.
A revision plan that remembers what you know and shows what to do next.
See which topics you have nailed and which need another look.
Quiz yourself on Protein Synthesis — Transcription and TranslationGet your flashcardsBuild my revision planTrack my progress🔬 Transcription: Reading the DNA Message
Where it happens: In the nucleus.
The DNA double helix cannot leave the nucleus — it is too large and too important to risk. Instead, the cell makes a single-stranded working copy of a single gene. This copy is called messenger RNA (mRNA). The process of making mRNA from DNA is called transcription.
Step-by-step: what happens during transcription
- RNA polymerase — an enzyme — binds to the DNA at the start of the gene.
- RNA polymerase unwinds the DNA double helix, breaking the hydrogen bonds between the base pairs.
- One strand of DNA — called the template strand — is read in the 3' to 5' direction.
- Free RNA nucleotides in the nucleus pair with the complementary bases on the template strand:
- Adenine (A) on DNA pairs with Uracil (U) on mRNA — note: RNA uses uracil, NOT thymine
- Thymine (T) on DNA pairs with Adenine (A) on mRNA
- Guanine (G) on DNA pairs with Cytosine (C) on mRNA
- Cytosine (C) on DNA pairs with Guanine (G) on mRNA
- RNA polymerase joins the RNA nucleotides together by covalent bonds, forming a growing mRNA strand.
- The mRNA strand peels away from the DNA; the DNA double helix reforms behind the enzyme.
- The completed mRNA molecule leaves the nucleus through nuclear pores in the nuclear envelope.
- The mRNA travels through the cytoplasm to a ribosome.
Key rule: The mRNA sequence is complementary to the template strand, so it is identical in sequence to the coding (non-template) strand — except that RNA has U where DNA has T.
Quick Check: Where does transcription take place, and what enzyme carries it out?
Transcription takes place in the nucleus. It is carried out by RNA polymerase, which reads the template strand of DNA and assembles a complementary mRNA strand.
Make this stick
Signing in gives access to all PrepWise features.