Molecular Basis of Inheritance
Transcription
Transcription is the cell copying one gene from DNA into a strand of RNA. It is how the instructions in a gene leave the safe DNA and become a working message.
An enzyme, RNA polymerase, binds the start of a gene, unwinds a short stretch of DNA, and reads one strand. It builds an RNA copy using base pairing, but with one change: RNA uses uracil (U) in place of thymine (T), so it pairs U with A.
The finished messenger RNA carries the gene's message out to the ribosomes, where it is read to build a protein. Only one strand of the DNA is read, called the template strand.
Where students slip up
Only one DNA strand is read as the template, not both. And RNA uses U instead of T. Students often copy the DNA letter for letter and forget the T to U swap, or try to read both strands at once. One strand, and every A on it becomes U on the RNA.
Hold onto this
One gene, one strand read, T becomes U. That is transcription.
Why it helps in the exam: the template versus coding strand, and the U-for-T rule, are classic traps.
Where this connects
The RNA made here is not the end. It travels to the ribosome to be read into a protein, so transcription and translation are two halves of one flow: DNA to RNA to protein.
The next step: translation →Quick check
During transcription, the RNA base that pairs with adenine (A) on the DNA template is:
- AThymine (T)
- BUracil (U)
- CGuanine (G)
- DCytosine (C)