BIOB 160 Principles of Living Systems · Unit 4: Molecular genetics · on Final exam
4.3 Gene expression: transcription and RNA processing
Study notes for Gene expression: transcription and RNA processing in BIOB 160 Principles of Living Systems at Montana State University: the big ideas, a worked example, common mistakes and an exam tip. The same topic has endless practice questions and flashcards in StudyCat.
Big ideas
- The central dogma: DNA → RNA (transcription) → protein (translation). In eukaryotes transcription happens in the nucleus and translation in the cytoplasm.
- RNA polymerase binds a promoter (in eukaryotes with the help of transcription factors, often at a TATA box), unwinds DNA and builds RNA 5′ → 3′ by reading the template strand 3′ → 5′. No primer is needed.
- The mRNA matches the coding (non-template) strand except that U replaces T.
- Eukaryotic pre-mRNA is processed: a 5′ cap and a poly-A tail are added (protection and export), and introns are removed while exons are joined by the spliceosome.
- Alternative splicing lets one gene produce several different proteins.
Worked example
The template strand reads 3′-TACGGATTC-5′. Write the mRNA.
Show the solution
Pair each template base (A→U, T→A, G→C, C→G) and run antiparallel: 5′-AUGCCUAAG-3′. It starts with AUG, the start codon.
Common mistakes
- Transcribing from the coding strand. The template strand is read; the mRNA matches the coding strand with U for T.
- Putting T in RNA.
- Thinking introns are translated. They are removed before the mRNA leaves the nucleus.
Exam tipReading: Campbell ch. 17 (pp. 335–347). Write the 5′ and 3′ labels on every strand in transcription problems.
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