WACE Biology — Unit 3
Gene Expression — Flashcards & Quiz
Gene expression is the process by which genetic information in DNA is used to produce functional products, usually proteins. WACE Biology Year 12 Unit 3 expects you to describe transcription and translation in detail, explain the genetic code and codon-anticodon pairing, and discuss how gene expression is regulated at multiple levels in eukaryotes and prokaryotes.
Key Points
- Central dogma: DNA → RNA → Protein. Transcription in the nucleus, translation at the ribosome.
- Transcription: RNA polymerase reads the template strand 3'→5' and synthesises mRNA 5'→3' using U instead of T.
- Pre-mRNA processing in eukaryotes: 5' cap added, poly-A tail added, introns spliced out.
- Translation: ribosome reads mRNA in codons (3-base groups); tRNA delivers matching amino acids via anticodon-codon pairing.
- The genetic code is degenerate (multiple codons per amino acid) and nearly universal across species — evidence of common ancestry.
- Regulation layers (eukaryotes): chromatin remodelling, transcription factors, alternative splicing, mRNA stability, translational control, protein degradation.
Common Mistakes to Avoid
- Confusing transcription (DNA → RNA, in nucleus) with translation (RNA → protein, at ribosome).
- Writing that transcription uses both DNA strands — only the template strand is read.
- Forgetting U replaces T in RNA.
- Mixing up codons (mRNA, 3 bases) with anticodons (tRNA, 3 bases).
- Claiming gene regulation is always at the transcription level — eukaryotes regulate at many levels.
Exam Strategy
SCSA Unit 3 gene expression questions ask you to describe transcription and translation or explain regulation. Method: (1) draw or describe each step with enzyme and strand specificity, (2) for translation, describe initiation, elongation and termination, (3) for regulation, name at least three levels with examples. Use diagrams to show ribosomes and tRNA clearly.
Sample Flashcards
Q1: State the central dogma of molecular biology.
The central dogma describes the flow of genetic information: DNA → (transcription) → mRNA → (translation) → protein. DNA is transcribed into messenger RNA, which is then translated into a polypeptide chain at the ribosome.
Q2: Distinguish between the template strand and coding strand of DNA.
The template strand (antisense) is read by RNA polymerase during transcription (3' to 5') and is complementary to the mRNA produced. The coding strand (sense) has the same base sequence as the mRNA (with T instead of U) and is not directly read during transcription.
Q3: What is the role of mRNA, tRNA and rRNA in protein synthesis?
mRNA (messenger RNA) carries the genetic code from DNA to the ribosome as a sequence of codons. tRNA (transfer RNA) has an anticodon that matches a specific codon and carries the corresponding amino acid to the ribosome. rRNA (ribosomal RNA) forms part of the ribosome structure and catalyses peptide bond formation between amino acids.
Sample Quiz Questions
Q1: The central dogma of molecular biology states that information flows from protein to RNA to DNA.
Answer: FALSE
The central dogma states information flows from DNA → RNA → protein (transcription then translation). The reverse direction (protein → DNA) does not occur in normal biological processes.
Q2: tRNA molecules carry amino acids to the ribosome during translation.
Answer: TRUE
Each tRNA has an anticodon that recognises a specific mRNA codon and carries the corresponding amino acid. The ribosome facilitates the matching and peptide bond formation.
Revision Tip
Transcription and translation are diagram-heavy topics — build a Revizi deck with labelled diagrams for each step and quiz yourself on enzyme functions.
Last updated: March 2026 · 3 flashcards · 2 quiz questions