Genes and gene expression — A/L Biology

What must I remember about Genes and gene expression?

• Central Dogma of Molecular Biology: Genetic information flows unidirectional from DNA (replication) to mRNA (transcription) to polypeptide (translation).
• Transcription in eukaryotes: RNA Polymerase II binds the promoter region (TATA box), transcribes the template strand from 3' to 5', synthesizing precursor mRNA in the 5' to 3' direction.
• Post-transcriptional modifications: 5' methylguanosine cap addition, 3' poly-A tail addition, and RNA splicing (spliceosomes excise non-coding introns and ligate coding exons).
• The Genetic Code: Triplet code (codons on mRNA), non-overlapping, universal, unambiguous, and degenerate (redundant: 64 codons total, 61 code for 20 amino acids, 3 stop codons: UAA, UAG, UGA).
• Translation stages: Initiation (small subunit binds 5' cap, scans for start codon AUG/Met, large subunit docks), Elongation (tRNA anticodons match mRNA at A, P, E sites forming peptide bonds via peptidyl transferase), and Termination (release factor binds stop codon).

Test yourself (1 minute)

1. Template vs Coding strand

   The template strand (3' to 5') is complementary to mRNA; the coding (non-template) strand (5' to 3') has the identical sequence to mRNA, with T replaced by U.

2. tRNA structure

   Cloverleaf secondary structure with an anticodon triplet at one loop and an amino acid attachment site (CCA-3') at the 3' terminus.

3. Start codon dual role

   AUG codes for the amino acid Methionine (Met) as well as serving as the universal translation initiation signal.

Practise Genes and gene expression questions today

Source: NIE G.C.E. (A/L) Biology Syllabus & Resource Book, Unit 6

What should I study first?

What comes next?

Next in the syllabus

Where does Genes and gene expression fit in the syllabus?

Year 1 · Term 2