Gene expression

Question 1

Central dogma of gene expression

Answer 1

Genes go through two steps to become polypeptides: transcription and translation

Question 2

Transcription

Answer 2

• RNA pol with transcription factors (for frequency) binds to promoter on the 3’->5’ antisense/template DNA strand
• From trascription start site RNA pol denaturates the double helix and catalyzes transcription 5’->3’
• Pre-mRNA is a copy of the 5’->3’ sense/coding DNA strand

Question 3

Post-transcriptional processing

Answer 3

• 7-methylguanosine cap in 5’ for stability and transportation
• Poly-A sequence in 3’ anti degradation
• Splicing removes GU-introns-AG to keep only exons

Question 4

tRNA

Answer 4

Cloveleaf structure from intramolecular H-bonds, transportation / adaptor RNA, 20 (one for each amino acid), their anticodon correspond to the mRNA’s codon

Question 5

Translation

Answer 5

• Initiation: mRNA and ribosome’s subunits assemble on the start codon AUG
• tRNA for Met arrives in the P site
• Elongation: moving 5’->3’ the ribosome reads the next codon and the corresponding tRNA comes to the A site
• Peptidyltransferase catalyzes the peptide bond between -COOH of one and -NH2 of the next
• The ribosome moves, the uncharged tRNA moves to the E site and exits while the charged tRNA is now in the P site
• Termination: the ribosome reads a stop codon (UGA, UAA, UAG) that calls for release factor