Key Points of DNA Translation Process

ACT 1 - Initiation 

• The smaller Subunit of Ribosome charged with tRNA and the amino acid Methionine encounters mRNA
• They attach and start to scan for the start signal 
• The small subunit ribosome finds the starting sequence (AUG), the codon (triplet) for amino acid Methionine
• The large subunit of ribosome joins the small subunit to form the complete ribosome 
• Ribosomal subunit for Prokaryotic cells - 50 S and 30 S
• Ribosomal subunit for Eukaryotic cells - 60 S and 40 S

Act 2 - Elongation 

• A new tRNA + amino acid enter the A site of the ribosome 
• Anti-codon matches with mRNA codon basepairs, ribosome can link the 2nd amino acid together 
• tRNA shifts from A site to P site, P site to E site and leaves the ribosome without any amino acid
• The ribosome itself moves one triplet forward and a new tRNA + amino acid will enter the ribosome
• Procedure is repeated 

Act 3 - Termination 

• When ribosome reaches 1 of the 3 stop codons (UGA, UAG and UAA), there are no corresponding tRNAs
• Termination proteins bind to the ribosome and stimulate the release of the amino acid chain (polypeptide chain) 
• Large and small subunit dissociate as ribosome released from mRNA 

Key Points of DNA Transcription

ACT 1 - Initiation 

• Transcription factors (TFs) recognize and locates the promoter region (TA-TA Box)
• RNA Polymerase II binds the TFs and creates a transcription initiation complex
• DNA begins to unwind and then stabilized 
• RNA Transcription takes place in the complimentary strand of DNA
• RNA Polymerase II begins to transcribe 

ACT 2 - Elongation 

• RNA grows from 5' to 3'
• RNA Polymerase II adds nucleotides to the 3' end of the growing pre-mRNA
• Pre-mRNA is anti parallel with the Template DNA Strand (Antisense), and it's similar with the Coding DNA strand (Sense)
• Uracil replaces thymine within the pre-mRNA
• The direction of the Transcription goes from upstream towards downstream of the DNA strands

ACT 3 - Termination  

• RNA Transcription stops when it reaches the terminating region (AAAUAAAA) 
• Pre-mRNA turns into mRNA (messenger RNA) by applying a G-cap and poly-A tail 
• Introns of the pre-mRNA are cut by Spliceosome and exon parts are bind together