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level: 8.4 Protein synthesis - transcription and slicing

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level questions: 8.4 Protein synthesis - transcription and slicing

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Protein synthesis- Assembling amino acids into proteins
The simple steps of protein synthesis- Transcription - Splicing - Translation
Transcription- Process of making pre-mRNA using part of the DNA as a template
Process of transcription (1)- Enzyme causes specific region on DNA strand to separate - Exposes nucleotide bases in that region
Process of transcription (2)- Free nucleotides in the nucleus bind by specific base parings as there is an exposed polynucleotide strand, template strand - RNA polymerase joins nucleotides together on strand to form pre-mRNA
Process of transcription (3)- As RNA poly. joins nucleotides, the DNA strands re-join behind it - So, only about 12 base pairs on DNA are exposed
Process of transcription (4)- When RNA poly. reaches the 'stop-code' DNA strand it detaches - Production of pre-mRNA is then complete
Splicing of pre-mRNA in eukaryotes- Introns + exons copied into mRNA during transcription - pre-mRNA = mRNA strand with introns + exons - Splicing occurs, introns removed, exons joined together, forming mRNA strands - Takes place in nucleus - mRNA leaves nucleus for translation
Splicing of pre-mRNA in prokaryotes- mRNA made directly from DNA - Without splicing, as prok. DNA has no introns + exons
2 Process of transcription (1)- RNA polymerase unwinds DNA - By breaking hydrogen bonds - Length of 1 gene
2 Process of transcription (2)- One strand acts as a template - Free mRNA nucleotides bind to complementary DNA nucleotides
2 Process of transcription (3)- Phosphodiester bonds form between nucleotides by condensation
2 Process of transcription (4)- This forms Pre RNA - Introns are removed to form mRNA (splicing)