| 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) |
