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Protein synthesis
Transcription and translation pre-mRNA
| Term | Definition |
|---|---|
| How are proteins created | Proteins are created on ribosomes. The production of proteins from the DNA code occurs in 2 main stages Transcription and Translation |
| What is transcription | Where one gene on the DNA is copied into mRNA |
| What is translation | Where the mRNA joins with a ribosome and corresponding tRNA molecules bring the specific amino acid the codon codes for |
| How are proteins made in transcription | A complementary mRNA copy of one gene on the DNA is created in the nucleus mRNA is much shorter than DNA so it is able to carry genetic code to the ribosome in the cytoplasm to enable the protein to be made |
| What are the steps for transcription Step 1 | The DNA helix unwinds to expose the bases to act as a template |
| Step 2 | Only one chain of the DNA acts as a template |
| Step 3 | Like with DNA replication this unwinding and unzipping is catalysed by DNA helicase |
| Step 4 | DNA helicase breaks hydrogen bonds between bases |
| Step 5 | Free mRNA nucleotides in the nucleus align opposite exposed complementary bases |
| Step 6 | The enzyme RNA polymerase bonds together the RNA nucleotides to create a new RNA polymer chain. One entire gene is copied |
| Once copied the mRNA is modified and then leaves the nucleus through the nuclear envelope pores | |
| After transcription | Pre mRNA has to be modified to become mRNA that is ready to leave the nucleus and take part in translation |
| How are introns spliced out | They are spliced out by a protein called spliceosome. This leaves behind just the exons the coding regions |
| What is translation | This is the stage in which the polypeptide chain is created using both the mRNA base sequence and the tRNA |
| Translation step 1 | Once the mRA has left nucleus it attaches to a ribosome in the cytoplastym |
| Translation step 2 | The ribosome attaches to the start codon |
| Translation step 3 | The tRNA molecule with the complementary anticodon to the start codon aligns opposite the mRNA held in place by the ribosome |
| Translation step 4 | The ribosome will move along the the mRNA molecules to enable another complementary tRNA to attach to the next codon on the mRNA |
| Translation step 5 | The 2 amino acids that have been delivered by the tRNA molecule are joined by a peptide bond. This is catalysed by an enzyme and requires ATP |
| Translation step 6 | This continues until the ribosome reaches the stop codon at the end of the mRNA molecule. The stop codon does not code for an amino acid and therefore the ribosome detaches and translation ends |
| The polypeptide chain is now created and will enter the golgi body for folding and modification |
Created by:
yHya