Transcription Flashcards
(12 cards)
What is transcription
It is the process of making RNA from DNA
What is RNA used for
It synthesis proteins
What are the 3 things needed to make RNA from DNA
- DNA template — the strand of DNA that provides the instructions to copy.
- RNA nucleotides — building blocks used to assemble the new RNA strand.
- RNA polymerase — the enzyme that reads the DNA template and builds the RNA strand by matching RNA nucleotides.
What are the 3 steps of making RNA
- Initiation
- Elongation
- Termination
Step 1: initation
- RNA polymerase binds to segment of DNA near the beginning of gene called promoter (Each gene has its own promoter)
- RNA polymerase then separates the DNA strand exposing the single stranded templates
Step 2: Elongation
• RNA polymerase adds complementary nucleotide to the DNA template strand in the 5’ - 3’ direction
• Instead of an Thymine (T) base, RNA uses uracil (U)
Step 3: Termination
• Sequences called terminators will signal the RNA transcript is done
• once done, the transcript (now called mRNA) is released
Termination methods
- Hairpin: mRNA form a hairpin loop and RNA polymerase “falls off” DNA
- Rho dependent: rho protein bins to mRNA and stops transcription
What has to happen after to the RNA after the final step?
After transcription, mRNA is now called pre-mRNA, and it’s not yet ready to leave the nucleus
Has to undergo post transcriptional methods:
1. 5’ cap
2. Poly-A tail
3. Splicing
What is the 5’ cap method?
7 G’s are added to become the initial binding site for ribosome
What is poly-A tail method?
Addition of 50-200 A’s on 3’ end
• Protects from enzyme digestion in cytosol
What is splicing ?
pre mRNA has both coding and non-coding regions
• Exons → coding region
• Introns → non-coding region → must be removed by spliceosome
