Translation Flashcards
what is translation?
- RNA-directed synthesis of a polypeptide
- message in mRNA is interpreted by tRNA
where does tRNA get amino acids from? where does it transfer them to?
from the cytoplasm to the ribosome (location of polypeptide formation)
what are the three stages of translation?
- Initiation
- Elongation
- Termination
what happens during initiation stage of translation?
mRNA, tRNA with first amino acid (Met), and the two ribosomal subunits are all brought together to form initiation complex
how does initiation complex bind together? where does mRNA bind? where does tRNA bind, what does this establish?
- mRNA binds to the small ribosomal subunit near it’s 5’ end
- tRNA binds to start codon on mRNA
- establishing reading frame - Large ribosomal subunit binds to complex, completing Translation initiation complex
what happens during elongation stage? which direction does ribosome move along mRNA?
- Amino acids are added one by one to polypeptide.
- moves along the mRNA from 5’ to 3’
what are the three steps in elongation cycle?
i. Codon Recognition
ii. Peptide Bond Formation
iii. Translocation
Ribosome moves down 3 bases
(one codon)
what happens during codon recognition step?
- anticodon of incoming tRNA base-pairs with complementary mRNA codon in A site
what happens during peptide bond formation step?
- Bond is formed between incoming amino acid and growing polypeptide chain (energy requiring)
- Polypeptide chain transferred to tRNA in A site
what happens during translocation step?
- Ribosome moves down 3 bases (one codon)
- Empty tRNA released from E site (energy releasing)
- tRNA with polypeptide chain moves into P site
- Next codon to be translated moves into A site
- Ribosome ready for next tRNA
how long does elongation stage continue for?
Steps are repeated until the STOP codon reaches A site
what happens during termination stage of translation?
- Stop codon reaches the A site of the ribosome
- Release Factor binds to the stop codon
- Hydrolyses bond (adds water to bond) holding polypeptide to tRNA –> Completed polypeptide is released
- Small and large subunits of ribosome separate and mRNA is released