7.3 Translation (HL) Flashcards
What are ribosomes comprised of?
Proteins (for stability) and ribosomal RNA (for catalytic activity)
What are the functions of the two RNA subunits?
Small subunit -> mRNA binding site
Large subunit -> tRNA binding site
What are the large subunit binding sites?
A (aminoacyl)
P (peptidyl)
E (exit)
What are the 4 main regions of a tRNA molecule?
Acceptor stem (ACC)
Anticodon (associates with the mRNA codon)
T arm (associates with the ribosome via the binding sites)
D arm (associates with the tRNA activating enzyme)
How is tRNA activated?
tRNA activating enzyme, amino acid and tRNA D arm bind creating a tRNA-amino acid complex which separates and is now ‘charged’
What are the 3 steps of translation?
Initiation
Elongation
Termination
What occurs in initiation of translation?
Small ribosomal subunit binds to the 5’ end of mRNA and moves it along until the start codon
The appropriate tRNA binds here
The large ribosomal subunit aligns itself with the tRNA molecule at the P site
What occurs in elongation of translation?
Next tRNA binds to the A site and the amino acid in the P sire covalently attaches (peptide bond) to that in the A site
Then the deacylated tRNA moves into the E site and is released as the mRNA moves along to the next codon and the A site tRNA moves into the P and a new, charged tRNA binds to the A site etc…
What occurs in termination of translation?
The mRNA stop codon is reached which recruits a release factor
The polypeptide is released and the ribosome disassembles into it’s original subunits
What is a polysome?
A group of two or more ribosomes translating the same mRNA simultaneously
(new ribosomes attach to the 5’ end)
Where does the ribosome go if the protein is targeted for intracellular use?
Free ribosomes in the cytosol
Where does the ribosome go if the protein is targeted for secretion, membrane fixation of use in lysosomes?
Rough ER (bound ribosomes)
What is the function of the SRP?
Single recognition particles halt translation and then docks the ribosome complex on a receptor on the ER (creating the rough ER)
The translation of the polypeptide chain will continue into the lumen of the ER
