Translation Part 1 Flashcards
Why is the fidelity of transcription and translation low compared to DNA replication?
There is no genetic information that is being passed down to progeny in both of these processes. With transcriptional errors, this can be compensated by translation.
Which part of the tRNA is charged with the amino acid and how is this part relevant in translation?
the CCA at the 3’ end. The CCA binds EF-Tu, which helps bring the charged tRNA in during elongation
How many tRNA species are there?
30-40
Why are there only 30-40 tRNA species?
One tRNA can recognize multiple anticodons through wobbling with the 3rd base.
Possible wobbles: U:G, G:U, I:C, I:U, I:A
How many tRNA synthetases are there?
20 (1 for each amino acid)
What is the mechanism for charging by tRNA synthetases? (3)
- Amino acid is activated by linking carboxylic acid group to phosphate of AMP
- Transfer of activated amino acid to 2’ or 3’ OH of adenosine sugar.
- Hydrolysis of pyrophosphate, which is very exergonic
How can 20 tRNA synthetases charge 30-40 tRNAs?
Synthetases recognize tRNAs in different ways. A lot o them recognize modifications or specific base pairs within the tRNA structure. The anticodon is only looked at for charging methionine.
How do tRNA synthetases ensure high fidelity when charging tRNAs? (4 mechanisms)
Synthetase can occlude larger amino acids from sites that are supposed to fit smaller amino acids.
They also have proofreading pockets. If an amino acid can enter the binding pocket with perfect complimentarity, the tRNa is deacylated.
How many classes of tRNAs are there and what are the differences between them (2)?
2 classes. Class 1 has Rossman fold and esterifies 2’ hydroxyl. Class 2 has Beta sheets and esterifies 3’ hydroxyl.
Note: Esterification can migrate chemically because they are energetically labile.
What are the small and large subunits of the prokaryotic and eukaryotic ribosomes?
30 S and 50 S make 70 S
60 S and 40 S make 80 S
What domains of the ribosomes are conserved?
Any domain that is involved in the function of the core ribosome. These are conserved across all species!
How and why are the RNA domains and proteins assembled differently between the small and large subunits of the ribosome?
In small subunit, three domains of rRNA segregate into different parts. In large subunit, the 6 domains overlay to create a larger, immobile structure.
The small subunit has to move when translocating the mRNA:tRNA complex, so it needs multiple domains to facilitate that. The large subunit is only involved in catalysis, so it can rely on small subunit for movement.
What is significant about the RNA found in the large subunit?
The rRNA in the large subunit makes up the active site of the ribosome. It’s involved in the catalysis!
What is significant about ribosomal proteins?
They have globular domains with long extensions. These extensions are positively charged, so they are primarily involved in maintaining ribosome structure.
