RR11 Flashcards
What are 3 critical RNAs in protein synthesis?
tRNAs
rRNAs (80% of total cellular RNA)
mRNAs
What is the arrangement of pre-rRNA transcription units?
They are repetitive clusters that create membrane-less nucleolus, this is where rRNA is made.
What is the difference between ribosomes in bacteria and in eukaryotes?
In bacteria: 23s, 16s and 50s gives rise to structure. 50s + 30s come together to form 70s complete ribosome.
In Eukaryotes: 60s + 40s form 80s ribosome which has an additional RNA large subunit.
What is the structure of rRNA?
It folds into conserved stem-loops which are highly conserved among species. In eukaryotes and prokaryotes it is critical.
What are the steps of processing pre-tRNAs?
1) 5’ end sequence is removed
2) sequence is removed from loop
3) CCA is added to 3’ end
4) modification of internal bases
anticodon is critical for decoding of mRNA.
What is Aminoacyl- tRNA synthetase? What is its function and how does it work?
It is required to charge tRNA with amino acids. It recognizes and binds their cognate tRNAs. It attaches amino acid to tRNA and binds 2 substrates by forming ester bond between carboxy on amino acids and hydroxyl on tRNA nucleotide. tRNA is charged with its amino acid and critical for protein formation. There code is considered ‘degenerate’, several codons can result in the same thing, tRNAs will be bound to their amino acid and charged to be used in protein synthesis.
Can a single tRNA bind to more than one single codon?
Yes
What is the function of tRNAi met? What are the two types?
The function is for initiation of a polypeptide chain. There are two types.
1) used whenever methionine comes up (the one without the i)
2) other is required for initiation (tRNAi met)
How is tRNAi met distinguished from tRNA met?
It depends on the organism.
Prokaryotes: add formyl group to show its an initiator
Eukaryotes: structurally different, can bind to specific sites (P site) in ribosome
How is the pre-initiation complex formed?
tRNAmet is bound to GTP and interatcs with E1F2. EIF2 aids in this binding. The complex binds to small ribosomal subunit that is also bound by other initiation factors, this creates 43s pre initiation complex.
How can bad conditions block synthesis?
It can cause phosphorylation that blocks EIF2 from tRNAmet.
What do we need for efficient translational initiation of mRNA?
We need a 5’ cap which enhances synthesis. Only class II mRNA transcripts are efficiently translated. We use cap-binding proteins for efficient translational initiation.
What cap-binding protein increases efficient translational initiation?
7mGDP cap (it does not impact uncapped transcripts)
What is the function of eIF4? What is the process that it is involved in?
It plays an instrumental role in recruiting mRNA to the pre-initiation complex. It binds 5’ cap of mRNA.
EIF4e interacts with cap, bringing down whole complex to 5’ end of an mRNA to be translated. At the same time, tRNAimet interacts with EIF2 on small subunit, and eIF4 interacts with 5’ end. They come together and mediate by EiF4 g - binding EIF3 and PABPC.
What happens if there is too much eIF4?
It cause protein over expression which is associated with tumour formation.
