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Translation is the only process in the cell requiring all three types of what?
RNA
Describe the structure of tRNA? (Stems? Loops?)
4 stems, 3 loops.
Which RNA polymerase transcribes tRNA?
RNA pol III
A charged tRNA is a tRNA with an amino acid. Where is the amino acid added on the tRNA?
3' end.
True or False: amino acyl tRNA synthetase is an enzyme that can add ANY amino acid to any tRNA.
FALSE. amino acyl tRNA synthetase are enzymes with specificity for ONE amino acid.
What bond combines the amino acid to the 3' Adenosine? What is the linkage between a.a. and tRNA?
High-energy covalent bond. 2' or 3' linkage.
Which RNA polymerase is the most produces the majority of a cell's RNA? Why?
RNA pol I. It produces rRNA which accounts for 80% of total RNA in cell.
Correctly give the order of RNA transcribed in the highly conserved units in Eukaryotic rRNA.
18S, 5.8S, 28S
Where is the pre-rRNA transcript extensively processed? What kind of processing is done by which kind of RNAs?
In the nucleolus. Cleavage and modification of bases occurs, mostly by small nuclear RNAs, part of snoRNPs.
What makes 5S rRNA unique from the others?
Transcribed by RNA pol III outside NUCLEOLUS.
What is rRNA?
ribosomal RNA.
TRUE or FALSE? 5S rRNA isn't transcribed in the nucleus.
FALSE. It IS transcribed in the nucleus, just not the nucleolus. It later diffuses into the nucleolus to interact with the other rRNAs.
rRNA folds into a conserved stem-loop structure. Why might this be?
The folding may affect the catalytic nature of the rRNA.
Is the 70S ribosome found in prokaryotes or Eurkaryotes?
Prokaryotes.
The 70S ribosome comprises the 50S and 30S subunits. Which of the following rRNAs are found in which subunit? 5S, 16S, 23S
50S : 5S & 23S.
30S: 16S.
The 80S ribosome is found in Eukaryotes or Prokaryotes?
Eukaryotes.
The 80S is composed of the 60S and 40S subunits. Which of the following rRNAs belong to which subunit? 5.8S, 5S, 18S, 28S. (Hint: 40S only has 1 rRNA.)
60S: 5S, 5.8S, 28S.
40S: 18S
Which RNA is found in the large subunits of both prokaryotic and eukaryotic ribosomes?
5S
What Eukaryotic initiation factors (eIFs) keeps the ribosomal subunits apart when mRNA isn't being translated?
eIF3 for the 40S and eIF6 for the 60s.
Which ribosomal subunit interacts with mRNA first? Large or small?
Small.
What comprises the initiation complex in eukaryotes?
eIF1A, eIF4 and eIF3 on the 40S subunit. and mRNA.
How is the preinitiation complex assembled? (involves eIF1A, eIF2-GTP)
eIF1A binds 40S subunit and recognizes eIF2-GTP + Met - tRNAiMEt
Protein synthesis can be negatively regulated by phosphorylation when the cell is nutrient deficient. Where? (Think factors)
At the eIF2 factor. Hydrolyzing the eIF2-GTP to GDP inactivates it.
What makes tRNAi^Met so special?
It is the the only tRNA that can interact with the P site in the ribosome.
What modification of tRNAi^Met is unique to bacteria?
Formyl (-CHO) modification.
tRNAi^Met is required for _______ while tRNA^Met is required for _______.
Initiation, elongation.
TRUE or FALSE: both tRNAi^Met and tRNA^Met are charged by amino acyl tRNA synthetase.
TRUE.
Why are only mRNA transcripts capped? (Hint: unique feature of RNA pol II)
Because dimeric guanyltransferase (capping enzyme) binds to phosphorylated CTD of RNA pol II
eIF4 is crucial for recruitment of mRNA to the preinitiation complex. What does it recognize in mRNA?
The 5' cap.
eIF4 is a cap-binding complex. Describe what the component G does.
eIF4-G: interacts with eIF3 to come down on the mRNA to be translated.
eIF4 is a cap-binding complex. Describe what the component A does.
eIF4-A has helicase activity with ATP. Removes the secondary structures (UTR) of mRNA to access AUG. Called 'Scanning'.
eIF4 is a cap-binding complex. Describe what the component B does.
eIF4-B: a structural component.
eIF4 is a cap-binding complex. Describe what the component E does.
eIF4-E is the cap binding protein.
Describe what the Shine-Dalgarno is and how it faciliates initiation. (Hint, interaction with 30S subunit)
5-8bp sequence able to base pair with the 16S rRNA in the Small ribosomal subunit.
What does the AUG-Kozak sequence do? ACCAUGG
In mammlian cells, it aids recognition of start codon.
Which factors aid the association of the 60S ribosomal subunit in eukaryotes to the initiation complex?
eIF5-GTP (and eIF6, which is already there). Hydrolysis dissociates eIF6 and 80S ribosome is formed.