tRNA, rRNA & Translation (10) Flashcards
RNA in the nucleus
hnRNA mRNA rRNA tRNA snRNA
RNA in the cytoplasm
mRNA
tRNA
rRNA
RNA pol II
makes hnRNA
RNA pol I
makes rRNA
RNA Pol III
makes tRNA & 5S rRNA
tRNA function
translates mRNA into AA of the polypeptide
carrier of AAs
bind to codon
what causes the 3D shape in tRNA?
internal complementarity
What are the chemical modifications of tRNA after transcription? & why is this done?
some uridines are converted to dihydrouridine or pseudouridine
some nucleotides are methylated
required for correct 3D shape & chemistry to provide the correct function
where is the AA attachment site?
AA attachment site is located at the top of the tRNA, the Adenine in the CCA sequence at the 3’ end
What significant about the sequence of the AA attachment site?
not encoded in DNA, sequence is added at the end
anticodon
3 sequential nucleotides in the middle of the loop which function in the recognition of the complementary mRNA codon
why does tRNA have loops & stems?
enables the molecule to fit into the ribosome
what does tRNA serve as an adaptor to?
AA to tRNA
codon to anticodon
genetic code
consists of grps of 3 of 3 nucleotides called codons
how many diff codons are there?
64 (4^3)
how many diff AAs are there?
20
what provides the redundancy in the genetic code
64 codons for 20 AAs
wobble position & what does it create
The 3rd position of the anticodon can sometimes bind to non-complementary nucleotides
degenerate code
Different nucleotide in a codon coding for the same AA differs in the ___
wobble position
Why is there a wobble position?
buffers any deficiencies or errors to prevent anything from going wrong
what is the role of aminoacyl-tRNA synthetase?
charges/activates tRNA by adding the correct AA
what are the steps in aminoacyl tRNA synthetase activating tRNA?
- AA & ATP bind to enzyme
- 2 Ps are released, AMP binding activates the AA
- tRNA binds to synthetase, AA covalently bonds to the tRNA & AMP is released
- Charged tRNA is released with AA
AA is added to the CCA end
How does aminoacyl tRNA synthetase correctly add AAs?
recognizes unique parts of each tRNA (adapter function), assures correct anticodon
aminoacyl tRNA
complex of AA & tRNA
What sort of relationship exists b/w tRNAs & codons? & tRNA genes with tRNAs?
not a 1:1
a 1:1
how many tRNA genes are in humans?
1300
why do humans have so many tRNA genes?
more copies of the genes will produce more tRNA transcripts
humans require a lot of tRNA to build the PROs that they’re composed of
What is the size of a eukaryotic ribosome?
80S
lrg subunit: 60S
small subunit: 40S
What is the composition of ribosomes?
PROs & rRNA
where are ribosomes assembled?
nucleus
what is the composition of the large subunit of a prokaryote?
3 diff rRNA + 49 PROs = 60S
what is the composition of the small subunit of a eukaryote?
18S + 33 PROs = 40S
what does internal base pairing in rRNA produce?
secondary & tertiary structure
ribosome structure is both ___ & ___
structural & catalytic
what are the post-transcriptional modifications of tRNA & rRNA?
a) RNA with conventional base-pair folding
b) RNA with nonconventional base-pair interactions
c) Structure of actual RNA molecule
What modifications occur in the RNA encoding 3 rRNAs?
large 45S rRNA is copied & cut into 3 rRNAs:
28S
18S
5.8S
What RNA gene is outside the nucleus?
5S
where does ribosome assembly occur & how is it done?
nucleolus
bringing together the 45S transcript, processing enzymes & PROs
How & where do the rRNA genes occur?
appear in multiple copies in clusters in the nucleolar organizer regions
what rRNA gene is responsible for the tree appearance of the tRNA?
45S
How are 45S transcripts modified? & what does this?
removal of spacers & base modifications
done by snoRNPs & other PROs
How is 5S rRNA made?
transcribed by RNA pol III & shipped to the nucleolus post synthesis
nucleolar organization region rRNA?
18S, 28S & 5.8S
what polymerase isn’t involved in translation of NOR rRNA?
pol III (5S)
ribosome role in translation
guide tRNAs along mRNA
what are the modifications of mRNA?
5' cap 5' UTR Coding region with start & stop codons 3' UTR PolyA region
which subunit is assoc with IFs?
small subunit
what is the starting codon &AA?
MET
where does ribosome machinery assemble?
mRNA strand
how is the reading frame properly established?
properly aligning the 1st codon
shine dalgarno sequence & how is it recognized?
ribosome binding site upstream of AUG in prokaryotes
subunit recognizes the special sequence by base pairing
what size is the small subunit rRNA in prokaryotes?
16S
What facilitates tRNA to bind to the mRNA?
hydrolysis of GDP
how does the shortening of the polyA tail determine the half-life?
will weaken the eIFS & cause the molecule to de-circularize
What are the diffs in initiation in eukaryotes & prokaryotes?
There is an eIF with GTP that becomes hydrolyzed, GTP is separate in prokaryotes
mRNA is capped, looks for cap to initiate translation, eIFs cause the polyA tail to loop on itself so its close to the 5’ cap, mRNA isn’t capped in prokaryotes
Indicator codon is directed by the eIF on the cap scanning for the first AUG & in prokaryotes shine-dalgarno signifies the 1st codon
When does an E burning step occur in translation?
tRNA is delivered to the A site & GTP –> GDP + P
peptidyl transferase
ribozyme on the large rRNA, covalently binds the AA in the A site to the AA in the P site in translation
what enables the tRNA to exit the ribosome?
AA bound to polypeptide chain
What occurs in initiation of translation? (details)
- Attachment of the small subunit (with IFs complex)
Small subunit, GTP, IFs/eIFs
Small subunit binds to IFs/eIFs & GTP binds to IFs/eIFs & then binds to small subunit
Slides along molecule looking for shine-dalgarno - Bring in 1st AA
fMet in prokaryotes of initiator codon in Eukaryotes - Complete initiation complex large subunit attaches, IFs/eIFs are lost, GTP GDP
What occurs in elongation of translation? (details)
- Selection anticodon binds with correct codon
1st tRNA binds to the T site & GTP GDP + P
EF brings charged tRNA to the site
After the very 1st tRNA, tRNA is delivered into the A site & GTP GDP + P
An elongation factor removes GDP from tRNA & replaces it with a GTP recharges the tRNA - Peptide bond formation (peptidyl transferase activity)
AA in A site covalently bonds (peptide bond) to the AA in the P site performed by peptidyl transferase (ribozyme of large subunit)
AA leaves tRNA in the P site - Translocation
Ribosome moves down 1 codon due to an elongation factor
Empty tRNA shifts to the E site & peptide chain is in the P site
AA bound to the chain enables tRNA to exit - Release of de-acylated tRNA
What occurs in termination in translation?
Reach stop codon
Release factor is inserted (mimics tRNA anticodon)
Polypeptide is released & subunits fall apart
what are the steps in initiation?
- Attachment of the small subunit
- Bring in 1st AA
- Complete initiation complex
what are the steps in elongation?
- Selection
- Peptide bond formation (peptidyl transferase activity)
- Translocation
- Release of de-acylated tRNA
how does the RF manage to get inserted in the ribosome?
PRO mimics a tRNA anticodon
same size of tRNA so it can have access
what are the diffs in termination in prokarytoes & eukaryotes?
Same in Eukaryotes & Prokaryotes except: 2 release factors in eukaryotes & 3 in prokaryotes
what enables the 5’ cap to attach to the polyA tail?
eIFs & polyA binding PRO
how is tetracycline effective?
binds to the small subunit
how is streptomycin effective?
binds to the 16S rRNA & inhibits initiation
