Protein Translation Flashcards
What is a nuclear pore receptor?
- finds nuclear pore binding site and uses ATP to get mRNA out
- needed for macromolecules, including finished mRNAs
What is nuclear pore complex?
- Aqueous channel from nucleus to cytoplasm
- Diffusion for small molecules only (<50K daltons)
Does rRNA need a protein?
no
What forms around the gene cluster of 18S, 5.8S, & 28S?
Nucleolus forms around this gene cluster
Where does the rRNA (5S) get imported into?
the nucleolus
Where is telomerase RNA found?
nucleolus
What creates the large subunit of a ribosome?
5.8S, 28S, & 5S rRNAs
What creates the small subunit of a ribosome?
18S rRNA
What has many copies of the same DNA sequence for rRNA?
rDNA
Why is redundancy expected?
because there are 64 combinations of 3 NT possible, but only 20 amino acids
How many anticodons/tRNAs do we have?
48
What are common features of many cancers?
Frame shift mutation & truncated proteins
What has a template independent addition of CCA?
tRNA
What is the structure of tRNA?
cloverleaf
What is important to note about tRNA?
20 amino acetyl transferase enzymes that only charge each tRNA with one amino acid, the amino acid is specific to the different tertiary stuctures
Where is the wobble position?
at 5’ tRNA position (3’ mRNA position)
What is important for a wobble base?
inosine
What helps with wobble & provide binding sites for aminoacyl-tRNA synthetases?
tRNA base modifications
What allows for wobble?
modification on the tRNA molecule
What is specific for a particular amino acid?
tRNA synthetase
What happens if an incorrect amino acid is added?
it will end up in the editing site (of the tRNA synthetase) and it will get degraded/hydrolyzed
During peptide bond formation, where is the new peptidyl-tRNA molecule atatched to?
C terminus of growing polypeptide chain
What are the steps of peptide growth in the ribosome?
- P site holds the proceeding tRNA w/ AA (3), the A site holds the new tRNA with the next AA (4)
- The amino group of AA 4 attacks the carboxy grp of AA 3 to create a new peptide bond
- tRNA that once held AA 3 moves to the E site, the P site holds the newly attached AA 4 tRNA (the tRNA and AA still attached until next attacks)
- tRNA that once held AA 3 leaves the ribosome and the process continues growing the poly peptide from N-terminus to the C-terminus, linking each AA with a peptide bond
What is peptide bond formation catalyzed by?
rRNA
Are ribosomes a ribozyme?
yes because they have catalytic energy and bring 10^7 fold increase in reaction rate
How does tetracycline (antibiotic) inhibit protein synthesis?
Binds to bacterial 30s or 50s ribosomal subunit-> this prevents the attachment of aminoacyl-tRNAs to the acceptor site of the ribosome
What is the mechanism of tetracycline resistance that is related to ribosome function?
Tet (M,O,Q,S) are bacterial resistance genes that make a cytoplasmic proteins to interact with ribosomes-> this makes it insensitive to tetracycline
What can help stabilize the codon-anticodon interaction?
rRNA
What are the important initiation factors of ribosome assembly?
- One that binds to the poly A tail binding proteins
- Another that binds the CBC (eIF4E)
rRNA can help to stabilize what?
stabilize the codon-anticodon interaction
How do Met & IF travel along the mRNA?
using ATP
What is GTP used for in GTP assembly?
for bringing the amino acid to the ribosome
If there is no GTP, can translation occur?
no
What preferentially dissociates?
incorrectly base-paired tRNAs
What are the steps for ribosome assembly & initiation?
- An initiation factor (IF) w/ bound GTP is attached to a initiator tRNA (with Met), w/ the small ribosomal subunit it moves along mRNA with ATP until the start codon is reached
- the initiation factor with GTP can be released and the large subunit of the ribosome binds to the small
- Elongation factors continue to bring in the proper tRNAs, with the help of GTP
- Once one of the 3 stop codons (UAG, UAA, UGA) are reached, a releasing factor helps bring translation to an end
What are the roles of rRNA i the ribosome?
- Forms overall structure
- Forms the A, P, and E sites
- Stabilizes codon-anticodon base pairing
- Catalyzes peptide bond formations
What blocks translation partway through the polypeptide formation to create N terminus fragments due to the C terminus not being made as yet?
puromycin
What are the antibiotics that interfere with translation?
- puromycin ->causes premature re;ease of nascent polypeptides chains by its addition to growing end
- tetracycline -> blocks binding of aminoacyl-tRNA to A site fo ribosome
- macrolides
What is the purpose of caperone proteins?
- use ATP/heat from folding too early
- heat shock proteins involved
What is an example of a chaperone protein?
HSP70 that coats polypeptide when it needs to prevent initial folding
What are the 3 phases of protein folding?
- correctly folded without help
- correctly folded with help for molecular chaperone
- incompletely folded & digested by the proteasome
Does rRNA have repeats?
yes
