Translation Flashcards
export of mRNA from nucleus to cytoplasm
requires:
1) nuclear export receptor
2) CBC (cap-binding complex)
3) energy
nuclear export receptor
a complex of proteins that attaches to mature mRNA and aids in transporting mRNA out of nucleus into cytoplasm for translation
where in the cell does translation occur
in the cytoplasm
eIF4G and eIF4E
displace the CBC (cap-binding complex) from mRNA transcript in the cytosol; bind to the proteins bound to poly-A tail
wobble base
there is some redundancy at the third position of a codon, so changes in the 3rd position can sometimes still encode for the same amino acid
what are the 3 stop codons
UAA, UGA, UAG
(U Are Annoying, U Go Away, U Are Gone)
*indicate the end of translation
what is the start codon
AUG (codes for methionine)
silent (synonymous) mutations
change in a codon sequence that does NOT change what amino acid is coded for
non-sense mutation
a point mutation that changes a codon that should code an amino acid to a STOP codon (UAA, UGA, UAG)
mis-sense (conservative) change
mutation that causes an amino acid to change to a different but similar amino acid (may or may not change the protein function)
mis-sense (non-conservative) change
mutation that causes an amino acid to change to a different but NOT similar amino acid
-ex. hydrophobic aa to a charged aa
reading frame
critical for proper translation; determines where you would start in the sequence; changes in the reading frame can completely alter the amino acid sequence
frameshift mutation
insertion or deletion, which shifts the reading frame and changes the amino acid sequence
tRNA key components
1) anticodon (anneals to mRNA with reverse complement)
2) CCA at 3’ end (where the amino acid is bound)
activation of tRNA
aminoacyl-tRNA synthetases add the amino acid to the tRNA; specific to the AMINO ACID (not to the codon)
subunits of prokaryote ribosome
50S and 30S
subunits of eukaryote ribosome
60S and 40S
small subunit of ribosome
matches the mRNA with the tRNA anti-codons
*binds mRNA first
large subunit of ribosome
catalyzes the peptide bond formation between amino acids on the growing chain
what are ribosomes made of
ribonucleoproteins (RNA and proteins)
***ribosomes assembled in the nucleolus
locations of ribosomes in the cell
1) free ribosomes (in cytoplasm)
2) ER-bound ribosomes
large subunit - 3 sites
A site, P site, E site
A (aminoacyl) site of large subunit
where the new tRNA, bound to an amino acid, comes into the ribosome
P (peptidyl) site of large subunit
where the peptide bond is formed; growing peptide chain is here
E (exit site) of large subunit
where the old tRNA (without its amino acid) leaves the ribosome
peptidyl transferase
the enzyme that catalyzes peptide bond formation between amino acids on growing polypeptide chain
translation initiation
1) small subunit associates with initiator tRNA and eIF2 and binds to 5’ end of mRNA
2) small subunit moves along the mRNA until it reaches a start codon
3) large subunit binds and initiator tRNA enters the P-site
4) a new tRNA enters the A site; a peptide bond forms between Met and the new aa, causing large subunit to shift, such that:
-initiator tRNA moves to E site (and leaves)
-tRNA from A site moves to P site, holding the polypeptide chain
-a new tRNA can enter the A site
translation termination
1) release factor binds to the A site once a stop codon is encountered
2) water is transferred to the peptide chain, releasing it from the ribosome
3) ribosome complex dissociates
inhibitors of transcription or translation
important for drug development or treatment of disease (some could affect prokaryotes, eukaryotes, both, etc)
