Eukaryotic Translation Flashcards
___% of a mammalian cell’s energy production is used for the process of protein translation
30%
major stages of protein translation
- load amino acids onto tRNAs
- initiation
- elongation
- termination
key design principles of protein translation
- load ribosome onto mRNA at right location = correct start site
- prevent ribosome form starting before fully assembled = placeholder proteins
- need to move along mRNA to continue translating = use proteins like ratchets and physically push mRNA and new peptides through ribosome
- when translation is done, make sure all components get taken apart FULLY to start next round = peptide release, tRNA release, ribosome subunits
- use similar shaped components when possible = tRNAs, elongation & termination factors share similar structures because they all need to fit well in the A-site
Prokaryotic translation
- transcription & translation simultaneous
- mRNAs unstable = few secs to mins
- cap-independent initiation
- 3 initiation factors = IF1, IF2, and IF3
- polycistronic = can code for more than one protein per mRNA
eukaryotic translation
- eukaryotic transcription &trnalsation are discontinuous processes
- mRNAs = quite stable = few hrs to days
- cap-dependent and cap-independent initiation
- 9 initiation factors are involved = eIF, 1, 2, 3, 4A, 4B, 4C, 4D, 5 & 6
- monocistronic (& polyc??)
4 complexes of initiation
- 43S pre-initiation complex (43S PIC) = complex ready to accept mRNA
- eIF4-mRNA complex = prepping mRNA so positioned properly for when it bonds to 43S PIC
- 48S initiation complex = ribosome binding to mRNA and scanning for start codon
- 80S elongation complex = bringing 60S to start translation
step 1 of translation initiation (prepping ribosome)
binding of ______ and _____ causes conformational changes that opens up channel allowing mRNA access
eIF1 (E) and eIFA (A)
- blocks A and E site access by tRNAs
eIF2
- ternary complex
- essential for delivery of initiator Met-tRNA to 40S
- eIF2B is a guanine exchange factor required to make eIF2 competent for reloading with Met-tRNAi^Met
the only tRNA that binds directly to P-site of ribosome
Met-tRNAi^Met
largest initiation factor with 13 subunits
eIF3
- forms many contacts that stabilizes the 43S PIC
> multiple initiation factors and the ribosome subunits
> mRNA and the 5’-m7G cap
> subunits near the mRNA entry and exit tunnel
analogous to a double-sided tape
eIF3
= seals entry and exit + protects ribosomes from starting initiation and physically blocks to stop other factors from coming in
eIF5
- GTPase activating protein (stimulates GTP hydrolysis of eIF2y
- eIF5 activity repressed by eIF1 in 43S PIC & 48S initiation complex
> to prevent premature hydrolysis of GTP
initiation factors in 43S complex
eIF1
- with eIF1A induces confirmation of 40S
- binds near E-site, close enough to P site; AUG codon recognition
eIF1A
- with eIF1 = confirmation of 40S
- binds to A site; 60S subunit assembly, and inhibits premature elongation
eIF2
- delivery Met-tRNA^Met to P-site of 40S
eIF3
- large scaffolding protein complex
eIF5
- stimulates GTPase activity of eIF2
what is the purpose of the 5’ cap on mRNA?
- to regulate nuclear export of mature mRNAs
- to inhibit degradation of mRNA by exonucleases
- to assist in the assembly of an mRNA-ribosome complex during translation initiation
eIF4
eIF4A
- RNA helicase
- unwinds the mRNA hairpin
eIF4E
- cap-binding protein
- recognize cap on mRNA
- differentiates between bacterial and human
eIF4G
- scaffold
- binds to eIF3
- binds to polyA binding protein (PABP)
NOTE: eIF4B enhances helicase activity of eIF4A
