Study BMB 400 Chap 14 Translation Flash Cards

 
Pile Management Card
BMB 400 Chap 14 Translation

loading
Can mRNA tell if the aa is wrong?
-NO
-The Ribosome Is Unable to Discriminate between Correctly and Incorrectly Charged tRNAs
Are tRNAs accurate?
YES, ma'am.
-tRNA synthetases proofread, too
-<1 in 1,000 have errors
-Some enzymes “check” the amino acid at the aminoacyl-adenylate intermediate. If incorrect, hydrolyzed

-other enzymes “check” the aminoacyl-tRNA product, and cleave off incorrect amino acids
-Use editing pocket in enzyme
how do tRNA synthetases know they have the right aa?

b/c CCA on all?
-anticodon!
-acceptor stem!
-both!

-if >1 codon for aa, synthetase must rely on determinants outside of the anticodon
Some bacteria have __ tRNA sythetases
<20
-why?
-b/c they have an enzyme which modifies a charged tRNA to another aa form
-ex:

Glu-tRNAGln -> (amination) -> Gln-tRNAGln
-recognizes Gln, but attached Gln
Most organisms have __ different tRNA synthetases
(only one tRNA synthetase attaches each amino acid)
isoaccepting tRNAs
-aminoacyl tRNA synthetase recognizes and charges more than one tRNA (b/c >1 codon for most aas)
What's the driving force of tRNA synthetase?
-pyrophophotase cleaves pyrophosphate (PP) to prevent reverse reaction
there are ___ classes of tRNA Synthetases
2
adenylyation
-adding AMP
2 steps of Aminoacyl tRNA Synthetases
1. aa is activated by adenylylation (adding AMP)
2. Activated aa is transferred to the 2’ or 3’ OH of the adenosine of tRNA (release of AMP)
There are two classes of tRNA synthetases
Driving force: pyrophophotase cleaves pyrophosphate to prevent reverse reaction.
Aminoacyl tRNA Synthetases work in ___ steps
2
how to charge tRNA?
Aminoacyl tRNA Synthetases
energy situation of the ribosome
-Ribosomes use a lot of GTP hydrolysis, but only to increase translational accuracy
-no energy needed for making/breaking bonds
acyl linkage
-how the aa is linked to tRNA
-between the aa carboxyl group and the 2’- or 3’-OH group of A
-5’-CCA-3’
-high-energy bond
-thermodynamic energy to drive protein synthesis,
therefore, ribosome doesn’t need extra energy
(Ribosome and its translation factors use a lot of GTP hydrolysis, but all of them to increase translational accuracy)
charged tRNA
-tRNA molecule with aa attached
FAT L
SigmaU loop + aa acceptor stem

D stem + anticodon arm

-aa acceptor stem is maximally separated from the anticodon loop
Why the D loop?
-Reduction of a double bond in uridine gives dihydrouridine, “D”
4 loops of tRNA
-variable loop
-anticodon loop
-D loop
-SigmaU loop (TsigmaC loop)
post-transcriptional bases in tRNA
-not essential for tRNA function
-but, reduce growth for cells lacking these bases
-show improved tRNA function
do tRNA have the usual base?
-and more!
-created post-transcriptionally
-not essential for tRNA function…
…but cells lacking these modified bases show reduced rates of growth
…improved tRNA function
How does 5’-CCA-3’ get on euk tRNA?
-CCA polymerase
sequence to attach cognate aa in tRNA
5’-CCA-3’
-universally conserved
-
how many nucleotides in tRNA?
75 to 95 nucleotides
Place this card into pile: