Translation

Question 1

nonsense mutation

Answer 1

stop codon causes truncation of protein, length of mRNA stays the same

Question 2

only step of translation that requires ATP

Answer 2

charging tRNA with its amino acid!

aminoacyl-tRNA synthetase uses ATP

Question 3

aminoacyl-tRNA synthetase

Answer 3

enzyme that adds amino acids to tRNA using ATP.

Only step of translation with proofreading, and only step of translation that requires ATP.

Question 4

only step of translation that requires GTP

Answer 4

moving the charged AA-tRNA into A site

Question 5

1st codon in proks

Answer 5

formylated, tRNA-F-met

Question 6

1st codon in euks

Answer 6

tRNA-i-met (i for initiator)

Question 7

initiation in proks

Answer 7

16S rRNA binds Shine-Dalgarno sequence putting tRNA-F-met in P site

Question 8

initiation in euks

Answer 8

initiator proteins scan mRNA for Kozak sequence, 40/60S subunits bind and tRNA-i-met is put in P position

Question 9

mutations in Kozak sequence

Answer 9

translational inefficiency because the ribosomal complex can’t find the initiator proteins as well, ex: beta thalassemia minor

Question 10

global regulation of protein synthesis

Answer 10

(eiFs) eukaryotic initiation factors that increase protein synthesis, ex: stimulated by ER stress or insulin

Question 11

eiF2

Answer 11

represses protein synthesis when phosphorylated on alpha subunit, which blocks GDP-GTP conversion. Phosphorylation occurs when cell is under stress (ER stress, hypoxia, AA starvation).
Otherwise, it is activated when bound to GTP, and can help initiate translation of proteins.

**high levels of eiF2-P are assc with Alzheimers, Parkinson’s, Huntington’s indicating an increase in unfolded/misfolded proteins in the cells (ER stress)

Question 12

eiF4E

Answer 12

normally inhibited by hypophosphorylated 4E-BP

insulin activates kinases that phosphorylate the 4E-BP, activating eiF4E and causing it to dissociate, increasing protein synthesis

Question 13

mRNA binding proteins

Answer 13

regulate translation by dictating the 3D structure of the RNA thus blocking translation when bound to the mRNA.

Ex: iron response elements (IREs) in untranslated regions of mRNA and IRPs

Question 14

iron response elements

Answer 14

IRPs bind iron when present, but otherwise bind the IREs, blocking translation at the 5’ end and stabilizing mRNA on the 3’ end

Question 15

how do viruses hijack our machinery?

Answer 15

viruses use proteases to degrade our eiFs involved in cap-dependent translation, thus freeing up ribosomes for their own cap-independent use

they also use internal ribosome entry sites (IRES) which allow them to use ribosome without a cap on mRNA

Question 16

IRES

Answer 16

internal ribosome entry sites allow viral mRNA to use our ribosomes without caps