Translation and Protein Processing Flashcards
The mRNA is translated __’ to __’ into protein (_’ to _’)
5’ to 3’
N’ to C’
STart codon
The first AUG in the open reading frame of an mRNA sequence; codes for the start methionine (first Met in the coding sequence)
How to stop codons work?
Stop codon: last codon of the mRNA open reading frame; UAA, UAG, UGA; does not encode an amino acid
Degeneracy of the genetic code
An amino acid can be coded by more than one codon (usually at the third position)
Frameshift mutation
Insertion or deletion of one or two dNTs, shifting/altering the ORF and changing all the amino acids downstream (3’) of the mutation
Silen tmutations
A point mutation that has no effect on the encoded amino acid because of redundancy in the genetic code’s third position (Wobble hypothesis)
Missense mutation
A POINT mutation that changes the amino acid of a single codon; probably changed the first or second position of the codon.
Nonsense mutaiton
Poin tmutation that changes a codon from one that encodes for an amino acid into a stop codon (UAA, UAG, UGA)
Structure of tRNA
Cloverleaf-shaped molecules read by RNA poly 3 that are post-transcriptionally modified to have a CCA sequence at their 3’ end
Activation of tRNAs
Activated at the 3’ end with an amino acid, forming an aminoacyl-tRNA complex. The tRNA anticodon hydrogen bonds w the mRNA codon.
What powers translation initiation factors?
GTP hydrolysis
Translation initiation process
- eIF3 binds to the 40S ribsomal subunit to maintain the 40S and 60S subunits separate
- eIF2 helps bind the initiation tRNAiMet to the 40S to form the preinitiation complex (ribosome+tRNAiMet)
- The mRNA of the eIF4F complex is brought to the 40S subunit
-
eIF4A unwinds the mRNA and eIF4B scans it to find the translation start site
- Initiation complex (ribosome+tRNAiMet+mRNA+eIF4F)
- 60S ribosomal subunit binds, eIF3 is lost
eIF3
eIF3 binds to the 40S ribsomal subunit to keep the 40S and 60S subunits separate
eIF2
eIF2 positions the aminoacyl-tRNAiMet over the 40S subunit at the P site to form the preinitiation complex (ribosome+tRNAiMet)
eIF4A & B
eIF4A unwinds the mRNA and eIF4B scans the mRNA to find the translation start site
A site of the ribosome
A site: where newly activated aminoacyl-tRNA molecules enter the ribosome, as dictated by the mRNA codon
(Blocked by tetracycline)
P site of the ribosome
Where the mRNA start codon and the tRNAiMet anticodon hydrogen bond
Where the growing peptide forms peptide bonds with the aa at the A-site
E-site
Exit site for tRNA molecules that have given up their amino acid.
Peptidyltransferase reaction of elongation
The a-amino group of the AA2 in the A-site attacks the a-carboxyl group of the amino acid (Met) in the P site, forming a peptide bond.
This breaks the bond between the Met and the 3’ end of the tRNAiMet in the P-site.
Now, the A-site holds a dipeptide and the P-site holds the deaacylated tRNAiMet
(Blocked by chloramphenicol)
translocation
The entire ribosome moves along the mRNA by one codon towards the 3’end of the mRNA, thus shifting the dipeptidyl-tRNA from the A site to the P-site and leaving the A site empty
Powered by the GTP hydrolysis
(Blocked by erythromycin)
Tetracycline
blocks binding of aminoacyl-tRNA to the A-site
Streptomycin
Prevents transition from initiation complex to chain elongaiton; also causes miscoding