Protein Synthesis and Genetic Code Flashcards
Makes up the genetic code
codon
Translation of the genetic code would be carried out through meditation of adapter molecules such as
tRNA
(Features of the Genetic Code)
multiple codons decode the same amino acid - due to wobble
Degenerate/Degeneracy
AA that do not have a degenerate feature
- methionine
- tryptophan
(Features of the Genetic Code)
specific codon will only code for a single AA
Unambiguous
(Features of the Genetic Code)
the genetic code during translation does not involve any overlap of codons
Non-overlapping
(Features of the Genetic Code)
Once the reading is commenced at a specific codon, there is no punctuation between codons
Message is read in a continuing sequence of nucleotide triplets until termination codon is reached
Not punctuated
(Features of the Genetic Code)
- tRNA in the mitochondria reads 4 codons different from the cytoplasm
- 22 tRNA for genetic code of mitochondria
- 31 tRNA for cytoplasmic translation
Universal
3 of the 64 codons DO NOT code for specific amino acids termed as () - utilized as translation termination signals
non-sense codons
RNA directed synthesis of polypeptides
Translation
a two step reaction catalyzed by the aminoacyl-tRNA synthetases
Charging (recognition & attachment)
- of amino acid and tRNA
Amino acid activation forms (1) using the enzyme (2)
The enzyme attaches the AA to the alpha-phosphate of ATP with the concomitant release of pyrophosphate
(1) AMP-amino acid enzyme complex
(2) aminoacyl-tRNA synthetase
What happens after amino acid is activated?
attachment of the activate AA to tRNA
What enzyme catalyzes the transfer of the amino acid to either the 2’- or 3’-OH of the ribose portion of the 3’-terminal adenosine residue of the tRNA generating the activated aminoacyl-tRNA
aminoacyl-tRNA synthetase
link between the amino acid and tRNA
ester linkage
(True/False)
Each tRNA is specifically charged (made) to adapt (carry) any amino acid
False
Each tRNA is specifically charged (made) to adapt (carry) a SPECIFIC amino acid
REGIONS OF tRNA RELEVANT IN TRANSLATION PROCESS
(1) D arm - site for proper recognition of a tRNA by its proper aminoacyl-tRNA synthetase
(2) T^C arm - binds the aminoacyl-tRNA to the ribosome
(3) Acceptor arm - at 3’-OH adenosyl terminal, the AA is attached
(4) anticodon region - anticodon for mRNA
when the base pairing between the last nucleotide and its corresponding nucleotide of the anticodon is NOT strictly by the Watson-Circk rule (at the 3rd nucleotide of the codon)
wobble
(True/False)
There is no proofreading during translation only decoding
True
Active translation of mRNA to protein occurs on
polyribosomes/polysomes
Protein synthesis begins at (1) where chain elongation occurs by sequential addition of amino acids to the (2) of the ribosome bound polypeptide
(1) N-terminus
(2) C-terminus
Initiator tRNA
met-tRNA for methionine AA as the start
Regulation of initiation step of protein synthesis is by
elF-2alpha
Elongation involves several specific non-ribososmal proteins
elongation factors (EFs)
(True/False)
During protein synthesis (translation) the ribosome moves down the mRNA to the next codon
True
Sites in the Ribosome
(1) A site - aminoacyl or acceptor site
(2) P site - peptidyl or polypeptide site
(3) E site - deacylated tRNA exit site
Elongation Sequence:
1 - translocation of the ribosome on the mRNA
2 - Binding of aminoacyl-tRNA to the A site
3 - Expulsion of the deacylated tRNA from the P and E sites
4 - Peptide bond formation
2, 4, 1, 3
(True/False)
phosphorylation of the eEF-2 enzyme in the elongation process, by the eEF2 kinase (eEF2K) will inhibit its function
True
Protein factors for termination of protein synthesis
releasing factors
The termination codons are
UAG, UAA, UGA
proteins that hydrolyze the peptidyl-tRNA bond when a stop codon occupies the A site
releasing factors (RF)
Releasing Factors:
(1) recognizes that a stop codon resides in the A site
(2) recognized the termination codons UAA and UGA
(3) promotes hydrolysis of the bond between the peptide and the tRNA occupying the psite
(1) RF1
(2) RF2
(3) RF3 with GTP and the peptidyl transferase
Initiation factor that is a prime target for regulation
eIF-4E
