Genetic Code and Translation Flashcards
What is the order of transcription, translation, and mRNA degradation in prokaryotes
they are simultaneous occurrences
In eukaryotes where do transcription and translation occur
transcription - nucleus
translation - cytoplasm
Why does mRNA last longer in eukaryotes
in prokaryotes all steps occur in the same location simultaneously, in eukaryotes transcription and translation occur in different parts of the cell so mRNA exists for longer in eukaryotes
What researchers led to the “one gene one collinear protein” conclusion
Beadle and Tatum
What bond holds amino acids together
peptide bond (carboxyl of one bonded to amino of the other)
What code does the genetic code follow
triplet code
4^3 = 64 possible codons
How were codons discovered
homopolymers and copolymers were tested and were found to produce polypeptides with different amino acids
How many codons are there
64
How many of the 64 codons are stop codons
3
What does it mean when saying the genetic code is degenerate
some amino acids are specified by more than one codon
What 2 amino acids are specified by only one codon
methionine (start) and tryptophan
Why does degeneracy occur in the genetic code
the binding at the third codon position is flexible
- known as the wobble position
How does wobble occur in translation (think tRNA modification)
since tRNA can be modified at the nucleotide level, nucleotides can be substituted for other nucleotides and create wobble
What is the basics of the wobble hypothesis
nonstandard pairings can occur at the third position of a codon
What is a nickname for the ribosome
RNA machine - plays a role in protein synthesis, including the formation of peptide bonds between amino acids
What are the 4 important macromolecules of translation
- ribosomes
- amino acid activating enzymes
- tRNA molecules
- soluble proteins involved in initiation, elongation and termination
What is the function of aminoacyl tRNA synthetase
charges the tRNA molecule with its specific amino acid
What is the 2 step reaction between the amino acid and tRNA via aminoacyl tRNA synthetase
- amino acid reacts with ATP to our aminoacyl AMP
- amino acid is transferred to tRNA and AMP is released
How to tRNAs work
hold the anticodon for the codon of mRNA
What is another term for translation
protein synthesis
What is required to initiate translation
mRNA, large and small ribosomal subunits, initiation factors, and GTP
What is the initiation complex of translation in prokaryotes
Shine Dalgarno sequence
Where is the complement to the Shine dalgarno sequence held
in the 16S component of the 30S small ribosomal subunit
What is the Shine Dalgarno sequence
UAAGGAGGU
How does the small subunit bind first to prokaryotic mRNA in translation, without the binding of the large subunit
IF-3 binds to the large unit, preventing it from binding, causing only the small subunit to bind (has complementary sequence to Shine Dalgarno)
What positions fMet-tRNA over the start codon
IF-1 and IF-2
What makes up the 30S initiation complex
fMet-tRNA + 30S small subunit + IF2-GTP + IF-1 + IF-3
How does the large subunit then attach to the mRNA in prokaryotic translation initiation
IF-3 dissociates
How are the IF-2 and IF-1 factors dissociated from the initiation complex in prokaryotic translation
GTP is hydrolized into GDP and dissociates the remaining IF factors
What is the final complex at the start of prokaryotic translation called
the 70S complex (think of the overall subunits and complex of prokaryotic ribosomes)
What is the E site
exit site
What is the P site
peptidyl site
What is the A site
aminoacyl site
What is the difference in methionine between prokaryotes and eukaryotes
prokaryotes = fMet
eukaryotes = Met (not formylated)
What is the difference about the initiation complex location in prokaryotes and eukaryotes
prokaryotes = Shine Dalgarno
eukaryotes = initiation complex binds at 5’ cap and scans inwards to find first AUG codon
What is the sequence involved in eukaryotic translation
Kozak sequence
What is the purpose of the Kozak sequence
influence the efficiency of which AUG in the vicinity is used to begin translation
What happens between the poly A tail and the 5’ cap structure in eukaryotic mRNA translation
the mRNA strand curls and proteins attached to the poly A tail interact with the proteins bound to the 5’ cap to create a cap binding protein complex
What is the cap binding protein complex
when binding proteins on the poly A tail and binding proteins on the 5’ cap of eukaryotic mRNA interact during initiation of translation
What is the Kozak sequence
5’ - C[A/G]NCAUG - 3’
Where does fMet - tRNA first attach in translation elongation
the P site (skips A site)
What two things come together to form a complex as the second tRNA molecule comes into translation elongation
Ef-Tu and GTP bind to charged tRNA to form a complex
- enters the A site of the ribosome (the second tRNA)
What happens when the SECOND charged tRNA in elongation binds to the A site in translation
GTP is cleaved to GDP and the Ef-Tu complex is released
Explain the basics of elongation in translation
- first tRNA binds to the P site
- second tRNA binds to Ef-Tu and GTP to form a complex, binds to the A site, and released the complex
- peptide bond forms between the amino acids in the P and A sites
- the ribosome moves down the mRNA strand to synthesize the amino acid chain
*tRNA moves from the A site to P site to E site (with the first tRNA starting at the P site)
Where does tRNA go after being used in translation
released into cytoplasm
What specifically in the large subunit catalyzes the formation of peptide bonds
rRNAs
Which subunit catalyzes the peptide bond formation between amino acids
large subunit
What is needed in order for translocation (movement of tRNA from one site to the next) to occur
the Ef-Tu GTP complex
What does it mean for tRNA to be “charged”
has a bound amino acid
What direction does the ribosome move along mRNA in translation
5’ - 3’
In what direction does growth of the polypeptide occur
N-teminal to C-terminal
Which site on the ribosome contains the growing peptide chain
the P site
Are there notable differences in translation elongation between prokaryotes and eukaryotes
no - they are very similar
When does termination occur in translation
when a stop codon is encountered at the A site of the ribosome
Why does translation stop when a stop codon is encountered at the A site
because there are no corresponding tRNAs that match stop codons
What happens when a stop codon is encountered instead of tRNA binding
a release factor binds (RF)
What does RF-1 recognize
UAG and UAA
What does RF-2 recognize
UAA and UGA
What does the binding of RF-1 and RF-2 do to the translation process
alters the activity of peptidyl transferase and the amino acid chain is released, termination translation
What factors assist in dismantling the ribosomal complex in translation post termination
RF-3 and GTP
What is the difference between prokaryotic and eukaryotic termination of translation
they are very similar
- release factors are symbolized as eRF-1 and eRF-2 in eukaryotes
What enzyme attaches amino acids to tRNAs in tRNA charging of translation
aminoacyl-tRNA synthetases
What is the energy source used to bind amino acids to tRNAs
ATP
What is the function of elongation factor Tu
binds GTP and charged tRNA - brings charged tRNA to A site on ribosome
What is the function of elongation factor Ts
regenerates active elongation factor Tu
What is the function of elongation factor G
stimulates translocation of ribosome to next codon
What is the function of GTP
provides energy
What is the function of the 23S rRNA in the large ribosomal subunit
form peptide bonds between amino acids in the P and A sites
What step of translation does chloromycetin inhibit
formation of peptide bonds
What step of translation does erythromycin inhibit
translocation of mRNA along ribosome
What step of translation does neomycin inhibit
interactions between tRNA and mRNA
What step of translation does streptomycin inhibit
initiation of translation
What step of translation does tetracycline inhibit
binding of tRNA to ribosome
What step of translation does paromomycin inhibit
validation of mRNA-tRNA match
What are some neurological diseases associated with translation
amyotrophic lateral sclerosis
frontotemproal dementia
spinal musclar atrophy
alzheimers
parkinsons
huntingtons
autism
down syndrome
