Translation Flashcards
How much energy is used by the cell for translation?
~50% of its energy reserves
What are the key stages of protein synthesis?
- amino acid activation
- initiation
- elongation
- termination
- recycling
- co/post-translational processing
What is the adaptor hypothesis?
base pairing of codon to anticodon in antiparallel fashion. Something needs to link the anticodon to the amino acid
Contrast degeneracy with lack of ambiguity
Degeneracy means that there are multiple codons for the same amino acid. Lack of ambiguity means that no one codon can code for more than one amino acid.
What phenomenon describes the fact that some cells have less tRNAs than codons
wobble hypothesis
Describe the wobble hypothesis.
The first base of the anticodon is sometimes converted to hypoxanthine (H) by deamination, and can pair with A, U, or C, meaning that the anticodon can interact with multiple codons and allow the cell to not need as many tRNAs as codons.
What does it mean for the genetic code to be quasi-universal?
It means almost all codons encode for the same amino acids, except for mitochondria usage of codons among different organisms.
Where do nonsense mutations normally occur?
In the last exon of the mRNA.
Which part of tRNA is phosphorylated?
The 5’ terminus.
What are the primary active sites of tRNA?
The anticodon loop and the CCA 5’ terminus where the amino acid is attached.
Which player in translation does the actual translation?
aminoacyl-tRNA synthetase
Describe the activation of amino acids/charging of tRNA.
- carboxyl end of amino acid is activated by the addition of AMP, resulting in loss of pyrophosphate
- pyrophosphate is hydrolyzed, driving forward the reaction
- tRNA is charged by forming an ester linkage to the carbonyl oxygen, breaking the AMP ester bond.
how many aminoacyl-tRNA synthetases are there?
20! each one recognizes its amino acid based on D-loop and variable region and anticodon
How is the fidelity of tRNA charging maintained?
aminoacyl-tRNA synthetase has proofreading and editing function and can destroy an incorrect pair. This is important because the ribosome reads the anticodon, not the amino acid.
How are ribosome components measured and named?
Based on there sedimentation in a sucrose gradient. Dependent on size and shape.
What are the components of prokaryotic ribosomes?
- 50S large subunit (more proteins than small)
- 30S small subunit (less proteins than large) containing 16S RNA
- 70S assembled ribosome
What are the components of eukaryotic ribosomes?
- 60S large subunit
- 40S small subunit
- 80S assembled ribosome
Describe the main function of the small ribosome subunit.
It decodes the anticodon
It controls the fidelity of pairing
Describe the main function of the large ribosome subunit.
peptidyl transferase site
tunnel through which nascent protein is funnelled
Which are the large translation events which dictate initiation?
mRNA binds small subunit and to initiating charged tRNA. The larger subunit then joins the small subunit and the A, P, E sites are formed.
Describe the steps of translation initiation.
- GTPase eIF2 binds initiating tRNA which associates with 40S subunit
- eIF4 factors associated with mRNA direct it cap-first to the 40S subunit
- 40S scans mRNA until AUG is found and interacts with initiating tRNA anticodon
- 60S associates, eIF2 GTP is hydrolyzed (no more charge), and eIF2 and anti-association factor eIF3 bound to 40S is released
Which site of the ribosome is initiating tRNA in upon initiatioon?
The P site.
Describe the circularization of mRNA in eukaryotic translation and the role of eIF4 proteins.
- eIF4E binds 5’ cap
- PABP’s bind polyA tail
- eIF4G bind eIF4E to PABP
How does the ribosome find the initiation codon?
It uses energy and catalysis from eIF4A to scan along the mRNA.
