25 translation Flashcards
How many nucleotides are required to encode each AA?
at least 3 nucleotide residues of nucleic acid
if only 2 and theres 4 code letters available 4^2 = 16 = insufficient to cover all the 20 AA
group of 3 can yield 4^3 = 64 diff combinations
What is the poly-U experiment?
Objective: This experiment aimed to determine which amino acid corresponds to a specific RNA sequence.
Methodology:
* They used a synthetic RNA molecule composed solely of uracil (poly-U).
* The researchers introduced this RNA into a cell-free system that synthesized proteins.
Key Findings:
* The resulting polypeptide was composed entirely of the amino acid phenylalanine.
* This indicated that the codon UUU (the codon for phenylalanine) was being translated from the poly-U RNA.
Importance: This experiment demonstrated that a single RNA sequence could direct the incorporation of a specific amino acid into a protein, laying the groundwork for understanding the genetic code.
What is the Triplet Binding Assay experiment?
Added A and C
and found that Poly(A) encodes polylysine
and Poly(C) encodes polyproline
it seems like one letter seems to just encode one AA, how about the other ones? there are 20
What did Khorana’s experiment use?
use a variety of polyribonucleotides with 2, 3 or 4 nucleotide repeats
found consistent AA produced when repeating 3 nucleotides
What are the properties of genetic code?
- 3 bases made up a codon
- each codon specify one AA
- degenerate - multiple codons encode the same AA
- nearly universal - same codons for same AA across most organism
- non-overlapping - codons are read sequentially without sharing nucleotides between them
Why is nonoverlapping better than overlapping?
if mutate, the impact is less
What is the adaptor hypothesis?
tries to explain how codons on mRNAs interact with AA
suggests that adaptor molecules carry AA, interact with mRNA codons rather than AA directly interact with mRNA codons
How did they find out that tRNA is the adaptor?
- by accident
- radioactive leu to a pool of RNA with ribosomes then mixed it and incubate and centrifuge
- found tRNA in supernatant and AA in protein
- AA are transferred from tRNAs to growing pp
How did they test the adaptor hypothesis?
- converted the AA attached on tRNA of Cys from Cys to Ala
- the in vitro translation using a poly(UG) mRNA = possible codons from this do not contain alanine codon
- analyze AA in the resulting peptide
- found AA on tRNA is not involved in codon recognition
- alanine was still incorporated into the polypeptide even tho no codon was present for it
Is AA on tRNA involved in codon recognition
no
what does the conformation (3d) shape of tRNA result from?
base pairing (H bonds) within the molecule
What is the sequence on the 3’ end on tRNA?
always CCA: the AA attachment site
What is an anticodon?
the site of base pairing with mRNA. unique for each species of tRNA
is reverse complementary to mRNA
What is aminoacyl-tRNA synthetases?
for charging each tRNA with the correct AA
is specified
link AA to tRNA
What is the structure of ribosome?
large and small ribosomal subunit
then E P A site
What does A P E site bind to?
A site binds tRNA charged with AA
P site binds tRNA carrying the growing ppc
E site is where tRNA sits before being released
What are the 3 phases of translation?
initiation
elongation
termination
What is the start codon?
AUG
What are the stop codons?
UAA, UAG, UGA
In what direction are mRNA read?
5’ to 3’
from which terminus to which are protein synthesized?
from N-terminus to C-terminus
In bacterial mRNA, what procedes the start codon?
ribosome binding site (shine-darlgarno sequence)
what is the ribosome binding site (shine-darlgarno sequence) in bacterial mRNA like?
- complementary to RNA in small subunit of ribosome
- help to assemble ribosome over the start codon
Can bacterial mRNA encode several protein?
yes
H
How can bacterial mRNA encode several protein?
they have multiple ribosome binding site
can generate multiple protein with a single transcript
ONLY bacterial cell
How is initiation in eukaryotes initiated?
ribosome binds to 5’ cap and moves along the mRNA to find the first start codon
in eukaryotic mRNA, where does translation start?
initiates near 5’ cap
How mnay proteins can eukaryotic mRNA encode?
1
What is 5’ cap and poly(A) tail role in initiation of translation?
- ribosome bind to 5’ cap
- then cap-binding proteins bind to the cap
- Poly(A) tail interact with the cap-binding protein
- and enhance the binding of the ribosome to the 5’ end of the mRNA
- initiates
What is the initiation process of translation?
- small subunit of ribosome bind to mRNA
- initator tRNA binds to start codon
- binding of large subunit of ribosome to the initiation complex
- starts at P
what is the elongation process of translation?
- a charged tRNA binds to A site
- formation of peptide bond between AA attached to tRNA in P site and A site
- robosome moves down mRNA in the 5’ to 3’ direction
What is the termination process of translation?
- protein synthesis terminates when ribosome reach the stop codon
- release factors recognize stop codon and bind to ribosome (no tRNA for stop codon)
- pp released from tRNA
what can happen posttranslation?
can be chemically modified
proteins may be targeted to diff organelles or secreted out of the cell
can transcription and translation occur at the same time?
yes for bacterial cells
not seperate processes
