This is a comprehensive and detailed final exam summary for Bio 140.
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Can read more than one protein from a single RNA
-Each protein initiates at a AUG after a Shine-Dalgarno Sequence
-The flu virus is eukaryotic it initiates translation at the first AUG after the 5’ cap
Answer: D
3 stop codons: start with U
Start translating at first AUG after 5’ cap
The cell does not have a codon table. How is mRNA decoded in a cell?
● Transfers RNAs (tRNAs) interpret to nucleotide code
● Cells have a trna that recognizes each possible codon that codes for an amino acid
● The area of the tRNA runs the opposite direction of the mRNA 3’ to 5’
● A three letter section of its called an anti-codon recognizes each mRNA codon
● The right amino acids is attached to the 3’ end of the tRNA to match the right AA to the
codon
,The methionine tRNA--There are two types
1. The initiator tRNA--starts the process recognizes the first AUG and holds methionine
2. Elongation tRNAs--Recognize all later codons including internal methionine and hold the
AA that is designated by the anticodon’s sequence
The second step in translation is translation initiation
This step means bringing together all of the pieces you need to start translation
Meet the ribosome
Ribosomes contain RNA known as rRNA or ribosomal RNA and protein
It has two subunits called the large and small ribosomal subunits
When both subunits come together they make 3 sites for holding tRNA
1. The A site
(aminoacyl site)
2. The P site
(peptidyl-site--where the
initiator tRNA fits)
3. The E site (exit
site)
,Translation initiation→ involves lining everything up in the ribosome so the initiator tRNA goes
into the P site orienting so that it matches the start AUG in the mRNA
-Cells have a set of proteins called initiation proteins that helps guide all of this machinery
together
Third phase: translation elongation--3 steps
1. Decoding→ A charged elongation tRNA whose anticodon matches the next codon is
brought into the A site
2. Peptide bond formation→ the ribosome catalyzes a peptide bond to form between the
amino acid from the first tRNA and the one on the second tRNA
, 3. Translocation→ the mRNA is pulled through the ribosome with the tRNA attached to the
tRNA in the P site moves to the E site and is rejected. While the tRNA in the A site
moves to the P site
Elongation steps repeat over and over again
Phase 4: translation termination--a stop codon is reached
● Protein called release factor binds the codon instead of a tRNA
● Binding of the release factor catalyzes the addition of water to the peptide chain
releasing it causing everything else to break apart
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