Chapter 11 Questions Flashcards
(12 cards)
Why is the genetic code redundant?
Because it is degenerate, amino acids may be specified by more than one codon.
What are the two amino acids coded for by one only codon?
Tryptophan and methionine.
Explain the concept of the wobble position.
When the codon of the mRNA and the anticodon of the tRNA join, the first 5’ base of codon pairs with the 3’ base of the anticodon, then the middle codon and anticodon pair, and finally, the third base pairs weakly and there may be flexibility in their pairing. It is nonstandard base pairing.
What are the 3 terminator codons?
UAA, UAG and UGA.
In which direction is protein synthesis?
A ribosome attaches near the 5’ end of an mRNA strand and moves towards the 3’ end. Synthesis begins at the amino end of the protein and elongates towards the carboxyl end.
Amino acids bind to which part of the tRNA?
The 3’ end.
What are the steps in the initiation of translation?
First, the mRNA binds to the small subunit of the ribosome. Second, initiator tRNA binds to the mRNA through codon to anticodon base pairing. Third, the large ribosome joins the initiation complex.
What is different about translation initiation in eukaryotes?
The identification if the start codon is facilitated by the presence of the consensus sequence (Kozak sequence) that surrounds the start codon, and it require at least 12 initiation factors. The poly a tail also plays a role.
Describe the elongation cylce after the initiator tRNA
A charged tRNA and its amino acid occupy the A site, a peptide bond forms between the amino acids and A and P site, and the ribosome translocates to the next codon. Throughout the cycle, the polypeptide chain remains attached to the tRNA in the P site.
Why does no tRNA enter the A site in termination
Because there are no tRNAs with anticodons complementary to the termination codons.
What causes premature termination?
If the wrong tRNA was added, the alignment between the mRNA and tRNA will be incorrect.
In a polyribosome, the polypeptides associated with which ribosome are the longest?
Those at the 3’ end of the mRNA, because they move 5’ to 3’.
