Genetic Code

Question 1

tRNA

Answer 1

adaptor molecule that reads the mRNA in codons of 3 bases and translates it into an amino acid
2D cloverleaf shape, 3D L-shape
at on of the loops (2/4 from 5’ end) has codon which base pairs with mRNA
at 3’ end, has corresponding amino acid
charged/activated by tRNA aminoacyltransferases

Question 2

Aminoacyl-tRNA-Synthetase

Answer 2

enzyme that links each amino acid to the correct tRNA
anticodon is important in the process (the enzyme has a pocket for it)
other sites also help with recognition
uses hydrolysis of ATP->AMP to charge the amino acid, then transfers from the synthetase to tRNA specific to that AA
because of high energy bond between AA & tRNA, no extra energy needed later

Question 3

Degeneracy of Genetic Code/Wobble Base Pairing

Answer 3

some amino acids have multiple codons that code for them, usually changes in the third nucleotide (wobble base pairing at 3’ of codon, 5’ of anticodon because least affected by pi stacking); one tRNA can recognize more than one codon

Question 4

Open Reading Frames

Answer 4

protein coding region that is framed by a start and stop codon within a reading frame
six potential reading frames, could be caused by frameshift mutations (insertions/deletions)

Question 5

Nirenberg Experiment

Answer 5

began to crack the genetic code
synthesized synthetic RNA templates that code for protein polymers in cell extracts (treated with RNase and DNase)
they tried poly-U code, and determined by incubating the RNA with the cell extracts and then radioactively labeling one protein at a time
expanded their findings for the other nucleotides and double codes
limitation that not all triplet RNA sequence induced tight binding of tRNA to the ribosome
Khorana developed chemical method make short sequences of 2, 3, or 4 repeats, able to determine the other amino acids

Question 6

Genetic Code

Answer 6

nucleotides on the mRNA A,U,C,G are read in triplets, which correspond to a specific amino acid, which are attached to each other sequentially

Question 7

Reading Frame

Answer 7

grouping pattern in which we read the triplet codons
the three nucleotides that are read and correspond to an anticodon on the tRNA
nonoverlapping