Genetics 6

Question 0

Ionsine

Answer 0

• created by deamination of guanine

- When present in wobble position, tRNA can recognize either U/C in euks or U/C/A in bacteria

Question 1

Codons that code for the same AA tend to contain…

Answer 1

the same nucleotides at the 1st and 2nd positions- vary at 3rd.

Question 2

AA Activation

Answer 2

• activated by aminoacyl tRNA synthetase in 2 steps
  1) Uses ATP to adenylate AA at OH group, giving AA linked to AMP at carboxy
  2) creates aminoacyl-tRNA
• *AA is now linked at carboxy group to tRNA by a high energy ester linkage.

Question 3

Hydrolytic editing

Answer 3

• function of aminoacyl-tRNA synthetase
• wrong AA attached to synthesis site= improper binding to enzyme–> shunted to editing site, AA is hydrolyzed off.
• tRNA synthetase enzymes are specific for each tRNA.

Question 4

One the AA is attached to tRNA, accuracy is entirely dependent on…

Answer 4

The correct complementation of the codon to the anti-codon.

Question 5

Kozak/Shine-Dalgarno sequence

Answer 5

Consensus sequences that tell helicase to “start here.”

Question 6

Elongation Factors

Answer 6

• chaperones

- ensure correct tRNA is binding to codon

Question 7

EF-Tu/EF-1

Answer 7

Binds GTP, helps tRNA into A site.

• transient binding.
• permanent binding only if pairing is correct.

Question 8

EF-G/EF-2

Answer 8

• bound to GTP
• Provides energy for shifting ribosomal subunits by hydrolyzing GTP.
• Temporarily binds in A site, dissociates when small subunit rejoins complex.
• binding of EF-G causes tRNAs in A and P site to lean, creating hybrid sites.

Question 9

Releasing factor

Answer 9

• Binds in the A site when a stop codon is encountered in the mRNA strand.
• Mimics the activity of tRNA
• dissolves elongated peptide off tRNA (water hydrolysis)
• ribosome complex dissociates from mRNA

Question 10

Riboswitch self cleavage

Answer 10

Riboswitch activates self-cleaving ribozyme activity, leads to degeneration of mRNA, turns translation off.

Question 11

Riboswitch initiation interference

Answer 11

Riboswitch changes nature of initiation codon, makes it appear in the wrong context. Turns translation off.