In the original publication of the 1QF6 structure (Sankaranarayanan et al., 1999), the authors were able to clarify the secondary and tertiary structure of the bacterial threonyl-tRNA synthetase, and to show that it folds into multiple domains (i.e. independently-folding regions).

The image below from the article shows the 'domain structure' of the enzyme, while also emphasizing its secondary structure (with cylinders representing alpha-helices and thin ribbons representing beta-strands):

(You may notice that the image resolution is somewhat low. This sometimes happens with older publications such as this one, which were not originally released in digital format and were scanned later.)

To create successful conditions for generating the 3D 1QF6 structure, the researchers note that they provided the enzyme with the appropriate tRNA as well as ATP, and that the final crystal structure contained AMP (but not ATP).

Thinking back to the information provided about this enzyme, which one of the following best explains why the nucleotide in the 1QF6 structure has two fewer phosphates than the nucleotide that was originally provided to the enzyme?

Question

In the original publication of the 1QF6 structure (Sankaranarayanan et al., 1999), the authors were able to clarify the secondary and tertiary structure of the bacterial threonyl-tRNA synthetase, and to show that it folds into multiple domains (i.e. independently-folding regions).

The image below from the article shows the 'domain structure' of the enzyme, while also emphasizing its secondary structure (with cylinders representing alpha-helices and thin ribbons representing beta-strands):

(You may notice that the image resolution is somewhat low. This sometimes happens with older publications such as this one, which were not originally released in digital format and were scanned later.)

To create successful conditions for generating the 3D 1QF6 structure, the researchers note that they provided the enzyme with the appropriate tRNA as well as ATP, and that the final crystal structure contained AMP (but not ATP).

Thinking back to the information provided about this enzyme, which one of the following best explains why the nucleotide in the 1QF6 structure has two fewer phosphates than the nucleotide that was originally provided to the enzyme?

BlackTom AI · Accepted Answer

To approach this question, I will assess each option in turn and connect the reasoning to how ATP is used in aminoacyl-tRNA synthetase reactions.
Option 1: 'This enzyme couples a highly exergonic reaction (ATP hydrolysis) to a reaction that is otherwise not especially favorable (esterifying a tRNA on to an amino acid)'. This statement reflects the core biochemical logic: the ATP hydrolysis provides the energy to drive the formation of the aminoacyl-tRNA bond, which on its own would be unfavorably spontaneous because esterifying the tRNA with an amino acid is not highly favorable without activation. The enzyme uses ATP to activate the amino acid and create an aminoacyl-adenylate intermediate, lowering the activation barrier for tRNA charging. This aligns with the known mechanism of aminoacyl-tRNA synthetases.
Option 2: 'Pairing a codon and an anticodon are sufficiently favorable that a molecule of ATP can be consumed in the process'. This is incorrect because codon-anticodon pairing occurs during translation and does not consume ATP in aminoacylation; ATP consumption occurs in activating the amino acid prior to charging the tRNA, not during codon-anticodon recognition on the ribosome. The assertion incorrectly attributes ATP use to codon-anticodon pairing rather than amino acid activation.
Option 3: 'Phosphates are needed at the 5' end of the tRNA, and ATP serves as the donor'. This is misleading: while tRNA has a phosphate backbone, the phosphate groups of ATP are not being donated to the tRNA in the charging step. Instead, the amino acid is activated to form aminoacyl-adenylate, and the aminoacyl moiety is transferred to the tRNA's 3'-OH end. The statement overstates the role of 5' phosphates and misstates the chemistry of the charging reaction.
Option 4: 'Because this enzyme creates peptide bonds, a molecule of ATP must be expended in the process'. This confuses general peptide bond formation in the ribosome with the aminoacylation step. The enzyme amin
oacyl-tRNA synthetase forms the aminoacyl-tRNA intermediate, not a peptide bond; peptide bond formation occurs later during translation on the ribosome. While ATP is used earlier to activate the amino acid, describing the step as creating peptide bonds is incorrect for this context.
Option 5: 'Because ATP hydrolysis is so thermodynamically favorable, it tends to rapidly hydrolyze in water'. This statement describes a general property of ATP hydrolysis but does not explain the role of ATP in the specific enzymatic reaction here. It does not address why the enzyme uses ATP to drive the esterification process; it instead makes an incomplete, and somewhat misleading, thermodynamic claim about ATP stability in aqueous solution without tying it to substrate activation.

类似问题

An enzyme known as ___________ attaches an amino acid to the of a tRNA, thereby producing …………………

Assume a mutation in the CCA arm of tRNAThr occurs that reduces the flexibility of this region of the molecule but still allows the 3′ end of the tRNA to enter the aminoacyl-tRNA synthetase activation site. Which of the following is the most likely outcome?

Two distinct classes of aminoacyl-tRNA synthetases exist. What might explain this? Please choose the correct answer from the following choices,

Question at position 18 Establishing a wholly-owned subsidiary provides the quickest access to a new market.TrueFalse

Question at position 17 Leading companies should recognize that a firm based in a country with a national competitive advantage is not guaranteed ............................ as it implements its chosen international business-level strategy.dominanceplansuccessNone of the Above

Question at position 16 Costs associated with the issues firms face when entering foreign markets, including unfamiliar operating environments, economic, administrative, and cultural differences, are known as regionalization costs.TrueFalse

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单