Question

imagine a drug binds at the a site, preventing the incoming trna from binding to codons in mrna. what would be the most likely outcome?
translation would speed up by making anticodon - codon binding faster and more effective.
translation would stop. if enough drug molecules are present to bind to most ribosomes in the cell, the cell might die.
translation would not be affected, because the a site is not absolutely critical to the function of the ribosome.
suppose a different drug binds to the channel above the a, p, and e sites through which the newly synthesized protein emerges from the ribosome. the drug would clog this channel. what would be the most likely outcome?
translation would speed up because the growing protein would exit the ribosome more efficiently.
there would be no effect on translation because there are multiple ways for a newly formed protein to exit the ribosome.
the growing protein would get jammed up in the channel and prevent translation from continuing. if enough drug molecules were present to affect most of the ribosomes in the cell, the cell could die.

Explanation:

• First Question:
• The A - site is crucial for tRNA binding during translation. If tRNA cannot bind (due to the drug), the addition of amino acids to the growing polypeptide chain stops. Without continued amino - acid addition, translation cannot proceed. If most ribosomes are affected (by enough drug molecules), the cell, which relies on protein synthesis (translation) for survival, may die.
• Anticodon - codon binding is part of the normal translation process at the A - site. If the A - site is blocked (as in the first case), this binding cannot occur, so translation cannot speed up. Also, the A - site is critical for ribosome function in translation.
• Second Question:
• The channel through which the newly synthesized protein emerges is an essential part of the ribosome's function in translation. If the channel is clogged (by the drug), the growing protein will get stuck. As the ribosome moves along the mRNA during translation, a stuck protein will prevent further translation steps (such as the addition of new amino acids as the ribosome progresses). If most ribosomes are affected (by enough drug molecules), the cell, which needs functional proteins from translation, could die.
• If the exit channel is clogged, the protein cannot exit efficiently, so translation cannot speed up. Also, there is a specific exit channel for the newly formed protein in the ribosome, and there are not multiple alternative exit ways in the normal ribosome structure for the newly synthesized protein.

Answer:

• First Question: Translation would stop. If enough drug molecules are present to bind to most ribosomes in the cell, the cell might die.
• Second Question: The growing protein would get jammed up in the channel and prevent translation from continuing. If enough drug molecules were present to affect most of the ribosomes in the cell, the cell could die.