BIOLOGy multiple choice question help?

46) There are 61 mRNA codons that specify an amino acid, but only 45 tRNAs. This is best explained by the fact that


A) the rules for base pairing between the third base of a codon and tRNA are flexible.


B) some tRNAs have anticodons that recognize two or more different codons.


C) many codons are never used, so the tRNAs that recognize them are dispensable.


D) A and B only


E) A, B, and C





91) A mutation that inactivates the regulatory gene of a repressible operon in an E. coli cell would result in


A) complete inhibition of transcription of the structural gene controlled by that regulator.


B) inactivation of RNA polymerase.


C) irreversible binding of the repressor to the operator.


D) continuous transcription of the structural gene controlled by that regulator.


E) both B and C





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BIOLOGy multiple choice question help?
46) I think there is something wrong with the question? There should be 64 mRNA codons since there are 4 bases so 4x4x4=64. There are 61 tRNAs which code for the 20 amino acids with 3 codons (UAG/UAA/UGA) which act as "stop signals" for the termination of the polypeptide chain synthesis during translation.





91) D. The regulatory gene codes for the repressor which binds to the operator region and prevent transcription of the structural genes. When the regulatory gene is inactivated, the repressor is not synthesized and DNA polymerase can bind freely to the operator to carry out transcription.
Reply:46- D


91- A





just my guess...