49. Tautomerization of nucleotides A) is important as a cause of errors in DNA r

Question

49. Tautomerization of nucleotides

A) is important as a cause of errors in DNA replication

B) is important as a cause of errors in transcription

C) is important in formation of the wobble pairs important in protein translation

D) is irreversible process

E) does not lead to formation of isomers

50. __ promotes the formation of covalent bonds between ____ thymine residues in a DNA strand creating a ____ ring

called a thymidine dimer.

A) Visible light; adjacent; cyclohexyl

B) Visible light; nearby; cyclobutyl

C) UV light; adjacent; cyclobutyl

D) UV light; nearby; cyclohexyl

E) IR light; adjacent; cyclobutyl

51. The ____strand has the same nucleotide sequence and direction as that of the RNA transcript, with the ____ end of mRNA encoding the N-terminus of the protein.

A) template; 3'

B) template; 5'

C) nontemplate; 3'

D) nontemplate; 5'

E) lagging; 5'

Explanation / Answer

Ans 49. Tautomerization of nucleotides

A) is important as a cause of errors in DNA replication

Explaination: Most replication errors were caused by what are called tautomeric shifts. Both the purine and pyrimidine bases in DNA exist in different chemical forms, or tautomers, in which the protons occupy different positions in the molecule (Figure 1). The Watson-Crick model required that the nucleotide bases be in their more common "keto" form (Watson & Crick, 1953). Scientists believed that if and when a nucleotide base shifted into its rarer tautomeric form (the "imino" or "enol" form), a likely result would be base-pair mismatching.

Ans 50. UV promotes the formation of covalent bonds between adjacent thymine residues in a DNA strand creating a cyclobutyl ring called a thymidine dimer.

51. The nontemplate strand has the same nucleotide sequence and direction as that of the RNA transcript, with the 5' end of mRNA encoding the N-terminus of the protein.

Point to remenber: Wherever a gene exists on a DNA molecule, onestrand is the coding strand (or sense strand or non-template strand), and the other is the noncoding strand (also called the antisense strand, anticodingstrand, template strand, or transcribed strand).

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