40. Which of the following descriptions is(are) false? 1. The difference between a ribonucieotide and a deoxyribonucleotide is that a ribonucleotide has an --OH instead of an -H at C-2. 2. The DNA copies of mRNA found in a cDNA libtary are made by reverse transcriptase. 3. Type II restriction enzymes cleave DNA only at recognition sequences specific to a given restriction enzyme 4. Deamination of the nucleotide base 5-methylcytosine yields nucleotide base thymine. 5. Type II restriction enzymes may make staggered (off-center) cuts within their recognition scquences. (A) 5 only (B) 3 only (C) 4 only (D) 1 and 2 (E) Nonc of the descriptions are false.

43. Which of the following statements in the enzyme cofactors involved in one-carbon transfer reactions is false? (A) Tetrahydrofolate, S-adenosylmethionine, and biotin are important cofactors involved in the reactions of one-carbon transfers. (B) S-Adenosylmethionine is synthesized from ATP and methionine. (C) In the activated-methyI cycle for the synthesis of methionine and S-adenosylmethionine, homocysteine is converted to methionine through the donation of the methy! group frommethylenetetrahydrofolate. (D) Acetyl-CoA carboxylase, which catalyzes the formation of malonyl-CoA from acetyl-CoA, contains a biotin prosthetic group. (E) The methyl group donated from S-adenosylmethionine is more reactive than that donated from N5-methyltetrahydrofolate.

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