21. Which of the following is true of chromatin?
(A) Heterochromatin has more acetyl groups on the histones.
(B) Heterochromatin has fewer methyl groups on the DNA.
(C) Active genes are not bound by nucleosomes.
(D) Sequence-specific DNA binding proteins can only activate transcription.
(E) The chromatin structure on a particular gene may be different in different cells.

17. If the homeotic genes are mutated and cannot be expressed in an orchid during flower development. What would be the consequence? (A) The orchid will not develop cotyledons. (B) The orchid will die. (C) The orchid will become dwarf. (D) The orchid will develop flowers instead of leaves. (E) The orchid will develop leaves instead of flowers.

18. Adenylyl cyclase is to cAMP as ____________ is to AMP. (A) protein kinase C (B) phospholipase C (C) phosphodiesterase (D) phosphatase (E) Ras

19. For cloning of genomic DNA sequences, yeast artificial chromosome (YAC) and bacterial artificial chromosome (BAC) are two popular cloning vector systems. Which of the following is NOT correct? (A) A BAC would be circular and a YAC would be linear. (B) A YAC would have telomeres and a BAC would not. (C) A YAC would have a centromere and a BAC would not. (D) A YAC would be bound to histones in the cell and a BAC would not. (E) A BAC would contain a much larger DNA insert than a YAC.

20. Which of the following processes does NOT occur in the eukaryotic nucleus? (A) RNA splicing. (B) RNA polyadenylation. (C) DNA synthesis. (D) RNA capping. (E) Production of charged tRNAs.

22. In E. coli, biosynthesis of tryptophan can be repressed. The repressor protein of the trp operon (A) is activated by the binding of tryptophan. (B) is inactivated by the binding of tryptophan. (C) is not affected by tryptophan. (D) is activated by the binding of free tRNA. (E) is only synthesized in the presence of tryptophan.

23. The major lipids found in membranes are (A) triacylglycerols and cholesterol. (B) cholesterol and sphingomyelin. (C) phospholipids, glycolipids, and cholesterol. (D) phospholipids and free fatty acids. (E) cholesterol, inositol, and glycolipids.

24. During glycolysis NADH is produced in the cytosol. Under aerobic conditions, what is the primary fate of this NADH? (A) It accumulates in the cytosol. (B) It diffuses into the mitochondria. (C) It transfers its reducing equivalents directly to NADP+. (D) The reducing equivalents are transferred by a shuttle system to the mitochondrial electron transport system. (E) It is used to reduce glucose to sorbitol.

25. Which of the following is NOT a post-translational modification? (A) Phosphorylation. (B) Glycosylation. (C) Acetylation. (D) Methylation. (E) Ubiquitination.

26. Which one of the following components is NOT necessary in an expression plasmid to be useful in the construction of recombinant DNA? (A) A multiple cloning site. (B) A tag coding sequence. (C) A promoter and a terminator. (D) Multiple cloning sites. (E) A coding sequence that is for antibiotic resistance.

27. Inheritance of phenotype sometimes does not directly involving the nucleotide is termed epigenetic inheritance. The epigenetic inheritance (A) only refers to genomic imprinting. (B) only effects female offspring. (C) only effects male offspring. (D) only refers to X inactivation. (E) can result in the expression of different alleles in different generations.